3 | GE Oil & Gas
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Figure 1 - Principles of Operation
Direct Acting VRP-600-SB-PID-40 (High Gain) Yellow Spring
“False Signal”
Needle Valve
Output
Orifice
(Derivative)
P4
P3
Output
Block
Valve
Sensing
Pressure
P1
P1
P2
P4
P3
P2
Metering Valve
(Integral)
Power
Gas
Top Balance Valve
In the case of a
decrease in sensing
pressure, the bottom
balance valve will open
and the controller will
bleed gas.
Figure 1B
Figure 1C
Figure 1D
Figure 1A
Bottom Balance Valve
The arrows in Figure 1A represent
the steady state or “balanced”
condition where the spring force
and force on the sensing diaphragm
are equal. If the sensing pressure
increases, the net force on the
sensing diaphragm is down. If the
sensing pressure decreases, the
net force on the diaphragm is up.
When spring and sensing diaphragm
forces are equal to each other, the
controller is balanced, and at steady
state. In the additional diagrams (1C,
1D) the dynamics of balance valves
for a decrease in setpoint is shown.
A high gain controller uses small
rings (shown in Figure 1B). Middle
gain controllers use large rings
(shown below). Low gain pilots use
no rings.
The derivative function is
introduced by applying a
portion of the output signal to
the bottom of the feed-back
diaphragm. The orifice is
adjusted to ensure system
stability. The integral function
is introduced by applying a
portion of the output signal
to the top of the feedback
diaphragm. The metering valve
provides adjustability of reset
rate.
In the case of a decrease
in sensing pressure, the
top balance valve closes,
and cuts off the power
gas. Arrows in figures
1C and 1D represent the
direction of gas flow.
