GB2118329A

GB2118329A - Improved pneumatically assisted relief or safety valve

Info

Publication number: GB2118329A
Application number: GB08210568A
Authority: GB
Inventors: Leonard William Lamburn; Daphne May Russell
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-04-08
Filing date: 1982-04-08
Publication date: 1983-10-26
Also published as: GB2118329B

Abstract

A pressure relief/safety valve is provided with a supplementary actuator, which defines two pressure chambers 3A, 3B, one on each side of a piston or diaphragm 26, each having means, YA and YB, for connecting the chambers into a suitable control system (Figure 1, not shown) to supply pneumatic pressure to one or the other of the chambers to inhibit or promote opening of the valve. A lost motion connection in the supplementary actuator displaceable member, in the form of a slideable sleeve 27, coupling to and around valve spindle 12, permits operation of the valve by inlet pressure at 9 without pneumatic assistance should the servo-control system fail. <IMAGE>

Description

SPECIFICATION Improved pneumatically assisted relief or safety valve This invention relates to fluid pressure systems incorporating relief or safety valves such as are employed to relieve excessive pressure in pipe lines, processing vessels and like equipment subjected to internal fluid pressure.

In accordance with the invention there is provided a spring loaded relief or safety valve embodying a double acting actuator having a displaceable mem bercapable of response to pneumatic pressure applied or removed above or below it, instigated by a suitable pilot and/or relay controls, an operative connection between the relief, or safety valve and the said member, the latter, on changes of pneumatic pressures applied to it assisting the closing or opening of the valve. The operative connection is so disposed that on failure of the pneumatic supply the relief or safety valve may operate in the conventional manner, independently of the actuator.

The following descriptive text is accompanied by drawings, in which: Figure 1 Is a diagrammatic representation of a fluid pressure relief system.

Figure 2 Is an axial sectional view of a relief or safety valve with an associated actuator.

Referring to Figure 1,the relief or safety valve is shown mounted on a pressure vessel 2 and arranged to relieve excessive fluid pressure from the said vessel. The valve 1 is fitted with a double acting pneumatically operated diaphragm type actuator 3 which is mounted above the valve spring as an integral part of the valve. The actuator 3 is adapted so that upper and lower chambers 3A and 3B respectively may be fed with air or gas pressure, or exhausted, to either supplement the closing load on the relief or safety valve or assist in opening, in accordance with pressure conditions within the fluid pressure vessel or system.

The relief or safety valve 1 as shown in Figure 2 may comprise a body 6 having an inlet 7 and an outlet 8, the inlet being fitted with a tapered nozzle 9 provided at its upper end with a seating 10 engageable by a valve disc 11 carried in a hollow housing 1 1A to which is screwed a spindle 12 directed axially upward through a guide 13 and extending through a valve spring 15, thence through an adjusting bolt 18 into a pneumatic actuator 3. The valve seating area is optionally balanced by a bellows 14 on the discharge side of the valve. The valve disc is loaded by a valve spring 15 constrained between lower washer 16 and upper washer 17 the valve disc normally sealing the valve at 10 against discharge from the protected fluid system at 2, Figure 1.The lower washer rests on a peripheral shoulder formed on the valve spindle and the upper washer abuts on to the convex lower flanged face of the thrust collar 19. The adjusting bolt 18 is externally screw-threaded to provide manually set vertical adjustment within the valve bonnet upper flange at 21 to initially compress spring 15 to the valve relieving pressure in the conventional manner. At such time, the flange end of the thrust collar 19 is trapped between the spring upper washer 17 and the adjusting bolt lower end 18, at 23. The adjusting bolt is bored to axially receive the slideable thrust collar shank 19 and diaphragm bolt follower 20.

The actuator 3, is secured above the valve bonnet 21, is defined into upper and lower chambers 3A and 38 respectively, by a displaceable diaphragm assembly 26A. Aflexible diagraphm 26 is clamped peripherally between upper and lower casings and the assembly is axially secured together by a diaphragm bolt 27 in conjunction with diaphragm bolt hollow nut 28, the two chambers thus being isolated from each other. The upper chamber is closed by a screwed cap 31 which provides access to relative adjustment, at 33C, of diaphragm springs 33A and 33B. The diaphragm bolt is slideably guided and '0' ring sealed through the top boss of the lower chamber housing at 22.This bolt together with follower 20, and thrust collar 19, form a hollow articulated thrust column to transmit downward force from the diaphragm assembly 26A to the other spring upper washer when the actuator upper chamber 3A is pressurised.

The diaphragm bolt is externally screw-threaded within the lower chamber space to accept a travel stop nut 24 fitted with radial locking screw and trapped friction washer 24A.

The position of the stop nut is determined after the spring initial adjustment is made, and is governed by the distance of its lower face above the corresponding upper face of the lower chamber housing at 25, representing the further spring compression to produce the required supplemented valve load as, and when, the stop nut arrests the downward travel of the actuator diaphragm assembly.

The valve spindle 12 protrudes slideably through the thrust collar 19 and diaphragm bolt 27 into the diaphragm bolt nut 28 and terminates with a flanged nut 29.

The pneumatic operations on the relief or safety valve depend on the provision of a suitable pilot which will accept and interpret signals from the protected fluid system and relay responses to the valve actuator. This has been assumed in the functional cases II and Ill below, shown in block form in Figure 1 and in confirmation ofthefollowing described operational states of the valve due to pneumatic intervention. Apart from illustrative purposes the pneumatic auxiliaries have no part in this specification. The pilot is numbered 5, the pneumatic supply shown at 11, the connections to upper and lower actuator chambers 3A and 3B are AY and BY respectively, the pneumatic discharge is indicated by Z and the fluid pressure connection from the fluid pressure system to the pilot is numbered 47.

The relief or safety valve subject matter of this specification is suitable for service employing pilot(s) and relay system (5) part subject of patent application no. 8018753, serial no. 2077393A and, as far as possible, identification part numbering is common.

There are three functional states of the relief or safety valve, case II being indicated in Figure 2.

Case / Conventional operation without pneumatic assistance Valve set to required relieving pressure by adjusting bolt, the spring reacting upwards through the thrust collar 19 to the adjusting bolt lower end at 23.

In this condition the actuator diaphragm assembly is held in an inoperative position by springs 33A and 33B and by the lower face of the spindle nut 29 so adjusted to stand clear of the corresponding upper face of the diaphragm bolt at 30.

Therefore, the valve responds only to fluid pressure in the protected system acting on the valve seating area and discharges only in accordance with the valve design characteristics.

Case II Under normal service conditions with pneumatic supplemented loading Actuator upper chamber 3A pneumatically activated and lower chamber 3B exhausted, diaphragm assembly depressed, transmitting full supplemented load through the diaphragm bolt 27, follower 20, thence by thrust collar 19 at 23, to spring upper washer 17 and spring 15, the downward travel and thrust of the actuator being arrested with the stop nut 24 contacting the lower chamber housing at 25, the flanged end of the thrust collar having simultaneously separated from the support of the lower end of the adjusting bolt at 23.

Case 111 Valve operating with pneumatic assistance.

Upper Actuator Chamber 3A exhausted and lower chamber pneumatically activated:Diaphragm assembly 26A raised from depressed supplemented spring compressed position as Case II and through 'inoperable' position, Case I, diaphragm 27, thence contacting spindle nut 29 at 30 and assisting the valve disc 11 to lift against initial spring loading.

Following assisted discharge the actuator conditions revert to Case II as dictated by the pneumatic controls and lower case 3B exhausts, upper case 3A is reactivated, positively closing the relief or safety valve, independent of valve characteristics.

A valve lift limiting setscrew 32 may be fitted in the upper chamber top plug 31 to prevent diaphragm overtravel and excessive valve lift. Also a degree of supplemented valve loading may be provided by a similarly placed setscrew in the top plug to depress the diaphragm assembly on protracted pneumatic failure but dnly if the protected fluid system can tolerate the increased pressure due to conventional operation of the valve at the higher spring setting.

The valve disc may be gagged for vessel testing purposes by removing setscrew 32 and diaphragm nut plug 28A, temporarily removing chamber top plug in order to do so and then inserting suitable gag screw in the replaced top plug to engage top end of valve spindle at 12A.

The actuator shown in Figure 2 may have piston or bellows type displaceable member as distinct from the diaphragm type illustrated. Also the chambers may be isolated by bellows instead of'O' ring type stuffing boxes.

A second embodiment, not illustrated, would be to provide the relief or safety valve with manual lifting gear to contact the lower face of the diaphragm bolt at 20, Figure 2, and to make the actuator supporting structure of skeletal design, ensuring that the valve disc upper face and valve spring are at atmospheric pressure. These features are to meet boiler code requirements for steam boiler safety valves, the principle and design of pneumatic assistance being as described.

It has been shown that fluid upthrust beneath the valve disc is the determining factor in relief or safety valve functioning. However, the reactive forces on the valve disc assembly due to escaping fluid is a major factor in the functioning of such valves especially when conventionally operated. This factor, though no part of this specification can cause irregular valve operation when a relief valve is maladjusted. The pneumatically assisted system does give prompt and effective overriding control beyond conventional operation and is advantageous when plan cannot be shut down for nicety or relief valve adjustment.

Valve tightness under pneumatic assistance may be more effective than by normal spring loading. In practice that may also mean that valve relieving pressure may be set closer to the normal fluid working pressure than with conventional operation.

Also, under pneumatic operation, full valve lift may be attained with zero fluid system pressure accumulation.

Claims

1. A relief or safety valve embodying an actuator having a displaceable member, which member is capable of applying force and movement through operative parts when fed with pneumatic pressure, in the first instance to increase the spring loading of the valve member or disc and, when pneumatic pressure supplies to the actuator so direct to remove the additional force and further, supply a force opposite in sense to the original to assist in opening the valve, the said operative parts being so devised to permit the valve to function freely and independently when the actuator is inoperative due to pneumatic failure.

2. A relief or safety valve as Claim 1, wherein the valve comprises a valve member or disc, a spindle on which the valve member is mounted, and a spring for urging the valve member on to an associated seating, said spindle being extended axially through and beyond the valve housings into the actuator displaceable member and being so coupled that the member, in practice being a diaphragm assembly or bellow or piston, is able to functionally position itself axially along the extended spindle to permit the actuator to operate under the influence of pneumatic pressure but not restrict the independent functioning of the relief or safety valve when pneumatic supplies are unavailable.

3. A relief or safety valve as claimed in either foregoing claim wherein a manual screw-threaded bolt is provided to initially compress the spring for conventional valve operation but which will facilitate further spring compression without disturbing the initial manual adjustment.

4. A relief or safety valve as claimed in any foregoing claim,wherein a limitable and removeable downward thrust is provided by a pneumatic actuator to increase the initial manually adjusted spring setting by means of an articulated thrust member extending below the actuator displaceable member, slideable through the adjusting bolt, thence engaging the spring upper washer.

5. A relief or safety valve as claimed in any foregoing claim, that provided with the correct sequence of pneumatic pressure and exhaust, the actuator will assist the valve to open at the initial valve spring setting at a similar pilot setting or any variation of comparative settings to suit the protected fluid pressure system.

6. A relief or safety valve as claimed in Claim 1, wherein the actuator displaceable member, shown as a diaphragm assembly, is axially guided and so arranged that the pneumatic pressures and discharge pressure from the relief or safety valve are each and all isolated from the other but that the valve spindle is free to move independently of the diaphragm assembly when the relief or safety valve functions without external pneumatic assistance.

7. A system as claimed in any foregoing claim wherein the actuator has a casing disposed when the relief or safety valve is in a normal upright position above the valve body and either above or below the spring bonnet so as to define on one side of the displaceable member an upper air or gas space and on the other side a lower air or gas space, both of which being serviceable to promote the functioning of the valve.

8. A system as in all previous claims as illustrated in Figures 1 & 2.

(Revised 21st February 1983)

4. A relief or safety valve as claimed in any foregoing claim, wherein a limitable and removeable downward thrust is provided by a pneumatic actuator to increase the initially manually adjusted spring setting by means of an articulated thrust member extending below the actuator displaceable member, slideable through the adjusting bolt, thence engaging the spring upper washer.

6. A relief or safety valve as claimed in previous claims that, following the assisted discharge of the valve, as in Claim 5 and subsequently, provided the correct sequence of pneumatic conditions are applied, the upward thrust of the actuator may be removed and replaced by a downward thrust, as in Claim 4, such reversal of thrust assisting in positively closing the valve, this closure completing a cycle of repeatable Relief/Safety Valve Operation.

7. A relief or safety valve as claimed in Claim 1, wherein the actuator displaceable member, shown as a diaphragm assembly, is axially guided and so arranged that the pneumatic pressures and discharge pressure from the relief or safety valve are each and all isolated from the other but that the valve spindle is free to move independently of the diaphragm assembly when the relief or safety valve functions without external pneumatic assistance.

8. A system as claimed in any foregoing claim wherein the actuator has a casing disposed when the relief or safety valve is in a normal upright position above the valve body and either above or below the spring bonnet so as to define on one side of the displaceable member and upper air to define on one side of the displaceable member an upper air or gas space and on the other side a lower air or gas space, both of which being serviceable to promote the functioning of the valve.

9. A system as in all previous claims as illustrated in Figures 1 & .