Hydraulic valve and system

1. An apparatus comprising:

a hydraulic circuit, said hydraulic circuit having a first conduit, a second conduit, a third conduit, and a valve assembly; and

said hydraulic circuit configured to control said valve assembly to affect fluid communication with said third conduit of said hydraulic circuit based on a flow of hydraulic fluid in said first conduit with respect to a pump, said valve assembly including a pilot piston moveable within said valve assembly, wherein a differential flow developed from said pump is applied to said pilot piston such that an increase or decrease in said differential flow biases said pilot piston to move within said valve assembly, and wherein said pilot piston is operable to affect said fluid communication with said third conduit in response to a threshold level of differential flow with respect to said pump.

2. The apparatus according to claim 1 , wherein said hydraulic circuit is configured to open communication with said third conduit of said hydraulic circuit based on the flow of hydraulic fluid in said first conduit exceeding a threshold.

3. The apparatus according to claim 1 , wherein said valve assembly includes a first inlet and a second inlet, each of said first and second inlets being in fluid communication with said first conduit, said valve assembly further includes a first outlet in communication with said second conduit, a third inlet in communication with said third conduit and a second outlet, wherein said valve assembly is configured to selectively open communication between said third conduit and said second outlet based on the flow of the hydraulic fluid in said first conduit when the flow of hydraulic fluid in said first conduit exceeds a selected threshold.

4. The apparatus according to claim 3 , wherein said valve assembly comprises a pilot operated control valve assembly, said pilot operated control valve assembly including a first chamber with said first inlet, said second inlet, said first outlet, and a pilot piston assembly mounted for movement in said first chamber.

5. The apparatus according to claim 4 , wherein said pilot piston assembly includes said pilot piston with a piston side facing said first inlet and a pilot rod, said pilot rod extending from said first chamber into a second chamber sealed from said first chamber, and said second chamber including said third inlet and said second outlet.

6. The apparatus according to claim 4 , wherein:

the pilot piston assembly is mounted for movement in said first chamber, and said pilot piston assembly includes said pilot piston with a piston side facing said first inlet and a pilot rod, said pilot rod extending from said first chamber into a second chamber sealed from said first chamber; and

said second inlet is in fluid communication with said first outlet of said first chamber so that fluid flows through said first outlet of said first chamber during operational fluid flow conditions.

7. The apparatus according to claim 6 , wherein said second chamber includes an inlet in communication with said third conduit, an outlet, and a valve poppet movably mounted in said second chamber between a closed position wherein said inlet of said second chamber is not in fluid communication with said outlet of said second chamber and one or more open positions wherein said inlet of said second chamber is in fluid communication with said outlet of said second chamber.

8. The apparatus according to claim 7 , wherein when the fluid flow to said first inlet of said first chamber exceeds a preselected flow rate, back pressure at said first inlet of said first chamber will move said pilot piston and cause said pilot rod to move said valve poppet from said closed position to one of said open positions to allow fluid flow from said inlet of said second chamber to said outlet of said second chamber to open fluid flow between said third conduit and said outlet of said second chamber.

9. A pilot operated control valve assembly comprising:

a first chamber with a first inlet for fluid communication with a first conduit, a second inlet, an outlet for fluid communication with a second conduit, and a pilot piston assembly mounted for movement in said first chamber;

a second chamber having an inlet for communication with a third conduit, an outlet, and a valve poppet movably mounted in said second chamber between a closed position and one or more open positions;

said pilot piston assembly includes a pilot piston with a piston side facing said first inlet of said first chamber and a pilot rod, said pilot rod extending from said first chamber into said second chamber to selectively move said valve poppet, said second chamber being sealed from said first chamber; and

said second inlet of said first chamber is in fluid communication with said outlet of said first chamber so that fluid flows to said outlet of said first chamber from said first inlet or said second inlet to allow fluid flow between said first conduit and said second conduit during operational fluid flow conditions.

10. The pilot operated control valve assembly of claim 9 , wherein, in said closed position, said inlet of said second chamber is not in fluid communication with said outlet of said second chamber, wherein, in said one or more open positions, said inlet of said second chamber is in fluid communication with said outlet of said second chamber to allow fluid flow from said third conduit through said outlet of said second chamber.

11. The pilot operated control valve assembly according to claim 9 , wherein when the fluid flow to said first inlet of said first chamber exceeds a preselected flow rate, back pressure at said first inlet of said first chamber moves said pilot piston and causes said pilot rod to move said valve poppet from said closed position to one of said open positions to allow fluid flow from said inlet of said second chamber to said outlet of said second chamber to allow fluid flow from the third conduit through said outlet of said second chamber.

12. The pilot operated control valve assembly according to claim 9 , wherein said pilot operated control valve assembly includes a valve body with the first and second chambers located in said valve body.

13. The pilot operated control valve assembly according to claim 12 , wherein said second inlet of said first chamber is formed in said valve body.

14. The pilot operated control valve assembly according to claim 13 , wherein said valve body includes a valve body wall, said second inlet being formed by two or more orifices formed in said valve body wall.

15. The pilot operated control valve assembly according to claim 12 , wherein said second inlet of said first chamber is formed by a passageway through said pilot piston.

16. The pilot operated control valve assembly according to claim 12 , wherein said valve body comprises a cylindrical valve body.

17. A patient handling apparatus comprising:

a hydraulic circuit and a hydraulic cylinder to raise or lower a component of the patient handling apparatus;

a pump;

a reservoir;

said hydraulic cylinder having a rod, a cap end chamber, and a rod end chamber, said hydraulic circuit having a control valve assembly operable to direct the flow of hydraulic fluid between said pump, said hydraulic cylinder, and said reservoir; and

said control valve assembly configured to affect fluid communication between a first chamber of said hydraulic cylinder and said reservoir based on a flow condition of the hydraulic fluid flowing to a second chamber of said hydraulic cylinder, said control valve assembly including a pilot piston moveable within said valve assembly, wherein a differential flow developed from said pump is applied to said pilot piston such that an increase or decrease in said differential flow biases said pilot position to move within said valve assembly, wherein said pilot piston is operable to affect said fluid communication with said third conduit in response to a threshold level of said differential flow with respect to said pump.

18. The patient handling apparatus according to claim 17 , wherein said control valve assembly maintains flow through said control valve assembly between said pump and said second chamber of said hydraulic cylinder during operational flow conditions and allows faster evacuation of the hydraulic fluid from said first chamber of said hydraulic cylinder.

19. The patient handling apparatus according to claim 17 , further comprising:

a frame;

a base; and

a lift assembly supporting said frame relative to said base, said hydraulic cylinder being configured to extend or retract said lift assembly to thereby raise or lower said base or said frame with respect to the other.

20. The patient handling apparatus according to claim 19 , wherein said first chamber comprises said cap end chamber, and said second chamber comprises said rod end chamber, and said control valve assembly being configured to selectively open to allow fluid to discharge at least some of the hydraulic fluid from said cap end chamber to said reservoir based on the flow condition of the hydraulic fluid flowing to said rod end chamber.

21. The patient handling apparatus according to claim 20 , wherein said control valve assembly is configured to selectively open when there is a high flow condition to said rod end chamber of said hydraulic cylinder to thereby allow faster discharge of the hydraulic fluid from said cap end chamber of said hydraulic cylinder to said reservoir.

22. The patient handling apparatus according to claim 21 , wherein said control valve assembly includes a pilot operated control valve.

23. The patient handling apparatus according to claim 22 , wherein said control valve assembly comprises:

a first chamber with a first inlet, a second inlet, an outlet, and a pilot piston assembly mounted for movement in said first chamber;

said pilot piston assembly including said pilot piston with a piston side facing said first inlet and a pilot rod, and said pilot rod extending from said first chamber into a second chamber sealed from the first chamber;

said second inlet of said first chamber being in fluid communication with said outlet of said first chamber so that fluid flows from said outlet of said first chamber;

said second chamber forming said pilot operated control valve and including an inlet, an outlet, and a valve poppet movably mounted in said second chamber between a closed position wherein said inlet of said second chamber is not in fluid communication with said outlet of said second chamber and one or more open positions wherein said inlet of said second chamber is in fluid communication with said outlet of said second chamber; and

wherein when the fluid flow to said first inlet of said first chamber exceeds a preselected flow rate, back pressure at said first inlet of said first chamber will move said pilot piston and cause said pilot rod to move said valve poppet from said closed position to one of said open positions to allow fluid flow from said inlet of said second chamber to said outlet of said second chamber.