A minimum flow valve, also known as the automatic recirculation valve, is a pump protection valve installed at the outlet of the feedwater pump to prevent the feedwater pump from being damaged due to overheating, severe noise, instability, and cavitation when the feedwater pump is running under load. As long as the flow rate of the feedwater pump is lower than a certain value, the bypass return port of the valve will automatically open to ensure the minimum flow required by the liquid feed water pump.
The minimum flow valve is connected to the outlet position of the pump. Like the check valve, the disc is opened by the thrust of the medium. When the pressure of the main channel remains unchanged, the flow rate of the main channel is different, and the opening of the disc is different. The main valve The flap will be determined at a certain position, and the flap of the main circuit will pass through a lever to transfer the action of the main flap to the bypass to realize the on-off state of the bypass.
When the main valve flap is opened, the valve flap drives the lever to move, and the lever force closes the bypass. When the flow of the main channel is reduced and the main valve flap cannot be opened, the main valve flap will return to the sealing position to close the main channel. The valve flap once again drives the lever to act, the bypass is opened, and the water flows from the bypass to the deaerator. Under the action of pressure, the water flows to the inlet of the pump and recirculates to protect the pump, as shown in the figure below.
The automatic recirculation valve has the following significant advantages
- The minimum flow valve is a self-operated control valve. The function of the lever will automatically adjust the bypass opening (system flow adjustment) according to the flow. It is completely mechanical and depends on the flow control valve and does not require additional energy.
- The bypass flow can be adjusted and controlled, and the overall operation of the valve is highly economical.
- Both the main channel and the bypass have the function of a check valve.
- The three-way T-shaped structure is suitable for recirculation pipelines.
- Bypass does not require continuous flow, reducing energy consumption.
- Integrate multiple functions into one, reducing the design workload.
- In terms of early product purchase, installation and adjustment, and later maintenance, it has significant cost advantages, reduces installation and maintenance costs, and the overall cost is lower than traditional control valve systems.
- Reduce the possibility of failure, minimize the possibility of failure caused by high-speed fluid, and no cavitation problems and electrical wiring costs.
- The stable operation of the pump can still be ensured under low flow conditions.
- Only one valve is needed to protect the pump, and no additional components are needed. Because it is not affected by faults, the main channel and the bypass become a whole, which is almost maintenance-free.