Pumps – With condition responsive pumped fluid control
Reexamination Certificate
1999-04-07
2001-06-26
Tyler, Cheryl J. (Department: 3746)
Pumps
With condition responsive pumped fluid control
C417S302000, C417S286000, C137S114000, C060S430000
Reexamination Certificate
active
06250894
ABSTRACT:
TECHNICAL FIELD
This invention is directed to a system for operating centrifugal pumps in parallel and more particularly to a load sharing valve for operating centrifugal pumps in parallel.
BACKGROUND ART
In pumping applications, it is sometimes desirable to operate two centrifugal pumps in parallel. In the aircraft industry it is desirable for single engine aircraft where safety requirements demand that two fuel pumps operate in parallel so that if one pump fails, the other one will continue to supply fuel to the engine. Centrifugal pumps have characteristics that do not allow them to operate in parallel at low flows without additional means. Centrifugal pumps are capable of operating in parallel at higher flows. However, aircraft fuel pumps must operate over a wide range of flows and if they are simply hooked together, all of the demand at low flows will be supplied out of one pump while the other pump will be back flowed by the higher pressure of the other pump.
DISCLOSURE OF INVENTION
The primary object of this invention is to provide an improved system that allows for operation of centrifugal pumps in parallel over a wide range of flows.
Another object of this invention is to provide a load sharing valve that allows for simultaneous operation of centrifugal pumps in parallel at low flows.
A further object of the subject invention is to provide a system that allows for simultaneous operation of pumps in parallel and prevents back flow through a parallel pump that ceases to operate.
The objects and advantages set forth herein are achieved by the system of the present invention for allowing for the operation of centrifugal pumps in parallel. The system comprises two centrifugal pumps arranged in parallel. A check valve is disposed in the outlet line of a first centrifugal pump and closes to prevent back flow through the first pump in the event that the first pump is not operational.
A flow sensing valve is disposed in the outlet of the first pump and second pump. If both pumps are providing flow the sensing valve remains in a closed position. If there is no flow from the second pump the sensing valve opens porting fluid from the first pump to a bypass portion of a load sharing valve.
The load sharing valve has three input ports, a first pump input port for receiving flow from the first pump, a second pump input port for receiving flow from the second pump, and a bypass input port for receiving an input from the sensing valve. The load sharing valve also has two output ports which are manifolded together to form a common or system output.
The load sharing valve comprises a second pump spool located within the load sharing valve which is positioned as a function of the flow demanded by a fuel control or other device positioned downstream of the load sharing valve. The position of the second pump spool determines the area of the second pump window. The second pump spool also maintains a constant pressure differential across the second pump window.
The second pump spool also has a first and a second metering window disposed along the length thereof. The first metering window allows for flow from the first pump input port to enter an interior cavity of the second pump spool. The second metering window provides fluid communication between the interior cavity of the second pump spool and the first pump output port. In the preferred embodiment the area of the first metering window is equal to the area of the second pump window.
Disposed within the second pump spool is a first pump spool which acts as pressure regulating valve for maintaining a pressure differential across the first metering window. The pressure differential maintained by the first spool valve is equal to that maintained by the second pump spool valve. Since the area of and pressure differential across the first metering window are equal to those of the second pump window, each pump provides one half the total flow demanded by the downstream fuel control.
There are three basic operating modes for the load sharing valve and system. In the first mode both pumps are operable with the first pump providing flow to the first pump input port of the load sharing valve and the second pump providing flow to the second pump input port of the load sharing valve. The check valve is open and the sensing valve is closed therefore the first pump is providing flow at a pressure to the first pump input port of the load sharing valve and the second pump is providing flow at a pressure to the second pump input port.
The total flow is set by a downstream fuel control. The position of second pump spool of the load sharing valve is set in response to the flow demand. This in turn sets an equal flow area for the second pump window and the first metering window. Since the second pump spool and first pump spool set an equal pressure differential across the second pump window and the first metering window, the flow through each window is equal, because Wf=&Dgr;P
{fraction (1/12)}
×A×Constant. Therefore each pump provides half the total flow.
The first spool maintains the differential pressure across the first metering window by varying the area of the second metering window such that the pressure differential across the second metering window equals the pressure output from the first pump minus the pressure differential across the check valve, minus the pressure differential across the first metering window minus the pressure output from the second pump minus the pressure differential across the second pump window.
In a second mode, the first pump fails to provide any flow. The check valve will close to prevent back flow through the first pump and the 100% of the flow output from the load sharing valve will be from the second pump.
In a third mode, the second pump fails to provide any flow. The sensing valve opens placing the output of the first pump in fluid communication with the bypass input port of the load sharing valve. The second pump spool transitions to close the second pump input port and places the bypass input port in fluid communication with the second pump/bypass output port. Therefore 100% of the flow output from the load sharing valve comes from the first pump.
REFERENCES:
patent: 2312686 (1943-03-01), Campbell
patent: 2835323 (1958-05-01), Booth
patent: 3442218 (1969-05-01), Wess
patent: 3540218 (1970-11-01), Finn, Jr.
patent: 3952510 (1976-04-01), Peterson
patent: 4378675 (1983-04-01), Otto
patent: 4478043 (1984-10-01), Kobavashi et al.
patent: 5829252 (1998-11-01), Hirata et al.
patent: 657651 (1995-06-01), None
patent: 1546337 (1979-05-01), None
Dyer Gerald P.
Reuter Charles E.
Tyler Cheryl J.
United Technologies Corporation
LandOfFree
Load sharing valve and system for operating centrifugal... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Load sharing valve and system for operating centrifugal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Load sharing valve and system for operating centrifugal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2486830