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Journal of Science & Technology 100 (2014) 042-046 Analysis and Design for Pressure-Reducing Valve of High Pressure Pneumatics with Throttle Spool Pham Xuan Hong Son", Tran Thien Phuc, Bui Trong Hieu Ho Chi Minh Cily University ofTechnology, 268, Ly Thuong Kiel 10 District Ho Chi Minh City Vietnam Received: Januaiy 9, 2014; accepted: April 22, 2014 Abstract Tbe structure and design method for a pressure-reducing valve of high pressure pneumatics of hydrogen vehicle is analyzed A pressure-reducing valve of high pressure pneumatics with throttle spool controls tiie maximum spool displacement by the inner structure and the control area is proportional to spool displacement The initial pressure, operation pressure, the maximum pressure and its accuracy can come true by the optimal design of the spring and its compressed displacement and spool size A high pressure: pneumatics pressure-reducing valve with throttle spool can keep the output pressure constant The results, are useful for design and analysis of control valve of hydrogen vehicle Keywords: Pneumatic technology; Pressure-reducing valve; Designing analysts, Throttle spool Introduction Pneumatic pressure control valves used to conUol working pressure of the pneumatic system Generally speaking, there is a strict requirement in weight and general size for aircraft and means of transports, so the devices must carry stored enough energy Therefore, the self-energy of plant has to use source of high pressure gas m storage In industry, pressure of high pressure gas bottles is often MPa But pressure of aircraft gas bottles is as high as 15 MPa to 80 MPa, such as the control pressure of propulsive systems for deep exploration or aerodynamic steering in gas tank and gas bottles, etc [I] In hydrogen cars, aluminum tank wrapped with carbon fiber composite for hydrogen systems With volume of tank is I60L, a hydrogen driving range of 300 km, hydrogen pressure maybe to 35 MPa; a hydrogenation driving distance of 500 km, hydrogen pressure permits to 70 MPa [2], Pressure-reducing valve IS a normally open control valve for a long period of stable pressure control, these components are important to self-supply pneumatic system, how to achieve acctuate control pressure is essential [3] At present, analysis of a pressure-reducing valve of high pressure pneumatics with throttle spool in hydrogen vehicle is still rare This paper analyzes characteristics of pressure-reducing valve of high pressure pneumatics with throttle spool for hydrogen vehicles Structure and Working Principle 1.1 Function PressLue-reducing valve of high pressure pneumatics is a device that probably adjusts • Corresponding author, Tel: (+84) 1248.794.705 Email: pxhongson@gmail.com pneumatic pressure, the supply pressure to the predetermined pressure in reducing for outlet pressure When the flow or load changes, through its own adjustable role, it is changing the size of orifice and loss pressure It will take a balance between the outlet pressure on valve spool and spring force and maintain automatically the outlet pressure stability, also known as pressure-reducing valve at output [4] 1.2 Schematic diagram and working principle A pressure-reducing valve of high pressure pneumatics stmctures in various forms, such as ball, tapered, and slide valve type So the sealing feature of spool valve is good Only having a small amount of leakage, and it automatically compensates for mbbing at valve port to meet the requirements of sealing for working long hours Small size of spool is easy to achieve miniaturization and integration Fig, I shows a stmcture for pressure-reducing valve of high pressure pneumatics with throttle spool in hydrogen vehicle Pressure-reducing valves give directly the output value that pre-determined, it is nonnally opening condition It is formed mainly by the spool and sleeve, valve springs and other components The pressure of chamber V^ is made up from valve spool and body of valve Geometric stiucture of valve has put a stopper of valve at maximum displacement of valve spool to determine the initial position of the spool when tt is in the amount of the maximum opening Before starting of pressure-reducing valve of high pressure pneumatics with throttle spool works, the spool and body valve contact with each other under the action of spring, and the valve port is opened after putting position in the amount of maximum opening Before the outlet pressure ^ ^ reaches the set Journal of Science & Technology 100 (2014) 042-046 Qp,P^ ^ Qcpc r^ -A f\!w ^ B_ Load QL,pL Fig Schematic diagram of pressure-reducing valve of high pressure pneumatics with throttle spool Fig- The local stinchire diagram of pressurereducing valve with throttle spool pressure p^.^ pressure-reducing valve of high pressure pneumatics maintains to the maximum amount of opening Through filling gas in pressure conttol chamber and the compression of the outlet pressure, until the output pressure of valve achieve to p^g Under the effect of the load pressure, p^ , the pressure of contiol cavity p^ equal to the load pressure pj , conttol pressure acting on the effective area of valve with throttle spool and force of spring pre-compression are balance When the pressure of contiol chamber p^^ is over pre-determined pressure of spring, the gas pressure on effective area of the spool is greater than force of spring, the spool will start to move to the right By balance of the control pressure with gas acting on valve spool and spring force, the conttol pressure at output port is set up operation in high pressure pneumatics accuracy in outlet value and Static Characteristics 2.1 Orifice area Fig shows the pressure-reducing valve with cone-shaped onfice in local stmcture diagram The orifice area of pressure-reducing valve with throttie spool is formed between valve seat and the smallest cross-section area, it is the area for cone-shaped ring of the edge BC Supposition, when the pressurereducing valve is in the initial position of opening, the axial opening amount is value of/i„ , i.e AB = h^ , then the valve spool is in the maximum amount of opening When the spool begins to move, orifice area of valve will gradually reduce in opening, orifice cross-section area is the smallest A{x) = 7til(ki;^ -.x:)sin a-7r(h„ - jc)^ sin ^ or cos a When the load flow Qj^ reduces or the supply increases, since the rise in outlet pressure p^ pressure pj^ ,the pressure conttol chamber p^ will also rise, and the mle of pressure changes in value on the effective area of spool, then valve spool moves to the right For this reason, the valve port closed small so that the pressure of conttol cavity of pressurereducing valve of high pressure pneumatics maintains basically in the vicinity of the setting value In conttast, when the load flow increases or the supply pressure decreases, the outlet pressure drops Then the pressure of contiol cavity falls, guiding to valve spool moves to the left, valve port opened large Similarly, the pressure of contiol cavity of pressurereducing valve of high pressure pneumatics maintains basically in the vicinity of the setting value As fluctuations in flow or pressure happen, basically it can maintain better the stableness of outlet pressure Therefore, salient features of this valve are its its (I) where, d is the inner diameter of the valve cover, h^ is the axial opening amount when the valve spool is in the initial position of opening, x is the spool displacement, a is the cone half-angle of valve with throttle spool, Afx) is the smallest orifice area for the valve displacement The amount opening of valve is generally smaller In Eq (1) the right of the latter is much smaller than the previous one, therefore, it is usually simpHfied to expression as follows A(x) = -nd(hf, -;c)siii (2) When pressure-reducing valve is in the initial position, it can be seen that the valve displacement is zero, i,e x = 0, the orifice area of pressure-reducing valve with throttle spool is the largest, and Mx) = A^^ When the spool reaches its maximum Journal ofScience & Technology 100 (2014) 042-046 displacement, i.e x = ho, orifice area of pressurereducing valve is the smallest, the valve port is closed, Afx) = From Eq (2) it can be learned that the opening area of pressure-reducing valve A(x) and the spool displacement x have linear relationship basically 2.2 The initial work pressure conttol pressure, A^ as the effective area on the spool has been acted by the inlet pressure When the outlet presstue of pressure-reducing valve is low, the supply presstu-e gets the greater impact to the outlet pressure ,(9) A, = — mJ^ -7z[d-(hg -x)siaacosa](ft|| -J:)SII When the pressure of conttol chamber p^^ in pressure-reducing valve with throttle spool attains to the setting pressure of spring, the spool will begin to move to the right At this point, the working pressure of valve is in the initial state Considering, the inlet pressure has effect of force on the spool, balance equation of force in the statics on the spool and the initial working pressure of pressure-reducing valve as follows = Kx (3) _KXQ-P,A,„ (4) A^ =7r[d-{k„-x)sJaacosa'}(ha-x)smacosa 2.4 Maximum control (10) pressure When the valve port of pressure-reducing valve with settmg output value is almost closing, the conttol pressure of pressure-reducing valve reaches Its maximum, then the flow of pressure-reducing, valve is equal to zero At this point, ttie spool displacement x attains to the maximum value h^ Balance equation of force in the static situation on the spool and the maximum contiol pressure of pressurereducing valve can be obtained by where, p^^ is the pressure of conttol chamber to start P.^A,^=K{xo+ho) (11) action on valve spool, A^^ is the initial effective area 4K{x^+ha) that has been acted by the contiol pressure on the (12) spool, A ^ IS the initial effective area that has been acted by the inlet pressure on the spool, K is the where, A^^^^ as the maximum effective area on die spnng stiffness, X^ is the initial setting value of the spool has been acted by the conttol pressure pre-compression of spring, it is compression force of A^^=nd^/4 (13) spring when it is the maximum opening of valve And 2.5 The mass flow equation of control orifice ^cD =~f^^ - j t : ( ( f - / i o s i n a c o s a ) / ; o s i n a c o s a (5) A^Q = ji(rf-/jQsinacosa)/;o s i n a c o s a (6) 2.3 Control pressure When the outlet pressure of pressure-reducing valve exceeds the setting pressure from spring, the conttol pressure p^ has action of force on the effective cross-section of spool, it is greater than the pre-compression of spring, the spool will move to the right The amount of opening fi'om valve port gets less and less until spring force and gas pressure that has action of force on effective area of throttle spool are balance, and the outlet pressure gets stable output in pressure-reducing valve Balance equation of force in the statics on the spool and contiol pressure of pressure-reducing valve is as follows p^A^+p^A^ = K{X^ +X) _ K\XQ +X)- By the mass flow of valve orifice, it is in two forms of subsonic velocity and supersonic velocity When the flow rates through orifice gets subsonic velocity (0.5283 < pJ p^< 1.0), the mass flow of gas through the orifice is defined by Qp = 2k k-l teJ-tef (14) where, C^ as the flow coefficient of valve port, R is gas constant, T is the absolute temperahire of gas, k as the coefficients of gas insulation When the flow rates through orifice gets supersonic velocity (0 < p^/ p,< 0.5283), the mass flow of gas tiirough the orifice is defined by ^J^ P^A^ Qp"' Cjp.Ajx) (8) where, p^ as pressure of conttol chamber, A^ as the effective area on the spool has been acted by the C^P^Ajx) JRT (15) i + l U + lJ Journal ofScience & Technology 100 (2014) 042-046 1" i •*i So.is a, ,^0,1 J 0,05 PI-35 (MPa) 0:2 0,4 Ot 0,S VbftiilaalawsQt^a) Pi-5(MP») 0,2 OA 0,« 0l8 TtefHitaaiiKfasQtgf*) (b) _p^=5MPa, _p^-0,16MPa (a) p^ = 35MPa, p^ = 5MPa ; Fig.3 2.6 Precision of control pressure where, Q is the supply flow that pass through the At the moment the spool just starts up, the contiol pressure of pressure-reducing valve at the output port is the minimum When valve port is going to close, the contiol pressure is the maximum From (4) and (12), we obtain value range for the conttol pressure of pressure-reducing valve ^^Pct„ (16) From Eq.(I6), it shows that, the range of outlet pressure is reduced, and improve in accuracy of pressure conttol for pressure-reducing valve with throttle spool As designing it should try to as follows; orifice of pressure-reducing valve, Q^ is the load flow; Q^ is the compressed flow in conttol chamber 3.2 The mass flow equation for compressibility gas in the pressure control chamber of To consider of gas compression, continuity equation for fluid in conttol chamber follows that g ^ i ^ ^ P A ^ kRT dt RT dl (18) where, V^ is the volume of conttol chamber; t is time To get spring stiffness, K, that is as small as possible, and diameter of valve d is as large as possible, but we also must consider effects these factors on the dynamic characteristics 3.3 Balance equation of force for spool When the control pressure p^ movement m output port achieves setting value of pressure p^^ , then spool From Eqs.(2), (8), (10), (13) and (14), it can be dravm when the inlet pressure is constant, the outlet pressure and load flow is related to each other as diagrams Fig 3(a) shows that the mlet pressure of pressure-reducing valve is 35MPa, then the outlet pressure is 5MPa, the flow-pressure characteristics as diagram Fig 3(b) shows that the inlet pressure of pressure-reducing valve is 5MPa, then the outlet pressure is 0.16MPa, the pressure-flow characteristics as diagram Fig shows, after the parameters of pressure-reducing valve are determined, the outlet pressure can be conttolled within a certain range starts moving, balance equation of force for spool defined by movement r,dx (19) ^Kx-F., p^A^+p^A^ -KXQ dtwhere m is the quantity of components spool, B is the coefficient of viscous damping, L is the equivalent damping length of flow in valve, Fg^ is the aero-dynamic force m the steady-state, F„2 is the aero-dynamic force in the transient [3], p is the gas density, v is the rate of gas flow Fg^ -vpgpCosa Dynamic 3.1 The continuity equation pressure-reducing valve at control orifice of To consider the compression in contiol chamber, the equation of continuity at contiol orifice for pressure-reducing valve is as follows Qn-QL-Qc=^ (17) (20) Fii.=pL(dQ^jdt) The pressure and flow characteristics of pressure-reducing valve with throttle spool can carry out analysis by Eqs (2), (14), (15) and fi-om Eqs, (17) to (20), Journal of Science & Technology 100 (2014) 042-046 ^ ^6 J V ; ^ 0,01 11 / 0,02 Fig, 4, 1-K,=•15cm'; 2-V^ = 24cm'; 30cm' • 0,01 0.02 llidigiaiitti) 0.03 •• -K • ?' ^4 \ 03 Fig.5 1-rf= 4mm 2-d= 4,2mm; 3-rf = 5mm Design and Analysis The main design for pressure-reducing with throttle valve in the setting output includes orifice area, valve diameter, spring pre-compression, spring design, range of conttol pressure, dynamic characteristics, to check operating point of pressurereducmg valve and so on Fttstly, according to the input pressure p^ of valve, the outlet pressure p^ and the flow norm L ^re required It can be computed the orifice area Afx) of pressm-e-reducing valve by Eqs,(14) and (15) Diameter d is the initial selectton for pressurereducing valve of high pressure pneumatics with throttle spool, then tapering angle of spool a , and the amount of size for initial opening h^ It can be calculated norms for the spool displacement x at operatmg point by Eq,(2) ^ ^ Q.D1 0.D2 1tiMgiaii((j) 0.D3 Fig 1- p - 3SMPa; 2- p = 30MPa i-p ^ = 25MPa spool Fig shows the impact of response to the outlet presstue at inlet pressures m pressLU"e-reducing valve with throttle spool, Conclusion Through the internal schematic diagram of pressure-reducing valve of high pressure pneumatics with throttle spool, it can cany on the contiol for the maximum valve opening on spool Basically, spool displacement and area of valve opening are linear relationship The initial working pressure, the control pressure, the maximum conttol pressure and the precision of pressure control can be designed appropriately hy the spring stiffness, the initial high pressure gas, and the diameter of valve or other parameters to achieve The output value can be maintained almost constant in pressure-reducing valve of high pressure pneumatics with throttle spool pre-compression X^ by Eq,(3) As design spring To propose design methods and mathematical models for pressure-reducing valve of high pressure pneumatics with throttle spool Besides, it provides a reference for design or analysis of this valve stiffness, also it need to consider the maximum spring References displacement h^ and from Eqs, (3), (7), (I I) and (16) [1] mn^ ^^^^mmmmm^m^ [J]= m^m it^J^A, (2007)49-51 [2] ^mm, ^'h^= m&'k^^m&m\i!,a&m mfn-jfii:m%[j] ^f5iija,34(2oog)i-5 [3] mmi^, m^tn mmmn^^mmm&H^^ HHwaa-^^tt^)-^ [J], ^mxmum^U' 6(2008)310-315 From the minimum conttol pressure j D ^ , and it can be carried on design spring stiffiiess K and spring we cany out feedback for checking and calculating spring stiffiiess and the amount of initial opening Therefore, it satisfies the outlet pressure in range of contiol precision fi-om/7j.g to /^^n^x • From Eqs, (2), (14), (15) and (17) to (20), we carry out analysis about impact of the response for various parameters, and ensure that the spool displacement does not exceed the maximum value h^ Fig shows the impact of response to the outiet pressure at volumes of pressure-conttolling chamber in pressurereducing valve with throttle spool Fig shows the impact of response to the outlet pressure at spool diameters in pressure-reducing valve with throttle [4] Paul D, Henn, John M, Hollerbach, An analytical and experimental investigation of a jet pipe conttolled electro-pneumatic actuator IEEE Transations on Robots and Automatic, (1998) 601-611, ... mass flow of gas through the orifice is defined by Qp = 2k k-l teJ-tef (14) where, C^ as the flow coefficient of valve port, R is gas constant, T is the absolute temperahire of gas, k as the... pressure of spring, the gas pressure on effective area of the spool is greater than force of spring, the spool will start to move to the right By balance of the control pressure with gas acting on valve... temperahire of gas, k as the coefficients of gas insulation When the flow rates through orifice gets supersonic velocity (0 < p^/ p,< 0.5283), the mass flow of gas tiirough the orifice is defined by
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