A guide bushing closely fitted to the valve stem and aligned with the seat. Good stem guiding is essential to minimising packing leakage.
SUPPLY PRESSURE :The pressure at the supply port of a device such as a controller, positioner or transducer. Common values of control valve supply pressure are 20 psig. for a 3-15 psig output and 35 psig. for a 6-30 psig output.