- Email: [email protected]
A comparative study of the breathing and clearing characteristics of different types of snorkels
Ocean Engng. Vol. 7, pp. 459-475. Pergamon Press Ltd. 1980. Printed in Great Britain
A COMPARATIVE STUDY OF THE BREATHING AND CLEARING CHARACTERISTICS OF DIFFERENT TYPES OF SNORKELS A. BAZ* and N. ZOGHEB Mechanical Engineering Department, Cairo University, Egypt
Abstract--This article presents a comparative study of the breathing resistance and clearing characteristics of several types of commercially available snorkels in an attempt to devise quantitative means that enable the divers to select the best snorkel and the designers to see the possible directions and modifications necessary for improving the performance of such important life support devices. Two test stands have therefore been built, the first to measure the breathing resistance and the second to monitor the clearing efficiencyand speed of some of the commonly used snorkels. The tested snorkels varied from the simple J-type to the sophisticated wrap-around snorkels with convoluted flexible hoses and flared ends. The results obtained show that large diameter snorkels of the wrap-around design with sweeping barrels and flared ends (as the AMF Swimmaster snorkel number 2S55) offer the least breathing resistance, As for the clearing characteristics snorkels with small diameters and of the simple J-type (as the Spanish Aquasub snorkel: The Canarias) or with large diameters and sweeping barrels (as the Power Tuned snorkel of U.S. divers) possess the best clearing figure of merit. I. I N T R O D U C T I O N
NUMEROUS historical evidences testify to the fact that divers have used several types of breathing tubes, commonly known nowadays as "snorkels", to bring ambient air into their lungs while cruising on the water surface. Among these evidences are the words of the Greek philosopher Aristotle, as quoted by SWEEN~Y(1970) : Divers made instruments that allowed them to stay for a long time underwater by breathing the air from the surface, just as nature has endowed elephants with trunks to be used for analogous purposes.
Snorkels being, as pictured by Aristotle, extensions to the diver's airways they constitute a very important part of his life support system. Special attention must therefore be paid to the design and development of such essential diving gear in order to give the diver the breath that he needs in the most comfortable and safe way. Equally important is the selection process for the snorkel that best suits the diver's needs. Such a process is not an easy task, particularly as the diver has to select his snorkel from a wide range of commercially available snorkels, the performance characteristics of which are generally incomplete or non-existent. It is therefore the purpose of this study to investigate, in a comparative fashion, the performance characteristics of several types of commonly used snorkels in an attempt to devise quantitative means to enable the divers to select the best snorkel for their needs, and *Present address: Department of Mechanical Engineering, University of Wisconsin, Madison, Wisconsin 53705, U.S.A. 459
460
A. tlAZ allot N. Z()Cittl:l ~, Air compressor
!-.ZL., Ad~k~ble differential 1 - - - ' 1 1 1 pressure regulofor L~_J •~ - 7 Orifice meier 8" t 9
I / " I Bubblelevel Inclined n~nomefer I0 - - - - - - / ~ /
4
J
Z_~
12 Vernier manometer
Snorkel
FIG. 2.
A schematic drawingof the test stand used for monitoring the breathingcharacteristics of snorkels.
the designers to see possible modifications to improve the performance of such important life support devices. Emphasis is made on studying the characteristics of the snorkels during both the breathing and clearing phases. These two phases take place in succession in almost all diving situations and in spite of the fact that snorkels are intended mainly for breathing they are likely to be filled with water, in many instances, and divers must clear them before they can resume breathing. Therefore the breathing resistance as well as the clearing parameters, namely the speed and efficiency, are determined for a wide variety of diving snorkels in order to give a complete picture of the performance characteristics of these snorkels during their two equally important phases of operation. The effect of the snorkel geometry and configuration on its breathing and clearing characteristics has been quantified by calrying out tests on snorkels which vary from the simple J-type to the sophisticated wrap-around snorkels with converted flexible hoses and flared ends. The range of snorkels tested also covered those with small and big barrels and those with sweeping barrels. Some of those tested are manufactured by U.S. diving companies, others by French, Italian and Spanish outfits. Figure 1 shows photographs of all the different types of snorkels tested in this study. The snorkel type, the name of the manufacturer, the dimensions and all the other geometrical parameters are given next to each snorkel. Two test stands were used in this study; the first monitors the breathing resistance of snorkel as a function of the diver breathing late while the second is used to determine the clearing efficiency and clearing time for different snorkels at different exhalation levels. The results obtained show that the AMF Swilnmaster snorkel: type 2S55 has the least breathing resistance for diver breathing rates up to 120 l/min. But its clearing efficiency is almost 16% lower than the simple J-shaped snorkel (type Tubaflex of the Italian
Breathing and clearing characteristics of snorkels
(I) C,anarias (Ref. 3013) Manufacturer: Aquasub Made in Spain
I
Design features : d= 1.46 cm L= 3 5 0 cm R= 3.25 cm
Canarias Aquasub
R
(i"r) Tuboflex Manufacturer: Technisub Made in Italy
-t~-d
Design features : Technisub Tubaflex
d = 1.75 cm L : 35.0 cm R=3.6 cm
lr (~T) Super snorkel (Ref. 152140) d Manufacturer : La Spirotechnique Made in France
d=2
-X~x
Design features :
~
15 cm
dequivalent:
4 x c.$. ore(I contour "J
. i \!
L : 35.0 cm. = 2 0 6 5 cm
L:
R : 2 . 0 cm 60cm
FIG. la.
I Super snorkel Spirotechnique
~.
t
Photographs of the snorkels of the first group with different cross-sectional geometries,
461
462
A. BAZ and N. ZOGHEB (~Z) Super flex aqualung
(Ref. 7318-10)
Manufacturer: U.S. Divers Co. Made in US A.
d I1!
i
°_
Design features : d :1.9 cm L : 34.5 cm R:5Ocm L =60cm
Super flex
Ji
i
i
,R
I
Power tuned aqualung (Ref. 7323) Manufacturer: U.S. Divers Ca. Mode in U S A Design fealures : d : 1.85 cm D= 2.6 ¢m L : 2 8 0 cm R: 14 0 cm y:60 °
D
J d Tuned
.i
~z s-"
FIG. lb.
b.
Photographs of the snorkels of the second group with different barrel designs.
Breathing and clearing characteristics of snorkels
~
(3E) Off-set jet snorkel (Cot. NQ 258) Monufocturer : Scubolxo Made in USA. Design feotures: d : 2 . 1 cm L~ : 8.5 cm, Lz=I50cm Rj = 15.0cm Rz= 6.0 cm - 40o
463
d
~i
;4o* ),=60 °
I×
('o'.) Turboflex
(Mod. NBT)
Monufocturer : DACOR Mode in U.S.A. exoctly like No "Err d --2Jcm L~ : 8.5cm L2 = 12.0 cm, Rr = 15.0 cm R2= 6.0 cm
Turl~oflex
a = 40 °
,8 -- 40 ° T =60°
IX
('vnl)
t, ~-.
.AMF Swimmoster(Ref. 2 5 55)
D ~
~,
Manufocturer:U.S. Div~ngCo Mode ~ u.s.A.
!~/~/
~ /d~ . ~""
d = 2.1 cm cm
~'/'/~R
O=4.0
L I -" 8 . 5
= : 40 °
B:4o o u
= 40 °
y =60 °
MF
cm
Lz : 12.0 cn', L3 = 5.0 cm R = 15.0cm
.j
vimmeihlr
~,~,%! ~, ~\ 7
F[o. lc.
Photographs of the snorkels of the third group with the wrap-around and flarexi-cnd desigm,
FIG. 3a.
A photograph of the Vernier reading Ascania micromanometer
Breathing and clearingcharacteristics of snorkels
465
Technisub Company) which on the other hand exhibits nearly 3 times as much breathing resistance. The Power-Tuned snorkel, manufactured by the U.S. Divers, has the best combination of clearing speed and efficiency of all the snorkels tested. It is also interesting to note that the small-diametel Spanish Aquasub snorkel "The Canarias" is as good as the Power Tuned for clearing characteristics, but it has much poorer breathing characteristics. Therefore, the Power Tuned snorkel is favoured over the Spanish Canarias. 2. EXPERIMENTAL EVALUATION OF THE BREATHING CHARACTERISTICS OF SNORKELS 2.1 Testing facility A specially designed test stand has been built to monitor the bleathing effort necessary to overcome the pressure drop across each snorkel at different breathing rates. The layout of the test stand is shown in Fig. 2, illustrating its different components as well as the measuring instruments used. The used test stand incorporates three distinct sections, namely the air supply section, the breathing rate metering section, and the breathing effort measuring section. 2.1.1 Air supply section. It utilizes a two-stage reciprocating compressor to supply the remaining sections of the stand with a continuously-regulated air flow. The compressor is fitted with a large storage tank whose internal pressure is maintained constant by a special automatic refilling controller. The tank acts as an accumulator that guarantees that the flow going to test sections is continuous and free of oscillations. A pressure regulator 1 receives the compressed air from the tank and controls its pressure before delivering it to the test section. As the breathing monitoring setup is an open type system exhausting through the snorkels to the atmosphere, then the pressure regulator 1 also acts as a flow control valve. 2.1.2 Breathing rate metering section. In this section, the downstream of regulator 1 is connected through a flexible nose 2 that represents an extra accumulator, to a flow control regulator 3 which is intended for fine meteling of any desired flow rate. The incoming flow is measured by the standard orifice meter 7 and the differential inclined manometer 10. The orifice meter is calibrated by comparing the manometer reading in mm water against the flow rate reading in l/min as indicated on a calibrated float rotameter. The metering section has been designed to be capable of varying and measuring accurately breathing rates up to 120 l/rain in order to cover diver breathing rates corresponding to his requirements while performing light to heavy work. 2.1.3 Breathing effort measuring section. The metered air flow passes now into the breathing effort monitoring section which begins with a pressure tapping 4 to measure the inlet air pressure. The flow is then directed into a plastic pipe 5 whose end is so shaped that it fits nicely inside the mouthpiece of each of the snorkels tested. The other end of the snorkel is left open to the ambient atmosphere in ordel to study the effect of the shape of the snorkel end, especially the flared end, on its performance. In this way, the pressure at the inlet of the snorkel will attain a magnitude enough to overcome, for a given air flow rate, the pressure drop across the tested snorkel and therefore give an indication of the breathing effort corresponding to the breathing rate under consideration. The magnitude of the snorkel's inlet pressure is measured by connecting the pressure
A . BAZ a n d N. ZOOHEB
466
7 Mic,rometer ,, .....
Cistern
U-tube
I
/
-
/~--
3
MQtlsurit~ chamber
4
Steel
.....
5
Eye- piece
6
/
F~o. 3b.
nee~Je
Reflector
L a y o u t of the A s c a n i a m i c r o m a n o m e t e r .
tapping 4 to the Ascania micro-differential micromanometer 12. A photograph of the micromanometer is shown in Fig. 3a and a schematic drawing illustrating the assembly of its different components is shown in Fig. 3b. The manometer is essentially a U-tube manometer capable of monitoring pressure differences in the order of a few hundredths of a millimeter of water with an accuracy of 0.02 ram. The manometer relies in its operation on adjusting the level of chamber 3, using the micrometer 7, until the gap between the needle 4 and its reflected image vanishes. When a pressure differential is applied across the manometer, the gap develops and chamber 3 must be moved until the tips of the needle and its image coincide again. The movement of chamber 3, as indicated on the vernier 8, gives an indication of the differential pressure. For more details about the design, principle of operation and use of the manometer, C. F. Casell & Co. Ltd of London should be consulted. 2.2 Results The test stand of Fig. 2 has been used to compare the breathing characteristics of several of the commercially available snorkels in an attempt to find the merits and limitations of each design and to favour one design over the others on a quantitative basis. The eight snorkels, shown in Fig. l, have been sorted into three groups. The first group, Fig. 1a, is chosen to study the effect of the geometry of the cross section of the snorkel on its breathing resistance characteristics. The second group, Fig. lb, is intended to investigate the influence of the barrel of the snorkel on the diver breathing effort, while the third group, Fig. lc, is used to indicate the effects of the wrap-around design and the flared ends. Figure 4a shows the breathing characteristics of the snorkels of the first group. From the figure, we can see that snorkel I, which has a small circular cross section of diameter 1.46 cm, exhibits the highest breathing resistance over the whole range of breathing rates. At a breathing rate of 100 l/min, it requires almost 2.25 times the breathing effort of snorkel II. Therefore, increasing the diameter of the snorkel reduces considerably its breathing resistance. For the French Spirotechnique, snorkel III, the truncated circular cross section seems to really help in dropping the breathing resistance to almost half that of snorkel II over the entire breathing rate range. This however is attributed to the fact that the mean hydraulic diameter of this snorkel, i.e. the diameter of the equivalent circular cross section tube, is much larger than the diameters of the other two snorkels.
Breathing and clearing characteristics of snorkels
e
-
o / P
•
I-O
P
o Cor~rios., !
7 -
467
Tuboflex .. 11"
-
o /
Spirotechnique .. ' m 6
E E 5 O
2 4 =
n'.O
•
3
d5 Z
I
0
I0
20
30
40
50
60
8reothing rote,
70
80
90
E)O
,J
t[O
t/rnin
The effect of the geometry of the snorkel's cross section on its breathing resistance at different levels of breathing rate.
FIG. 4a.
For the second group of snorkels, Fig. 4b shows that the sweeping barrel snorkel V with flared end does definitely have an edge over the snorkel IV which has a convoluted flexible barrel. The addition of the sweeping barrel drops the breathing resistance at 100 l/rain to almost half that of the convoluted barrel snorkel. In Fig. 4c, the snorkels of the third group show a considerable improvement in the breathing characteristics mainly because of the wrap-around design and because they have been designed with large diameter tubes as well as with sweeping barrels.
sF
4 [
rcr
o Superflex.. r~r
3[-
e Po.r.ed
7
,. ~Z
{, '~
~ 0
IO
J
I
I
1
l
I
1
1
20
30
40
5o
60
70
80
90
Breofhing rote,
Fro. 4b.
I K30
E/rain
The effect of the barrel shape and the flared end of the snorkel on its breathing resistance at different levels of breathing rate.
468
A. BAZ and N. Zo(im R
~4
•
Off-se~'jef
o
Turboflex
.. ~ZI
[]
AMF-Swimmoster
.
~rr ..
t~
,.-Tr
I0
20
30
40
50
B r e a t " h i n g rare,
60
?0
80
90
100
IlO
L/rain
FIG. 4C. The effect of the wrap-around design and the flared end of the snorkel on its breathing resistance at different levels of breathing rate.
Of all the tested snorkels, snorkel VIII, which is the A M F Swimmaster snorkel type 2S55, has the least breathing resistance. At a breathing rate of 100 1/min, this snorkel requires only 1.5 nun of water breathing effort compared to 9 mm for the Spanish-made snorkel I. The low-breathing characteristics of the A M F Swimmaster snorkel compared with the other two wrap-around snorkels VI and VII are attributed to the fact that its top has a flared end, which minimizes the air resistance due to the turbulence that occurs when the flowing air meets the surrounding still ambient air. 3. E X P E R I M E N T A L
EVALUATION OF THE CLEARING OF SNORKELS
CHARACTERISTICS
This part of the study deals with the clearing characteristics of the snorkels. Such characteristics are of the utmost importance since snorkels are susceptible to being filled with water, in many situations, and divers find themselves compelled to exert sufficient effort to blow their breathing tubes clear before they can resume breathing.
3.1 Testing facility and procedure A special test stand has been built to measure two important parameters, the clearing speed and the clearing efficiency, since each can be taken as a measure of the diver's clearing effort and consequently of his comfort. The layout of the used test stand is shown in Fig. 5 indicating its main components as well as the measuring instrumentation. In Fig. 5, pressurized air from a storage tank is regulated by the bleed-off back pressure regulator A before it goes into the test section. A flexible tube B is inserted after the regulator A to act as a pneumatic accumulator in order to prevent any drop in the pressure at the snorkel inlet once the solenoid valve F is energized open. The flexible tube B is connected to a transparent plastic tube C which plays the role of a water level indicator. The end of this plastic tube is shaped in such a way that it fits nicely inside the mouthpiece of the snorkel
Breathing and clearing characteristics of snorkels
469
Air cotrotassor
Bleed off bock pressurere(:JulOtor
A
G Solenoid v(]lve
ir reserv~
\
FJ~~ - ~ -
~-- D U~ tube rnonometer
E~ J ~ ' ~ ~C Waterlevel indico,or Snorkel Layout of the test set-up used for measuring the clearing characteristics of snorkels. FIo. 5. under consideration. The flow from the other end of the snorkel is controlled by a twoposition solenoid valve F which is of the normally closed type. The pressure at the down-stream of the pressure regulator A is monitored by a regular U-tube manometer D inserted at the junction between the regulator A and the flexible tube B. To measure the clearing characteristics of the different snorkels, the solenoid valve is energized and the snorkel under consideration is filled with water from the port G, 0.3175 mm in diameter, of the solenoid valve until the water level can be seen through the transparent tube C. The solenoid valve is then de-energized to close the port G and the pressure regulator A is adjusted to maintain a predetermined pressure, say Pc, in its down-stream as monitored on the manometer D. The solenoid valve is energized carefully to release the extra water that fills the transparent tube above the level L - L and the valve is then closed. A timer is used to keep track of the time when the solenoid valve is energized again. Water will effiux out of the port G and when the flow starts to be discontinuous the timer is stopped to record a time of efflux te, and the valve is de-energized at the same time to retain a volume V, which remains uncleared. If the snorkel volume is V,, then the clearing efficiency rio after an efflux time t, under the influence of the constant clearing effort Pe will be defined as follows: ,c = (v, -
vr)/ v,.100.
(1)
The clearing speed S c will be in effect inversely proportional to the efflux time t e, or: Sc = K/t,
(2)
where K is a proportionality constant. The clearing characteristics, measured by the above procedure, are therefore determined in effect by subjecting the snorkel when completely filled with water to a controlled step pressure in order to simulate the possible effort levels exerted by the diver during the clearing process. The developed set-up and the proposed measuring techniques have been utilized to
470
A. BAZ a n d N . ZOOHEB
90 o Canarias .. I {Po=O 5 0 m water]
80
• Tubaflex. TT[Po=O26m water] m Spirotechnique . TIT [Po=O 52rn water]
70 I 6O
r~ 50
rrr 40 ~0
~0
I0
o
0.5
LO
L5
Clearing effort (pe-pollPo
FxG. 6a. The clearing efficiencyat different levels of clearing effort for the Canarias (I). Tubaflex (II) and Spirotechnique super snorkel (liD.
compare in a quantitative fashion the clearing efficiency qc and clearing speed S~ of the three groups of snorkels considered. 3.2 Results Figure 6a shows the effect of the diver clearing effort Pe on the clearing efficiency 11o as defined by (1), for the snorkels of the first group. The plot is presented in a dimensionless fashion by referring the diver effort to the effort necessary to just get the water column, inside the snorkel, to start flowing out of it. This reference effort is called the "NO FLOW E F F O R T . . . P0" and is mainly a measure of the pressure necessary to support the weight of the water column inside the snorkel. From Fig. 6a we can see that increasing the clearing effort increases the clearing efficiency but not in a linear fashion. Therefore, the bulk of the water inside the snorkel is cleared by a relatively small effort. Figure 6a indicates also that increasing the hydraulic diameter of the snorkel reduces considerably its clearing efficiency. Consequently, the snorkel I, which has been the poorest regarding its breathing characteristics, is now on top of the snorkels of its group since it shows the highest clearing efficiency at any clearing effort. In Fig. 6b, the clearing speeds of the three snorkels of the first group are given as a function also of the dimensionless clearing effort. The clearing speed increases, in a pattern similar to the clearing efficiency, with the increase of the clearing effort. But from the figure
Breathing and clearing characteristics of snorkels
471
o Conorio~ .. :I ,, Tuboflex .. n'
Spirofechr~ ..m
O,B
Q ~r
o,e
, ~ 0.4
15 02
I 0
I
05
I
I0
Cleoring efforf
1,5
(Pe "Po)./P o
FIG. 6b. The clearing speed at different levels of clearing effort for the Canarias (I), Tubaflex (II), and Spirotechnique super snorkel (1II). snorkel I I I exhibits faster clearing speeds than snorkel I and I I especially at high clearing effort. T o combine the effect o f the clearing effort on b o t h the clearing efficiency and speed, the product of the two p a r a m e t e r s is plotted against the clearing effort as shown in Fig. Oe. Such a product is used because it is equally i m p o r t a n t to clear the snorkel efficiently as well
.
0,30
Z
/ I - Conorios 1"I - Tuboflex
/ /
/ /
1t" J
.E
~ 0.20 K
u
~ u
010
,..
I 0 5
Cleoring effort
1 I0
I ~15
(Pe-Po)/Po
FIG. 6¢. The product of the clearing efficiency and clearing speed at different levels of clearing effort for Canarias (I), Tubaflex (II) and Spirotechnique super snorkel (III).
472
A. BAZ a n d N. Zo(;He~
o Superflex . ] ~ 70
• Power tuned ~[
[P~,=032 m woter] [Po=O 2 8 m
woter]
60
Eso ~ ~ Z
5Z
g
' ~ 4O
~
3O
-
7
2O
10 F 0
r
05
I
IO
15
Clearing effort (Pe-Po)/P,,
FIG. 7a.
The clearing efficiency at different levels of clearing effort for the Superflex (IV) and the Aqualung power-tuned snorkel (V).
as quickly for any level of clearing effort. Therefore, the snorkel which has the highest product of its two clearing parameters will be the best for clearing characteristics. From Fig. 6c, we conclude that snorkel I is better than II[ and III is better than II. For the snorkels of the second group, Fig. 7a indicates that snorkel IV is more efficient than snorkel V since it shows higher clearing efficiencies at any clearing effort. This is exactly the opposite to the breathing characteristics of these two snorkels. Also, comparison between Fig. 6a and Fig. 7a shows that the simple J-type snorkels [ 10
o Superflex
T~7
• Power tuned ,. O8
~-
- 06
_
.~./o
E
r-_ 0 4
O2
0
L
05
I
!0
~
I5
Clearing effort ( p -Po)/Po
Flo. 7b. The clearing speed at different levels of clearing effort for the Superflex (IV) and Aqualung power-tuned snorkel (V).
Breathing and clearing characteristics of snorkels 0.30
473
I
~ - Superflex
. . I ~
l~r
._~0; g-
g
~olc
I 0
0,5
I
I
I0
15
CleorhOefforf (Pe'Po)/Po
FIG. 7c. The product of the clearing e~ciency and clearing speed at different levels of clearing effort for the Suparflex (IV) and the Aqualung power-tuned snorkel (V).
and II have higher clearing efficiencies than snorkels with convoluted or sweeping barrels. Regarding the clearing speed, snorkel V shows faster clearing speeds than snorkel IV for all the considered clearing efforts as manifested by Fig. 7b. From the plot of the combined clearing parameters, shown in Fig. 7c, the relatively low cleating efficiency of snorkel V has been compensated by its fast clearing time to make this snorkel more favourable than snorkel IV. Hence, snorkels with sweeping barrels are much better than those fitted with convoluted flexible hoses. Interesting to note that cross comparison between Fig. 6c and Fig. 7c shows that wlaen the combined clearing parameters are considered, snorkel V with the sweeping barrel appears to be equally as good as the so far leading Spanish J-type snorkel I. This shows that it is reasonable to look to the combined effect of the clearing parameter before drawing any conclusions because a snorkel that has a high clearing efficiency is not necessarily the best snorkel since it may have a poor cleating speed. Finally, for the snorkels of the third group, Fig. 8a shows the clearing efficiency of these snorkels at different levels of the clearing effort. In this figure, snorkel VI exhibits the highest clearing efficiency of the snorkels of its groups. Snorkels VII and VIII have very similar clearing efficiencies over the entire range of the clearing effort considered. It is also clear from Fig. 4a and Fig. 8a that snorkel VI which has been the poorest of its group regarding the breathing characteristics is now taking the lead as far as the clearing efficiency is concerned. A similar trend can also be seen from Fig. 8b but with snorkel VIII showing also the highest cleating speed. It is then followed by snorkels VI and VII in that order. Looking now into the plot of the combined clearing parameters for the snorkels of the third group, given in Fig. 8c, we can see that snorkel VI ranks highest and is then followed
474
A. BAz and N. ZOGHEB o O f f - s e t jet .. ~ . 60-
[P~=0:30 m w o f e r ]
•
Turboflex
D
AMF Swirnrnoster
wofer]
.~11". [po=o30rn ~
, [Po=O.27m
wofer]
50-
0
30
o
~0
L 0
05
I0
Cleorino effort
~
15
(Pe'Po)/p o
FIG. 8a. The clearing efficiency at different levels of clearing effort for the Off-set jet (VI), Turboflex (VI) and AMF Swimmaster (VII) snorkels. by snorkels VIII and VII. The figure shows also, when compared with Fig. 6c and Fig. 7c, that snorkel V has the highest clearing figure of merit, i.e. the product of the clearing efficiency and speed, of all the snorkels tested. Accordingly, snorkels with large diameter tubes, sweeping barrels such as the U.S. Diver's Power Tuned snorkel V will exhibit the best clearing characteristics. 4. CONCLUSIONS This study has presented a comparative investigation of the breathing and cleating characteristics of several of the commonly used and commercially available snorkels. Two test stands have been built, the first to monitor the breathing resistance offered by each
IO
o
0ff-set jet
• TurbOflex
..
.. "PTT
AMF Swm~moster .. 08
o
O2
L
05
Cleonng effort
FIG. 8b.
i I0
15
(Pc -Po } / p o
The clearing speed at differentlevels of clearing effort for the Off-setjet (VI), Turboflex (VII) and AMF Swimmaster (VIII) snorkels.
Breathing and clearing characteristics of snorkels
475
o3o~' ~ - Off- set jef
"vrt Tudooflex 3 ~ - AMF Swirnmaster
"of
//~l~r
u
o~o
.[ I 0
05
t LO
1 I
5
Cleonng effort (l~-Po)/Po FxO. 8c.
The product of the clearing efficiency and clearing speed at different levels of clearing
effort for the Off-set jet (VI), Turboflex (VII) and AMF Swimmaster (VIII) snorkels.
snorkel at the different breathing rates, and the second to quantify the cleating efficiency and speed of the different snorkels when subjected to controlled constant clearing efforts. The tested snorkels have been grouped in three groups to study the effects of the geometry of the snorkel's cross section, the shape of its barrel, as well as the effect of the wraparound design and flared ends on its breathing and clearing characteristics. We have shown that increasing dimensions of the snorkel's cross section, incorporating sweeping barrels and using wrap-around snorkels with flared ends improves considerably the breathing characteristics. In this respect, the AMF Swimmaster snorkel number 2S55 exhibits the least breathing resistance over the entire range of diver's breathing rates. Regarding the clearing characteristics, snorkels with large diameters, and sweeping barrel design are considered to possess the best clearing figure of merit which combines the effects of both the clearing efficiency and speed. In this regard, the U.S. Diver's Power Tuned snorkel has the highest cleating figule of merit of all the snorkels tested. In spite of the fact that the AMF Swimmaster snorkel VIII has shown almost half the breathing resistance of the Power Tuned V of U.S. Divers, yet the latter snorkel has a clearing figure ofmerit which is nearly one and a half times as much as snorkel VIII. If more emphasis is to be placed on the breathing effort, since it extends over a long duration, then AMF Swimmaster snorkel is favoured over the U.S. Diver snorkel. But if the emphasis is placed on the clearing characteristics, since it requires more extraneous effort, then the U.S. Diver's Tuned snorkel is definitely the answer. Acknowledgement--Special thanks are due to Dr R. ~OYD, Director of Petrie's Scuba Lab. in Madison, Wisconsin, U.S.A., for granting the U.S. made snorkels used in this study. Without such a 8enerous grant this study would have been impossible. REFERENCE Sw~er,~Y, J. B. 1970. A Pictorial History of Oceanographic Submersibles, Crown Publishers, New York.
A COMPARATIVE STUDY OF THE BREATHING AND CLEARING CHARACTERISTICS OF DIFFERENT TYPES OF SNORKELS A. BAZ* and N. ZOGHEB Mechanical Engineering Department, Cairo University, Egypt
Abstract--This article presents a comparative study of the breathing resistance and clearing characteristics of several types of commercially available snorkels in an attempt to devise quantitative means that enable the divers to select the best snorkel and the designers to see the possible directions and modifications necessary for improving the performance of such important life support devices. Two test stands have therefore been built, the first to measure the breathing resistance and the second to monitor the clearing efficiencyand speed of some of the commonly used snorkels. The tested snorkels varied from the simple J-type to the sophisticated wrap-around snorkels with convoluted flexible hoses and flared ends. The results obtained show that large diameter snorkels of the wrap-around design with sweeping barrels and flared ends (as the AMF Swimmaster snorkel number 2S55) offer the least breathing resistance, As for the clearing characteristics snorkels with small diameters and of the simple J-type (as the Spanish Aquasub snorkel: The Canarias) or with large diameters and sweeping barrels (as the Power Tuned snorkel of U.S. divers) possess the best clearing figure of merit. I. I N T R O D U C T I O N
NUMEROUS historical evidences testify to the fact that divers have used several types of breathing tubes, commonly known nowadays as "snorkels", to bring ambient air into their lungs while cruising on the water surface. Among these evidences are the words of the Greek philosopher Aristotle, as quoted by SWEEN~Y(1970) : Divers made instruments that allowed them to stay for a long time underwater by breathing the air from the surface, just as nature has endowed elephants with trunks to be used for analogous purposes.
Snorkels being, as pictured by Aristotle, extensions to the diver's airways they constitute a very important part of his life support system. Special attention must therefore be paid to the design and development of such essential diving gear in order to give the diver the breath that he needs in the most comfortable and safe way. Equally important is the selection process for the snorkel that best suits the diver's needs. Such a process is not an easy task, particularly as the diver has to select his snorkel from a wide range of commercially available snorkels, the performance characteristics of which are generally incomplete or non-existent. It is therefore the purpose of this study to investigate, in a comparative fashion, the performance characteristics of several types of commonly used snorkels in an attempt to devise quantitative means to enable the divers to select the best snorkel for their needs, and *Present address: Department of Mechanical Engineering, University of Wisconsin, Madison, Wisconsin 53705, U.S.A. 459
460
A. tlAZ allot N. Z()Cittl:l ~, Air compressor
!-.ZL., Ad~k~ble differential 1 - - - ' 1 1 1 pressure regulofor L~_J •~ - 7 Orifice meier 8" t 9
I / " I Bubblelevel Inclined n~nomefer I0 - - - - - - / ~ /
4
J
Z_~
12 Vernier manometer
Snorkel
FIG. 2.
A schematic drawingof the test stand used for monitoring the breathingcharacteristics of snorkels.
the designers to see possible modifications to improve the performance of such important life support devices. Emphasis is made on studying the characteristics of the snorkels during both the breathing and clearing phases. These two phases take place in succession in almost all diving situations and in spite of the fact that snorkels are intended mainly for breathing they are likely to be filled with water, in many instances, and divers must clear them before they can resume breathing. Therefore the breathing resistance as well as the clearing parameters, namely the speed and efficiency, are determined for a wide variety of diving snorkels in order to give a complete picture of the performance characteristics of these snorkels during their two equally important phases of operation. The effect of the snorkel geometry and configuration on its breathing and clearing characteristics has been quantified by calrying out tests on snorkels which vary from the simple J-type to the sophisticated wrap-around snorkels with converted flexible hoses and flared ends. The range of snorkels tested also covered those with small and big barrels and those with sweeping barrels. Some of those tested are manufactured by U.S. diving companies, others by French, Italian and Spanish outfits. Figure 1 shows photographs of all the different types of snorkels tested in this study. The snorkel type, the name of the manufacturer, the dimensions and all the other geometrical parameters are given next to each snorkel. Two test stands were used in this study; the first monitors the breathing resistance of snorkel as a function of the diver breathing late while the second is used to determine the clearing efficiency and clearing time for different snorkels at different exhalation levels. The results obtained show that the AMF Swilnmaster snorkel: type 2S55 has the least breathing resistance for diver breathing rates up to 120 l/min. But its clearing efficiency is almost 16% lower than the simple J-shaped snorkel (type Tubaflex of the Italian
Breathing and clearing characteristics of snorkels
(I) C,anarias (Ref. 3013) Manufacturer: Aquasub Made in Spain
I
Design features : d= 1.46 cm L= 3 5 0 cm R= 3.25 cm
Canarias Aquasub
R
(i"r) Tuboflex Manufacturer: Technisub Made in Italy
-t~-d
Design features : Technisub Tubaflex
d = 1.75 cm L : 35.0 cm R=3.6 cm
lr (~T) Super snorkel (Ref. 152140) d Manufacturer : La Spirotechnique Made in France
d=2
-X~x
Design features :
~
15 cm
dequivalent:
4 x c.$. ore(I contour "J
. i \!
L : 35.0 cm. = 2 0 6 5 cm
L:
R : 2 . 0 cm 60cm
FIG. la.
I Super snorkel Spirotechnique
~.
t
Photographs of the snorkels of the first group with different cross-sectional geometries,
461
462
A. BAZ and N. ZOGHEB (~Z) Super flex aqualung
(Ref. 7318-10)
Manufacturer: U.S. Divers Co. Made in US A.
d I1!
i
°_
Design features : d :1.9 cm L : 34.5 cm R:5Ocm L =60cm
Super flex
Ji
i
i
,R
I
Power tuned aqualung (Ref. 7323) Manufacturer: U.S. Divers Ca. Mode in U S A Design fealures : d : 1.85 cm D= 2.6 ¢m L : 2 8 0 cm R: 14 0 cm y:60 °
D
J d Tuned
.i
~z s-"
FIG. lb.
b.
Photographs of the snorkels of the second group with different barrel designs.
Breathing and clearing characteristics of snorkels
~
(3E) Off-set jet snorkel (Cot. NQ 258) Monufocturer : Scubolxo Made in USA. Design feotures: d : 2 . 1 cm L~ : 8.5 cm, Lz=I50cm Rj = 15.0cm Rz= 6.0 cm - 40o
463
d
~i
;4o* ),=60 °
I×
('o'.) Turboflex
(Mod. NBT)
Monufocturer : DACOR Mode in U.S.A. exoctly like No "Err d --2Jcm L~ : 8.5cm L2 = 12.0 cm, Rr = 15.0 cm R2= 6.0 cm
Turl~oflex
a = 40 °
,8 -- 40 ° T =60°
IX
('vnl)
t, ~-.
.AMF Swimmoster(Ref. 2 5 55)
D ~
~,
Manufocturer:U.S. Div~ngCo Mode ~ u.s.A.
!~/~/
~ /d~ . ~""
d = 2.1 cm cm
~'/'/~R
O=4.0
L I -" 8 . 5
= : 40 °
B:4o o u
= 40 °
y =60 °
MF
cm
Lz : 12.0 cn', L3 = 5.0 cm R = 15.0cm
.j
vimmeihlr
~,~,%! ~, ~\ 7
F[o. lc.
Photographs of the snorkels of the third group with the wrap-around and flarexi-cnd desigm,
FIG. 3a.
A photograph of the Vernier reading Ascania micromanometer
Breathing and clearingcharacteristics of snorkels
465
Technisub Company) which on the other hand exhibits nearly 3 times as much breathing resistance. The Power-Tuned snorkel, manufactured by the U.S. Divers, has the best combination of clearing speed and efficiency of all the snorkels tested. It is also interesting to note that the small-diametel Spanish Aquasub snorkel "The Canarias" is as good as the Power Tuned for clearing characteristics, but it has much poorer breathing characteristics. Therefore, the Power Tuned snorkel is favoured over the Spanish Canarias. 2. EXPERIMENTAL EVALUATION OF THE BREATHING CHARACTERISTICS OF SNORKELS 2.1 Testing facility A specially designed test stand has been built to monitor the bleathing effort necessary to overcome the pressure drop across each snorkel at different breathing rates. The layout of the test stand is shown in Fig. 2, illustrating its different components as well as the measuring instruments used. The used test stand incorporates three distinct sections, namely the air supply section, the breathing rate metering section, and the breathing effort measuring section. 2.1.1 Air supply section. It utilizes a two-stage reciprocating compressor to supply the remaining sections of the stand with a continuously-regulated air flow. The compressor is fitted with a large storage tank whose internal pressure is maintained constant by a special automatic refilling controller. The tank acts as an accumulator that guarantees that the flow going to test sections is continuous and free of oscillations. A pressure regulator 1 receives the compressed air from the tank and controls its pressure before delivering it to the test section. As the breathing monitoring setup is an open type system exhausting through the snorkels to the atmosphere, then the pressure regulator 1 also acts as a flow control valve. 2.1.2 Breathing rate metering section. In this section, the downstream of regulator 1 is connected through a flexible nose 2 that represents an extra accumulator, to a flow control regulator 3 which is intended for fine meteling of any desired flow rate. The incoming flow is measured by the standard orifice meter 7 and the differential inclined manometer 10. The orifice meter is calibrated by comparing the manometer reading in mm water against the flow rate reading in l/min as indicated on a calibrated float rotameter. The metering section has been designed to be capable of varying and measuring accurately breathing rates up to 120 l/rain in order to cover diver breathing rates corresponding to his requirements while performing light to heavy work. 2.1.3 Breathing effort measuring section. The metered air flow passes now into the breathing effort monitoring section which begins with a pressure tapping 4 to measure the inlet air pressure. The flow is then directed into a plastic pipe 5 whose end is so shaped that it fits nicely inside the mouthpiece of each of the snorkels tested. The other end of the snorkel is left open to the ambient atmosphere in ordel to study the effect of the shape of the snorkel end, especially the flared end, on its performance. In this way, the pressure at the inlet of the snorkel will attain a magnitude enough to overcome, for a given air flow rate, the pressure drop across the tested snorkel and therefore give an indication of the breathing effort corresponding to the breathing rate under consideration. The magnitude of the snorkel's inlet pressure is measured by connecting the pressure
A . BAZ a n d N. ZOOHEB
466
7 Mic,rometer ,, .....
Cistern
U-tube
I
/
-
/~--
3
MQtlsurit~ chamber
4
Steel
.....
5
Eye- piece
6
/
F~o. 3b.
nee~Je
Reflector
L a y o u t of the A s c a n i a m i c r o m a n o m e t e r .
tapping 4 to the Ascania micro-differential micromanometer 12. A photograph of the micromanometer is shown in Fig. 3a and a schematic drawing illustrating the assembly of its different components is shown in Fig. 3b. The manometer is essentially a U-tube manometer capable of monitoring pressure differences in the order of a few hundredths of a millimeter of water with an accuracy of 0.02 ram. The manometer relies in its operation on adjusting the level of chamber 3, using the micrometer 7, until the gap between the needle 4 and its reflected image vanishes. When a pressure differential is applied across the manometer, the gap develops and chamber 3 must be moved until the tips of the needle and its image coincide again. The movement of chamber 3, as indicated on the vernier 8, gives an indication of the differential pressure. For more details about the design, principle of operation and use of the manometer, C. F. Casell & Co. Ltd of London should be consulted. 2.2 Results The test stand of Fig. 2 has been used to compare the breathing characteristics of several of the commercially available snorkels in an attempt to find the merits and limitations of each design and to favour one design over the others on a quantitative basis. The eight snorkels, shown in Fig. l, have been sorted into three groups. The first group, Fig. 1a, is chosen to study the effect of the geometry of the cross section of the snorkel on its breathing resistance characteristics. The second group, Fig. lb, is intended to investigate the influence of the barrel of the snorkel on the diver breathing effort, while the third group, Fig. lc, is used to indicate the effects of the wrap-around design and the flared ends. Figure 4a shows the breathing characteristics of the snorkels of the first group. From the figure, we can see that snorkel I, which has a small circular cross section of diameter 1.46 cm, exhibits the highest breathing resistance over the whole range of breathing rates. At a breathing rate of 100 l/min, it requires almost 2.25 times the breathing effort of snorkel II. Therefore, increasing the diameter of the snorkel reduces considerably its breathing resistance. For the French Spirotechnique, snorkel III, the truncated circular cross section seems to really help in dropping the breathing resistance to almost half that of snorkel II over the entire breathing rate range. This however is attributed to the fact that the mean hydraulic diameter of this snorkel, i.e. the diameter of the equivalent circular cross section tube, is much larger than the diameters of the other two snorkels.
Breathing and clearing characteristics of snorkels
e
-
o / P
•
I-O
P
o Cor~rios., !
7 -
467
Tuboflex .. 11"
-
o /
Spirotechnique .. ' m 6
E E 5 O
2 4 =
n'.O
•
3
d5 Z
I
0
I0
20
30
40
50
60
8reothing rote,
70
80
90
E)O
,J
t[O
t/rnin
The effect of the geometry of the snorkel's cross section on its breathing resistance at different levels of breathing rate.
FIG. 4a.
For the second group of snorkels, Fig. 4b shows that the sweeping barrel snorkel V with flared end does definitely have an edge over the snorkel IV which has a convoluted flexible barrel. The addition of the sweeping barrel drops the breathing resistance at 100 l/rain to almost half that of the convoluted barrel snorkel. In Fig. 4c, the snorkels of the third group show a considerable improvement in the breathing characteristics mainly because of the wrap-around design and because they have been designed with large diameter tubes as well as with sweeping barrels.
sF
4 [
rcr
o Superflex.. r~r
3[-
e Po.r.ed
7
,. ~Z
{, '~
~ 0
IO
J
I
I
1
l
I
1
1
20
30
40
5o
60
70
80
90
Breofhing rote,
Fro. 4b.
I K30
E/rain
The effect of the barrel shape and the flared end of the snorkel on its breathing resistance at different levels of breathing rate.
468
A. BAZ and N. Zo(im R
~4
•
Off-se~'jef
o
Turboflex
.. ~ZI
[]
AMF-Swimmoster
.
~rr ..
t~
,.-Tr
I0
20
30
40
50
B r e a t " h i n g rare,
60
?0
80
90
100
IlO
L/rain
FIG. 4C. The effect of the wrap-around design and the flared end of the snorkel on its breathing resistance at different levels of breathing rate.
Of all the tested snorkels, snorkel VIII, which is the A M F Swimmaster snorkel type 2S55, has the least breathing resistance. At a breathing rate of 100 1/min, this snorkel requires only 1.5 nun of water breathing effort compared to 9 mm for the Spanish-made snorkel I. The low-breathing characteristics of the A M F Swimmaster snorkel compared with the other two wrap-around snorkels VI and VII are attributed to the fact that its top has a flared end, which minimizes the air resistance due to the turbulence that occurs when the flowing air meets the surrounding still ambient air. 3. E X P E R I M E N T A L
EVALUATION OF THE CLEARING OF SNORKELS
CHARACTERISTICS
This part of the study deals with the clearing characteristics of the snorkels. Such characteristics are of the utmost importance since snorkels are susceptible to being filled with water, in many situations, and divers find themselves compelled to exert sufficient effort to blow their breathing tubes clear before they can resume breathing.
3.1 Testing facility and procedure A special test stand has been built to measure two important parameters, the clearing speed and the clearing efficiency, since each can be taken as a measure of the diver's clearing effort and consequently of his comfort. The layout of the used test stand is shown in Fig. 5 indicating its main components as well as the measuring instrumentation. In Fig. 5, pressurized air from a storage tank is regulated by the bleed-off back pressure regulator A before it goes into the test section. A flexible tube B is inserted after the regulator A to act as a pneumatic accumulator in order to prevent any drop in the pressure at the snorkel inlet once the solenoid valve F is energized open. The flexible tube B is connected to a transparent plastic tube C which plays the role of a water level indicator. The end of this plastic tube is shaped in such a way that it fits nicely inside the mouthpiece of the snorkel
Breathing and clearing characteristics of snorkels
469
Air cotrotassor
Bleed off bock pressurere(:JulOtor
A
G Solenoid v(]lve
ir reserv~
\
FJ~~ - ~ -
~-- D U~ tube rnonometer
E~ J ~ ' ~ ~C Waterlevel indico,or Snorkel Layout of the test set-up used for measuring the clearing characteristics of snorkels. FIo. 5. under consideration. The flow from the other end of the snorkel is controlled by a twoposition solenoid valve F which is of the normally closed type. The pressure at the down-stream of the pressure regulator A is monitored by a regular U-tube manometer D inserted at the junction between the regulator A and the flexible tube B. To measure the clearing characteristics of the different snorkels, the solenoid valve is energized and the snorkel under consideration is filled with water from the port G, 0.3175 mm in diameter, of the solenoid valve until the water level can be seen through the transparent tube C. The solenoid valve is then de-energized to close the port G and the pressure regulator A is adjusted to maintain a predetermined pressure, say Pc, in its down-stream as monitored on the manometer D. The solenoid valve is energized carefully to release the extra water that fills the transparent tube above the level L - L and the valve is then closed. A timer is used to keep track of the time when the solenoid valve is energized again. Water will effiux out of the port G and when the flow starts to be discontinuous the timer is stopped to record a time of efflux te, and the valve is de-energized at the same time to retain a volume V, which remains uncleared. If the snorkel volume is V,, then the clearing efficiency rio after an efflux time t, under the influence of the constant clearing effort Pe will be defined as follows: ,c = (v, -
vr)/ v,.100.
(1)
The clearing speed S c will be in effect inversely proportional to the efflux time t e, or: Sc = K/t,
(2)
where K is a proportionality constant. The clearing characteristics, measured by the above procedure, are therefore determined in effect by subjecting the snorkel when completely filled with water to a controlled step pressure in order to simulate the possible effort levels exerted by the diver during the clearing process. The developed set-up and the proposed measuring techniques have been utilized to
470
A. BAZ a n d N . ZOOHEB
90 o Canarias .. I {Po=O 5 0 m water]
80
• Tubaflex. TT[Po=O26m water] m Spirotechnique . TIT [Po=O 52rn water]
70 I 6O
r~ 50
rrr 40 ~0
~0
I0
o
0.5
LO
L5
Clearing effort (pe-pollPo
FxG. 6a. The clearing efficiencyat different levels of clearing effort for the Canarias (I). Tubaflex (II) and Spirotechnique super snorkel (liD.
compare in a quantitative fashion the clearing efficiency qc and clearing speed S~ of the three groups of snorkels considered. 3.2 Results Figure 6a shows the effect of the diver clearing effort Pe on the clearing efficiency 11o as defined by (1), for the snorkels of the first group. The plot is presented in a dimensionless fashion by referring the diver effort to the effort necessary to just get the water column, inside the snorkel, to start flowing out of it. This reference effort is called the "NO FLOW E F F O R T . . . P0" and is mainly a measure of the pressure necessary to support the weight of the water column inside the snorkel. From Fig. 6a we can see that increasing the clearing effort increases the clearing efficiency but not in a linear fashion. Therefore, the bulk of the water inside the snorkel is cleared by a relatively small effort. Figure 6a indicates also that increasing the hydraulic diameter of the snorkel reduces considerably its clearing efficiency. Consequently, the snorkel I, which has been the poorest regarding its breathing characteristics, is now on top of the snorkels of its group since it shows the highest clearing efficiency at any clearing effort. In Fig. 6b, the clearing speeds of the three snorkels of the first group are given as a function also of the dimensionless clearing effort. The clearing speed increases, in a pattern similar to the clearing efficiency, with the increase of the clearing effort. But from the figure
Breathing and clearing characteristics of snorkels
471
o Conorio~ .. :I ,, Tuboflex .. n'
Spirofechr~ ..m
O,B
Q ~r
o,e
, ~ 0.4
15 02
I 0
I
05
I
I0
Cleoring efforf
1,5
(Pe "Po)./P o
FIG. 6b. The clearing speed at different levels of clearing effort for the Canarias (I), Tubaflex (II), and Spirotechnique super snorkel (1II). snorkel I I I exhibits faster clearing speeds than snorkel I and I I especially at high clearing effort. T o combine the effect o f the clearing effort on b o t h the clearing efficiency and speed, the product of the two p a r a m e t e r s is plotted against the clearing effort as shown in Fig. Oe. Such a product is used because it is equally i m p o r t a n t to clear the snorkel efficiently as well
.
0,30
Z
/ I - Conorios 1"I - Tuboflex
/ /
/ /
1t" J
.E
~ 0.20 K
u
~ u
010
,..
I 0 5
Cleoring effort
1 I0
I ~15
(Pe-Po)/Po
FIG. 6¢. The product of the clearing efficiency and clearing speed at different levels of clearing effort for Canarias (I), Tubaflex (II) and Spirotechnique super snorkel (III).
472
A. BAZ a n d N. Zo(;He~
o Superflex . ] ~ 70
• Power tuned ~[
[P~,=032 m woter] [Po=O 2 8 m
woter]
60
Eso ~ ~ Z
5Z
g
' ~ 4O
~
3O
-
7
2O
10 F 0
r
05
I
IO
15
Clearing effort (Pe-Po)/P,,
FIG. 7a.
The clearing efficiency at different levels of clearing effort for the Superflex (IV) and the Aqualung power-tuned snorkel (V).
as quickly for any level of clearing effort. Therefore, the snorkel which has the highest product of its two clearing parameters will be the best for clearing characteristics. From Fig. 6c, we conclude that snorkel I is better than II[ and III is better than II. For the snorkels of the second group, Fig. 7a indicates that snorkel IV is more efficient than snorkel V since it shows higher clearing efficiencies at any clearing effort. This is exactly the opposite to the breathing characteristics of these two snorkels. Also, comparison between Fig. 6a and Fig. 7a shows that the simple J-type snorkels [ 10
o Superflex
T~7
• Power tuned ,. O8
~-
- 06
_
.~./o
E
r-_ 0 4
O2
0
L
05
I
!0
~
I5
Clearing effort ( p -Po)/Po
Flo. 7b. The clearing speed at different levels of clearing effort for the Superflex (IV) and Aqualung power-tuned snorkel (V).
Breathing and clearing characteristics of snorkels 0.30
473
I
~ - Superflex
. . I ~
l~r
._~0; g-
g
~olc
I 0
0,5
I
I
I0
15
CleorhOefforf (Pe'Po)/Po
FIG. 7c. The product of the clearing e~ciency and clearing speed at different levels of clearing effort for the Suparflex (IV) and the Aqualung power-tuned snorkel (V).
and II have higher clearing efficiencies than snorkels with convoluted or sweeping barrels. Regarding the clearing speed, snorkel V shows faster clearing speeds than snorkel IV for all the considered clearing efforts as manifested by Fig. 7b. From the plot of the combined clearing parameters, shown in Fig. 7c, the relatively low cleating efficiency of snorkel V has been compensated by its fast clearing time to make this snorkel more favourable than snorkel IV. Hence, snorkels with sweeping barrels are much better than those fitted with convoluted flexible hoses. Interesting to note that cross comparison between Fig. 6c and Fig. 7c shows that wlaen the combined clearing parameters are considered, snorkel V with the sweeping barrel appears to be equally as good as the so far leading Spanish J-type snorkel I. This shows that it is reasonable to look to the combined effect of the clearing parameter before drawing any conclusions because a snorkel that has a high clearing efficiency is not necessarily the best snorkel since it may have a poor cleating speed. Finally, for the snorkels of the third group, Fig. 8a shows the clearing efficiency of these snorkels at different levels of the clearing effort. In this figure, snorkel VI exhibits the highest clearing efficiency of the snorkels of its groups. Snorkels VII and VIII have very similar clearing efficiencies over the entire range of the clearing effort considered. It is also clear from Fig. 4a and Fig. 8a that snorkel VI which has been the poorest of its group regarding the breathing characteristics is now taking the lead as far as the clearing efficiency is concerned. A similar trend can also be seen from Fig. 8b but with snorkel VIII showing also the highest cleating speed. It is then followed by snorkels VI and VII in that order. Looking now into the plot of the combined clearing parameters for the snorkels of the third group, given in Fig. 8c, we can see that snorkel VI ranks highest and is then followed
474
A. BAz and N. ZOGHEB o O f f - s e t jet .. ~ . 60-
[P~=0:30 m w o f e r ]
•
Turboflex
D
AMF Swirnrnoster
wofer]
.~11". [po=o30rn ~
, [Po=O.27m
wofer]
50-
0
30
o
~0
L 0
05
I0
Cleorino effort
~
15
(Pe'Po)/p o
FIG. 8a. The clearing efficiency at different levels of clearing effort for the Off-set jet (VI), Turboflex (VI) and AMF Swimmaster (VII) snorkels. by snorkels VIII and VII. The figure shows also, when compared with Fig. 6c and Fig. 7c, that snorkel V has the highest clearing figure of merit, i.e. the product of the clearing efficiency and speed, of all the snorkels tested. Accordingly, snorkels with large diameter tubes, sweeping barrels such as the U.S. Diver's Power Tuned snorkel V will exhibit the best clearing characteristics. 4. CONCLUSIONS This study has presented a comparative investigation of the breathing and cleating characteristics of several of the commonly used and commercially available snorkels. Two test stands have been built, the first to monitor the breathing resistance offered by each
IO
o
0ff-set jet
• TurbOflex
..
.. "PTT
AMF Swm~moster .. 08
o
O2
L
05
Cleonng effort
FIG. 8b.
i I0
15
(Pc -Po } / p o
The clearing speed at differentlevels of clearing effort for the Off-setjet (VI), Turboflex (VII) and AMF Swimmaster (VIII) snorkels.
Breathing and clearing characteristics of snorkels
475
o3o~' ~ - Off- set jef
"vrt Tudooflex 3 ~ - AMF Swirnmaster
"of
//~l~r
u
o~o
.[ I 0
05
t LO
1 I
5
Cleonng effort (l~-Po)/Po FxO. 8c.
The product of the clearing efficiency and clearing speed at different levels of clearing
effort for the Off-set jet (VI), Turboflex (VII) and AMF Swimmaster (VIII) snorkels.
snorkel at the different breathing rates, and the second to quantify the cleating efficiency and speed of the different snorkels when subjected to controlled constant clearing efforts. The tested snorkels have been grouped in three groups to study the effects of the geometry of the snorkel's cross section, the shape of its barrel, as well as the effect of the wraparound design and flared ends on its breathing and clearing characteristics. We have shown that increasing dimensions of the snorkel's cross section, incorporating sweeping barrels and using wrap-around snorkels with flared ends improves considerably the breathing characteristics. In this respect, the AMF Swimmaster snorkel number 2S55 exhibits the least breathing resistance over the entire range of diver's breathing rates. Regarding the clearing characteristics, snorkels with large diameters, and sweeping barrel design are considered to possess the best clearing figure of merit which combines the effects of both the clearing efficiency and speed. In this regard, the U.S. Diver's Power Tuned snorkel has the highest cleating figule of merit of all the snorkels tested. In spite of the fact that the AMF Swimmaster snorkel VIII has shown almost half the breathing resistance of the Power Tuned V of U.S. Divers, yet the latter snorkel has a clearing figure ofmerit which is nearly one and a half times as much as snorkel VIII. If more emphasis is to be placed on the breathing effort, since it extends over a long duration, then AMF Swimmaster snorkel is favoured over the U.S. Diver snorkel. But if the emphasis is placed on the clearing characteristics, since it requires more extraneous effort, then the U.S. Diver's Tuned snorkel is definitely the answer. Acknowledgement--Special thanks are due to Dr R. ~OYD, Director of Petrie's Scuba Lab. in Madison, Wisconsin, U.S.A., for granting the U.S. made snorkels used in this study. Without such a 8enerous grant this study would have been impossible. REFERENCE Sw~er,~Y, J. B. 1970. A Pictorial History of Oceanographic Submersibles, Crown Publishers, New York.