How to correctly choose the positive and negative reaction mode of pneumatic control valve

Pneumatic control valve is compressed gas as the power source, with the cylinder as the actuator, and with the help of valve positioner, solenoid valve, gas filter and other accessories to drive the valve, to achieve switching or proportional adjustment.

Pneumatic control valve

The mode of action of the pneumatic control valve has two types of gas open and gas close. The gas open valve increases with the increase of signal pressure, and the opening degree increases. When there is no pressure signal, the valve is in a fully open state, and the gas close is the opposite.

Reasonable selection of the mode of action of the regulating valve is crucial to ensure production safety, improve product quality and reduce economic losses. It can also achieve the role of fault position maintenance through the correct choice of gas on and gas off modes.

1. Gas opening and gas closing selection of regulating valve

The choice of the mode of action of the regulator should be determined according to the requirements of the production process, considering that when the signal pressure is interrupted (such as the regulator failure, instrument power supply interruption or air supply interruption), the regulator is opened or closed according to the position. The harm caused to the production process depends on the size. If the valve is in the open position when the harm is small, the gas close type should be selected; On the contrary, the gas open type is selected, usually considering the following factors:

(1) First consider personal and equipment safety

When the air supply is interrupted, the instrument power supply is interrupted, the regulating system has faults in each link and the diaphragm of the actuator is broken, etc., so that the regulating valve can not work normally, so that the valve core is in a state of no energy, the opening or closing position of the regulating valve should be able to ensure the safety of the person and the equipment, and will not cause accidents.

(2) Secondly, consider the characteristics of the medium

When regulating the medium flow into the process equipment, if the medium is flammable, explosive or toxic gas, it should be selected as the gas open, when the signal pressure is interrupted, the valve is in a fully closed state to avoid harmful gas leakage; If the medium is easy to crystallize, easy to solidify materials, in order to prevent clogging, it should be selected as a gas-closed type.

(3) Finally consider ensuring quality and reducing economic losses

When the regulating valve signal pressure is interrupted and can not work normally, the open or closed state of the valve should not cause product quality decline and waste of raw materials and waste of semi-finished products.

The above factors are of priority, special attention should be paid to, and the primary factor that should be considered in the selection of the mode of action of the regulating valve is the safety of the person and the equipment.