- Email: [email protected]
CFD analysis of pressure loss during flow by hydraulic directional control valve constructed from logic valves
Energy Conversion and Management 65 (2013) 285–291
Contents lists available at SciVerse ScienceDirect
Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
CFD analysis of pressure loss during flow by hydraulic directional control valve constructed from logic valves E. Lisowski a,⇑, J. Rajda b a b
Cracow University of Technology, al. Jana Pawła II 37, 31-864 Kraków, Poland PONAR Wadowice S.A., ul. Wojska Polskiego 29, 34-100 Wadowice, Poland
a r t i c l e
i n f o
Article history: Received 7 December 2011 Received in revised form 15 August 2012 Accepted 16 August 2012 Available online 17 October 2012 Keywords: Directional control valve Logic valve Computational Fluid Dynamics
a b s t r a c t The aim of this paper is to investigate the reduction of flow resistance in a hydraulic system. The undertaken matter is focused on a spool type directional control valve with pilot operated check valves. In the paper there is a proposition of replacing a 4-way directional control valve with pilot operated check valves by suitable unit consisting of logic valves. Therefore, a body of new directional control valve has been designed. Four logic valves are mounted on the body and closed with a cover on which electromagnetic pilot valve is assembled. The hydraulic ports of the body are in accordance with the standard ISO 4401 – 08-07-0-94, so the proposed new directional control valve can be applied alternatively to a directional spool valve. An important task given during the work is to create the systems of flow paths inside the body, which are assumed to be performed with simple technologies like: drilling, boring and milling. The system of the designed flow paths is verified by CFD analysis with the use of ANSYS/FLUENT program on three-dimensional model. Obtained results are compared with the results of the characteristics given in catalogues and coming from experimental research of the prototype. The difference in pressure loss during flow for the logic valve taken from CFD calculation and the catalogue do not exceed 5%. Presented in the paper directional control valve may operate for volumetric flow rate up to 450 dm3/min and the pressure up to 42 MPa. In the proposed solution, although simple technologies of making flow paths were applied, the pressure losses were reduced over 35%. The developed solution is close to a standard directional spool valve and can be assembled on an identical sub-plate. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction There is a tendency for reduction energy consumption of working machines by minimizing pressure losses on hydraulic drive systems. Significant losses of pressure usually appear in the areas of changes in cross sections, changes of the flow direction, and in the places where the swirls are formed. Such areas exist in hydraulic valves, particularly in directional control valves. The problem of losses evaluation in such components is a complex matter. In order to analyze the flow in these type of elements the CFD systems are very useful. To obtain effective solution some authors apply models with different level of simplification in CFD analysis of hydraulic valves. The easiest approach is using 2D models [1–3] or axisymmetrical [4–6]. In case of flow in complex geometry in order to simulate flow phenomena it is necessary to apply three dimensional models [6–9]. During the work, the possibility of pressure loss reduction in directional control valve was investigated. As a result there was a ⇑ Corresponding author. E-mail addresses: [email protected] (E. Lisowski), [email protected] (J. Rajda). 0196-8904/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.enconman.2012.08.015
proposition of equivalent solution by the usage of logic valves. There is assumption, that the way of assembly of the new directional control valve to mounting plate will be identical to directional spool valve, that is by the usage of a manifold with standard ports. There is also assumption, that the construction of the body of directional control valve will be produced by the usage of simple machining (drilling, boring or milling). In the work the solution of new directional control valve with logic valves was presented. The design was prepared in Solid Edge software. Pressure losses were evaluated by using ANSYS/FLUENT package and the simulation results were verified [10]. 2. Hydraulic system The subject of the study is a typical hydraulic system illustrated on Fig. 1, with hydraulic cylinder as a working element. In this system the electromagnetic directional control valve (1) controls the main spool of directional control valve (2). Backflow from cylinders is secured by pilot operated check valves (3). The hydraulic system is designed for volumetric flow rate up to 450 dm3/min and working pressure up to 35 MPa. In the system the following components are used: directional control valve
286
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
Nomenclature A, B P T X Y AT BT
actuator ports pressure port return port pressure port for the pilot valve return port for the pilot valve flow path A–T flow path B–T
PA flow path P–A PB flow path P–B A1, A2, A3 control area of logic valve Q volumetric flow rate p pressure of working liquid Dp pressure loss CFD Computational Fluid Dynamics
Fig. 3. Double check valve, pilot operated Z2S22 [11] in standard [14].
Fig. 1. Hydraulic system diagram: (1) electromagnetic directional valve (pilot stage), (2) directional spool valve (main stage), (3) pilot operated check valves, (4) hydraulic cylinder, and (5) power unit.
Fig. 4. Losses of pressure in directional control valve WEH22 at viscosity of hydraulic liquid 41 mm2/s: (1) path AT, (2) PA and PB path, and (3) BT path.
Fig. 2. Directional control valve, electro-hydraulically operated type WEH22 [13] in standard [14].
Comparison of Figs. 4 and 5 shows that the loss of pressure for flow path BT (at Q = 450 dm3/min) goes up to 2.55 MPa (reaches the rate over two times higher than the loss for flow through directional spool valve only). A question has been asked: how much will the pressure losses reduce when the unit of directional control spool valve WEH22 with double pilot operated check valve Z2S22 is replaced by logic type of directional control valve? The pressure loss in logic valve for example: URZS25 [15] (Fig. 7) are smaller, if we compare with a single flow path of directional valve. Furthermore, when piloting system is leak tight, there is no need for application of check valves pilot operated because the logic valves are poppet type.
3. Logic valves WEH22 (Fig. 2) and pilot operated check valve Z2S22 (Fig. 3) – according to catalogues [11–13]. For volumetric flow rate 450 dm3/min the losses of pressure in directional control valve WEH22 reach values from 0.79 MPa to 1.15 MPa (Fig. 4). The biggest value of pressure loss occurs on flow path BT. If we take into consideration the losses of pressure resulted from the flow through pilot operated check valve, then total losses of pressure will reach values as on Fig. 5.
Logic valves (Fig. 6) are Fig. oat>built as 2/2 way cartridge valve. They are composed of the cartridge insert and the cover (4) with control holes. The cartridge insert consist of the bushing (1), the spring (3) and the poppet (2). The poppet is pressed down to valve seat by means of the spring (3). The valve allows for flow from A to B or reversely from B to A. The valve poppet has three important areas for its operation. The annular area A2 is 7% or 50% of area A1. The area ratio A1:A2 is therefore either 14.3:1 or 2:1. The area
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
Fig. 5. Total losses of pressure in flow by directional spool valve WEH22 and pilot operated check valve Z2S22 at viscosity of hydraulic liquid 41 mm2/s: (1) path AT, (2) PA and PB path, and (3) BT path.
A3 is A1 + A2 and can be either 107% or 150% of area A1. The valve opens in both flow directions if surface A3 is not affected by pressure (port X is unpressurised) and pressure force affecting the adequate surfaces A1 and A2 exceeds force of the spring (3). If surface A3 is affected by control pressure the valve poppet is pressed down to its seat, irrespectively of the spring (3) force. The valve may be opened by unloading surface A3 (connecting the chamber X to return line) or by appropriately high pressure on port A or B. The resistance of flow by logic valve is lower compared with the resistances of flow by directional spool valve and significantly lower when compared when the flow resistances of unit: directional spool valve and pilot operated check valves. Taking into consideration the reduction of pressure losses in the hydraulic unit, it seems that research conduction on the using of logic valves in hydraulic system is purposeful. 4. Logic valve model In order to build directional control valve logic type, realizing the functions as on Fig. 1, there is a proposition for usage of four logic valves with area ratio A2:A1 = 50%, which is presented on Fig. 8. The model of four logic valves has been created in form of brick applying Solid Edge software. Relevant assembly cavities have been designed in the body and adequate flow paths. One common cover for four logic valves has been provided in the design. It forms both mounting plate for pilot valve (1), and enables to bring pilot flow to the logic valves (2–5). The prepared design of directional control valve has been presented on Fig. 9 in the form of overall view and in section on Fig. 10. The new-built model of directional
287
Fig. 7. Pressure loss of logic valve URZS25 [15], at viscosity of hydraulic liquid 41 mm2/s: Dpmax = 0.55 MPa at Q = 450 dm3/min.
Fig. 8. Schematic diagram of directional control valve logic type performing the function of directional spool valve WEH22 with the valve Z2S22 in standard [14]: (1) directional control valve (pilot valve), (2–5) logic valves.
control valve (Fig. 8) can be mounted on the same sub-plate as a standard directional control valve. The logic valves are placed in parallel in one surface in body (Fig. 10), what simplified the creating inlet and outlet ports to the sub-plate and enabled to maintain the similar overall dimensions like for the directional spool valve WEH22. The outlet and inlet paths to the logic valves are mostly designed as simple bores. 4.1. CFD flow simulation in directional control valve logic type There might be used various flow models in simulation of flow for directional control valve [16]. Literature [8,16,17] shows that in similar analysis with hydraulic oil as working medium model k e generally was used. Therefore for simulation research available in
Fig. 6. Design of logic valve: (1) body, (2) poppet, (3) spring, and (4) cover.
288
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
Fig. 9. Directional valves: on the left 3D model of directional control valve logic type, on the right directional control spool valve WEH22.
Fig. 10. Directional control valve logic type: (1) logic valve open, (2) logic valve closed, (3) pilot valve, and (4) body.
Fig. 12. Grid for model of BT flow path.
ANSYS/FLUENT standard model of turbulence k e has been chosen [16,17]. The turbulence kinetic energy k and its rate of dissipation e are obtained from the following transport equations:
@ @ @ ðqkÞ þ ðqkui Þ ¼ @t @xi @xj
lþ
lt @k þ Gk þ Gb qe Y M þ Sk rk @xj ð1Þ
@ @ @ ðqeui Þ ¼ ðqeÞ þ @t @xi @xj
lþ
C 2e q
e2 k
lt @ e e þ C 1e ðGk þ C 3e Gb Þ re @xj k
þ Se
ð2Þ
In these equations, Gk represents the generation of turbulence kinetic energy due to the mean velocity gradients, calculated as described in modelling turbulent production in the k e models. Gb is the generation of turbulence kinetic energy due to buoyancy, calculated as described in effects of buoyancy on turbulence in the k e models. YM represents the contribution of the fluctuating dilatation in compressible turbulence to the overall dissipation rate, calculated as described in effects of compressibility on turbulence in the k e models. C1e, C2e and C3e are constants. Sk and Se are the turbulent Prandtl numbers for k and e, respectively. Sk and Se are user-defined source terms. The turbulent (or eddy) viscosity, lt, is computed by combining k and e as follows: 2
Fig. 11. Grid model of PA flow path.
lt ¼ qC l
k
e
ð3Þ
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
289
Fig. 13. Distribution of pressure on walls of the PA path.
where Cl is a constant. Model constants: the model constants have the following default values [16,17]: C1e = 1.44, C2e = 1.92, C3e = 1, Cl = 0.09, Sk = 1.0, Se = 1.3. 4.2. Geometric model and discerte model (grid) Geometric models of four flow paths have been created from 3D model of directional valve, that is: PA, PB, AT and BT. Each of these has different geometry and different total length. For example: on Fig. 11 the flow path PA has been depicted, which is the shortest, while on Fig. 12 the model of path BT, which is the longest. While generating grid the following requirements for cells dimensions have been defined: 3 inner wall layers along walls have been assumed, the grid in the places of complex geometry has been refined. Grid information for flow path PA: minimum size 0.09 mm, average size 2 mm, maximum size 6 mm, number of cells 634,110, tetrahedral 472,198, wedges 161,857, pyramids 55. The grid for model of flow path BT (Fig. 12) has been generated applying the same requirements. For path BT, the model contained 653,966 cells.
Fig. 14. Velocity distribution along streamline for PA path.
4.3. Boundary conditions and results The calculation has been conducted for four values of inlet velocity of hydraulic liquid: 4, 8, 12 and 16 m/s (Velocity Inlet). For outlet boundary condition type Pressure Outlet has been assumed – constant pressure on outlet p = 0.1 MPa. Intensity of turbulence has been assumed for calculation on the value of 2% for the length of scale 2 mm. Remaining assumptions:
no slip on walls, the liquid is incompressible (hydraulic oil), the liquid properties are constant, the model is in conditions of thermal equilibrium, viscosity of hydraulic liquid is 41 mm2/s.
As a result of conducted simulations for each of the analyzed flow paths distribution of pressure on the walls of channels and velocity in the designated intersections have been received.
Fig. 15. Distribution of pressure on walls of BT path.
Streamlines allowed for evaluation of stream swirl places. For example on Fig. 13 distribution of pressure on the walls has been depicted for flow path PA, and on Fig. 15 for flow path BT. As a result of analysis of these drawings in the case of flow path BT it was found that, there were more significant pressure losses, than in case of flow path PA.
290
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
Fig. 16. Velocity distribution on the plane of logic valve BT path.
Fig. 19. Pressure losses in directional control valve logic type: (1) PA path and (2) BT path (pressure losses max 0.93 MPa and 1.67 MPa).
Fig. 17. Velocity distribution along streamline for BT path.
Fig. 18. Comparison of pressure losses on logic valve: (1) experimental research and (2) result from CFD simulation (the difference is smaller than 5%).
On Fig. 16 the distribution of hydraulic liquid velocity has been depicted in plain of logic valve hole. The logic valve has four inlet ports. As results from Fig. 16, the flow is realized mainly by the hole joined directly to return port T. It can be also noticed in analysis of the streamlines (Figs. 14 and 17). 4.4. Pressure losses Evaluating the way of pressure losses of hydraulic valves is defined in ISO standard [18]. It allows to compare the solutions from
different manufacturers. The same way of evaluating pressure losses was used in CFD simulation. For four values of liquid velocity at valve inlet (4, 8, 12, 16 m/s) were conducted simulations and as a results pressure losses have been obtained. The calculation of pressure losses has been conducted on the single logic valve. The pressure losses were calculated as a difference of average pressure on outlet and inlet. Fig. 18 presents comparison of characteristic of pressure losses for valve obtained by CFD methods (curve 2) and catalogue characteristic (curve 1) [15]. Differences are very small and do not exceed 5%. The pressure losses of proposed design of control valve obtained with CFD method have been presented on Fig. 19 for flow paths PA and BT. If we compare these characteristics with Fig. 5 (directional spool valve and pilot operated check valves), then it is clearly visible, that the proposed solution of directional control valve logic type allowed to significant reduction of pressure losses. For flow path PA about 61%, while for flow path BT 35%. 5. Experimental research A prototype of directional control valve logic type has been prepared based on model presented on Figs. 9 and 10. It was used on experimental test stand presented on Fig. 20. The stand allowed to set constant volumetric flow rates Q = 111, 215, 306, 430 dm3/min. The experimental conditions were in conformity with ISO standard [18]. Results from the experimental research (Fig. 21) have been approximated with polynomial curves 3 and 4. Curves 1 and 3 refer to pressure loss on flow path PA, curves 2 and 4 – on flow path BT. The results obtained from the experimental research are closed to those from CFD model. Difference
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
291
using in hydraulic system logic type directional valve, instead of directional spool valve, allows for significant reduction of pressure losses. It was from 35% up to 61% in analyzed hydraulic system. The proposed logic type directional control valve did not need to apply a body with complex flow paths. The needed flow path can be performed by simple machining process like: drilling, boring and milling. Furthermore, it can be noticed that logic type directional control valve can be used for other needs, for example: lower switching time, work in higher pressures. Application of ANSYS/FLUENT program enabled to obtain characteristics of pressure losses with deviation about 5%, in comparison to experimental test. References Fig. 20. Prototype of directional control valve logic type at experimental stand.
Fig. 21. Comparison of experimental results with CFD analysis: (1) CFD analysis for flow path PA, (2) CFD analysis for flow path BT (3) experimental results for flow path PA, and (4) experimental results for flow path BT.
of pressure losses in the range of flow up to 430 dm3/min does not exceed 5%. 6. Conclusions The paper concerns the proposition of replacement of directional spool valve by logic valves built in the body mounted on the sub-plate complying with standard ISO [14] as used for directional spool valves. In this way the possibility of change of these components has been obtained. The proposed solution has been verified by experimental test on prepared test stand. CFD analysis with the usage ANSYS/FLUENT showed, that proposed solution of
[1] Vescovo GD, Lippolis A. Three-dimensional analysis of flow forces on directional control valves. Int J Fluid Power 2003;4(2):15–24. [2] Vescovo GD, Lippolis A. Optimization of flow through a pneumatic control valve using CFD analysis and experimental validation. Fluid Power 2007;1:31–41. [3] Pan X, Wang G, Lu Z. Flow field simulation and a flow model of servo-valve spool valve orifice. Energy Convers Manage 2011;52(10):3249–56. http:// dx.doi.org/10.1016/j.enconman.2011.05.010. [4] Amirante R, Moscatelli P, Catalano L. Evaluation of the flow forces on a direct (single stage) proportional valve by means of a computational fluid dynamic analysis. Energy Convers Manage 2007;48(3):942–53. http://dx.doi.org/ 10.1016/j.enconman.2006.08.024. [5] Amirante R, Vescovo GD, Lippolis A. Evaluation of the flow forces on an open centre directional control valve by means of a computational fluid dynamic analysis. Energy Convers Manage 2006;47(13–14):1748–60. http://dx.doi.org/ 10.1016/j.enconman.2005.10.005. [6] Lisowski E, Momeni H. CFD analysis of pilot operated relief valve. In: Proceedings of 5th FPNI-PhD symposium, Kraków; 2008. p. 493–500. [7] Domagala M, Lisowski E. Optimization hydraulic components using fluid-solid interaction simulation. In: Proceedings of 4th FPNI-PhD symposium, Florida – Sarassota; 2006. p. 151–9. [8] Domagala M. CFD analysis of a flow control valve. In: Proceedings of 5th FPNIPhD symposium, Kraków; 2008. p. 445–50. [9] Lisowski E, Domagala M. Determination of static characteristic of direct acting relief valve. In: Proceedings of the 1st international conference on computational methods in fluid power technology, Melbourne; 2003. p. 211–20. [10] ANSYS/Fluent: users guide, 13th ed.; 2011. [11] Bosch Rexroth. Catalogue: check valve pilot operated re 21564/07.10; 2010. [12] Bosch-Rexroth. Catalogue: 3/2, 4/2 and 4/3 directional valves, internally pilot operated, externally pilot operated re 24751/08.08; 2010. [13] PONAR Wadowice. Catalogue: directional spool valve; 2001. [14] ISO 4401:2005 Hydraulic fluid power – four-port directional control valves – mounting surfaces; 2005. [15] PONAR Wadowice. Catalogue: 2/2 – way catridge valve; 2010. [16] Launder BE, Spalding DB. The numerical computation of turbulent flows. Comput Methods Appl Mech Eng 1990:269–89. [17] Launder BE, Spalding DB. Lectures in mathematical models of turbulence. London (England): Academic Press; 1972. [18] ISO 6403:1988 Hydraulic fluid power – valves controlling flow and pressure – test methods.
Contents lists available at SciVerse ScienceDirect
Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman
CFD analysis of pressure loss during flow by hydraulic directional control valve constructed from logic valves E. Lisowski a,⇑, J. Rajda b a b
Cracow University of Technology, al. Jana Pawła II 37, 31-864 Kraków, Poland PONAR Wadowice S.A., ul. Wojska Polskiego 29, 34-100 Wadowice, Poland
a r t i c l e
i n f o
Article history: Received 7 December 2011 Received in revised form 15 August 2012 Accepted 16 August 2012 Available online 17 October 2012 Keywords: Directional control valve Logic valve Computational Fluid Dynamics
a b s t r a c t The aim of this paper is to investigate the reduction of flow resistance in a hydraulic system. The undertaken matter is focused on a spool type directional control valve with pilot operated check valves. In the paper there is a proposition of replacing a 4-way directional control valve with pilot operated check valves by suitable unit consisting of logic valves. Therefore, a body of new directional control valve has been designed. Four logic valves are mounted on the body and closed with a cover on which electromagnetic pilot valve is assembled. The hydraulic ports of the body are in accordance with the standard ISO 4401 – 08-07-0-94, so the proposed new directional control valve can be applied alternatively to a directional spool valve. An important task given during the work is to create the systems of flow paths inside the body, which are assumed to be performed with simple technologies like: drilling, boring and milling. The system of the designed flow paths is verified by CFD analysis with the use of ANSYS/FLUENT program on three-dimensional model. Obtained results are compared with the results of the characteristics given in catalogues and coming from experimental research of the prototype. The difference in pressure loss during flow for the logic valve taken from CFD calculation and the catalogue do not exceed 5%. Presented in the paper directional control valve may operate for volumetric flow rate up to 450 dm3/min and the pressure up to 42 MPa. In the proposed solution, although simple technologies of making flow paths were applied, the pressure losses were reduced over 35%. The developed solution is close to a standard directional spool valve and can be assembled on an identical sub-plate. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction There is a tendency for reduction energy consumption of working machines by minimizing pressure losses on hydraulic drive systems. Significant losses of pressure usually appear in the areas of changes in cross sections, changes of the flow direction, and in the places where the swirls are formed. Such areas exist in hydraulic valves, particularly in directional control valves. The problem of losses evaluation in such components is a complex matter. In order to analyze the flow in these type of elements the CFD systems are very useful. To obtain effective solution some authors apply models with different level of simplification in CFD analysis of hydraulic valves. The easiest approach is using 2D models [1–3] or axisymmetrical [4–6]. In case of flow in complex geometry in order to simulate flow phenomena it is necessary to apply three dimensional models [6–9]. During the work, the possibility of pressure loss reduction in directional control valve was investigated. As a result there was a ⇑ Corresponding author. E-mail addresses: [email protected] (E. Lisowski), [email protected] (J. Rajda). 0196-8904/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.enconman.2012.08.015
proposition of equivalent solution by the usage of logic valves. There is assumption, that the way of assembly of the new directional control valve to mounting plate will be identical to directional spool valve, that is by the usage of a manifold with standard ports. There is also assumption, that the construction of the body of directional control valve will be produced by the usage of simple machining (drilling, boring or milling). In the work the solution of new directional control valve with logic valves was presented. The design was prepared in Solid Edge software. Pressure losses were evaluated by using ANSYS/FLUENT package and the simulation results were verified [10]. 2. Hydraulic system The subject of the study is a typical hydraulic system illustrated on Fig. 1, with hydraulic cylinder as a working element. In this system the electromagnetic directional control valve (1) controls the main spool of directional control valve (2). Backflow from cylinders is secured by pilot operated check valves (3). The hydraulic system is designed for volumetric flow rate up to 450 dm3/min and working pressure up to 35 MPa. In the system the following components are used: directional control valve
286
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
Nomenclature A, B P T X Y AT BT
actuator ports pressure port return port pressure port for the pilot valve return port for the pilot valve flow path A–T flow path B–T
PA flow path P–A PB flow path P–B A1, A2, A3 control area of logic valve Q volumetric flow rate p pressure of working liquid Dp pressure loss CFD Computational Fluid Dynamics
Fig. 3. Double check valve, pilot operated Z2S22 [11] in standard [14].
Fig. 1. Hydraulic system diagram: (1) electromagnetic directional valve (pilot stage), (2) directional spool valve (main stage), (3) pilot operated check valves, (4) hydraulic cylinder, and (5) power unit.
Fig. 4. Losses of pressure in directional control valve WEH22 at viscosity of hydraulic liquid 41 mm2/s: (1) path AT, (2) PA and PB path, and (3) BT path.
Fig. 2. Directional control valve, electro-hydraulically operated type WEH22 [13] in standard [14].
Comparison of Figs. 4 and 5 shows that the loss of pressure for flow path BT (at Q = 450 dm3/min) goes up to 2.55 MPa (reaches the rate over two times higher than the loss for flow through directional spool valve only). A question has been asked: how much will the pressure losses reduce when the unit of directional control spool valve WEH22 with double pilot operated check valve Z2S22 is replaced by logic type of directional control valve? The pressure loss in logic valve for example: URZS25 [15] (Fig. 7) are smaller, if we compare with a single flow path of directional valve. Furthermore, when piloting system is leak tight, there is no need for application of check valves pilot operated because the logic valves are poppet type.
3. Logic valves WEH22 (Fig. 2) and pilot operated check valve Z2S22 (Fig. 3) – according to catalogues [11–13]. For volumetric flow rate 450 dm3/min the losses of pressure in directional control valve WEH22 reach values from 0.79 MPa to 1.15 MPa (Fig. 4). The biggest value of pressure loss occurs on flow path BT. If we take into consideration the losses of pressure resulted from the flow through pilot operated check valve, then total losses of pressure will reach values as on Fig. 5.
Logic valves (Fig. 6) are Fig. oat>built as 2/2 way cartridge valve. They are composed of the cartridge insert and the cover (4) with control holes. The cartridge insert consist of the bushing (1), the spring (3) and the poppet (2). The poppet is pressed down to valve seat by means of the spring (3). The valve allows for flow from A to B or reversely from B to A. The valve poppet has three important areas for its operation. The annular area A2 is 7% or 50% of area A1. The area ratio A1:A2 is therefore either 14.3:1 or 2:1. The area
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
Fig. 5. Total losses of pressure in flow by directional spool valve WEH22 and pilot operated check valve Z2S22 at viscosity of hydraulic liquid 41 mm2/s: (1) path AT, (2) PA and PB path, and (3) BT path.
A3 is A1 + A2 and can be either 107% or 150% of area A1. The valve opens in both flow directions if surface A3 is not affected by pressure (port X is unpressurised) and pressure force affecting the adequate surfaces A1 and A2 exceeds force of the spring (3). If surface A3 is affected by control pressure the valve poppet is pressed down to its seat, irrespectively of the spring (3) force. The valve may be opened by unloading surface A3 (connecting the chamber X to return line) or by appropriately high pressure on port A or B. The resistance of flow by logic valve is lower compared with the resistances of flow by directional spool valve and significantly lower when compared when the flow resistances of unit: directional spool valve and pilot operated check valves. Taking into consideration the reduction of pressure losses in the hydraulic unit, it seems that research conduction on the using of logic valves in hydraulic system is purposeful. 4. Logic valve model In order to build directional control valve logic type, realizing the functions as on Fig. 1, there is a proposition for usage of four logic valves with area ratio A2:A1 = 50%, which is presented on Fig. 8. The model of four logic valves has been created in form of brick applying Solid Edge software. Relevant assembly cavities have been designed in the body and adequate flow paths. One common cover for four logic valves has been provided in the design. It forms both mounting plate for pilot valve (1), and enables to bring pilot flow to the logic valves (2–5). The prepared design of directional control valve has been presented on Fig. 9 in the form of overall view and in section on Fig. 10. The new-built model of directional
287
Fig. 7. Pressure loss of logic valve URZS25 [15], at viscosity of hydraulic liquid 41 mm2/s: Dpmax = 0.55 MPa at Q = 450 dm3/min.
Fig. 8. Schematic diagram of directional control valve logic type performing the function of directional spool valve WEH22 with the valve Z2S22 in standard [14]: (1) directional control valve (pilot valve), (2–5) logic valves.
control valve (Fig. 8) can be mounted on the same sub-plate as a standard directional control valve. The logic valves are placed in parallel in one surface in body (Fig. 10), what simplified the creating inlet and outlet ports to the sub-plate and enabled to maintain the similar overall dimensions like for the directional spool valve WEH22. The outlet and inlet paths to the logic valves are mostly designed as simple bores. 4.1. CFD flow simulation in directional control valve logic type There might be used various flow models in simulation of flow for directional control valve [16]. Literature [8,16,17] shows that in similar analysis with hydraulic oil as working medium model k e generally was used. Therefore for simulation research available in
Fig. 6. Design of logic valve: (1) body, (2) poppet, (3) spring, and (4) cover.
288
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
Fig. 9. Directional valves: on the left 3D model of directional control valve logic type, on the right directional control spool valve WEH22.
Fig. 10. Directional control valve logic type: (1) logic valve open, (2) logic valve closed, (3) pilot valve, and (4) body.
Fig. 12. Grid for model of BT flow path.
ANSYS/FLUENT standard model of turbulence k e has been chosen [16,17]. The turbulence kinetic energy k and its rate of dissipation e are obtained from the following transport equations:
@ @ @ ðqkÞ þ ðqkui Þ ¼ @t @xi @xj
lþ
lt @k þ Gk þ Gb qe Y M þ Sk rk @xj ð1Þ
@ @ @ ðqeui Þ ¼ ðqeÞ þ @t @xi @xj
lþ
C 2e q
e2 k
lt @ e e þ C 1e ðGk þ C 3e Gb Þ re @xj k
þ Se
ð2Þ
In these equations, Gk represents the generation of turbulence kinetic energy due to the mean velocity gradients, calculated as described in modelling turbulent production in the k e models. Gb is the generation of turbulence kinetic energy due to buoyancy, calculated as described in effects of buoyancy on turbulence in the k e models. YM represents the contribution of the fluctuating dilatation in compressible turbulence to the overall dissipation rate, calculated as described in effects of compressibility on turbulence in the k e models. C1e, C2e and C3e are constants. Sk and Se are the turbulent Prandtl numbers for k and e, respectively. Sk and Se are user-defined source terms. The turbulent (or eddy) viscosity, lt, is computed by combining k and e as follows: 2
Fig. 11. Grid model of PA flow path.
lt ¼ qC l
k
e
ð3Þ
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
289
Fig. 13. Distribution of pressure on walls of the PA path.
where Cl is a constant. Model constants: the model constants have the following default values [16,17]: C1e = 1.44, C2e = 1.92, C3e = 1, Cl = 0.09, Sk = 1.0, Se = 1.3. 4.2. Geometric model and discerte model (grid) Geometric models of four flow paths have been created from 3D model of directional valve, that is: PA, PB, AT and BT. Each of these has different geometry and different total length. For example: on Fig. 11 the flow path PA has been depicted, which is the shortest, while on Fig. 12 the model of path BT, which is the longest. While generating grid the following requirements for cells dimensions have been defined: 3 inner wall layers along walls have been assumed, the grid in the places of complex geometry has been refined. Grid information for flow path PA: minimum size 0.09 mm, average size 2 mm, maximum size 6 mm, number of cells 634,110, tetrahedral 472,198, wedges 161,857, pyramids 55. The grid for model of flow path BT (Fig. 12) has been generated applying the same requirements. For path BT, the model contained 653,966 cells.
Fig. 14. Velocity distribution along streamline for PA path.
4.3. Boundary conditions and results The calculation has been conducted for four values of inlet velocity of hydraulic liquid: 4, 8, 12 and 16 m/s (Velocity Inlet). For outlet boundary condition type Pressure Outlet has been assumed – constant pressure on outlet p = 0.1 MPa. Intensity of turbulence has been assumed for calculation on the value of 2% for the length of scale 2 mm. Remaining assumptions:
no slip on walls, the liquid is incompressible (hydraulic oil), the liquid properties are constant, the model is in conditions of thermal equilibrium, viscosity of hydraulic liquid is 41 mm2/s.
As a result of conducted simulations for each of the analyzed flow paths distribution of pressure on the walls of channels and velocity in the designated intersections have been received.
Fig. 15. Distribution of pressure on walls of BT path.
Streamlines allowed for evaluation of stream swirl places. For example on Fig. 13 distribution of pressure on the walls has been depicted for flow path PA, and on Fig. 15 for flow path BT. As a result of analysis of these drawings in the case of flow path BT it was found that, there were more significant pressure losses, than in case of flow path PA.
290
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
Fig. 16. Velocity distribution on the plane of logic valve BT path.
Fig. 19. Pressure losses in directional control valve logic type: (1) PA path and (2) BT path (pressure losses max 0.93 MPa and 1.67 MPa).
Fig. 17. Velocity distribution along streamline for BT path.
Fig. 18. Comparison of pressure losses on logic valve: (1) experimental research and (2) result from CFD simulation (the difference is smaller than 5%).
On Fig. 16 the distribution of hydraulic liquid velocity has been depicted in plain of logic valve hole. The logic valve has four inlet ports. As results from Fig. 16, the flow is realized mainly by the hole joined directly to return port T. It can be also noticed in analysis of the streamlines (Figs. 14 and 17). 4.4. Pressure losses Evaluating the way of pressure losses of hydraulic valves is defined in ISO standard [18]. It allows to compare the solutions from
different manufacturers. The same way of evaluating pressure losses was used in CFD simulation. For four values of liquid velocity at valve inlet (4, 8, 12, 16 m/s) were conducted simulations and as a results pressure losses have been obtained. The calculation of pressure losses has been conducted on the single logic valve. The pressure losses were calculated as a difference of average pressure on outlet and inlet. Fig. 18 presents comparison of characteristic of pressure losses for valve obtained by CFD methods (curve 2) and catalogue characteristic (curve 1) [15]. Differences are very small and do not exceed 5%. The pressure losses of proposed design of control valve obtained with CFD method have been presented on Fig. 19 for flow paths PA and BT. If we compare these characteristics with Fig. 5 (directional spool valve and pilot operated check valves), then it is clearly visible, that the proposed solution of directional control valve logic type allowed to significant reduction of pressure losses. For flow path PA about 61%, while for flow path BT 35%. 5. Experimental research A prototype of directional control valve logic type has been prepared based on model presented on Figs. 9 and 10. It was used on experimental test stand presented on Fig. 20. The stand allowed to set constant volumetric flow rates Q = 111, 215, 306, 430 dm3/min. The experimental conditions were in conformity with ISO standard [18]. Results from the experimental research (Fig. 21) have been approximated with polynomial curves 3 and 4. Curves 1 and 3 refer to pressure loss on flow path PA, curves 2 and 4 – on flow path BT. The results obtained from the experimental research are closed to those from CFD model. Difference
E. Lisowski, J. Rajda / Energy Conversion and Management 65 (2013) 285–291
291
using in hydraulic system logic type directional valve, instead of directional spool valve, allows for significant reduction of pressure losses. It was from 35% up to 61% in analyzed hydraulic system. The proposed logic type directional control valve did not need to apply a body with complex flow paths. The needed flow path can be performed by simple machining process like: drilling, boring and milling. Furthermore, it can be noticed that logic type directional control valve can be used for other needs, for example: lower switching time, work in higher pressures. Application of ANSYS/FLUENT program enabled to obtain characteristics of pressure losses with deviation about 5%, in comparison to experimental test. References Fig. 20. Prototype of directional control valve logic type at experimental stand.
Fig. 21. Comparison of experimental results with CFD analysis: (1) CFD analysis for flow path PA, (2) CFD analysis for flow path BT (3) experimental results for flow path PA, and (4) experimental results for flow path BT.
of pressure losses in the range of flow up to 430 dm3/min does not exceed 5%. 6. Conclusions The paper concerns the proposition of replacement of directional spool valve by logic valves built in the body mounted on the sub-plate complying with standard ISO [14] as used for directional spool valves. In this way the possibility of change of these components has been obtained. The proposed solution has been verified by experimental test on prepared test stand. CFD analysis with the usage ANSYS/FLUENT showed, that proposed solution of
[1] Vescovo GD, Lippolis A. Three-dimensional analysis of flow forces on directional control valves. Int J Fluid Power 2003;4(2):15–24. [2] Vescovo GD, Lippolis A. Optimization of flow through a pneumatic control valve using CFD analysis and experimental validation. Fluid Power 2007;1:31–41. [3] Pan X, Wang G, Lu Z. Flow field simulation and a flow model of servo-valve spool valve orifice. Energy Convers Manage 2011;52(10):3249–56. http:// dx.doi.org/10.1016/j.enconman.2011.05.010. [4] Amirante R, Moscatelli P, Catalano L. Evaluation of the flow forces on a direct (single stage) proportional valve by means of a computational fluid dynamic analysis. Energy Convers Manage 2007;48(3):942–53. http://dx.doi.org/ 10.1016/j.enconman.2006.08.024. [5] Amirante R, Vescovo GD, Lippolis A. Evaluation of the flow forces on an open centre directional control valve by means of a computational fluid dynamic analysis. Energy Convers Manage 2006;47(13–14):1748–60. http://dx.doi.org/ 10.1016/j.enconman.2005.10.005. [6] Lisowski E, Momeni H. CFD analysis of pilot operated relief valve. In: Proceedings of 5th FPNI-PhD symposium, Kraków; 2008. p. 493–500. [7] Domagala M, Lisowski E. Optimization hydraulic components using fluid-solid interaction simulation. In: Proceedings of 4th FPNI-PhD symposium, Florida – Sarassota; 2006. p. 151–9. [8] Domagala M. CFD analysis of a flow control valve. In: Proceedings of 5th FPNIPhD symposium, Kraków; 2008. p. 445–50. [9] Lisowski E, Domagala M. Determination of static characteristic of direct acting relief valve. In: Proceedings of the 1st international conference on computational methods in fluid power technology, Melbourne; 2003. p. 211–20. [10] ANSYS/Fluent: users guide, 13th ed.; 2011. [11] Bosch Rexroth. Catalogue: check valve pilot operated re 21564/07.10; 2010. [12] Bosch-Rexroth. Catalogue: 3/2, 4/2 and 4/3 directional valves, internally pilot operated, externally pilot operated re 24751/08.08; 2010. [13] PONAR Wadowice. Catalogue: directional spool valve; 2001. [14] ISO 4401:2005 Hydraulic fluid power – four-port directional control valves – mounting surfaces; 2005. [15] PONAR Wadowice. Catalogue: 2/2 – way catridge valve; 2010. [16] Launder BE, Spalding DB. The numerical computation of turbulent flows. Comput Methods Appl Mech Eng 1990:269–89. [17] Launder BE, Spalding DB. Lectures in mathematical models of turbulence. London (England): Academic Press; 1972. [18] ISO 6403:1988 Hydraulic fluid power – valves controlling flow and pressure – test methods.