Minimum flow valve, also known as automatic recirculation valve, is a pump protection valve installed at the outlet of the feed pump to prevent damage caused by overheating, serious noise, instability and cavitation when the feed pump is operating below load. As long as the feed pump flow falls below a certain value, the bypass return port of the valve opens automatically to ensure the minimum flow required for the liquid feed pump.

First, the working principle

Minimum flow valve is connected to the pump export position, as well as check valve, thrust open the disc on medium under the condition of the constant pressure in the main, the main flow is different, the opening of the disc, the disc will determine in a certain position, the main valve disc through a lever, transfer the motion of the main valve disc to bypass, to realize the bypass switch state.

Ii. Working process

When the main disc is open, the disc drives the lever, which closes the bypass. When the main flow is reduced, can't open the main valve disc, the main valve disc will come back to seal position, make the main closed, the disc drive lever action again, bypass opened, the water flow from bypass to deaerator, under the action of pressure, water flow to the pump imports, recycling movement, so as to protect the pump, see below.

Figure 1: Main valve closed, bypass open state

Figure 2: Main valve open, bypass closed state

Three advantages,

Minimum flow valve (also known as automatic control valve, automatic recirculation valve, automatic backflow valve), is a variety of functions in one valve.

It has the following significant advantages:

1, the minimum flow valve for self-operated control valve, lever action, will automatically adjust the bypass opening according to the flow (system flow regulation), completely mechanical structure, rely on flow control valve, do not need additional energy.

2, bypass flow can be adjusted control, the overall operation of the valve has high economy.

3, the main channel and bypass have the function of check valve.

4, three-way T structure, suitable for recirculating pipeline.

5, bypass does not need continuous flow, reduce energy consumption.

6, multi-function in one, reduce the design workload.

7, in the early product procurement, installation mode, and later maintenance, has a significant cost advantage, reduce installation and maintenance costs, the overall cost is lower than the traditional control valve system.

8, reduce the possibility of failure, the high-speed fluid caused by the possibility of failure to minimize, no cavitation problems and electrical wiring costs.

9, low flow conditions can still ensure the stable work of the pump.

10, pump protection only need a valve, do not need other additional components, because not affected by failure, the main channel and bypass become a whole, almost maintenance-free.

Four, installation,

The minimum flow valve is installed at the outlet of the pump, and should be installed near the protected centrifugal pump as far as possible. The distance between the outlet of the pump and the inlet of the valve should not exceed 1.5 meters, in order to prevent the low-frequency water strike caused by the pulsation of the liquid. Flow direction from bottom to top. Vertical installation or horizontal installation is preferred.

Five, maintenance, maintenance, and use matters needing attention

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

2, long-term storage valve should be regularly checked, remove dirt. Special attention should be paid to the cleaning of the sealing surface to prevent the damage of the sealing surface.

3, before installation should carefully check whether the valve mark is consistent with the use requirements.

4, before installation should check the valve cavity and sealing surface, if there is dirt, should use a clean cloth to wipe clean.

5, the valve should be regularly checked after use, check sealing surface, O ring. If damaged, should be repaired or replaced in time.

Source: Coal chemical industry - air compressor network - Zhejiang Shanhai Machinery Co., LTD