Pressure compensation control of a fixed displacement pump in a pumping and metering system and associated method
A fuel system includes a pump unit having at least a fixed displacement pump supplying pressurized flow. A fuel control assembly receives flow from the pump unit and includes at least one metering valve and at least one throttling valve. A control (bypass valve control) for the fixed displacement pump receives first and second pressure signals indicative of a pressure differential across the throttling valve, or across the metering valve/throttling valve combination, for altering output from the fixed displacement pump in response to the pressure differential. In other embodiments, the pump unit includes a centrifugal pump and a fixed displacement pump that can be fully or partially redundant depending on sizing of the pumps, and the system requirements.
1. A fuel system comprising:
a pump unit that supplies pressurized flow, the pump unit includes a first pump that communicates with an inlet of a second pump, at least one of the first and second pumps being a fixed displacement pump;
a fuel control assembly receiving flow from the pump unit, the fuel control assembly including at least one metering valve and at least one throttling valve receiving flow from the metering valve; and
a control for the fixed displacement pump including a bypass valve that selectively alters operation of the fixed displacement pump in response to a pressure differential across the throttling valve.
2. The fuel system of claim 1 wherein a first signal of the pressure differential across the throttling valve is received by the control from downstream of the metering valve.
3. The fuel system of claim 2 wherein a second signal of the pressure differential across the throttling valve is received by the control from downstream of the throttling valve.
4. The fuel system of claim 1 wherein a first signal of the pressure differential across the throttling valve is received by the control from downstream of the metering valve and upstream of the throttling valve.
5. The fuel system of claim 4 wherein a second signal of the pressure differential across the throttling valve is received by the control from downstream of the throttling valve.
6. The fuel system of claim 1 wherein the control is a hydromechanical pressure compensation assembly and first and second signals of the pressure differential across the throttling valve are pressure signals.
7. The fuel system of claim 1 wherein if more than one throttling valve is present a first signal of the pressure differential across the throttling valve is representative of the throttling valve with the lowest differential pressure.
8. The fuel system of claim 1 wherein the other of the first and second pumps is a centrifugal pump and at a minimum differential pressure only the centrifugal pump provides pressure to the fuel control assembly.
9. The fuel system of claim 8 wherein at higher differential pressures, the fixed displacement pump is fully bypassed by the control.
10. The fuel system of claim 8 wherein if the differential pressure falls below the minimum differential pressure, the control reduces an output flow amount that is bypassed from the fixed displacement pump and provides enough pressure to maintain the minimum pressure level across the throttling valve.
11. The fuel system of claim 1 wherein the first and second pumps are driven at different relative rotational speeds.
12. The fuel system of claim 11 wherein the other of the first and second pumps is a centrifugal pump and the fixed displacement pump is driven at approximately 50% of the rotational speed of the centrifugal pump.
13. The fuel system of claim 11 wherein the other of the first and second pumps is a centrifugal pump and the fixed displacement pump and the centrifugal pump are coaxially driven.
14. The fuel system of claim 1 wherein the other of the first and second pumps is a centrifugal pump and further comprising an inducer stage driven at a reduced rotational speed to operatively improve inlet performance characteristics of the centrifugal pump.
15. A method of operating a fuel system comprising:
providing a pump unit that includes first and second pumps, at least one of the pumps being a fixed displacement pump to supply pressurized flow;
providing a fuel control assembly that receives flow from the pump unit, the fuel control assembly including at least one metering valve and at least one throttling valve;
monitoring pressure differential across the throttling valve wherein the monitoring step includes receiving a first signal from downstream of the metering valve; and
controlling operation of the pump unit including using a bypass valve that selectively alters operation of the fixed displacement pump in response to the pressure differential.
16. The method of claim 15 wherein the monitoring step includes receiving a second signal from downstream of the throttling valve.
17. The method of claim 15 wherein the monitoring step includes receiving the first signal from upstream of the throttling valve.
18. The method of claim 17 wherein the monitoring step includes receiving a second signal from downstream of the throttling valve.
19. The method of claim 15 wherein the other of the first and second pumps is a centrifugal pump and at a minimum differential pressure the method includes using only the centrifugal pump to provide pressure to the fuel control assembly.
20. The method of claim 19 wherein if the differential pressure falls below the minimum differential pressure, the method includes closing a bypass valve operatively associated with the fixed displacement pump to provide enough pressure to maintain the minimum pressure level across the throttling valve.
21. A fuel system comprising:
a pump unit that supplies pressurized flow, the pump unit includes a fixed displacement pump;
a fuel control assembly receiving flow from the pump unit, the fuel control assembly including at least one metering valve and at least one throttling valve; and
a control for the fixed displacement pump including a bypass valve that selectively alters operation of the fixed displacement pump in response to receiving first and second signals indicative of a pressure differential across at least the throttling valve, wherein the first signal is received from downstream of the metering valve.
22. The fuel system of claim 21 wherein the second signal is received from downstream of the throttling valve.
23. The fuel system of claim 21 wherein the first signal is received from upstream of the throttling valve.
24. The fuel system of claim 23 wherein the second signal is received from downstream of the throttling valve.
25. A method of operating a fuel system comprising:
providing a pump unit that includes a fixed displacement pump to supply pressurized flow;
providing a fuel control assembly that receives flow from the pump unit, the fuel control assembly including at least one metering valve and at least one throttling valve;
monitoring pressure differential across the throttling valve, or across the throttling valve and metering valve combination, wherein the monitoring step includes receiving a first signal from downstream of the metering valve; and
controlling operation of the pump unit including using a bypass valve that selectively alters operation of the fixed displacement pump in response to the pressure differential.
26. The method of claim 25 wherein the monitoring step includes receiving a second signal from downstream of the throttling valve.
27. The method of claim 25 wherein the monitoring step includes receiving the first signal from upstream of the throttling valve.
28. The method of claim 27 wherein the monitoring step includes receiving a second signal from downstream of the throttling valve.