GB2184814A - Pressure reducing valve - Google Patents

Abstract

A pressure-reducing valve assembly comprises a piston (58) reciprocatable within a bore (52), and having a pressure-regulating valve (94, 128, 108) located between a chamber (92) within the piston and an outlet chamber (96). The valve closes as the pressure of outlet 100 reaches a desired value. The inlet (90) to the chamber (92) is arranged so that, when the valve is closed, fluctuations in inlet pressure produce no resultant axial force on the piston (58), and so that, when the valve is open, upward fluctuations in the inlet pressure tend to act to close the valve. <IMAGE>

Description

SPECIFICATION Pressure reducing valve The invention relates to pressure reducing valves, It is particularly, though not exclusively, concerned with a valve for reducing the pressure in a gas from a high value (for example 6000 psi or 41 MPa) to a substantially lower value (for example 3000 psi or 21 MPa).

Pressure reducing valves for use at low pressures are well known, but are not suitable for high-pressure high-accuracy use. It is an aim of the present invention to provide a valve suitable for such use, and which is capable of maintaining the pressure on the output side of the valve substantially constant over a range of input pressures (for example to within 30 psi (207 kPa) of 3000 psi (21 MPa) for input pressures varying between 5800 psi and 6200 psi, that is 40 MPa to 43 MPa).

According to a first aspect of the present invention a pressure reducing valve comprises a body with a bore formed therein, an inlet to the bore and an outlet from the bore, a valve member reciprocatable within the bore and including an internal chamber in communication with the inlet, an outlet from the chamber having a valve therein, the side of the valve remote from the chamber being in communication with the outlet, means controlling the valve in dependence upon the position of the valve member, the valve member being spring biased in the valve-opening direction; and the valve assembly being constructed and arranged so that, with the valve open and with a steady-state flow, an upward fluctuation of pressure at the inlet tends to close the valve.

According to a second aspect of the invention a pressure-reducing valve comprises a body with a bore formed therein, an inlet to the bore and an outlet from the bore, a valve member reciprocatable within the bore and including an internal chamber in communication with the inlet, an outlet from the chamber having an axially-positioned valve therein, the side of the valve remote from the chamber being in communication with the outlet via a radially-extending passageway in the valve member, means controlling the valve in dependence upon the position of the valve member, and the valve member being spring biased in the valve-opening direction.

The invention may be carried into practice in various ways, and two specific valves embodying the invention will now be described, with reference to the accompanying drawings in which: Figure 1 is a schematic longitudinal section of a valve according to a first embodiment af the invention; and Figure 2 is a longitudinal section of a valve according to a second embodiment of the invention, and illustrating two possible versions of an adjustment mechanism.

The valve shown schematically in Figure 1 comprises a body 10 (shown in outline hatching) having a bore 12 formed in it. Mounted for reciprocating motion within the bore is a generally cylindrical valve-member 14. At one end 16 the valve member is closed, and at the other it is formed with a stepped bore 18, 20. Located within the bore 20 is a valve pin 22 which, at its left hand end as seen in the drawing, abuts an end face 24 of the body 10. Formed on the pin 22 is a valve head 26 including a frusto-conical valve surface 28 which, in combination with a shoulder 30 in the bore 18, provide the valve mating surfaces. The valve member 14 is biased towards the left (in a direction to open the Valve) by a first spring 32, acting between the right hand end 34 of the body and the end 16 of the valve member.A second spring 36 is also provided; this is located within the valve member 14 and abuts at one end the valve head 26 and at the other end 16. This second spring acts to urge the pin to the left, against its abutment 24.

A gas inlet passage 38 is formed in the body 10, radially of the bore 12. In the region where the inlet 38 enters the bore the bore is provided with an annular groove 40; an annular inlet cavity 42 is thus present between the body 10 and the valve member 14. Gas within this cavity can pass into the valve member via several inlet holes 44 formed in the wall of the valve member; it is prevented from leaking between the bore 12 and the valve member 14 by means of two o-rings 47, 49 mounted in annular recesses 51, 53 respectively, formed in the bore. Near the left hand end of the bore is radially-extending outlet passage 46, formed in the body 10.

Finally, a passage 48 is provided on the righthand side of the valve member 14, to allow for pressure-equalisation.

The operation of the valve of Figure 1 will now be described; reference will be made to the areas Al to A5, shown in the Figure. The input pressure will be referred to as PI and the output pressure as P2. Initially, when the input and output pressures are equal, the valve will be in the wide-open position shown in the drawing, with the valve member being urged to the left by the spring 32, and the pin 22 urged against its abutment 24 by the spring 36. Gas passes along the inlet 38, through the cavity 42, through the inlet holes 44 to the interior of the valve member. From there is passes past the valve mating surfaces 28, 30, between the pin 22 and the bore 18, and along the outlet passage 46. Clearly, in this position the valve member 14 can remain balanced with the spring force to the left equal to the gas pressure force to the right.

Since input and output pressures are equal, this force is simply the bore area (A4) times the pressure P1 (or P2).

Now as the output pressure P2 rises to its design value, the valve member 14 will move to the right to maintain the balance. Eventually, the gap between the valve head surface 28 and the valve seat 30 will become small enough to throttle the gas flow, and to set up a pressure difference on either side of the valve. In the steady-state throttling position (with the valve positioned at the point which will maintain the pressure P2 at its correct value) the pressure forces acting on the valve member are as follows: P1 acts on the righthand end 16 over its area Al; this is offset by P1 acting on the left-hand end, over an area Al minus the area of the valve seat, A2.

The pressure P2 acts on the left-hand end of the valve member over the annular area between the bore 12 and the valve seat 30; this is thus A4 - A2. Accordingly, the combined force to the right (against the spring force to the left) is P1 A2 + P2 (A4 - A2).

As the design pressure P2 is reached, the valve will close. As it does so, the reaction force of the pin 22 on the face 24 is instantaneously transferred to the valve seat 30.

Should the pressure P2 rise above the design value, the pin 22 will be lifted from its abutment as the valve member 14 moves further to the right. In this position, the valve member is enitrely closed, and the axial force due to the input pressure P1 disappears. Instead the force to the right, against that of the spring 32, is now P2 times A4.

Comparing the steady-state position and the closed position it will be seen that as soon as the valve closes the force to the right due to gas pressure is reduced by A2 (P1 - P2). At the same time, the force to the left is increased from the force of the spring 32 minus that of the spring 36 to that of the spring 3 1 alone. There is thus very little tendency for the valve to overshoot. Conversely, as P2 decays to below its design value, the valve opens again and P1 again becomes an influence. This pressure P1, in the steady state position, acts to reinforce the load, tending to close the valve once the design pressure is re-established. Any upward fluctuations in the input pressure will tend to cause the valve to close and any downward fluctuations will tend to cause it to open further, thus maintaining a substantially constant pressure on the outlet side.One may, in fact, regard P1 as providing a rapid response analogous to a pilot-pressure servo. On the other hand, when the valve is closed (because the outlet pressure is too high) neither upward nor downward fluctuations in the input pressure will have any tendency to open the valve again: the only effective pressure then is the outlet pressure P2.

With the characteristics shown, the valve response is "dead beat" in each direction; vibration induced resonance should therefore be unlikely. Also, the opening-closing hysterisis is small, since there is little tendency for the valve to remain in either the open or the closed position due to overshoot or variable pressure/area effects. (In conventional poppet pressure-regulating valves, where the pressure is sensed by the valve head, there is a tendency for the head to present a larger sensing area when it is closed than when it is open-because of the additional area of the valve seat when closed-and thus a higher pressure is required to close the valve than that against which it can open).

Turning now to Figure 2, a second specific embodiment of the invention is shown (at the right-hand end of this diagram two versions of an adjustment mechanism are indicated, above and below the axis; these will be described in more detail below). The left-hand end of the drawing will be referred to as the forward direction. The valve assembly in this embodiment, comprises a body 50 having a stepped bore 52, 54 formed within it. The larger part 54 of the bore is screw-threaded and screwed into it is a cup-shaped closure member 56 having an end wall 57. Slideably received within the smaller part 52 of the bore is a plunger 58 comprising a generally-tubular shaped member 60 having, at its rearward end, a flange 62 surmounted by a cylindrical wall 64 which carries an internal screw thread 63. A bore 67, of variable cross section, passes through the plunger 58.This bore is closed at the rearward end of the plunger by a plug member 66 which is screwed into the screw thread 63. An o-ring 65 is positioned between the two to maintain a seal. A main spring 68, positioned between the flange 62 and the end wall 57, acts to urge the plunger 58 to the left until the flange 62 abuts a shoulder 70 in the main bore. A secondary spring 74 is also provided. This is located within the main spring and abuts, at one end, a shoulder 72 on the plug member 66, and at the other a shoulder 75 on an adjustment member 76. This adjustment member is of generally solid cylindrical shape, with a pressure-relieving throughbore 78. It is screwed into a hole 80 in the end wall 57 of the cupshaped member 56.

Details of the valve itself will now be described. Gas enters the body from an inlet 82, through a radially-bored hole 84 into an annular intermediate chamber 86. This chamber is formed between, on the outside, a groove 88 in the bore 52, and, on the inside, the tubular part 60 of the plunger. The chamber is sealed at each end by two o-rings 87, 89 located within grooves 91, 93 respectively. Gas passage from the intermediate chamber 86 to the interior of the tubular member 60 is by way of two radial holes 90. From the interior of the tubular member 60 (a chamber 92) gas can pass through the valve (generally indicated at 94) to an output chamber 96, and along a radial passageway 98 to the output 100. The valve 94 comprises an elongate valve member 102 which is guided for axial movement within a collar 104 formed on the forward end of the plug member 66.The valve member is biased to the left by means of a valve spring 105 which surrounds the valve member and is positioned between the collar 104 and a shoulder 106 of the valve member (being the rear part of a valve head 108). The outer radius of the valve head 108 is stepped to correspond to a step 110 in the bore 67. The forward end of the bore 67 is further stepped to produce a narrower section 112 and a yet narrower section 114. The valve head 108 is of generally cylindrical type and has, received within it, a valve pin 116 having a head 118.

At its forward end this pin abuts an abutment member 120 which is received within the end of the bore 52. This member is secured to the body 10 by a screw 122, and is sealed by means of an o-ring 124. Within the narrow annular space between the pin 116, the valve head 108 and the narrow part 112 of the bore is a cylindrical sleeve 126, and in the space between this sleeve, the bore 110 and the end of the head 108 is a sealing o-ring 128.

Operation of the valve is as follows. It will be evident that the principles are identical with those already explained with respect to Figure 1, so the operation will be described only briefly. When the inlet and outlet pressures are substantially equal, the valve will be in its open position (as illustrated) with the flange 62 of the plunger abutting the shoulder 128.

As the pressure in the chamber 96 builds up to its design value it acts upon the left-hand end of the plunger 58, moving it to the right.

Since the pin 116 and the valve member 102 are forwardly biased by means of the spring 105 the former remains abutted against the abutment member 120. Eventually, as the outlet pressure reaches its design value, the valve closes, sealing the o-ring 128 between the bore 110 and the valve head 108. If the outlet pressure rises above the desired level the plunger is moved even further to the right, the step in the bore engages the step in the valve head (so preventing the o-ring 110 from being overcompressed) and the valve member 102 and the pin 116 are moved rightwards, as a unit, thus lifting the pin from its abutment.

Naturally as soon as the valve closes the pressure in the outlet 100 will tend to decay back to its design value, when the valve will open again.

The desired output pressure can be changed by replacing either or both of the springs 68, 74 with springs of other spring constants. For given springs 68, 74, adjustment is also possible by screwing the closure member 56 into the the bore 54. The member 56 can be locked in the desired position by means of a locking screw 128 which can be received in any one of six longitudinal slots 130 formed in the forward end of the closure member.

This adjustment naturally affects both of the springs. Fine adjustments can also be made by screwing the adjustment member 76 further into or out of the hole 80; as will been seen this affects only the secondary spring 74. There are two ways in which the member 76 can be held in its chosen position: these are shown above and below the axial line, respectively. A nut 132 can be screwed around the outside of the member, or, alternatively, the nut 132 can be omitted and a knurled, manually-removable cap 136 can be screwed onto a suitable screw thread 134.

The latter option allows easy manual adjustment of the outlet pressure.

Claims (9)

1. A pressure reducing valve assembly comprising a body with a bore formed therein, an inlet to the bore and an outlet from the bore, a valve member reciprocatable within the bore and including ari internal chamber in communication with the inlet, an outlet from the chamber having a valve therein, the side of the valve remote from the chamber being in communication with the outlet, means controlling the valve in dependence upon the position of the valve member, the valve member being spring biased in the valve-opening direction; and the valve assembly being constructed and arranged so that, with the valve open and with a steady-state flow, an upward fluctuation of pressure at the inlet tends to close the valve.

2. A valve assembly as claimed in Claim 1 in which, with the valve closed, pressure at the inlet produces substantially no resultant axial force on the valve menber.

3. A valve assembly as claimed in Claim 1 or Claim 2 in which the valve is positioned axially of the bore and the inlet communicates with the chamber via a radially-extending passageway in the valve member.

4. A valve assembly as claimed in Claim 1 or Claim 2 or Claim 3 in which the communication between the inlet and the chamber is via an annular intermediate chamber surrounding the valve member and being defined by the valve member and a groove in the bore.

5. A valve assembly as claimed in any one of the preceding claims in which the bore is stepped and the step co-operates with a flange formed on the valve member to produce a stop defining the position of the valve member when the valve is fully open.

6. A valve assembly as claimed in any one of the preceding claims which includes a spring-retaining cap screwed in to the bore at one end thereof, the spring biasing comprising a spring positioned between the cap and the valve member, the cap being lockable in one of a plurality of rotary positions to provide an adjustable spring bias.

7. A valve assembly as claimed in Claim 6 including a second-spring retainer mounted on the spring-retaining cap and a second spring positioned between the retainer and the valve member, the second-spring retainer being axially adjustable independently of the position of the cap to provide a fine adjustment of the spring bias.

8. A pressure reducing valve assembly comprising a body with a bore formed therein, an inlet to the bore and an outlet from the bore, a valve member reciprocatable within the bore and including an internal chamber in communication with the inlet, an outlet from the chamber having an axially-positioned valve therein, the side of the valve remote from the chamber being in communication with the outlet via a radially-extending passageway in the valve member, means controlling the valve in dependence upon the position of the valve member, and the valve member being spring biased in the valve-opening direction.

9. A pressure-reducing valve assembly substantially as specifically described herein with reference to either of the accompanying drawings or to any compatible combination of features shown therein.