GB2041501A - Pilot-assisted fluid flow control valve - Google Patents

Abstract

The main valve closure is in the form of a spool-like piston comprising a carrier portion (30) having secured therein, by means of an interference fit, a unitary plastics insert (32) one end face of which has a sealing surface (48) for sealing engagement with the main valve seat (18) and the other end face of which has a sealing surface for engagement with a pilot valve closure. The use of the unitary insert (32) substantially overcomes leakage problems encountered in prior valves of a similar kind and such an insert, in the event of it becoming worn as a result of repeated operation of the valve, can be readily and cheaply replaced with a new insert. <IMAGE>

Description

SPECIFICATION Valves The present invention relates to a fluid flow control valve comprising a main flow passage having an inlet and an outlet with a main valve closure sealingly engageable with a main valve intermediate said inlet and outlet, said closure having an auxiliary axial flow passage formed therein connecting the inlet and outlet, an auxiliary closure for said auxiliary passage and means for operating said auxiliary closure to open and close the auxiliary passage such that when the auxiliary passage is open the main valve closure is disengaged from said valve seat thereby leaving the main flow passage open and when the auxiliary passage is closed the main valve closure sealingly engages said valve seat thereby closing the main flow passage.A valve of this type will be referred to hereinafter as a valve "of the type described" and is commonly referred to as a pilot-assisted control value.

The operating means for the auxiliary closure is preferably a solenoid device, but this is not essential.

Prior Art Valves of the type described are already well known. An example of such a valve is shown in UK Patent Specification 821 903 and there are many known modifications of the general type of valve shown in that specification.

We have supplied for some years one form of valve of the type described, as illustrated in Fig. 1. The valve shown there comprises a body 10 with an inlet 12 and an outlet 14 each communicating with a chamber 1 6 in the body. The outlet 14 communicates with the chamber 1 6 via a valve seat 18, and the chamber 1 6 contains a piston in the form of a spool 20 which is slidable in the chamber 1 6 towards and away from the seat 1 8. Spool 20 is made of metal, but an annular sealing washer 22 is mounted in the base of the spool for co-operation with the seat 1 8.

Spool 20 has a through passage 24 communicating at one end with the outlet 14 and at at the other end with the upper portion (as viewed in Fig. 1) of the chamber 16. The portion of the spool 20 surrounding the upper end of the passage 24 is shaped to a frustocone for co-operation with a closure provided on an armature 26 of a solenoid device, the main body of which is indicated at 28. The main body of the solenoid device is secured to the body 10 of the valve to close and seal the upper end of the chamber 1 6. A generally suitable form of armature is illustrated in British Patent Specification 1 21 3 925, although we have not used the guide rings for the armature illustrated in that patent specification.

Although it is not shown in Fig. 1, the spool 20 has an additional bleed passage providing communicaton between the upper and lower portions of the chamber 16, so that fluid from the inlet 1 2 can pass via the bleed passage to the upper portion of the chamber 16 surrounding the armature 26. Alternatively or additionally the spool 20 may be a sufficiently loose sliding fit in the chamber 1 6 that fluid from the inlet 1 2 can pass over the outer surface of the spool 20 to the upper portion of chamber 1 6. The resultant operation of this type of valve is too well known to require detailed description.Briefly, when the passage 24 is closed by the armature 26, the inlet pressure acting on the upper end of the spool 20, together with the force of a compressed spring in the body of the armature 26, forces the spool downwardly to bring the washer 22 into sealing engagement with the seat 18, thereby closing the valve. When the armature 26 is lifted to open the passage 24, the resultant unbalanced conditions on the spool 20 cause it to lift and "float" on a cushion of fluid which'is permitted to flow from the inlet 1 2 to the outlet 14 via the opening in the seat 18.

We have experienced a number of difficulties in obtaining adequate sealing performance from valves as illustrated in Fig. 1.

There are two particular problem areas for leakage, namely: 1. the join between the annular washer 22 and the spool 20, where inlet fluid can leak around the reverse face of the washer 22 where it meets the spool, and 2. the contact region between the closure on the armature 26 and the frusto-cone on the spool 20, where both damage to the frusto-cone and lack of accurate alignment of the sealing face on the frusto-cone with the sealing face on the armature 26 can cause leakage.

Present Invention The present invention provides a valve of the type described wherein the main valve closure comprises a carrier portion having a bore therethrough and secured within the bore by means of an interference fit with the walls of the bore, a separately formed unitary insert comprising plastics material, said insert having a fluid flow passageway therethrough constituting the auxiliary flow passage, at least a part of one end face of said insert constituting a sealing surface for sealing engagement with the main valve seat and at least a part of the other end face of said insert constituting a sealing surface for sealing engagement with said auxiliary closure.

The plastics material is preferably wear resistant and can form a good seal with the auxiliary closure and with the main valve seat.

An example of a suitable material is polytet rafluoroethylene (PTFE). Preferably, the unitary body is arranged to snap fit in the carrier portion.

The unitary body may be generally tubular with a flange at one end. The through passage in that tubular body will be open-ended to provide said auxiliary flow passage. The flange may be arranged to engage a main valve seat in use.The other end of the tubular body may be generally normal to the axis of the through passage.

The auxiliary closure may have a rounded portion to engage said unitary body and so form a seal therewith. The rounded portion may be provided by an insert mounted in a carrier. A suitable insert is spherical in shape, although this is not essential since the rounded end could be provided in an elongate member is desired.

The carrier portion of the main valve closure may also be unitary in structure. It may be made of a metal, preferably a copper alloy such as brass. The carrier portion is slidable in a valve chamber, and it may be provided with the conventional bleed passage for providing fluid communication between regions of the chamber on opposite sides of the carrier portion.

Embodiment Illustrated in the Drawings An embodiment in accordance with the invention will now be described with reference to Figs. 2 and 3, in which: Figure 2 is a section through a carrier portion of a valve in accordance with the invention, the carrier portion being suitable for modifying the valve shown in Fig. 1, and Figure 3 is a corresponding side elevation of an insert for assembly with the carrier portion shown in Fig. 2.

Since the general construction of the valve according to the present invention is the same as that shown in Fig. 1, it will not be further described here. The main modification is the substitution of a spool as shown in Figs. 2 and 3 for the spool 20 shown in Fig. 1.

As shown by Figs. 2 and 3 type new form of spool comprises a carrier 30 and a unitary insert 32 snap fitted therein. The external shape of the sides of the carrier 30 is generally the same as that of the spool 20, thereby enabling the carrier the carrier 30 to slide in the chamber 1 6 in the same way as the previous spool. In Fig. 2 ther bleed passage 34 is shown extending through the end flanges of the carrier 30.

However, the carrier 30 differs from the spool 20 in that a bore 36 of relatively large diameter is substituted for the bore 24. Bore 36 has an internal shoulder provided by an internal flange 38 near its lower end as viewed in Fig. 2. Below the flange 38, bore 36 opens on to a rebate 40 in the lower end face of the portion 30. It will be noted also that the upper end face is no longer provided with a frustocone as in the case of the upper end of the spool 20.

The insert 32 shown in Fig 3 is assembled with the carrier 30 by snapping it past the flange 38. The external surface of the insert therefore includes a frusto-concial surface 42 to facilitate the assembly operation by pressing the insert into place in the carrier; a cylindrical surface 44 which engages the internal surface of the bore 36 above the flange 38 and provides location against rocking of the insert in the carrier; a groove 46 to receive the flange 38 on the carrier and a flange 48 which lies in the rebate 40 in the carrier. The insert 32 also has a through passage 50 which provides the auxiliary flow passage for the valve. The insert is therefore generally tubular, and one end surface of it (provided by the flange 48) provides a sealing suface for engaging the main valve seat 18 in use.The other end surface of the tubular insert (which is generally normal to the axis of the passagle 50) provides a sealing surface for engagement by the closure portion of the armature 26 of the valve.

In order to facilitate sealing co-operation between the auxiliary closure on the armature 26 and the tubular insert, the end face of the closure is preferably rounded. Thus, it can sit accurately in the end of the through passage 50 despite minor misalignment of the armature 26 in its guide passage in the solenoid device 28. The auxiliary closure makes initial line contact with the rim immediately surrounding the end of the auxiliary flow passage 50. With repeated opening and closing for the auxiliary flow passage, we have found that there is some "bedding-in" of th auxiliary closure in the insert, so that the intial line contact is changed to area contact on a frustospherical surface.However, provided the material of the insert 50 is sufficeintly wear resistant, the bedding-in process ceases after a substantially predetermined number of opening and closing operations, so that the subsequent operation of the valve continues reliably within designed performance limits. A suitable material for the insert is PTFE, although the invention is not limited to this. A suitable material for the carrier 30 is a metal, for example brass.

The closure portion on the armature 26 can be provided by an insert in the armature, for example as generally shown in the aforementioned British Patent 1 213 925. As indicated above, the generally plain selaing face pro vided on the insert shown in that patent specification should be generally rounded for use in the valve described with reference to Figs. 2 and 3. An alternative form of insert is a sphere adapted to lie generally within the body fo the armature by having a projecting portion which provides the sealing face with the upper end of the insert 32.

It will be apparent that any leakage around the reverse face of the flange 48 can no longer pass direct to the outlet 14 of the valve, but instead merely passes to the upper region of the chamber 1 6, ie it adds to the bleed via the passage 34. By eliminating the fursto-conical seat at the upper end of the spool 20, we have reduced the possibility of leakage through damage of that seat, and at the same time by rounding the end of the armature closure we have improved the sealing contact despite armature mislignment. In addition, a worn insert in a valve of the invention can be readily replaced with a new insert merely by pressing out the old one and inserting the new one.

Claims (9)

1. A valve of the type described wherein the main valve closure comprises a carrier portion having a bore therethrough and secured within the bore by means of an interference fit with the walls of the bore, a separately formed unitary insert comprising plastics material, said insert having a fluid flow passageway therethrough constituting the auxiliary flow passage, at least a part of one end face of said insert constituting a sealing surface for sealing engagement with the main valve seat and at least a part of the other end face of said insert constituting a sealing surface for sealing engagement with said auxiliary closure.

2. A valve according to Claim 1 wherein the bore of said carrier portion is of substantially circular cross-section and the unitary insert is substantially cylindrical.

3. A valve according to Claim 1 or Claim 2 wherein the insert is a snap fit within the bore of the carrier portion.

4. A valve according to Claim 3 wherein the insert has a peripheral groove which interlocks with a projection formed in the bore of the carrier portion.

5. A valve according to any one of Claims 1 to 4 wherein said plastics material is polytetrafluoroethylene.

6. A valve according to any one of Claims 1 to 5 wherein the auxiliary closure comprises a part spherical surface for sealing engagement with said other end face of the insert.

7. A valve according to any one of Claims 1 to 6 wherein the operating means for the auxiliary closure is a solenoid device.

8. A valve according to Claim 1 wherein said carrier portion and insert are substantially as hereinbefore described with reference to and as illustrated in Figs. 2 and 3 of the accompanying drawings.

9. A valve according to Claim 1 substantially as hereinbefore described with reference to and as illustrated in Fig. 1 of the accompanying drawings as modified with reference to and as illustrated in Figs. 2 and 3 of the accompanying drawings.