Pump protection valve function and working principle / how to choose

Pump protection valve function and working principle / how to choose

April 11, 2019

The automatic recirculation valve is also called the boiler feed water pump recirculation valve. In the power plant it is installed at the outlet of the feed pump and connected to the deaerator. The boiler feed pump draws water from the deaerator to the boiler. In order to prevent the feed water pump from overheating and to prevent cavitation, the flow rate of the feed water pump must in any case be not less than a specified safe flow rate, that is, the minimum flow rate. When the boiler feed water needs a small flow, for example, when the turbine trips, it is necessary to open the minimum flow valve in time, and return some of the high-pressure water from the pump outlet to the deaerator to ensure the safe operation of the feed pump. The system in which the valve is located is called a recirculation system.

Technical Parameters:

Valve body type: straight through casting ball valve;
Nominal diameter: DN20, 25, 32, 40, 50, 65, 80, 100, 200;

Main material:

Nominal pressure: PN 1.6, 2.5, 4.0, 6.4, 10, 16, 25Mpa, CLASS 150, 300, 600, 900, 1500Lb;
Connection method: flange FF, RF, RTJ, etc. Welding: SW, BW;
Actuator: Pneumatic: multi-spring actuator;

The role of the minimum flow regulating valve of the boiler feed water pump

  • Prevent the pump flow from being too small, and the boiler feed pump will cavitation;
  • If there is not enough flow in the pump when the boiler feed pump is started, the working fluid in the feed pump will be gasified, the pump will be damaged, and the pump will be recirculated to ensure that there is enough water in the pump to pass;
  • The minimum flow valve is set to prevent vaporization of the feed water pump. The fixed value is generally provided by the manufacturer. When the inlet flow rate of the feed water pump is lower than the minimum value, the minimum flow valve is opened. If the flow rate is lower than the minimum flow, the pump is protected by the jump pump. Water pump

How the minimum flow valve works

The minimum flow valve is generally installed on the branch pipe of the water pump outlet. When the water pump is running normally, the minimum flow valve is closed when the outer pipe is supplied with water. When the water pump is not operating normally, the pump is not stopped. The minimum flow valve is controlled by one of three ways: temperature, pressure, and outlet valve interlocking, and a part of small flow of high temperature water is discharged. Prevent pump cavitation and ensure normal continuous operation of the pump.

How small flow valves work

  • The high-pressure descaling water (PN25MPa) of the rolling mill is temperature-controlled, the descaling water is opened at 50 °C, and closed at 40 °C;
  • For general water pump is controlled by the outlet pressure of the pump. Install the pressure switch on the main pipe of the pump outlet. When the pressure exceeds a certain set value (according to the site, set by the designer), the minimum flow valve opens; when the pressure Below a certain set value, the minimum flow valve is closed. The pressure of the normal operation of the water pump fluctuates greatly with the supply of water to the outside and the water supply, and the design value of the minimum flow valve of the switch can be set by the design institute personnel;
  • The switch of the minimum flow valve is interlocked with the main valve for supplying water to the outside, the water is supplied to the outside, the main valve is opened, and the minimum flow valve is closed. Otherwise, the water is not supplied to the outside, the main valve is closed, and the flow valve is opened;