How to select Solenoid valve in Water treatment plant

Solenoid valve is an automatic basic component used to control the direction of fluid, belonging to the actuator; usually used in mechanical control and industrial valves, to control the switch of valve.

Working principle

There is a closed cavity in the solenoid valve, and through holes are opened at different positions. Each hole leads to a different oil pipe. There is a valve in the middle of the cavity, and two electromagnets on both sides. The magnet coil on which side is energized will attract the valve body. Where to go, by controlling the movement of the valve body to block or leak different oil discharge holes, and the oil inlet hole is normally open, the hydraulic oil will enter different oil discharge pipes, and then push the oil cylinder through the pressure of the oil. The piston, the piston drives the piston rod, and the piston rod drives the mechanical device to move. In this way, the mechanical movement is controlled by controlling the current of the electromagnet.

Solenoid valves are divided into three categories in principle

1) Direct acting solenoid valve:

Principle: When energized, the electromagnetic coil generates electromagnetic force to lift the closing member from the valve seat, and the valve opens; when the power is off, the electromagnetic force disappears, the spring presses the closing member on the valve seat, and the valve closes.

Features: It can work normally in vacuum, negative pressure and zero pressure, but the diameter generally does not exceed 25mm.

2) Distributed direct acting solenoid valve:

Principle: It is a combination of direct action and pilot type. When there is no pressure difference between the inlet and the outlet, after the power is turned on, the electromagnetic force directly lifts the pilot valve and the main valve closing member up in turn, and the valve opens. When the inlet and outlet reach the starting pressure difference, after the power is turned on, the electromagnetic force pilots the small valve, the pressure in the lower chamber of the main valve rises, and the pressure in the upper chamber drops, so that the main valve is pushed up by the pressure difference; when the power is off, the pilot valve uses a spring The force or medium pressure pushes the closing member, moving downward, causing the valve to close.

Features: It can also act safely under zero pressure difference or vacuum and high pressure, but the power is large and it must be installed horizontally.

3) Pilot solenoid valve:

Principle: When the power is turned on, the electromagnetic force opens the pilot hole, the pressure in the upper chamber drops rapidly, and a pressure difference between the upper and lower sides is formed around the closing member, and the fluid pressure pushes the closing member to move upward, and the valve opens; When the hole is closed, the inlet pressure passes through the bypass hole to quickly form a pressure difference between the lower and upper parts around the valve closing member, and the fluid pressure pushes the closing member to move down to close the valve.

Features: The upper limit of the fluid pressure range is high, which can be installed arbitrarily (need to be customized) but must meet the fluid pressure differential conditions.

Precautions for solenoid valve selection

1) Applicability

The fluid in the pipeline must be consistent with the medium calibrated in the selected solenoid valve series model. The temperature of the fluid must be lower than the calibration temperature of the solenoid valve.

The allowable liquid viscosity of the solenoid valve is generally below 20CST, and if it is greater than 20CST, it should be indicated. Working pressure difference, when the maximum pressure difference of the pipeline is less than 0.04MPa, direct acting and step-by-step direct acting types such as ZS, 2W, ZQDF, ZCM series should be used; when the minimum working pressure difference is greater than 0.04MPa, the pilot type (pressure Differential type) solenoid valve; the maximum working pressure difference should be less than the maximum calibration pressure of the solenoid valve; generally solenoid valves work in one direction, so pay attention to whether there is a back pressure difference, if there is a check valve installed.

When the cleanliness of the fluid is not high, a filter should be installed in front of the solenoid valve. Generally, the solenoid valve requires better cleanliness for the medium. Pay attention to the flow aperture and the diameter of the nozzle; the solenoid valve is generally only controlled by two switches; if the conditions permit, please install a bypass pipe to facilitate maintenance; when there is a water hammer phenomenon, the opening and closing time of the solenoid valve should be adjusted. Pay attention to the influence of ambient temperature on the solenoid valve. The power supply current and power consumption should be selected according to the output capacity. The power supply voltage is generally allowed to be about ±10%. It must be noted that the VA value is relatively high during AC starting.

2) Reliability

The solenoid valves used in water treatment plant commonly be divided into two types: Closed and Open; generally, the closed type is commonly be used, which is opened when power is on, and closed when it is powered off; but when the opening time is very long and the closing time is very short, the Open type should be selected. When the action time is very short and the frequency is high, the direct-acting type is generally selected, and the fast-acting series is selected for large diameters.

3) Safety

Generally the solenoid valve is not waterproof, we can customize the waterproof type for you if require.

The highest rated nominal pressure of the solenoid valve must exceed the highest pressure in the pipeline, otherwise the service life will be shortened or other unexpected situations will occur.

All stainless steel type should be used for corrosive liquids, and plastic king (SLF) solenoid valves should be used for strong corrosive fluids. Explosion-proof type also can be customized.

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