GB2073375A - Pneumatic-assisted check valve - Google Patents

Abstract

A pneumatic assisted check valve 30 comprises a valve body 32 having a fluid passage, a clapper 38 movably positioned within the valve body 32 for opening and closing the fluid passage, a clapper pin 40 rigidly attached to the clapper 38 and pivotally hinged to the valve body 32 for allowing movement of the clapper 38 between its open and closed positions, and a pneumatic drive assembly connected to the pin 40 for moving the clapper 38 from its open to its closed positions. The pneumatic drive assembly includes air storage means 50, a cylinder 42 with a piston 44 disposed therein attached to a rod 46 which is rigidly attached to the clapper pin 40, conduit 48 for pneumatically connecting the air storage means 50 to the cylinder 42, means 52 for controlling air delivered to the cylinder 42, and valve means 56 responsive to an electrical signal for activating and deactivating the pneumatic driver. In a modification, a pneumatic drive drives a cable carried on a pulley which moves the clapper. A pumping station including such a check valve is also disclosed. <IMAGE>

Description

SPECIFICATION Pneumatic-assisted check valve This invention relates to check valves such as used in pumping stations and comprising a valve body having a fluid pasageway therethrough and a clapper movably positioned within said valve body for closing said fluid passageway when in a closed position and allowing fluid to pass through said valve body when in an open position.

Many types of fluids are piped long distances to feed the requirements of a specific populated area. Examples of this are the transportation of crude oil and natural gas. In a piping system for such purposes it is necessary to provide pumping stations to accelerate the movement of the fluid through the piping system. It is generally common to place a check valve in such pumping stations as a primary blocking valve to separate the flow from an upstream pump suction to a downstream pump discharge. The check valves in the pumping stations permit the flow of fluids in one direction in the pipeline and prevent flow in the opposite direction. The check valve mechanism functions because the downstream pressure that results from the pump discharge head is always higher than the upstream suction pressure.

With the use of centrifugal pumps in the pumping stations a problem arises regarding water hammering and slamming of the check valves upon pump startup. When a centrifugal pump is started under load conditions, tremendous starting torques are required of the prime mover, particularly if the prime mover is an electrical motor that has instantaneous starting.These tremendous starting torques can cause the motor to draw excessive amperage which in turn can burn the windings of the motor, contacts, starter and other electrical components within the motor. To prevent this condition, a discharge block valve downstream from the centrifugal pump is brought to a near closed position before pump startup.

This allows the pump to operate at near zero load conditions. Once the motor has gained rpm and the starting in-rush current has dropped, the discharge valve is opened slowly to allow the centrifugal pump to boost the fluid velocity of the media being pumped.

When the fluid velocity is increased from the additional energy placed on the fluid by the pump, the fluid pressure downstream of the check valve exceeds the fluid pressure seen by the open check valve upstream. As a result the clapper of the check valve falls to its closed position, stopping all back flow into the upstream line. With the back flow stopped, the downstream piping pressure will rise, hoiding the check valve in its closed position until the pump is shut down and taken off line. If the discharge valve opens too rapidly, the closing pressure difference across the check valve will occur very rapidly, causing the check valve clapper to slam against its seat. This sudden closing will result in a water hammer effect of the fluid which can cause damage to the instrumentation, electronics, piping and other miscellaneous equipment that may be attached to the pipeline.

One method used to prevent the slamming has been to equip the check valve with spring loading device attached to a pin attaching the clapper to the valve body. The spring assists the clapper to close before the fluid has attained any substantial reverse flow velocity.

In some cases the spring forces are in adequate to move the clapper ahead of the reverse flow.

Other devices have been proposed to solve the problem of water hammering with the check valve. Among these are a check valve with dash-pot described in U.S. Patent 3,1 06,220. A control action check valve is disclosed in U.S. Patent 3,177,894. The latter valve is hydraulic in nature and its arrangement mainly retards the closing and so does not provide the rapid closing which is a requirement in a liquid system, the Patent being instead directed mainly to time delay dampening for gas applications.

An object of the invention is therefore to provide a check valve capable of effectively solving the above discussed problem.

Thus in its broadest aspect the invention provides a pneumatic assisted check valve comprising a valve body having a fluid passageway therethrough and a clapper movably positioned within said valve body for closing said fluid passageway when in a closed position and allowing fluid to pass through said valve body when in an open position, characterised by a pneumatic drive assembly connected for moving said clapper from an open to a closed position.

An' advantage of the pneumatic closing obtainable in a check valve in accordance with the invention is that the force on the clapper can be controlled without any danger of stress overload on any part of the check valve. A further advantage is that by the use of a controlled gas pressure to accomplish the closing, the closing force is maintained throughout the closing process until the closed position is reached. This cannot be accomplished with springs, as springs lose force as they unload.

The clapper of the check valve may be rigidly attached to a clapper pin pivotally hinged to the valve body to allow movement of the clapper, the pneumatic drive assembly being connected to the clapper pin externaliy of the valve body.

The pneumatic drive assembly may comprise a pneumatic driver having a piston cylinder with a piston disposed therein attached to a rod which is rigidly connected to said clap per-pin, means for pneumatically connecting a source of air under pressure with said piston cylinder, means for controlling air delivered from said source to said piston cylinder, and valve means responsive to an electrical signal for activating and deactivating said pneumatic driver.

In an alternative embodiment a cable drive may be interconnected with the air cylinder piston/rod assembly. The cable drive is connected to the valve clapper and effects the opening and closure of the clapper.

The source of air under pressure is conveniently a storage means such as a tank or bottle for storing air under pressure.

The means for controlling air delivered from the source to the piston cylinder conveniently comprises an air regulator in series with a gate valve.

The valve means may be a spring return solenoid valve.

There may be a pressure relief valve for releasing air from the piston cylinder upon deactivation of the pneumatic driver.

The invention also provides a pumping station utilising the check valve of the invention and comprising a fluid conducting pipeline, at least one centrifugal pump interconnected within said pipeline, a suction blocking valve interconnected within said pipeline and located upstream from said centrifugal pump, and a discharge block valve interconnected with said fluid conducting pipeline and located downstream from said centrifugal pump, the pneumatic assisted check valve being interconnected in said pipeline in parallel with the pipeline section including the suction blocking valve, the centrifugal pump and the discharge block valve.

The invention will be better understood from the following description taken in conjunction with the drawings, in which: Figure 1 is a schematic diagram of a pumping station utilizing a check valve in accordance with the present invention; Figure 2 is a diagrammatic side view of one embodiment of a pneumatic assisted check valve in accordance with the present invention; Figure 3 is a front view of the pneumatic assisted check valve of Fig. 2; and Figure 4 illustrates the modified drive assembly of another embodiment of an automatic check valve in accordance with the invention.

Fig. 1 shows a pumping station 10 in schematic form. The pumping station 10 is connected irito a fluid conducting pipeline 12, such that fluid will flow from direction 14 into the station 10 and continue through a check valve 1 6. The station includes a centrifugal pump 1 8 and when this is activated a suction blocking valve 20 is in the open position to allow fluid to be drawn from point 22 in the fluid piping system 1 2 through the suction valve 20 and into the centrifugal pump 18 downstream. A discharge valve 24 is located further downstream of the centrifugal pump 1 8. When the discharge valve 24 is in an open position the pump 1 8 will accelerate the fluid drawn through suction valve 20 into the pump and out the discharge valve 24.The fluid will finally be distributed downstream of the pumping station 10 in a direction 26.

During operation of the pumping station 10 with the pump 1 8 shut down, the check valve 1 6 will normally be in an open position allowing fluid to flow through its valve body downstream in the direction 26. During this operation the pressure differential across the check valve 1 6 is such that the pressure at point 22 is greater than the pressure found at point 28.

Thus, the fluid will keep a clapper in the check valve in an open position which allows fluid to pass through.

During startup of the pump 1 8 the discharge valve 24 will be closed to allow the pump to startup under zero load conditions.

During startup, suction valve 20 remains in an open position. Once the pump starts and builds up an rpm the discharge valve 24 is opened and allows fluid to proceed downstream in the direction 26. However, as previously stated this will reverse the pressure differential across the check valve 16, tending normally cause a backflow through the check valve 1 6 and so causing, in the case of a conventional check valve construction, the clapper to slam and cause a water hammer effect downstream. To avoid this problem a pneumatic assisted check valve 30 as shown in Fig. 2 and 3, or in Fig. 4, is utilized.

The pneumatic assisted check valve 30 of Figs. 2 and 3 includes a valve body 32 having a fluid passageway 34 whereby fluid may flow, normally in the direction 36, through the body. The valve body 32 houses a clapper 38 which is movably positioned within the valve body 32 and rigidly attached to a pin 40. The pin 40 is hinged to the valve.

body 32 to allow free movement of the clapper 38 within the valve body from an open to closed position. It will be noted that in the closed position of the clapper fluid will not pass through the valve body 32.

The pin 40 extends to the exterior of the valve body 32 and is mechanically attached to a pneumatic drive assembly for providing a force on the clapper 38 for moving it from the open to the closed position.

The pneumatic drive assembly includes an air cylinder 42 containing a piston 44 with a piston rod 46 that is this embodiment is directly connected to the pin 40. The air cylinder 42 is supplied with compressed air through a flexible conduit 48 which in turn is connected to an air tank 50. Air is controlled after release from the air tank 50 by an air regulator 52 and a gate valve 54.

Air flow through the flexible conduit to the cylinder 42 is further controlled by springreturn solenoid valve 56. The solenoid valve is electrically associated with the centrifugal pump 1 8 shown in Fig. 1 so that after startup of the centrifugal pump 1 8 an electrical signal is delivered to the spring-return solenoid valve 56 whereby the valve is placed in a position such that air is allowed to flow through the air cylinder 42 for purposes of activating the piston 44 and rod 46 to move the clapper 38 from its open to its closed position.

Operationally, the air tank 50 is preloaded with compressed air for delivery to the cylinder 42 to activate the pneumatic driver and force closing of the clapper 38. The air is regulated and delivered through the valve 54 where it may be blocked by the spring-return solenoid valve 56. Upon receiving the electrical signal from the centrifugal pump 1 8 the spring-return solenoid valve 56 will move into an open position allowing air to flow through the flexible conduit 48 and into the cylinder 42 for activating the piston 44 and rod 46 to move the clapper 38. Thus, the force directed by the piston and rod 44 and 46 on the pin 42 to effect closure of the clapper 38 within the valve body 32 is uniform throughout the closing process. This is unlike the use of a spring force which loses power during the unloading of the spring.The rapid closure of the clapper thus effected prevents water of other fluid to backflow in a direction opposite to direction 36 and so slam the clapper against its seat 58 found within the valve body 32. The prevention of such slamming avoids detrimental effects on the internal structure of the check valve body 32 and prevents water hammering downstream from the check valve 30.

Deactivation of the spring-return solenoid valve 56 allows air within the cylinder 44 to vent through conduit 48 and a pressure relief valve 60. A vent 62 is provided at the end of the cylinder 42 remote from the connection to conduit 48 to prevent interference with the motion of the piston when air is fed to or exhausted from the cylinder through conduit 48.

Under normal flow conditions with the pump 18 running, the clapper will be held in its closed position by the pressure differential created by the pump. However should the pump fail or be shut down the pressure differential resulting from the tendency of' the fluid to flow in direction 36 will cause the clapper to move to its open position. If this situation should arise while the pneumatic drive assembly is activated the resulting movement of the piston 44 will raise the pressure in the cylinder 42 above the setting of the pressure relief valve 60. By using compressed air in the system which is a compressible fluid rather than hydraulic fluid, this flexiblity is possible.

Any substantial fluid flow through the valve body 32 will force the clapper 38 to its open position without an excess of resistance from the pneumatic system. Also, when the cylinder 42 is deactivated, that is, when there is no air being delivered from the air cylinder 50, the clapper 38 is substantially resistanceless and in an optimal condition to be moved by the fluid flow into an open position.

Fig. 3 illustrates the clapper 38 and pneumatic drive assembly from the perspective of the flow 36. It will be noted that the cylinder 42 and piston and rod assembly are connected to the pin 40 which has a link 40a directly connected to the rod 46 o.f the piston/rod assembly. Fig. 3 demonstrates the external mounting of the pneumatic system to the pin 40 which is in turn pivotally hinged to the valve body 32 and rigidly connected to the clapper 38 for allowing movement from an open to a closed position within the valve body 32.

Fig. 4 illustrates a modification of the pneumatic drive assembly described with respect to Figs. 2 and 3. A cable drive assembly 62 including at least two pulleys 64 and 66 and a cable 72 is connected to a piston and rod assembly 68 associated with a cylinder 74 having an inlet 70 connected to a similar pneumatic air delivery system to that shown in Fig. 2. The cable 72 is connected to the piston and rod assembly 68 to effect movement of the pulley 64 which is connected to a pin 40 similar to that shown and described with respect to Fig. 2. Thus, operationally the clapper 38 will be moved from an open to closed position by the activation of a solenoid valve 56 similar to that shown in Fig. 2, which in turn allows air delivery to the cylinder 74 and movement of the piston/rod assembly 68.

While the present invention has been described with respect to a preferred embodiment it is to be understood that many modifications and changes may be made to the described device by those skilled in the art.

One such modification may be in the form of a pneumatic valve used to trigger the activation of the pneumatic assisted check valve in lieu of a solenoid valve activated by an electrical signal.

Claims (11)

1. A pneumatic assisted check valve comprising a valve body having a fluid passageway therethrough and a clapper movably positioned within said valve body for closing said fluid passageway when in a closed position and allowing fluid to pass through said valve body when in an open position, characterised by a pneumatic drive assembly for moving said clapper from an open to a closed position.

2. A pneumatic assisted check valve according to claim 1, in which the clapper is rigidly attached to a clapper pin pivotally hinged to the valve body to allow movement of the clapper and the pneumatic drive assembly is connected to the clapper pin externally of the valve body.

3. A pneumatic assisted check valve according to claim 1 or claim 2, wherein said pneumatic drive assembly comprises a pneumatic driver having a piston cylinder with a piston disposed therein attached to a rod which is rigidly connected to said clapper pin, means for pneumatically connecting a source of air under pressure with said piston cylinder, means for controlling air delivered from said source to said piston cylinder, and valve means responsive to an electrical signal for activating and deactivating said pneumatic driver.

4. A pneumatic assisted check valve according to claim 3, wherein the source of air under pressure comprises air storage means for storing air under pressure.

5. A pneumatic assisted check valve according to claim 3 or claim 4, wherein said means for controlling air delivered comprises an air regulator in series with a gate valve.

6. A pneumatic assisted check valve according to any one of claims 3 to 5, wherin said valve means comprises a spring-return solenoid valve.

7. A pneumatic assisted check valve according to any one of claims 3 to 6, further including a pressure relief valve for release of air from said piston cylinder.

8. A pneumatic assisted check valve substantially as described with reference to and as shown in Figs. 2 and 3 of the accompanying drawings.

9. A pneumatic assisted check valve substantially as described with reference to and as shown in Fig. 4 of the accompanying drawings.

10. A pumping station including a pneumatic assisted check valve as claimed in any one of claims 1 to 9, the station comprising a fluid conducting pipeline, at least one centrifugal pump interconnected within said pipeline, a suction blocking valve interconnected within said pipeline and located upstream from said centrifugal pump, and a discharge block valve interconnected with said fluid conducting pipeline and located downstream from said centrifugal pump, the pneumatic assisted check valve being interconnected within said pipeline in parallel with the pipeline section including the suction blocking valve, the centrifugal pump and the discharge block valve.

11. A pumping station according to claim 10 and substantially as -described with reference to Fig. p1 of the accompanying drawings.

1 2. Every novel feature and every novel combination of features disclosed herein.