US3865132A - Pilot operated relief valve - Google Patents

Abstract

An Assembly comprising of a piston/cylinder means adapted to a spring loaded pressure relieving valve wherein the piston area by being greater than the seat area of the valve will when the cylinder is in fluid communication with vessel pressure will operatively compress the valve spring from its maximum set pressure allowed by pressure vessel and boiler codes to a higher setting for greater seat loading as the pressure in the vessel on which the valve is attached approaches the normal set pressure value. When the pressure in the vessel reaches the normal set pressure value, a pilot valve responsive to pressure and normally open to the flow of vessel pressure to the cylinder will close the pressure to the cylinder and concurrently exhaust the pressure therein thus removing the force of the piston on the valve spring which now returns to its normal setting and the opening of the main valve without simmer. The piston by operatively engaging one end of the spring insures ''''fail safe'''' opening of the main valve by the resilience of the spring in the event the piston and/or pilot valve should malfunction in as much as the valve stem does not engage the piston. The stroke of the piston can be limited by a travel stop to control the compressing of the valve spring from its normal set pressure to a predetermined higher setting.

Description

ite States Patet H91 Wiegand 1 Feb.11,1975

[ PILOT OPERATED RELIEF VALVE [76] Inventor: Charles W. Wiegand, 18 Circuit Rd., New Rochelle, NY. 10805 [22] Filed: Aug. 17, 1973 [21] Appl. No.: 389,139

[52] 1.1.3. Cl 137/492.5, 137/489, 251/77, 251/63.4, 251/636 [51] llnt. Cl. Fl6k 17/02 [58] Field of Search 137/488, 489, 492.5; 251/614, 63.6, 63.4, 77

[56] References Cited UNITED STATES PATENTS 3,512,549 5/1970 Wiegand 137/4925 X Primary Examiner-Henry T. Klinksiek [57] ABSTRACT An Assembly comprising of a piston/cylinder means adapted to a spring loaded pressure relieving valve wherein the piston area by being greater than the seat area of the valve will when the cylinder is in fluid communication with vessel pressure will operatively compress the valve spring from its maximum set pressure allowed by pressure vessel and boiler codes to a higher setting for greater seat loading as the pressure in the vessel on which the valve is attached approaches the normal set pressure value. When the pressure in the vessel reaches the normal set pressure value, a pilot valve responsive to pressure and normally open to the flow of vessel pressure to the cylinder will close the pressure to the cylinder and concurrently exhaust the pressure therein thus removing the force of the piston on the valve spring which now returns to its normal setting and the opening of the main valve without simmer.

The piston by operatively engaging one end of the spring insures fail safe opening of the main valve by the resilience of the spring in the event the piston and/or pilot valve should malfunction in as much as the valve stem does not engage the piston.

The stroke of the piston can be limited by a travel stop to control the compressing of the valve spring from its normal set pressure to a predetermined higher setting.

4 Claims, 3 Drawing Figures PILOT OPERATED RELIEF VALVE The present invention relates to the conventional spring loaded pressure relieving valve used to protect vessels from excessive pressure. This tyoe of valve depends on seat tightness by the differential of the set pressure of the valve and the operating pressure in the vessel on which the valve is attached. The spring is limited to 100 percent loading on the valve disk.

The operating pressure is usually a fixed value and to minimize vessel cost, the Maximum Allowable Working Pressure (MAWP) is usually selected relatively close to operating pressure leaving little net spring force to differential remaining to be exerted on the valve disk. Pressure vessel codes limit the set pressure of the valve so as not to exceed the M.A.W.P. of the vessel. Currently in order to increase the differential, the set pressure and the spring loading must be higher which in turn increases the M.A.W.P. and the cost of the vessel.

The spring loaded valve is inherently prone to simmer (a phase just prior to opening) on gas and vapor service. The valve starts to simmer 3 to 5 percent below the normal set pressure. This simmer further reduces the differential or seat loading from the numerical difference of the set pressure and operating pressure. Should the vessel pressure reach the simmer phase but not to the set pressure and then recede to the normal operating pressure, the valve will continue to simmer.

This invention when operatively adapted to a conventional spring loaded pressure relieving valve will provide the necessary force from a piston when pressurized to compress the valve spring from its normal setting to a higher setting resulting in a greater differential and tighter valve than the conventional valve under similar operating and set pressure conditions. It will also permit the vessel operating pressure to be within 97 percent of the normal set pressure and the M.A.W.P. of the vessel due to the higher spring loading on the valve disk. Simmer is eliminated as the spring loading is reduced to the initial loading by the fast action of a pilot valve in exhausting of the pressure in the cylinder and on the piston when the set pressure value is reached in the vessel. There are valves that utilize the piston/cylinder means in which the force of the piston is applied directly on either the valve stem or on the valve disk. The pressure to the cylinder is controlled by a pilot valve. The lading fluid in the vessel and/or chemical treatment used on steam boilers may cause the piston to seize and/or the small orifices in the pilot valve to plug shut. In either case the main valve could be locked in a closed position.

The piston/cylinder means of this invention comprises a closed end cylinder axially affixed to the closed end of a bonnet on a main valve. A piston operatively positioned in the cylinder bore to engage the threaded end of a slidable shouldered rod which is axially interposed between the piston and one end of a compression spring encompassed by the bonnet. The shouldered rod is axially guided by a bushing threaded into the closed end of the bonnet. The lower annular surface of the bushing to engage the shoulder on the rod to initially load the spring to its normal set pressure by applying torque force to the bushing. The higher spring setting is obtained when the vessel pressure in the cylinder is exerted on the top of the piston and operatively on the spring as the vessel pressure approaches the set pressure of the main valve and the pilot valve. The free end of the valve stem is axially guided by a bore in the shouldered rod.

The piston area must be greater than the seat area of the valve in order for the piston force to further compress the spring from its normal setting (set pressure) to a higher setting. The higher setting of the spring is controlled by a nut threaded on the shouldered rod which limits the stroke of the piston. The adjustable gap between the nut and the top of the threaded bushing predicates the increase in spring force and loading desired from the piston force available.

A pressure responding pilot valve which is normally open to the flow of vessel pressure to the cylinder thus energizing the piston as the pressure approaches the set pressure of the main valve. The pilot valve is set to close the pressure to the cylinder and concurrently exhausting the presssure therein when the vessel pressure reaches the normal set pressure value thus removing the piston force on the main valve spring allowing it to return to its normal set pressure and the opening of the main valve without simmer.

A diaphragm or bellows can be used in place of the piston/cylinder illustrated in as much as the axial movement is miminal.

The conventional type lifting lever is not applicable to a valve using this invention. However a Navy type lever can be used, it operatively engages the lower end of the valve spring.

FIG. 1 is an outline drawing of the main valve show ing the location of the piston/cytinder means on the main valve, the pilot valve and the necessary conduit to interconnect vessel pressure to the pilot valve and the cylinder.

FIG. 2 is partial sectioned view of the main valve bonnet, spring and stem and full sectioned view of the piston/cylinder means and the pressure responding pilot valve at normal or static spring settings on both valves with no vessel pressure present.

FIG. 3 is the same shown in FIG. 2 except that it shows the piston at its maximum stroke when the cylinder is pressurized with vessel pressure by the pilot valve and the main spring compressed to its higher setting.

Referring to FIG. 1 the outline drawing shows the location of the piston/cylinder means on the bonnet of a spring loaded main valve and a pressure responding pilot valve with interconnecting conduits. The dotted line 9 is the vessel nozzle to which valve body 11 is attached, bonnet 12 is axially affixed to the valve body 1], one end of the cylinder 13 is closed by blind flange 14, tie rods 15 axially secure the flange l4 and cylinder 13 to the closed end of bonnet 12, conduit 28 connects pressure tap 10 to pilot valve 26, conduit 29 connects control valve 26 to blind flange 14., pilot valve 26 to exhaust the pressure in cylinder 13 through conduit 30.

Referring to FIG. 2, Cylinder 13 and blind flange 14 are axially held secure to the closed end of bonnet 12, by tie-rods l5, piston 16 is positioned in the bore of cylinder 13, valve stem 17 is guided in bore 40 in shouldered rod 21, threaded bushing 20 is axially engaging the closed end of bonnet 12 for initially loading spring 18 by engaging the shoulder on rod 21 and spring washer l9, bore in bushing 20 to axially guide rod 21,

the top of end of rod 21 is threaded to accomodate nuts 22 and 23 which act as a limit travel stop for piston 16 when cylinder 13 is subject to vessel pressure, gap 36 between nut 22 and top of bushing 20 predetermines the stroke of piston 16 and the compression of spring 18 from its normal setting position 37 to its higher setting position 38. (shown in FIG. 3).

Pressure responding pilot valve body 26 includes pipe taps for conduits 28,29 and 30, valve disk 32 to contain vessel pressure in cylinder 13, a spring 31 to load disk 32 up to the set pressure, a back seat 33 to close vessel pressure to conduit 29 and cylinder 13 when vessel pressure reaches the set pressure and concurrently discharge the pressure in cylinder 13 through conduits 29 and 30. Spacer 34 between valve disks 32 and 33 to dislodge disk 33 from its seat thus permitting disk 32 to reseat when the vessel pressure drops from its set pressure to a predetermined blow-down or is manually reset. Spring 35 to offset the weight of disk 33 and spacer 34 so that disk 33 can act as a check valve when disk 32 is in an open position, thus discharging pressure from cylinder 13 to conduit 30 and concurrently the closing of vessel pressure to conduit 29 by disk 33.

FIG. 3 shows the piston 16 under pressurized condition in which the vessel pressure has stroked piston 16 toward spring 18 until limit travel stop nut 22 engages the top of bushing thereby compressing spring 18 from its normal position 37 (shown in FIG. 2) to position 38 which operatively increases the spring loading on the main valve disk (not shown) as long as pilot valve 26 is in a closed position to atmosphere as shown in FIG. 2. Spring position 38 returns to position 37 (shown in FIG. 2) when pilot valve 26 has closed the flow of pressure to cylinder 13 and is concurrently exhausting the vessel pressure from cylinder 13 through conduits 29 and 30.

FIGS. 2 and 3 shows valve stem 17 guided in bore 40 in rod 21, the bore 40 to be of sufficient depth to permit the stem 17 and valve disk (not shown) to lift its necessary distance for full discharge capacity of the main valve in the event the pilot valve 26 and/or piston 16 malfunction as a fail safe feature.

The spring loaded pressure relieving valve mentioned above to include the common names of Safety, Safety- Relief and Relief Valve.

In view of the foregoing, it should be apparent that by the addition of a piston/cylinder means shown and described in the present invention is an improvement to the conventional valve by providing means whereby a given pressure design vessel M.A.W.P. can operate closer to the set pressure without leaking, eliminate simmer and provide fail-safe" operation of the valve in the event that the piston/cylinder and/or pilot valve should malfunction.

The pilot valve and/or the piston cylinder can be in spected and replaced at intervals without shutting down the vessel in as much as the valve spring furnishes 100 percent loading on the disk at the normal set pressure.

It will be understood that this invention may be embodied otherwise than shown and various changes in detail and construction and arrangement of parts may be made without departing from the idea of my invention within the scope of the appended claims.

I claim:

1. In a valve assembly adapted to relieve excess pressure from a pressure vessel, the assembly comprises a pressure relief valve, a pressure responsive means and a pilot valve,

whereas said relief valve is held in a closed position by a compression spring adapted to release pres sure when a predetermined pressure is reached,

whereas said pressure responsive means comprises a cylinder closed on one end and a piston slidable therein, the open end of said cylinder is mounted on the top of said relief valve so that said piston can operatively engage the top end of said compression spring when said cylinder is supplied pressure from said vessel through a conduit to activate said piston which by having a larger area than the seat area of said relief valve will urge said compression spring beyond its initial preset position thereby increasing the spring loading in said relief valve,

whereas said pilot valve being operable in response to pressure from said vessel and normally open to the flow of pressure from said vessel to said cylinder will activate said piston and at a predetermined pressure said pilot valve being positioned in said conduit will close the pressure to said cylinder and concurrently exhaust the pressure therein whereas said piston being deactivated will recede in said cylinder by the returning of said compression spring to its initial preset position wherein said relief valve will open at its initial set pressure.

2. In accordance to claim I wherein the stroke ofsaid piston when pressure activated can be predetermined by a travel stop positioned to operatively limit said stroke and in turn limit the further compressing of said compression spring beyond its initial preset position by the force from said piston on said compression spring.

3. In accordance with claim 1 wherein the disk of said relief valve being biased by said compression spring in said relief valve means providing a lost motion connection between said piston and said relief valve to allow it to open to relieve excess pressure from said vessel even though said piston should seize in said cylinder or should said pilot valve fail to close the pressure from said vessel to said cylinder and exhaust the pressure therein when a predetermined pressure is reached in said vessel.

4. In accordance to claim 1 wherein the end of the stem in said relief valve can rise in a space to permit discharging excess pressure from said vessel should said piston seize in said cylinder or should said pilot valve

Claims (4)

1. In a valve assembly adapted to relieve excess pressure from a pressure vessel, the assembly comprises a pressure relief valve, a pressure responsive means and a pIlot valve, whereas said relief valve is held in a closed position by a compression spring adapted to release pressure when a predetermined pressure is reached, whereas said pressure responsive means comprises a cylinder closed on one end and a piston slidable therein, the open end of said cylinder is mounted on the top of said relief valve so that said piston can operatively engage the top end of said compression spring when said cylinder is supplied pressure from said vessel through a conduit to activate said piston which by having a larger area than the seat area of said relief valve will urge said compression spring beyond its initial preset position thereby increasing the spring loading in said relief valve, whereas said pilot valve being operable in response to pressure from said vessel and normally open to the flow of pressure from said vessel to said cylinder will activate said piston and at a predetermined pressure said pilot valve being positioned in said conduit will close the pressure to said cylinder and concurrently exhaust the pressure therein whereas said piston being deactivated will recede in said cylinder by the returning of said compression spring to its initial preset position wherein said relief valve will open at its initial set pressure.

2. In accordance to claim 1 wherein the stroke of said piston when pressure activated can be predetermined by a travel stop positioned to operatively limit said stroke and in turn limit the further compressing of said compression spring beyond its initial preset position by the force from said piston on said compression spring.

3. In accordance with claim 1 wherein the disk of said relief valve being biased by said compression spring in said relief valve means providing a lost motion connection between said piston and said relief valve to allow it to open to relieve excess pressure from said vessel even though said piston should seize in said cylinder or should said pilot valve fail to close the pressure from said vessel to said cylinder and exhaust the pressure therein when a predetermined pressure is reached in said vessel.

4. In accordance to claim 1 wherein the end of the stem in said relief valve can rise in a space to permit discharging excess pressure from said vessel should said piston seize in said cylinder or should said pilot valve malfunction.

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