Testable Pneumatic Check Valves

OPERATION
These special type of swing-disk check valves are usually installed on the turbine steam bleeding lines of the feedwater preheating stages of modern power station cycles. The main function is the quick shut off of the bleeding steam pipes, in case of loss of turbine load, to prevent the dangerous water carryover from the preheater back to the turbine. Usually the actuator is composed of a pneumatic cylinder with a single effect piston, counterbalanced by a spring. The actuator is mounted on one side of the swing check valve body and connected to the valve disk by means of a shaft. The actuator air pressure range is typically between 4 and 11 bar. Under manual operation conditions, compressed air is fed in the cylinder to load the spring and the check valve is free to operate automatically in conventional way. In the upset or emergency condition of the turbine the compressed air is vented, the spring is free to extend inside the cylinder and the actuator piston rotates the valve disk to intercept the steam bleeding pipe. The main function of the spring is to overrun the starting friction on the packing and pivot bearings. Besides the usual optionals, we can supply also valves with: - antirotating, antioscillating feature; - damping device on the shaft operating the valve disk; - three-way valve (to be installed on the compressed air feed line) manually operated by a spring loaded lever (the spring is needed to run back the lever in the valve closed position) to test during maintenance the operation of the check valve and actuator; - microswitches on the actuator for the indication of: - check valve open during normal operation, - check valve closed.

CONTROL CIRCUIT
Control Circuit could be different depending on application. Please apply to our sale or technical department if you need to obtain more information about the control circuit.

RATING and SIZES
Rating and sizes usually manufactured are: - ASME Class 150 Bolted Bonnet Sizes 4" to 34" (DN 100 to 850) - ASME Class 300 Bolted Bonnet Sizes 4" to 34" (DN 100 to 850) - ASME Class 600 Pressure Seal Bonnet Sizes 4" to 20" (DN 100 to 500) - ASME Class 600 Bolted Bonnet Sizes 4" to 16" (DN 100 to 400) - ASME Class 1500 Pressure Seal Bonnet Sizes 4" to 12" (DN 100 to 300) - ASME Class 2500 (PN 420) Pressure Seal Bonnet Sizes 4" to 8" (DN 100 to 200)

CONNECTIONS, MATERIAL CODE and STANDARDS
Applied connections, Material Codes and Standards for design, rating, manufacturing, inspecting are the same as all C M I Valves.

DIMENSION and WEIGHT
As dimensions and weight of the system valve+actuator are dependent on the operating and design conditions, they will be communicated to the Client under request. Valve end to end available dimensions are those of ASME B16.10 Swing Check: Regular or Short Pattern.