GE Becker HPP-5, Installation And Maintenance Manual

3  |  GE Oil & Gas

© 2014 General Electric Company. All rights reserved.

Accessories

n

    Atmospheric Bleed Control (AB control): Maintains minimum 

pressure differential across the cylinder� The AB control is 

required to provide the necessary output to operate the control 

valve under all design conditions�

n

   NBV No Bleed Valve: Same function as DPS, no adjustments or 

tubing required� Works up to 150 psig power gas�

n

    DPS Series Non-Bleed Sensor: Achieves non-bleeding condi-

tions in either full open or full closed positions� Selection based 

upon power gas pressure and discharge gas pressure�

Principles of Operation

Close on Increasing Signal

The positioner is a force-balanced instrument that provides a 

control valve position proportional to the pneumatic input signal� 

The control valve will open on loss of input signal� The energy to 

operate the control valve is obtained from the differential between 

the supply and discharge pressures� In steady state, the forces 

imposed on the balance beam by the input signal diaphragm and 

the range spring are equal; therefore, the top and bottom balance 

valves in the positioner are at or near their closed positions� The 

cylinder top and bottom pressures are both equal to power gas 

pressure, and the control valve is stationary� An increase in the 

input signal pressure results in the opening of the lower balanced 

valve due to an imbalance in the beam forces� This decreases 

the pressure in the cylinder top, while the pressure in the cylinder 

bottom remains at power gas� The control valve begins to close� 

The actuator rod stretches the range spring, increasing its tension� 

This force, which opposes the force on the balanced beam caused 

by the increasing input signal, continues to increase until the 

balance beam forces are in equilibrium�

At this point the valve is in the correct position for the applied 

input signal� The positioner has a sensitivity adjustment that 

permits a balance between greater accuracy (from a smaller 

deadband) and minimal bleed gas�