The minimum flow valve, also known as the automatic recirculation valve, is a pump protection valve installed at the outlet of the multistage vertical turbine pump to prevent damage caused by overheating, severe noise, instability and cavitation when the pump is operating below load. . As long as the flow rate of the pump is lower than a certain value, the bypass return port of the valve will automatically open to ensure the minimum flow rate necessary for the liquid .

1. Working Principle

The minimum flow valve is connected to the outlet of the multistage vertical turbine pump . Like the check valve, it relies on the thrust of the medium to open the valve disc. When the main channel pressure remains unchanged, the flow rate of the main channel is different, and the opening of the valve disc is different. The main valve The flap will be determined at a certain position, and the valve flap of the main circuit will transmit the action of the main valve flap to the bypass through a lever to realize the switching state of the bypass.

2. Working Process

When the main valve disc opens, the valve disc drives the lever action, and the lever force closes the bypass. When the flow rate in the main channel decreases and the main valve disc cannot be opened, the main valve disc will return to the sealing position to close the main channel. The valve disc once again drives the lever action, the bypass opens, and water flows from the bypass to the deaerator. Under the action of pressure, water flows to the inlet of the pump and recirculates, thereby protecting the pump.

3. Advantages

Minimum flow valve (also called automatic control valve, automatic recirculation valve, automatic return valve) is a valve with multiple functions integrated into one.

Advantages:

1. The minimum flow valve is a self-operated control valve. The function of the lever will automatically adjust the bypass opening according to the flow rate (system flow adjustment). It has a completely mechanical structure and relies on the flow control valve and does not require additional energy.

2. The bypass flow can be adjusted and controlled, and the overall operation of the valve is highly economical.

3. Both the main channel and the bypass function as check valves.

4. Three-way T-shaped structure, suitable for recirculation pipelines.

5. Bypass does not require continuous flow and reduces energy consumption.

6. Multi-function integrated into one, reducing design workload.

7. It has significant cost advantages in terms of early product procurement, installation and adjustment, and later maintenance, reducing installation and maintenance costs, and the overall cost is lower than traditional control valve systems.

8. Reduce the possibility of failure, minimize the possibility of failure caused by high-speed fluid, and eliminate cavitation problems and electrical wiring costs.

9. The stable operation of the multistage vertical turbine pump can still be ensured under low flow conditions.

10. The protection of the pump requires only one valve and no other additional components. Since it is not affected by faults, the main channel and bypass become a whole, making it almost maintenance-free.

4. Installation

The minimum flow valve is installed at the outlet of the pump and should be installed as close as possible to the protected centrifugal pump. The distance between the outlet of the pump and the inlet of the valve should not exceed 1.5 meters to prevent low-frequency noise caused by the pulsation of the liquid. Water hammer. The direction of circulation is from bottom to top. Vertical installation is preferred, but horizontal installation is also possible.

Precautions for Maintenance, Care and Use

1. The valve should be stored in a dry, ventilated room, and both ends of the valve channel should be blocked.

2. Valves stored for a long time should be inspected regularly to remove dirt. Special attention should be paid to the cleaning of the sealing surface to prevent damage to the sealing surface.

3. Before installation, you should carefully check whether the valve mark complies with the usage requirements.

4. Before installation, check the inner cavity and sealing surface of the valve. If there is dirt, wipe it clean with a clean cloth.

5. The valve should be inspected regularly after use to check the sealing surface and O-ring. If it is damaged and fails, it should be repaired or replaced in time.