GE Masoneilan 4700P Maintenance Manual

Also see for Masoneilan 4700E: Instruction manual

Contents

© 2015 General Electric Company. All rights reserved .16 | =GE Oil & GasPilotThe pilot is essentially a three-way sliding valve. The plug regulates supply air flow to and fromthe actuator to the exhaust port. The position of this plug, governed by the diaphragm, deter-mines the output pressure of the positioner. The 4700P/4800P pneumatic positioner action maybe reversed by interchanging the supply and exhaust connections and changing cam lobe andlever arm orientation.Direct ActionIncreasing instrument signal pressure produces an increase in output pressure.Reverse ActionIncreasing instrument signal pressure produces a decrease in output pressure.CamThe cam is the intermediate element in the feedback mechanism between the actuator and thefeedback spring. Its profile determines the relationship between the valve plug position and thecontrol signal. Linear, Split Linear, or Percentage Control characteristics are available by selectionof proper lobe on cams supplied for Camflex II, Varimax, 87/88, and 87U/88U, actuators. Camssupplied on Ball and Butterfly valves maintain the inherent valve characteristic. Custom charac-teristics are available on special order.Optional bypass valve (4700P, Direct Acting Model only)During normal operation, the instrument signal is applied directly to the positioner diaphragmand the regulated supply pressure flows through the pilot valve to or from the actuator.The bypass valve module permits the positioner to be isolated for maintenance while operatingthe valve directly with the instrument signal. By turning the nylon bypass valve to the bypass po-sition (the raised arrow on the bypass valve aligned with the word Bypass on the face positionerbody indicates this position), the normal positioner output pressure to the actuator is blockedand the instrument signal is applied both to the positioner diaphragm and the actuator. The by-pass valve does not block supply pressure to the pilot. Therefore, the supply line should be shutoff before disassembling the positioner.