INSTALLATION, OPERATION, &
MAINTENANCE MANUAL
TITLE: F7000 / 8000 Series Rev. T
Pilot-Operated Safety Relief Valve Page 8 of 43
2.5 REMOTE SENSE / FIELD TEST CONNECTION (FTC)
A. PURPOSE
As shown in the figure on Page 9, the F7000 / 8000 remote sense connection feeds system pressure
directly into the pilot valve inlet line from the pressure vessel, bypassing the main relief valve inlet. Remote
sense is recommended for installations where there is excessive pressure loss (exceeding 3%) in the inlet
line between the vessel and an open, flowing safety relief valve.
The field test connection provides means to apply test pressure to the pilot valve to test its set pressure.
Operation is covered in detail in Section 6.4.
B. REMOTE SENSE INSTALLATION AND OPERATION
CAUTION: Extreme care must be taken and full compliance with procedures should be used
when servicing or testing a safety relief valve used in gas or incompressible fluid
service. These service media may be volatile or under high pressure and can be
very dangerous.
1) Select a remote sense connection point at a pressure tap on the vessel or other selected location
on the system. It is recommended to use a tap location that will not experience significant velocity
flow to the relief valve inlet line should the relief valve open.
2) Route tubing or pipe (1/2” minimum recommended) from the pressure tap to the connection at the
rear of the main valve. Minimize any bends or extensive lengths. Tighten all connections
thoroughly.
3) To feed system pressure to the pilot valve, open the manual valve at the connection to the pilot
inlet tubing. As main valve inlet pressure just below the seat lags pressure buildup in the vessel,
pressure in the remote sense tubing should override valve inlet pressure and have a direct flow
path to the pilot. The check valve or manual valve provided prevents back-flow into the relief valve
inlet line. The manual valve should remain closed when remote-sensing pressure. On older valves
where the remote sense line is connected to the field test assembly, the shuttle piston inside the
field test will function as a check valve to ensure pressure is routed to the pilot valve.
2.6 SET PRESSURE CONSIDERATIONS FOR BACK PRESSURE
In general, backpressure has no effect on the flow capacity of the FLOW SAFE F7000 / 8000 Series of
pilot-operated valves as long as a critical flow condition exists. The critical flow pressure ratio for a
particular gas may be estimated by equations given in API 520 Part I, or by contacting FLOW SAFE
Engineering.
Set pressures are not affected by backpressure when using the F300 or F500 pilot valves as they are
balanced against such pressure, or by the F200 as it is normally vented to atmosphere. Caution should be
used if the F200 vent is routed to the main valve discharge or other pressurized vessel, as the set pressure
and blowdown may be affected.
Backpressure greater than the system inlet pressure normally would cause the main valve piston to open.
Because the F200, F300, and F500 pilot valves are equipped with backflow preventers as standard
features this cannot occur on the F7000 / 8000 valves. The backpressure is routed to the main valve
piston dome, keeping the valve closed and bubble-tight.
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