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

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

April 18, 2019

The working mode of the pneumatic control valve is air opening and gas closing. The opening of the air opening valve increases with the increase of the signal pressure. When there is no pressure signal, the valve is in the fully open state, and the gas closing is opposite.

Reasonable selection of the mode of action of the control valve is essential to ensure production safety, improve product quality and reduce economic losses. It is also possible to achieve the function of fault retention by correct selection of the air opening and air closing modes.

Adjusting valve air opening and air closing selection

The choice of the mode of operation of the control valve should be determined according to the requirements of the production process. Consider the position where the control valve is opened or closed when the signal pressure is interrupted (such as the failure of the control valve, the interruption of the meter supply or the interruption of the air supply). It depends on the degree of harm caused by the production process. If the valve is in the open position, the hazard is small, then the gas-off type should be used; otherwise, the gas-open type is used, usually considering the following factors:

  1. First consider the safety of people and equipment
    When the air supply is interrupted, the power supply to the instrument is interrupted, the various links in the system are faulty, and the diaphragm of the actuator is broken, so that the control valve cannot work normally, so that the valve is in an energy-free state, the control valve is in the position The opening or closing position shall ensure the safety of the person and equipment and shall not cause an accident.
  2. Secondly consider the characteristics of the medium
    When adjusting the flow rate of the medium entering the process equipment, if the medium is flammable, explosive or toxic, it should be selected as air-open type. When the signal pressure is interrupted, the valve is in the fully closed state to avoid leakage of harmful gases; Crystallized, easy to solidify materials, in order to prevent blockage, should be selected as gas-tight.
  3. Finally consider ensuring quality and reducing economic losses
    When the pressure of the control valve signal is interrupted and cannot work normally, the opening or closing state of the valve should not cause deterioration of product quality, waste of raw materials and waste of semi-finished products.

The above factors are prioritized. Special attention should be paid to the selection of the mode of action of the valve. The primary factor to be considered is the safety of the person and equipment.