Piston valve is a seatless (soft seated) , glandless piston type globe valve.
PRINCIPLE OF OPERATION
Sealing between ports is achieved by piston (outer surface) coming in contact with the inner surface of soft ring (the lower ring).
Sealing towards atmosphere is achieved by the piston traveling upwards and by forming the sealing (outer surface of piston and inner surface of upper ring). Hence no gland is required.
Piston valve was Innovated by replacing the disk and seat of a conventional globe valve with a cylindrical piston and two resilient, replaceable sealing rings. Constant research and development have resulted in sealing rings that provide the piston valve with an extraordinary ability to seal line pressure and prevent leakage to the atmosphere.