Mooney Series 20 Relief Valve Instruction Manual | 7
Copyright 2021 Baker Hughes Company. All rights reserved.
Principle of Operation
The Mooney Series 20 Relief Valve controls system pressure
upstream of the valve. When system pressure is less than
the pilot set point, the pilot venting port is closed, and system
pressure from the main valve inlet is fed through the pilot to
equalize with the dome pressure. Since the area above the
main valve disc is larger than the area of the main valve seating
surface, the difference in area causes a net downward force,
keeping the main valve closed.
As system pressure increases, system media pushes against
the main pilot spring in the pilot sense chamber. The pilot opens
and relieves the dome pressure from the relief valve to the outlet
faster than is flowing into the dome through the restrictor. As the
dome pressure decreases the main valve disc begins to lift with
the inlet pressure force. The force balance at this moment is
equal between system pressure in the sense chamber and the
main pilot spring. As the pressure increases or decreases within
this balance, the pilot’s control of flow opens and closes and the
dome pressure decreases and increases, respectively, the valve
disc responding sensitively to the flow demand.
As inlet pressure increases further, the net upward force on the
main valve disc increases, allowing the main valve to relieve
more pressure. The disc obtains full lift (full capacity) at 1.5 psig
or 5% above set point, whichever is greater.
When discharging, the valve reduces system pressure below
the set point, allowing the pilot to reclose. The system pressure
continues to flow through the restrictor to equalize with the
pressure in the dome above the main valve disc. The downward
force created by the difference in areas of the disc allows the disc
to close. The disc obtains full reseat at 1.5 psig or 5% below set
point, whichever is greater.
Figure 3
Closed Position
Figure 4
Partially Open Position
