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Easy removal of abrasives from the seal chamber
S
PECIAL FEATURE
E asy removal of abrasives from the seal chamber P u m p u s e r s d e m a n d h i g h perform a n c e f r o m shaft s e a l i n g systems, b u t often a t t e n t i o n is f o c u s e d o n the s e a l itself a n d n o t o n the e n v i r o n . m e n t in which the s e a l operates. J o e D u n f o r d , a C a n a d i a n engineer, has been r e s e a r c h i n g the f l o w regimes w i t h i n the s e a l c h a m b e r f o r a n u m be r o f y e a r s . H e h a s d e s i g n e d a n d n o w sells t w o s e a l p r o t e c t i o n devices t h a t a l t e r t h o s e f l o w r e g i m e s to p r e v e n t the b u i l d u p o f v a p o u r a n d a b r a s i v e p a r t i c l e s , as well a s irrv p r o v i n g h e a t d i s s i p a t i o n . I n this article w e l o o k a t his n e w SpiralT r a c TM t h r o a t bushing.
be e l i m i n a t e d w i t h o u t recourse to the e x p e n s e of flush a n d r e c i r c u l a t i o n lines. The o p e r a t i n g principles of this p r o d u c t were described in a n earlier article in World P u m p s ( F e b r u a r y 1992) a n d since t h e n t h o u s a n d s of SealMates have been installed in a p p l i c a t i o n s i n c l u d i n g chemical processing, refinery duties, mining, p u l p & paper, a n d power generation. However, Dunford realised t h a t in certain applications, for e x a m p l e w h e n r e t e n t i o n of flush a n d recirculation was desirable, a n a l t e r n a t i v e solution was needed. The result of his c o n t i n u e d research in this area is the SpiralTrac, a spiral t h r o a t b u s h i n g t h a t acts to remove abrasive particles from the seal cavity.
[]
SpiralTrac: h o w d o e s it work?
Seal protection devices When Joe Dunford of Enviroseal i n v e n t e d the SealMate TM seal p r o t e c t i o n device, he provided p u m p users with a n a l t e r n a t i v e to complicated e n g i n e e r i n g s o l u t i o n s to p o o r seal c h a m b e r e n v i r o n m e n t s . By c h a n g i n g the c h a m b e r flow p a t t e r n s , this device e n a b l e d p r o b l e m s of heat transfer, v a p o u r v e n t i n g a n d abrasive particles to
Operating principles of the SpiralTrac throat bushing.
i
WORLD PUMPS DECEMBER 1995
In a seal chamber, the r o t a t i n g shaft i n d u c e s a r o t a t i n g flow p a t t e r n in the fluid. The SpiralTrac device converts some of this r o t a t i n g flow into a strong axial flow c o m p o n e n t . This axial flow is directed along the seal c h a m b e r bore, away from the gland towards throat. Since c o n t a m i n a n t s a r e c e n t r i f u g e d to t h e b o r e d u r i n g p u m p operation, the flow sweeps t h e m in the direction of the SpiralTrac a n d u p a shallow-angled lead-in section (see figure). The f u n c t i o n of this lead-in section is to increase the velocity of the particles, a n d hence increase the centrifugal force on them. A small groove m a c h i n e d at the head of the shallow r a m p t h e n collects the c o n t a m i n a n t s . This collection groove leads directly into the m a i n spiral which conveys the c o n t a m i n a n t s radially inwards, t h e n out of the seal c h a m b e r t h r o u g h the exit groove. The m a i n spiral c o n t i n u a l l y decreases in diameter, a n d the steadily increasing centrifugal effect forces the c o n t a m i n a n t s deeper in the groove. This allows the d e p t h a n d width of the groove to be steadily decreased as it n e a r s the shaft. Consequently, most of the fluid is spilled from the groove by the time the shaft is reached. This e x p l a i n s the axial flow in the seal chamber, a n d m e a n s t h a t only the apex of the spiral cut needs to be guided to the exit, m i n i m i z i n g fluid exchange. This m e a n s t h a t e x t e r n a l cooling of
© 1995, Elsevier Science Ltd 0262 1762/95/$7.00
S PECIAL
FEATURE
Type A SpiralTrac for standard API pumps.
Type S split SpiralTracs have been very successful in pulp and paper applications.
t h e seal a n d c a v i t y p r e s s u r i s a t i o n is still possible. A larger exit c h a n n e l can be used on fibrous c o n t a m i n a n t s to avoid plugging. An air v e n t is m a c h i n e d into the top surface of the SpiralTrac, users can drill a n o p t i o n a l c o n n e c t i n g hole in the back-plate to p u r g e air on initial p u m p flooding.
Type B: The s e c o n d c o n f i g u r a t i o n is for s t a n d a r d p r o c e s s p u m p s to A N S I / I S O / E N . Again this can be simply pressed into place. For retention, m o s t ANSI SpiralTrac designs i n c o r p o r a t e a l e n g t h of O-ring m a t e r i a l in a n e x t e r n a l d i a m e t e r groove. In a p p l i c a t i o n s where there is no flush, the exit groove should be e x t e n d e d to the p u m p a g e by filing or g r i n d i n g the cast-in throat. It is also r e c o m m e n d e d t h a t a v e n t hole is drilled at the top of the cast t h r o a t to allow air to purge on flooding the p u m p .
When to use the SpiralTrac The spiral t h r o a t b u s h i n g is a c o m p l i m e n t a r y p r o d u c t to the SealMate, b u t it is fitted with virtually no p u m p modification. Unlike the SealMate which works by m a i n t a i n i n g a strong flow into a n d o u t of the chamber, it c a n n o t replace flush a n d recirculation lines b e c a u s e it does n o t e x c h a n g e m u c h flow (flush rate is j u s t w h a t is n e e d e d for face cooling, typically a r o u n d 0.5 g a l / m i n ) . However, b e c a u s e it sets u p the same flow regime w i t h i n the chamber, it can offer r e d u c e d flush r e q u i r e m e n t s , removal of abrasives, the o p t i o n of air-venting a n d i n s t a l l a t i o n w i t h o u t modifications to the p u m p or p i p i n g a r r a n g e m e n t s . D i f f e r e n t versions of the device are a v a i l a b l e d e p e n d i n g o n t h e duty. M a t e r i a l o p t i o n s i n c l u d e bronze, 416 stainless steel, 316 stainless steel, a n d glass a n d c a r b o n filled PTFE. F u r t h e r e n g i n e e r i n g polymers are being investigated which m i g h t offer a b e a r i n g capability in u n s t a b l e shaft conditions. Three basic configurations are available: Type A: This b u s h i n g is designed for API610 s t a n d a r d p u m p s . The device is pressed into p o s i t i o n at the b o t t o m of the seal chamber. The b u s h i n g is designed to fit into the c o u n t e r bore a n d the exit groove e x t e n d s right t h r o u g h the p u m p housing.
Type S: The final configuration is a split version for use with e x t e r n a l seals or split seals. This has proved p a r t i c u l a r l y successful in the p u l p a n d p a p e r industry. A flush is n o r m a l l y required.
Summary By m a n i p u l a t i n g t h e flow w i t h i n t h e seal chamber, the seal e n v i r o n m e n t can be optimized. These two p r o d u c t s achieve t h a t a n d so c o n t a m i n a n t s , w h e t h e r v a p o u r or heavy abrasives, can be kept away from the seal faces a n d removed from the seal chamber. The result is reduced wear a n d improved seal performance: a d m i r a b l e benefits. The a d d i t i o n of the new SpiralTrac e x t e n d s the benefits of controlling seal c h a m b e r flows to new areas, i n c l u d i n g low speed a p p l i c a t i o n s a n d rotary positive d i s p l a c e m e n t p u m p s such as screw or progressing cavity types. •
For more information, contact: Joe Dunford, Enviroseal Engineering Products Ltd, 1310 Rocky Lake Drive, Waverley, Nova Scotia, Canada B0N 2S0. Tel: +1 902 861 3464; Fax: + 1 902 861 3522.
WORLD PUMPS DECEMBER 1995
PECIAL FEATURE
E asy removal of abrasives from the seal chamber P u m p u s e r s d e m a n d h i g h perform a n c e f r o m shaft s e a l i n g systems, b u t often a t t e n t i o n is f o c u s e d o n the s e a l itself a n d n o t o n the e n v i r o n . m e n t in which the s e a l operates. J o e D u n f o r d , a C a n a d i a n engineer, has been r e s e a r c h i n g the f l o w regimes w i t h i n the s e a l c h a m b e r f o r a n u m be r o f y e a r s . H e h a s d e s i g n e d a n d n o w sells t w o s e a l p r o t e c t i o n devices t h a t a l t e r t h o s e f l o w r e g i m e s to p r e v e n t the b u i l d u p o f v a p o u r a n d a b r a s i v e p a r t i c l e s , as well a s irrv p r o v i n g h e a t d i s s i p a t i o n . I n this article w e l o o k a t his n e w SpiralT r a c TM t h r o a t bushing.
be e l i m i n a t e d w i t h o u t recourse to the e x p e n s e of flush a n d r e c i r c u l a t i o n lines. The o p e r a t i n g principles of this p r o d u c t were described in a n earlier article in World P u m p s ( F e b r u a r y 1992) a n d since t h e n t h o u s a n d s of SealMates have been installed in a p p l i c a t i o n s i n c l u d i n g chemical processing, refinery duties, mining, p u l p & paper, a n d power generation. However, Dunford realised t h a t in certain applications, for e x a m p l e w h e n r e t e n t i o n of flush a n d recirculation was desirable, a n a l t e r n a t i v e solution was needed. The result of his c o n t i n u e d research in this area is the SpiralTrac, a spiral t h r o a t b u s h i n g t h a t acts to remove abrasive particles from the seal cavity.
[]
SpiralTrac: h o w d o e s it work?
Seal protection devices When Joe Dunford of Enviroseal i n v e n t e d the SealMate TM seal p r o t e c t i o n device, he provided p u m p users with a n a l t e r n a t i v e to complicated e n g i n e e r i n g s o l u t i o n s to p o o r seal c h a m b e r e n v i r o n m e n t s . By c h a n g i n g the c h a m b e r flow p a t t e r n s , this device e n a b l e d p r o b l e m s of heat transfer, v a p o u r v e n t i n g a n d abrasive particles to
Operating principles of the SpiralTrac throat bushing.
i
WORLD PUMPS DECEMBER 1995
In a seal chamber, the r o t a t i n g shaft i n d u c e s a r o t a t i n g flow p a t t e r n in the fluid. The SpiralTrac device converts some of this r o t a t i n g flow into a strong axial flow c o m p o n e n t . This axial flow is directed along the seal c h a m b e r bore, away from the gland towards throat. Since c o n t a m i n a n t s a r e c e n t r i f u g e d to t h e b o r e d u r i n g p u m p operation, the flow sweeps t h e m in the direction of the SpiralTrac a n d u p a shallow-angled lead-in section (see figure). The f u n c t i o n of this lead-in section is to increase the velocity of the particles, a n d hence increase the centrifugal force on them. A small groove m a c h i n e d at the head of the shallow r a m p t h e n collects the c o n t a m i n a n t s . This collection groove leads directly into the m a i n spiral which conveys the c o n t a m i n a n t s radially inwards, t h e n out of the seal c h a m b e r t h r o u g h the exit groove. The m a i n spiral c o n t i n u a l l y decreases in diameter, a n d the steadily increasing centrifugal effect forces the c o n t a m i n a n t s deeper in the groove. This allows the d e p t h a n d width of the groove to be steadily decreased as it n e a r s the shaft. Consequently, most of the fluid is spilled from the groove by the time the shaft is reached. This e x p l a i n s the axial flow in the seal chamber, a n d m e a n s t h a t only the apex of the spiral cut needs to be guided to the exit, m i n i m i z i n g fluid exchange. This m e a n s t h a t e x t e r n a l cooling of
© 1995, Elsevier Science Ltd 0262 1762/95/$7.00
S PECIAL
FEATURE
Type A SpiralTrac for standard API pumps.
Type S split SpiralTracs have been very successful in pulp and paper applications.
t h e seal a n d c a v i t y p r e s s u r i s a t i o n is still possible. A larger exit c h a n n e l can be used on fibrous c o n t a m i n a n t s to avoid plugging. An air v e n t is m a c h i n e d into the top surface of the SpiralTrac, users can drill a n o p t i o n a l c o n n e c t i n g hole in the back-plate to p u r g e air on initial p u m p flooding.
Type B: The s e c o n d c o n f i g u r a t i o n is for s t a n d a r d p r o c e s s p u m p s to A N S I / I S O / E N . Again this can be simply pressed into place. For retention, m o s t ANSI SpiralTrac designs i n c o r p o r a t e a l e n g t h of O-ring m a t e r i a l in a n e x t e r n a l d i a m e t e r groove. In a p p l i c a t i o n s where there is no flush, the exit groove should be e x t e n d e d to the p u m p a g e by filing or g r i n d i n g the cast-in throat. It is also r e c o m m e n d e d t h a t a v e n t hole is drilled at the top of the cast t h r o a t to allow air to purge on flooding the p u m p .
When to use the SpiralTrac The spiral t h r o a t b u s h i n g is a c o m p l i m e n t a r y p r o d u c t to the SealMate, b u t it is fitted with virtually no p u m p modification. Unlike the SealMate which works by m a i n t a i n i n g a strong flow into a n d o u t of the chamber, it c a n n o t replace flush a n d recirculation lines b e c a u s e it does n o t e x c h a n g e m u c h flow (flush rate is j u s t w h a t is n e e d e d for face cooling, typically a r o u n d 0.5 g a l / m i n ) . However, b e c a u s e it sets u p the same flow regime w i t h i n the chamber, it can offer r e d u c e d flush r e q u i r e m e n t s , removal of abrasives, the o p t i o n of air-venting a n d i n s t a l l a t i o n w i t h o u t modifications to the p u m p or p i p i n g a r r a n g e m e n t s . D i f f e r e n t versions of the device are a v a i l a b l e d e p e n d i n g o n t h e duty. M a t e r i a l o p t i o n s i n c l u d e bronze, 416 stainless steel, 316 stainless steel, a n d glass a n d c a r b o n filled PTFE. F u r t h e r e n g i n e e r i n g polymers are being investigated which m i g h t offer a b e a r i n g capability in u n s t a b l e shaft conditions. Three basic configurations are available: Type A: This b u s h i n g is designed for API610 s t a n d a r d p u m p s . The device is pressed into p o s i t i o n at the b o t t o m of the seal chamber. The b u s h i n g is designed to fit into the c o u n t e r bore a n d the exit groove e x t e n d s right t h r o u g h the p u m p housing.
Type S: The final configuration is a split version for use with e x t e r n a l seals or split seals. This has proved p a r t i c u l a r l y successful in the p u l p a n d p a p e r industry. A flush is n o r m a l l y required.
Summary By m a n i p u l a t i n g t h e flow w i t h i n t h e seal chamber, the seal e n v i r o n m e n t can be optimized. These two p r o d u c t s achieve t h a t a n d so c o n t a m i n a n t s , w h e t h e r v a p o u r or heavy abrasives, can be kept away from the seal faces a n d removed from the seal chamber. The result is reduced wear a n d improved seal performance: a d m i r a b l e benefits. The a d d i t i o n of the new SpiralTrac e x t e n d s the benefits of controlling seal c h a m b e r flows to new areas, i n c l u d i n g low speed a p p l i c a t i o n s a n d rotary positive d i s p l a c e m e n t p u m p s such as screw or progressing cavity types. •
For more information, contact: Joe Dunford, Enviroseal Engineering Products Ltd, 1310 Rocky Lake Drive, Waverley, Nova Scotia, Canada B0N 2S0. Tel: +1 902 861 3464; Fax: + 1 902 861 3522.
WORLD PUMPS DECEMBER 1995