Safety valve system for overpressure protection of hydraulic circuits

1. An overpressure protection system for a hydraulic system comprising:

an overpressure protection valve comprising:

a pilot operated check valve disposed upstream from a hydraulically driven tool, the pilot operated check valve having an inlet connected to a high pressure hydraulic supply line and an outlet connected to the hydraulically driven tool, hydraulic fluid flowing through the check valve to operate said hydraulically driven tool;

a pressure sense line connected to a low pressure portion of said hydraulic system which is downstream from the hydraulically driven tool;

a first hydraulically operated pilot valve having an inlet connected to the pressure sense line and an outlet connected to a pilot inlet on the check valve via a hydraulic passage; and

a manually operated valve which is opened to vent fluid there through and relieve pressure in said hydraulic passage.

2. The system of claim 1 , wherein the first hydraulically operated pilot valve opens at a predetermined pressure so as to allow hydraulic fluid to flow therethrough, apply pressure to the pilot operated check valve and thereby close the pilot operated check valve.

3. The system of claim 1 , wherein the pilot operated check valve stops flow of hydraulic fluid to the hydraulic system if pressure in said low pressure part of the hydraulic system exceeds a predetermined pressure.

4. The system of claim 2 , wherein, after fluid flow through the first hydraulically operated pilot valve, said hydraulic passage remains pressurized and prevents fluid flow through the pilot operated check valve until pressure in the hydraulic passage is manually relieved by opening the manually operated valve to vent fluid through the manually operated valve.

5. The system of claim 1 , wherein the overpressure protection system is contained internally within a single manifold body.

6. The system of claim 1 , wherein the overpressure protection valve consists essentially of the pilot operated check valve, the pressure sense line, the first pilot valve, and the hydraulic passage.

7. The system of claim 1 , further comprising a pressure relief valve comprising:

a second hydraulically operated pilot valve having an inlet connected to the low pressure portion and an outlet connected to an outlet passage to remove hydraulic fluid from the hydraulic system.

8. The system of claim 7 , wherein the second hydraulically operated pilot valve opens at a pressure which is equal to or greater than a pressure at which the first hydraulically operated pilot valve opens.

9. The system of claim 7 , wherein the second hydraulically operated pilot valve opens after the first hydraulically operated pilot valve has opened.

10. An overpressure protection system for a hydraulically driven device comprising:

an overpressure protection valve having:

a fluid inlet attached to a high pressure hydraulic source;

a fluid outlet attached to a hydraulically driven tool which is driven by said high pressure hydraulic source;

a check valve disposed between the fluid inlet and the fluid outlet to selectively prevent and allow flow therebetween, wherein the check valve is disposed upstream of the hydraulically driven tool;

a pressure sense line connected to a low pressure hydraulic circuit disposed downstream of said hydraulically driven tool wherein the pressure sense line is connected to the check valve such that when pressure in said low pressure hydraulic circuit exceeds a predetermined threshold the check valve is closed and flow is prevented between the fluid inlet and the fluid outlet.

11. The system of claim 10 , wherein the pressure sense line is connected to a first pilot valve and the first pilot valve is connected to the check valve via a hydraulic passage, and wherein when pressure in said pressure sense line exceeds a predetermined pressure the first pilot valve opens and allows fluid flow through the hydraulic passage and thereby closes the check valve.

12. The system of claim 11 , wherein the hydraulic passage remains pressurized and the check valve remains closed until a manually operated valve is opened to relieve pressure in the hydraulic passage.

13. The system of claim 10 , wherein the pressure sense line is connected to a low pressure hydraulic circuit of said machine adjacent a hydraulic fluid cooler.

14. The system of claim 10 , further comprising a hydraulic machine, the machine comprising a fluid inlet for receiving high pressure hydraulic fluid, a machine operated by said hydraulic fluid, and a fluid outlet, wherein the overpressure protection valve is connected to the machine fluid inlet, and the pressure sense line is connected to the fluid outlet.

15. The system of claim 11 , wherein the overpressure protection valve is contained within a single valve body.

16. The system of claim 11 , further comprising a pressure relief valve comprising:

a second pilot valve having an inlet and an outlet;

an inlet line connected to the pressure sense line and to the second pilot valve inlet;

an outlet line connected to the second pilot valve outlet; and

wherein, when pressure exceeds a predetermined threshold, the second pilot valve opens to vent hydraulic fluid from the hydraulic machine.

17. The system of claim 16 , wherein the second pilot valve opens at a pressure which is equal to or slightly higher than a pressure at which the first pilot valve opens.

18. The system of claim 16 , wherein the first pilot valve opens to close flow to the hydraulically actuated valve and the second pilot valve opens afterwards to relieve pressure in the pressure sense line.

19. The system of claim 11 , further comprising a manually operated valve which must be opened to vent fluid from the hydraulic passage and thereby relieve pressure in the hydraulic passage to open the hydraulically operated valve.