Field of the Invention The present invention is directed to a low pressur recirculation valve for recirculating fluid back to a centrifugal pump in order to cool the pump during interval when there is a minimum demand for the pumped fluid downstrea of the valve. More particularly, the present invention i directed to a recirculation valve having a multiple piece chec valve disk which can provide a larger effective disc allowin the use of a higher spring rate and providing- greater stabilit to the valve. The two piece disc also allows the use of a on piece body with a large disc providing a more economica design.

Background of the Invention Centrifugal pumps are used in a variety of applications. It is often desirable to recirculate fluid back to a centrifugal pump during intervals of low demand by an outlet device to prevent the pump from overheating. Overheating is caused by the exchange of heat between the running pump and stationary fluid present within the pump. Pump overheating lowers the vapor pressure resulting in fluid cavatation which can destroy the pump housing and impeller.

Recirculation valves are frequently used in centrifugal pumps to control overheating. One commonly used recirculation valve is a modulating flow control valve disclosed in U. S. Patent No. 4,095,611. The valve disclosed in Patent 4,095,611 has a circular disk-shaped check valve member interposed within a two-piece valve casing. During periods of normal downstream fluid demand, a pressure differential across the valve causes it to open and permit flow, while simultaneously blocking a fluid recirculation passageway. Conversely, during intervals of minimal downstream fluid demand, the disk-shaped check valve member returns to a closed position, thereby opening the fluid recirculation passageway and permitting fluid to recirculate back to the pump.

Another recirculation valve, disclosed in U. S. Patent No. 4,243,064, has a circular main valve disk and bypass valve disk axially displaced among both ends of a connecting rod. During periods of normal fluid flow, the connecting rod moves to an

open position causing fluid to flow out both the main outlet and the bypass outlet. When fluid flow is minimal, the bypass valve disk is superimposed over an annular seat which causes fluid to be redirected from the main outlet to the bypass outlet and recirculated through the centrifugal pump.

A problem encountered with the use of such recirculation valves is that they have complex structures, and are both costly to manufacture and difficult to maintain. Most of the recirculation valves presently available on the market, including the two described above, are constructed from two piece valve casings. A multiple piece casing is required because the valve members are too large to fit through the casing.

It is an object of the present invention to provide recirculation valve having a one-piece valve casing and multiple piece check valve member which can fit through and b assembled with the one piece casing and which regulates th flow of fluid from a centrifugal pump to a downstream device.

It is a further object of the present invention to provid a recirculation valve having a multiple piece valve membe which can be easily inserted into and removed from a unitar valve housing.

It is an additional object of the present invention t provide a recirculation valve mechanism having a nove recirculation valve mechanism operated in association with th

valve member so as to control the recirculation of fluid back to the centrifugal pump.

Summary of the Invention In accordance with the present invention a low pressure recirculation valve for cooling a centrifugal pump is disclosed. The invention comprises a unitary valve casing divided into first and second chambers. The casing has a first port for introducing fluids from a centrifugal pump into the first chamber and a second port for expelling fluids out of the casing through said second chamber. The first chamber furthe has a recirculation port for redirecting fluid from the firs chamber to the pump. A multiple piece check valve member i situated between said first and second chambers. The chec valve opens to permit flow from first chamber to said secon chamber and closes to impede fluid flow from said secon chamber to said first. A spring biases the check valve toward a closed position. Finally, a recirculation valve coupled t the check valve means opens the recirculation port when th check valve means is closed and closes the recirculation mean when the check valve is open.

Brief Description of the Drawings

The foregoing summary, as well as the following detailed description will be better understood when read in conjunction with the figures appended hereto. For the purpose of illustrating the invention, there is shown in the drawings an embodiment which is presently preferred, it. being understood, however, that this invention is not limited to the precise arrangement and instrumentalities shown.

Figure 1 is an elevated section view of one embodiment of a recirculation valve according to the present invention.

Figure 2 is an exploded view of the multiple pieced valve member of the preferred embodiment.

Figure 3 is an elevated section view of a recirculation valve having a solid stem member.

Figure 4 is an elevated section view of the recirculation valve of Figure 3 without a lip and having straight side walls along a lower portion of the valve casing.

Figure 5 is an elevated section view of the embodiment of Figure 1 in which the valve member is open and the recirculation conduit is closed.

Description of a Preferred Embodiment Referring to the drawings, there is shown in Figure 1 a elevated cross-section view of a low pressure recirculatio valve 10 in accordance with the present invention. Th recirculation valve 10 of the present invention is preferabl constructed from a corrosion-resistant material such a stainless steel, and comprises a unitary generally cylindrica valve casing 12. Valve casing 12 is divided into chambers 1 and 16. Chamber 14 has an inlet port 18 which is connected t a centrifugal pump located upstream of the valve. Chamber 1 is located downstream of chamber 14 and is connected to downstream fluid outlet device to receive the pumped fluid vi an outlet port 20. A recirculation port 22, located on th side of the casing within chamber 14 ' is connected to recirculation conduit or passageway 24 which redirects th fluid back to a receiving vessel or storage tank which supplie the inlet to the pump.

Located within the casing of the chamber 14 is a hollow generally cylindrical valve stem 23. Valve stem 23 has threaded top end 24, and is interposed within the first chamb of the valve casing 12 along a longitudinal central axis of t valve casing 12. The upper walls 26 of the valve stem 23 seen in Figure 1 form a ledge at a top portion of the val stem 23 directly below threaded top end 24. A plurality apertures 31 are provided in the valve stem 23. The apertur 31 define a recirculation valve between chamber 14 and t

recirculation port 22 and allow fluid to be recirculated back to the centrifugal pump during intervals of low downstream flow demand. Additionally, these apertures (31) provide a specific fluid restriction which reduces the pressure energy of the fluid so that recirculation flow may be discharged into a lower pressure receiving vessel which is connected to the inlet of the pump.

The recirculation valve 10 has a valve stem guide 34 which is integral to valve casing 12 within first chamber 14 and guides the valve stem 23 during its longitudinal movement along the central axis or valve casing 12. The valve stem guide 34 has a channel defined by slots 35, 35a located in the walls of the guide. When the valve stem 23 is in a closed position, the plurality of apertures 31 are aligned with the slots 35, 35a and apertures 31 serve a passageway through which fluid exits the recirculation port 22 from chamber 14.

The multiple check valve member 36 is now described with reference to the exploded view of Figure 2. The multiple piece check valve member 36 is axially placed over the threaded top end 24 of valve stem 23 and rests on the top portion of the stem. Valve member 36 acts as a pressure actuated check valve for the fluid flow system. Valve member comprises an apertured first disk segment 27 superimposed at a 90 degree angle over an apertured second disk 29. The disks are keyed 30 so that the remain locked when secured to the valve stem. Both disks are rectangular on one set of opposing sides and curvilinear o

another set of opposing sides. When superimposed, the keye superimposed disks form a circular valve member and obviate th need for a multiple piece housing. The non-circular shape o the disks permit them to fit individually through outlet por

20. A retaining nut 38 is screwed onto the threaded top end 2 of the valve stem 23. The nut 38 secures the multiple piec valve member 36 to the valve stem.

Valve stem 23 further includes a base member 39 connecte at a bottom end of the valve stem 23. Base member 39, a shown, is a cylindrical flange which is radially dispose relative to valve stem 23. The base member 39 is retained i position by an attachment pin 40 which is inserted through th valve stem. The valve stem 23 further incorporates a coile biasing spring 42 connected to the bottom end of the valve ste 23 between the valve stem guide 34 and base member 39. Coi spring 42 provides spring-loaded activation of the valve st 23 between a fully open and closed position and biases val stem 23 and multiple piece check valve member 36 toward t inlet port and the closed portion.

The valve casing 10 further includes a lip 44, situat between the first and second chambers. Lip 44 extends from t walls of the valve casing 12 and defines a seal on which t multiple piece check valve member 24 rests in the clos position. The lip divides the valve chambers 14 and 16 a enables valve member 36 to operate as a check valve for t

fluid flow system by preventing fluid from flowing back into the chamber 14.

Referring to Figure 3, an alternative embodiment of the recirculation valve 10 in accordance with the present invention is shown. In this embodiment, stem 23 is solid. In addition, the stem guide 34 has extensions 44, 44a which extend past base member 39 and which create a close fit with base member 39 thereby creating a piston chamber 46. Member 39 pushes trapped fluid out of chamber 46 as the stem 23 moves up when the valve opens and draws fluid into chamber 46 when the valve closes. The restricted flow in and out of chamber 46 serves to dampen any tendency.of the valve stem to oscillate.

An alternative embodiment is shown in Figure 4. In this r embodiment, the valve 10 solely performs a recirculating function. Lip 44 shown in Figure 1 is not present in this embodiment and valve member 36 does not operate as a check valve. The valve stem in this embodiment is retained in an initial position by shoulder 33 which mates with the valve stem guide. Upon demand downstream of the valve a pressure differential is formed on the sides of the multiple piece valve member 36 forcing the valve stem 23 and valve member 36 in an upward direction. This closes off the passageway defined b slots 35, 35a and apertures 31. When demand from th downstream outlet device reduces, the biased valve stem 23 an valve member 36 return to an initial position due to th pressure equilibrium on both sides of the valve member 24,

thereby realigning slots 35, 35a and apertures 31 and enabling fluid to flow through the recirculation port 22 to be recirculated through the centrifugal pump.

Operation

The operation of the present invention is now described with reference to the enclosed figures and most particularly Figures 1 and 5. The recirculation valve of the present invention is a combination multiple piece main check valve and recirculation valve for use in fluid flow systems which utilize a centrifugal pump. The recirculation valve redirects fluid back into the centrifugal pump to prevent it from overheating during intervals of minimum downstream flow.

Fluid emerging from the centrifugal pump enters the recirculation valve 10 through the inlet port causing the first chamber 14 to fill with fluid. During intervals of low downstream demand, the fluid pressure in chamber 16 approaches that of the chamber 14. Valve member 36 έnd valve stem 23 are retained in a closed position by spring 42 and fluid emitted from the pump is redirected through the recirculation port 22 via slots 34, 35a and apertures 31.

Upon demand downstream by an outlet device, a pressure differential is formed on both sides of the multiple piece valve member 36 wherein the fluid pressure in the first chamber 14 drops below that of the second chamber 16. When this pressure differential exceeds the preload from spring 42, valve member 36 and stem 23 to move in a longitudinal direction towards the fully open position. Coil spring 42 compresses until member 39 butts against guide 34. Apertures 31 move away from their aligned position relative to the slots 34, 35a

thereby terminating the redirection of fluid flow out o recirculation port 22. The longitudinal movement of the valv stem 23 towards the fully open position causes the multipl piece valve member 36 to dislodge from the seat 21, thereb breaking the seal and allowing to be discharged through th outlet port 20.

When demand by the downstream outlet device reduces, flui pressure within chamber 16 again builds up. The pressu differential across valve member 36 is reduced. The for created by the differential pressure is less than the for created by spring 42. Coiled biasing spring 42 connected the bottom end of the valve stem 23 expands and the valve st returns to its closed position so that the valve member 36 once again superimposed over lip 44. The valve stem apertur 31 are realigned with the slots 35, 35a in the valve stem gui and fluid flow is again redirected out of the recirculati port 22 to be recirculated back through the centrifugal pum The multiple-piece check valve means can be easily inserted a attached with the unitary housing.

It will be recognized by those skilled in the art th changes may be made to the above-described embodiment of t invention without departing from the broad inventive concep thereof. It is understood, therefore, that this invention not limited to the particular embodiment disclosed, but it intended to cover all modifications which are within the sco and spirit of the invention as defined by the appended claims