Outlet
Inlet
Outlet
Under Pressure
Trip Control
Valve
Over Pressure
Trip Control
Valve
Filter
Type 30
Restrictor
Type 24
Vent Valve
Unlatched
Vent
Actuator
Flowgrid Regulator &
Integral Slam Shut Valve
Pilot Sense
Pilot Series 20
Loading
Flapper Valve
(Between Open & Closed)
Center Port
Outlet
Inlet
Outlet
Under Pressure
Trip Control
Valve
Over Pressure
Trip Control
Valve
Filter
Type 30
Restrictor
Type 24
Vent Valve
Unlatched
Vent
Actuator
Flowgrid Regulator &
Integral Slam Shut Valve
Pilot Sense
Pilot Series 20
Loading
Flapper Valve
(Closed Position)
Slam Shut Sense
Center Port
4
|
Dresser
Figure 6 – Actuator & Latch Mechanism Midway
Figure 7 - Actuator & Latch Mechanism Closed
When the downstream pressure exceeds the over pressure set
point or is less than the optional under pressure set point, the
controller diaphragm and spring move opening a valve. The
open valve allows the sense pressure to flow under the latch
diaphragm, see Figure 6. The pressure acts on the diaphragm
which pushes on the pin. The pin moves the “L” shaped pawl
lever and releasing the flapper lever. When the flapper lever is
released, a set of springs pushes the flapper valve closed and
provides the initial force to seal the valve.
Once the flapper valve closes the inlet pressure is cut off
as shown in Figure 7. To return the system to operation the
technician closes the upstream and downstream block valves
to isolate the system. Then repairs are made as required to
correct the cause of the over or under pressure condition.
Resetting the slam shut requires equalizing the pressure up
and downstream of the flapper valve. The flapper valve can
then be rotated open and re-latched.
