Groth 1401E - Manual (Page 8)

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At any time that the tank pressure is greater than the
set pressure, the pilot valve will exhaust vapors from
the tank and/or from the relief valve actuator. If
exhausting to atmosphere is not acceptable, the pilot
valve discharge can be piped into the relief valve
discharge flange. Back pressure in the header will
have negligible effect on the operation of the pilot
valve, but if too high it may prevent the relief valve
actuator from opening fully.
Contact Groth Corporation if you plan to discharge
the pilot into a header with back pressure. A check
valve may be required to prevent header vapors
backflowing into the tank.
WARNING
The tank pressure required to discharge the normal
or emergency venting requirements of the tank will
be increased by the amount of back pressure in the
discharge header. Maximum possible discharge
header pressure must be considered when sizing the
pressure relief valve.
Fig. 9 Field Test Connection
A field test connection may be supplied for the
purpose of testing and setting the pilot valve in line
without increasing tank pressure.
A test connection with an isolation valve is provided
at the sense port of the pilot valve and a check valve
is installed in the sense line. Then an independent
pressure source (such as a portable nitrogen bottle
with the proper flow controls and pressure measuring
instruments) can be used to open the pilot valve and
measure the set pressure. The test medium will not
enter the tank, however tank vapors will be
discharged during the setting procedure.
Groth Corporation can supply the complete test
apparatus, including nitrogen bottle and
instrumentation, if desired.
Fig. 10 Manual/Remote Blowdown
A local or remote, manual or solenoid operated
blowdown valve provides the capability of opening
the relief valve without opening the pilot valve.
Either a manual or electrically operated valve may be
mounted either at the relief valve location or
remotely. The valve is used to discharge the relief
valve actuator to atmosphere or to a process vapor
discharge system. This option allows the pressure
relief valve to be used as a control valve for
discharging tank vapors.