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In a piston valve, the control of stem and seat leakage is obtained by tightness of the valve sealing rings to the body and valve plug. The bonnet compresses the valve sealing rings against the body and the valve plug. Flexible disc springs automatically assure a tight seal by exerting pressure on the valve sealing rings, keeping them compressed. Opening and Closing the TVS Isolation Valves The isolation valve begins to stop flow when the valve plug enters the lower valve sealing ring. When the isolation valve is completely closed, the valve plug is in contact with the full height of the valve sealing rings, ensuring the best possible seal. In fact, there is no advantage to be gained in torqueing the valve closed. Armstrong recommends that after closing the isolation valves completely, the handwheel should be turned back one half turn. This makes it easy to re-open the valve by avoiding metal to metal seizure. Troubleshooting – Isolation Valves A piston valve will retain its leak tightness for several years without maintenance. In severe service, such as rapid heating and cooling, some field maintenance may be required. Depending on the problem, these simple steps may help: ! ! ! ! ! Isolation Valve leaks, when the valve is closed . First, Check to make sure the valve is actually closed . Check to see if bonnet is seated on the body, if not, tighten the bonnet nuts until the bonnet seats. This recompresses the valve sealing rings against the body and the valve plug. If valve continues to leak, replace the isolation valve assembly
TVS – 811 Series Trap Valve Station Installation, Operation and Maintenance Instructions
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