GB2175980A - Pressure reducer - Google Patents

Abstract

A pressure reducer comprises a hollow body divided into three chambers (2,3,4) operative with fluid at a relatively high, intermediate and low pressure respectively, and first and second throttle means are provided between chambers (2,3) and (3,4), at least one of the throttle means being adjustable and provided with a resilient member movable to compensate for blockage of a throttle. As shown, first and second throttle means (5,10) and (6,11) are effective between the first and second and the second and third chambers respectively. A resilient member (18, or 19) supports part of each throttle means and is movable in response to variations in the pressure differential between the said intermediate pressure and that in the adjacent chamber. Each resilient member (18,19) is operative to counteract any changes in the intermediate pressure resulting from obstruction of one of the throttle means by acting on that part of the throttle means carried thereby. <IMAGE>

Description

SPECIFICATION Pressure reducers The invention relates to pressure reducers with blockage or obstruction compensation.

A pressure reducer of known type is constituted by a hollow body or casing in which three chambers are formed in succession and are separated by transverse partitions provided with orifices of adjustable section.

The adjustment is provided, for example, by axially movable, conical needles engaging in the orifices. The first chamber receives fluid under high pressure. This fluid then passes through a first throttle in order to enter into the second chamber under a reduced pressure. Then it traverses a second throttle in order to enter into the third chamber at a low pressure. The two fluid flow sections, thus arranged in series, cooperate in order to adjust the amount of fluid in the circuit, and thus the pressure drop through each throttle and the reduced pressure in the output chamber.

As a result of the reduced section provided for the passage of fluid between an orifice and its needle, impurities or metallic particles detached from the fluid circuit gives rise to the risk of obstructing one of the two throttles and to modify in a permanent or transient manner the flow section with as its consequence a modification in the reduced pressure and of its interpretation as far as control is concerned.

French Patents 1 391 769 and 1 373 171 describe pressure reducers and their use in various locations. In each, the obstruction of a throttle upsets the predetermined adjustment law in the absence of a compensating device.

In a different technical sphere of flow regulation, German Patent DE-C-812 972 teaches a flow regulator with three successive chambers provided by partitions equipped with spring-loaded valves in order to generate in the third, output chamber a specific flow law which is a function of the supply pressure. Any blockage or partial blockage of one of the valves upsets the flow law but there is no teaching of any means to compensate for this.

According to the present invention there is provided a pressure reducer comprising a hollow body divided into three chambers, each chamber having a flow passage communicating therewith, a first said chamber being operative with fluid at a relatively high pressure, a third said chamber being operative with fluid at a relatively low pressure and a second said chamber being operative with fluid at a pressure intermediate the relatively high and low pressures, first throttle means between the first and the second chambers, second throttle means between the second and third chambers, at least one of said throttles including means defining an orifice, and a member adjusta ble relative to the orifice whereby to vary the fluid flow section through that throttle, and a resilient member supporting one of said orifice defining means and of said adjustable member, said resilient member being movable in response to variations in the pressure differential between the said intermediate pressure and the respective chamber adjacent said first or third chamber, and said resilient member being operative to counteract any changes in said intermediate pressure resulting from obstruction of one of the throttles by acting on that part of the orifice defining means carried thereby.

Pressure reducers embodying the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a first embodiment of a pressure reducer embodying the invention; Figure 2 shows a second embodiment of a pressure reducer serving as a double servo-valve; Figure 3 shows a third embodiment of a pressure reducer also serving as a double servo-valve; Figure 4 shows a fourth embodiment of a pressure reducer serving as a simple servo-valve; Figure 5 shows a fifth embodiment of a pressure reducer incorporating sleeves and slides; and Figure 6 illustrates operational characteristics of various servo-valves, the pressure being shown as ordinate, and the displacement function as abscissa.

Figure 1 illustrates diagrammatically a pressure reducer comprising means for compensating for blockage or partial blockage of flow orifices of the reducer. The pressure reducer comprises a hollow body or casing 1 divided into three chambers 2,3,4 by two throttle valves 5,6. Each chamber is provided with a respective connecting tube or other passage 7,8,9. The throttle valves 5,6 are constituted respectively and in a similar manner by two pressure reducer elements in the form of: flow orifices 10,11 provided in a disc 12,13 and a needle 14,15 of which the conical end, mounted on the axis of the respective orifice, is capable of engaging to a greater or lesser depth in the flow orifice in order to give rise to a vairation in the fluid flow section. Each needle is mounted on an adjustment device constituted in this embodiment by a screw arrangement 16,17.

The displacement of each needle may be controlled in dependence upon an operational parameter of the apparatus incorporating the pressure reducer.

One of the reducer elements is carried by a resilient member 18,19 sensitive to pressure variations in the fluid which exist in the chamber which it defines. In this example, the reducer element is constituted by a flow orifice 10,11. The disc 12,13 in which the flow orifice is formed consitutes the base of a metallic bellows 18,19 which takes up, under the action of pressures existing in the two chambers which it separates, an equilibrium position.

In the form of pressure reducer illustrated, one of the bellows 18 carrying the flow orifice 10 is secured onto an internal division 20, provided in the body or casing 1 of the reducer, whilst the other bellows 19 is directly secured on the wall of the casing, the corresponding connecting tube or passage communicating with the interior of the bel lows.

The manner of operation of the pressure reducer hereinbefore described is as follows: fluid under pressure P1 enters through the tube 7 into the chamber 2, exhausts through the throttle valve 5 into the output chamber 3 which communicates through the throttle valve 6 with the chamber 4 and the tube 9 in which a pressure Po exists which is equal, for example, to atmospheric pressure, and through the tube 8 which supplies control members (not shown). A pressure P2 is established within the output chamber3, resulting from adjustments of the throttle valves 5 and 6. If a foreign body (for example impurities, metallic particles) obstructs at least partially the throttle valve 5, this gives rise to a reduction in the pressure P2 in the output chamber 3, and therefore contraction of the bellows 18 which increases the flow section of the throttle valve 5.

Correspondingly, the bellows 19 expands and thus causes a reduction in the flow section of throttle valve 6. A new equilibrium is thus obtained which re-establishes the pressure P2 at a value approximating to its initial value.

Conversely, if the foreign body partially obstructs the throttle valve 6,it causes an increase in the pressure P2 in the output chamber 3, which results in an expansion ofthe bellows 18 and contraction of the bellows 19, which respectively causes a re suction in the flow section of the throttle valve 5 and an increase the flow section of the throttle valve 6. It produces a new intermediate equilibrium which re-establishes the pressure P2 at a value similar to its initial value.

The increase in the flow section of the partially blocked throttle enables, in certain cases, the foreign body to be entrained by the fluid flow, the bellows then returning to their original equilibrium positions.

According to an embodiment not illustrated, the resilient member carrying the flow orifice is a circular resilient membrane pierced at its centre to form the orifice.

Figure 2 illustrates a second embodiment of two pressure reducers in accordance with the invention adapted to form a double servo-valve. This servovalve is formed by a hollow body or casing 20 divided into three chambers 21,22,23. The central chamber 22 is surmounted by an auxiliary casing 24 housing. an electromagnetic device comprising two windings 25 capable of actuating a movable armature 26. The armature is supported on the axis of the windings by a spring suspension 27 through the centre of which passes a rod carrying at its end a disc or other plate 28, maintained approximately at the centre of the central chamber 22.The end chambers 21 and 23 have on their respective axes an opening 29,30 which communicates with the interior of a bellows 31,32 of which the free end supports a nozzle 33,34 respectively enabling communication between the chambers 21 and 23 and the central compartment 22 and discharging against one of the faces of the disc or plate 28. The nozzles are capable of sliding in a fluidtight manner within dividers 35,36 provided respectively between the compartments 21 and 23and the chamber 22.

A pressure fluid P1 is supplied, through the intermediary of the first fixed throttles 37,38, to the chambers 21 and 23. Pressures P'2 and P"2 which become established within the chambers 21 and 23 are the resultants of the supply pressure P1, of the low pressure Po and the pressure drops dependent upon the flow sections of the throttles 37,38, on the one hand and upon those defined by the distances separating the flow orifices of the nozzles 33 and 34 from the faces of the disc or plate 28, on the other hand.

The pressure Po existing within the bellows 31,32 and the central chamber 22 is equal for example to atmospheric pressure.

The operation of the pressure reducer assembly is similar to that of the first embodiment, the compensation resulting from a reduction in the flow section as a result of a partial obstruction is made by modification of the length of the bellows of the chamber concerned.

Figure 3 shows two pressure reducers similar to those of Figure 2, the dividers and the bellows of the preceding embodiment having been replaced by circular, resilient diaphragms 39,40 supporting at their respective centres, nozzles 41,42 providing for respective communication between chambers 43,44 and a central chamber 45, a disc or plate 46 of the servo-valve being common to the two throttles, and each nozzle discharging against one of the faces of the disc or plate.

In the embodiment illustrated in Figure 3, the nozzles are inverted, that is to say that the flow orifice of one nozzle cooperates with the face of the disc directed towards the face of the supporting diaphragm of the other nozzle. Thus the nozzle 41 provides for communication with the chamber 43 where the pressure P'2 exists with the central chamber 45 at its orifice disposed opposite to the face of the disc or plate 46 directed towards the membrane 40 and defining the other chamber 44 where the pressure P"2 exists. In this-embodiment, only the central chamber 45 is at the pressure Po equal for example to atmospheric pressure.

Otherwise, similar elements to those described in the embodiment of Figure 2 have the same reference numerals.

Figure 4 illustrates a simple servo-valve pressure reducer having two chambers 47,48. The chamber 47 is defined by the internal volume of a bellows 49 carrying on its axis a nozzle-element 50 providing communication between the internal volume 46 and the chamber 48. The flow section is determined by the distance separating the end of the nozzle 50 from the face of a disc or plate 51 suspended as herein before described on the movable armature 26 of a winding 25.

The chamber 47 communicates through a tube 52 with a pressure source Po equal for example to atmospheric pressure.

A fluid at supply pressure P1 is supplied through the intermediary of a first throttle 37 to the chamber 48 of the pressure reducer in which the utilized pressure P2 exists.

The operation is at all points comparable to the preceding embodiments: an increase in the pressure P2, resulting from a partial obstruction of the flow section existing between the disc or plate and the nozzle, contracts the bellows 49 which acts to increase the distance between the nozzle and the disc or plate and as a consequence the flow section.

Figure 5 illustrates a shuttle type of reducer embodying the inventjon. A hollow body or casing 53 of the pressure reducer defines a cylindrical volume separated into two parts 54,55 by an internal divider 56 and closed at each of its ends by respective bases traversed by tubes 57,58. The first part 54 supports on its lateral wall a flow orifice 59, of which the flow section can be modified by a shuttle 60 mounted on the end of a resilient member 61 of which the other end is secured to the divider 56.

In the embodiment illustrated, the resilient member 61 is a helical spring. The second part 55 is subdivided into two chambers 62 and 63 by a shuttle 66. The chamber 62 carries in its lateral wall a tube 64 interconnected with the tube 59 of the part 54, and a flow orifice 65 of which the flow section can be modified by the shuttle 66 secured at the end of a resilient member 67, such as a helical spring, or which the other end is secured to the base of the part 55.

The fluid under high pressure P1 is introduced through the tube 58 into the chamber 68 defined within the part 54 between the base of the said part and the face of the shuttle 60, from whence it exhausts at the reduced pressure P2 through the tube 59 in the direction of the utilisation and to the chamber 62.

The chamber 62 communicates with the space located between the shuttle 60 and the divider 56 in which the resilient member 61 is located. A part of the fluid at reduced pressure P2 exhausts through the flow orifice 65 of which the flow section is capable of being adjusted by the shuttle 66, towards a pressure source Po equal for example to atmospheric pressure. The pressure in the chamber 63 in which the spring 67 of the shuttle 66 is located is equal to Po.

The operation is identical to that of the preceding examples. The partial obstruction of the flow section of one of the orifices 59 or 65 by a foreign body gives rise to a reduction or an increase, in dependance upon the orifice concerned, in the pressure P2 in the chamber 62 with a variation in an inverse sense to the flow sections of the orifices 59 and 65 tending to increase the flow section of the obstructed orifice and to reduce that of the other orifice and thus to compensate at least in part for the variation in the reduced pressure P2.

If the various embodiments of the pressure reducers hereinbefore described do not enable precise re-establishment of the initial reduced pressure, it is at least possible to reduce by more than half the influence of the obstruction by a foreign body on the reduced pressure in relation to known pressure reducers which do not provide for any compensation.

With regard to the operation of the double servovalves provided with the pressure reducers according to the invention, their characteristic curves, showing pressures reduced as a function of the displacement of the disc or plate with respect to its median position, is modified.

Figure 6 shows a characteristic curve 1 when the two nozzles are fixed, that is to say when the pressure reducers do not incorporate the features of the invention. The curve 2 corresponds to a double servo-valve equipped with pressure reducers embodying the invention without special adaption, and it will be noted that the curve flattens and spreads out. The displacement of the disc or plate is more substantial and the pressures are less than those provided with fixed nozzles.

This disadvantage can be almost completely avoided, for example by bringing the nozzles closer to the disc or plate or by modifying the flow sections of the various throttles.

It is therefore necessary to take into account these remarks in the initial dimensioning of the pressure reducers for a double servo-valve having the characteristics of the invention.

Claims (11)

1. A pressure reducer comprising a hollow body divided into three chambers, each chamber having a flow passage communicating therewith, a first said chamber being operative with fluid at a relatively high pressure, a third said chamber being operative with fluid at a relatively low pressure and a second said chamber being operative with fluid at a pressure intermediate the relatively high and low pressures, first throttle means between the first and the second chambers, second throttle means between the second third chambers, at least one of said throttles including means defining an orifice, and a member adjustable relative to the orifice whereby to vary the fluid flow section through that throttle, and a resilient member supporting one of said orifice-defining means and of said adjustable member, said resilient member being movable in response to variations in the pressure differential between the said intermediate pressure and the respective chamber adjacent said first or third chamber, and said resilient member being operative to counteract any changes in said intermediate pressure resulting from obstruction of one of the throttles by acting on that part of the orifice defining means carried thereby.

2. A pressure reducer according to claim 1, wherein the said resilient member is sensitive to variations in the pressure differentials between the intermediate pressure of the fluid existing in the second chamber and the relatively high pressure of the fluid existing in the first chamber.

3. A pressure reducer according to claim 1, wherein the resilient member is sensitive to variation in the pressure differentials between the intermediate pressure of the fluid existing in the second chamber, and the relatively low pressure existing in the third chamber.

4. A pressure reducer according to any one of claims 1 to 3, wherein the resilient member is a bellows and the throttles are respectively constituted by an orifice supported by the bellows and by a needle.

5. A pressure reducer according to any one of claims 1 to 3, wherein the resilient member is a bellows and the two throttles are respectively constituted by a nozzle supported by the bellows and by a plate.

6. A pressure reducer according to any one of claims 1 to 3, wherein the resilient member is a diaphragm and the two throttles are respectively constituted by an orifice supported by the diaphragm and by a needle.

7. A pressure reducer according to any one of claims 1 to 3, wherein the resilient member is a diaphragm and the two throttles are respectively constituted by a nozzle supported by the diaphragm and by a plate.

8. A pressure reducer according to any one of claims 1 to 3, wherein the resilient member is a helical spring and the two throttles are respectively constituted by a shuttle contacting the spring and being displaceable in a bore and by an orifice provided in the wall of the bore.

9. A pressure reducer according to any one of the preceding claims, wherein the throttles are each provided with a -resilient member reacting in an inverse sense to one another so as to match their forces so as to counteract possible changes in the intermediate pressure.

10. A double servo-valve incorporating two pressure reducers according to claim 1, wherein that part of each throttle not carried by the resilient member, is common to two throttles which respectively belong to each of the two reducers.'

11. A pressure reducer substantially as hereinbefore described with reference to the accompanying drawings.