A bidirectional pressure-regulator system has been devised for use in a regenerative fuel cell system. The bidirectional pressure- regulator acts as a back-pressure regulator as gas flows through the bidirectional pressure-regulator in one direction. Later, the flow of gas goes through the regulator in the opposite direction and the bidirectional pressure-regulator operates as a pressure- reducing pressure regulator. In the regenerative fuel cell system, there are two such bidirectional regulators, one for the hydrogen gas and another for the oxygen gas. The flow of gases goes from the regenerative fuel cell system to the gas storage tanks when energy is being stored, and reverses direction, flowing from the storage tanks to the regenerative fuel cell system when the stored energy is being withdrawn from the regenerative fuel cell system. Having a single bidirectional regulator replaces two unidirectional regulators, plumbing, and multiple valves needed to reverse the flow direction. The term "bidirectional" refers to both the bidirectional nature of the gas flows and capability of each pressure regulator to control the pressure on either its upstream or downstream side, regardless of the direction of flow.
The system includes a computer that runs software formulated specifically to control the operation of the bidirectional pressure regulators. Each bidirectional pressure regulator includes the following components:
- A ten-turn needle valve;
- Two pressure sensors on opposite sides (upstream and downstream) of the valve;
- A stepping motor, connected to the shaft of the needle valve, for increasing or decreasing the valve orifice size as needed to decrease or increase the difference between the upstream and downstream pressures;
- A ten-turn potentiometer for providing valve-position feedback to the software; and
- Interface circuits between the computer and the stepping motor, pressure transducers, and potentiometer.
The software provides a capability for modifying set points for either upstream or downstream pressure during operation to adjust to changing flow conditions, and/or to other changing system conditions, including changing pressure-control requirements. In addition, the software can easily be modified for application to different closed gas-flow systems. The performance of the bidirectional pressure regulator can be modified by the selection of the valve, the pressure transducers, the stepping motor, and the control parameters embedded within the software control code.
In traditional pressure-regulation practice, control of a differential pressure between two gases would typically involve the use of plumbing to couple the pressures of the gases to a differential-pressure-sensing device; such a device is said to be "hard plumbed." In contrast, the bidirectional pressure- regulator system can be said to be "soft-plumbed" because the connection between the pressures of the two gases is made only in software. In the event that the two gases are such as to pose a risk of fire, explosion, or toxicity if allowed to mix, soft plumbing offers an important safety advantage over hard plumbing by eliminating a potential source of leakage and mixing.
This work was done by Kenneth Burke and John R. Miller of Glenn Research Center and Ian Jakupca and Scott E. Sargi of Analex Corp.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steve Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-17548-1.