Technical Guide
DAN-LIQ-TG-44-rev0813
November 2013
X
Z
Y
X
Z
Y
15
= Inlet Pressure
= Outlet Pressure
= Inlet Pressure
= Outlet Pressure
= Controlled Pressure
FULLY OPEN - NO CONTROL - Pilot is fully open. Y-port (P3) is open to Z-port (P2). The pressure
on the bottom of the piston (P1) is greater than the pressure at (P3) plus spring force. The valve
will not open unless the pressure drop across the valve (P1 minus P2) is slightly greater than
the force applied by the main valve spring. In a non-control state, the main valve is opened in a
percentage directly proportional to (P1 minus P2).
OPEN CONTROLLED POSITION - Pilot is partially open. Y-port (P3) is open to Z-port (P2) but
is being restricted by the control pilot. The pilot control is a variable orifice that regulates the
pressure at Y-port (P3) by controlling the flow through Z-port. By increasing or decreasing the
Y-port pressure (P3) causes the piston to change positions.
P1
P3
P2
P1
P3
P2
Figure 4-3
Figure 4-2
Manual Pilot Control Needle Valve/Strainer
Manual Pilot Control Needle Valve/Strainer
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