The valve is normally used to vent a pressurized tank. The valve can also be used to recirculate gas from a high pressure to low pressure system. The valve can have an orifice on the exit so that the flow is controlled. The valve is fully pneumatic so that no spring is present. The valve is piloted to act and the system operates to return the valve. The normally closed blow down valve is commonly used to blow down the air/oil separator tank of a rotary screw compressor.
The valve is attached to the tank so the tank pressure keeps the valve closed. To “blow down” the tank the valve is piloted open. The piston is designed so that the pilot pressure is less than the tank pressure. The Blow Down valve is a piloted normally open or normally closed valve.
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