Common Failure Modes Of Pneumatic Control Valves

Common Failure Modes Of Pneumatic Control Valves

Common Failure Modes Of Pneumatic Control Valves

(1) The control valve does not operate. Reasons: there is no signal pressure or diaphragm cracks, diaphragm leakage, diaphragm thrust reduction, valve core and valve seat or bushing jam, valve stem bending and other reasons make the control valve unable Action, solution: connect the signal line and the air supply connector firmly or replace the diaphragm, straighten the valve stem or replace the valve stem.

(2) The regulating valve is operating normally, but the regulating valve does not function. Reason: the valve core falls off or the pipeline is blocked. Solution: If the valve core falls off, connect the valve core and the valve stem firmly, and contact the competent authority for pipeline problems. Pipeline.

(3) The control valve is sluggish or pulsating. Reasons: the aging or dryness of the sealing packing increases the friction between the valve stem and the packing, the valve body contains highly viscous dirt and clogging, coking, etc., the pneumatic control valve diaphragm and ” O”-shaped sealing ring, etc. leaks, solutions: replace the sealing packing, readjust, remove dirt, coking, etc., tighten the membrane head, or replace the diaphragm, O-ring.

(4) The regulating valve is unstable or oscillating. Reason: The regulating valve diameter is selected too large, the flow direction of the single seat valve medium in the valve is the same as the closing direction, and the valve core and guide sleeve are severely worn. Solution: Replace the valve with a suitable diameter Valve, adjust the valve direction, improve the joint surface of the electric control valve (grind) or replace the valve core and guide sleeve.

The air-open type (normally closed type) means that when the air pressure on the membrane head increases, the valve moves in the direction of increasing opening. When the upper limit of the input air pressure is reached, the valve is fully open. Conversely, when the air pressure decreases, the valve moves toward Action in the closing direction. When there is no air input, the valve is fully closed. Generally, we call the air-opening control valve a fault-closed valve.

The action direction of the closed type (normally open type) of the air self-operated control valve is just opposite to that of the air open type. When the air pressure increases, the valve moves in the closing direction. When the air pressure decreases or does not exist, the valve moves in the opening direction or fully open. Gu usually we call the air-to-close control valve a failure-opening valve. The selection of air-to-open and air-to-close is based on the safety of process production. When the air source is cut off, whether the control valve is in the closed position or the open position is safe.

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