Hand jack
May be used either for local manual control in the event of signal failure. Or it may be used to prevent or limit opening of the valve
Valve glands
For accurate valve positioning it is important to keep friction to a minium. The largest source of friction is the valve gland. For steam valves using asbestos type packing a suitable lubricant must be applied. A better solution takes to form of a pack of several v seals made from teflon. Fins may be cast or machined into the galnd housing for cooling
Fail safe- air to open/close
The control valve may be so designed to fail in either a full open or full closed direction. In addition the pneumatic signal may open or close the valve
