Groth 1401E - Manual (Page 4)

3
When the tank pressure reaches the set pressure of
the pilot valve, force on the diaphragm overcomes
the spring and vapors begin to flow to the
atmosphere through the pilot seat (7) and exhaust
port (8). As the actuator is evacuated to atmosphere,
pressure is also reduced in the space between the
diaphragms, and additional lifting force is provided
by the booster (larger) diaphragm. The rate of
evacuation of the actuator is controlled by the
diameter of the adjustable orifice. As pressure on the
actuator is relieved, tank pressure forces the relief
valve seat (2) fully open.
As tank pressure decreases to the pilot valve setting,
the valve closes and tank pressure again flows
through the orifice to the relief valve actuator. As the
actuator is filled, the pressure relief valve seat is
forced closed. The size of the adjustable orifice
determines the speed of filling the actuator.
The adjustable orifice, or "blowdown needle", affects
both opening and closing of the pressure relief valve.
Opening can be varied from rapid, "snap action", to
incremental, "modulating". The pressure at which
the valve closes, "blowdown pressure", can vary
from set pressure to 7-10% below set pressure.
These characteristics are discussed in detail in the
operation section of this manual.
TABLE 1
PILOT VALVE SPECIFICATIONS
MODEL 1401E
Set pressure 2.0" WC to 15 PSIG
5 to 1033 mbar (metric)
Blowdown Zero to 10 %
Action "Snap Action" to
"Modulating"
Materials Carbon Steel/SS Trim
316 SS
Diaphragm Fluoropolymer
Elastomers
Buna-N, FKM, FFKM
WARNING
The pilot valve will exhaust the actuator of the
pressure relief valve as described in this manual.
This function does NOT assure that the relief valve
will open fully. The forces exerted by system
pressure and vapor flow must be sufficient to support
the weight of the pallet-support assembly to achieve
full opening. Relief valves built with heavy
components designed to withstand high pressure may
NOT open at low pressure even though the actuator
has been fully exhausted. Consult Groth
Corporation or the specific relief valve operation
manual when applying pilot operated pressure relief
valves at low pressure settings.
Eight springs are used with the screw adjustment to
obtain the required set pressure. For more detail see
Table 2 on page 5.
This manual is intended to provide recommended
procedures and practices for installation, operation,
and maintenance of the Groth Series 1401E Pilot
Valve. The pressure relief valve is covered by a
separate manual. Any standard procedures and
practices developed in a specific plant or process
should supersede this manual. Although this manual
cannot cover all possible contingencies, following
these guidelines should provide safe, reliable pilot
valve performance.
For information not contained in this manual, please
contact:
Groth Corporation
13650 N. Promenade Blvd.
Stafford, Texas 77477
281-295-6800 (phone)
281-295-6995 (fax)
SAFETY GENERAL INSTRUCTIONS
This section is an overview of safety guidelines that
should be followed during the installation, operation
and maintenance of Groth series 1401 pilot valves.
To understand the context of these instructions and
warnings, read and understand this complete manual.
WARNING
The purpose of a pilot operated pressure relief valve
is to prevent excessive pressure or vacuum in a tank
or process system. The valve must be designed for
the proper MAWP and flow requirements of the
system. Consult API Standard 2000 for tank
protection sizing procedures. An improperly
specified or functioning relief valve may result in
structural damage to the tank or system.
In the event of a diaphragm failure, the pilot valve
will vent pressure to the atmosphere, causing the
pressure relief valve to fail in the OPEN position.
Pressure may be vented slowly, simulating the action
of a modulating pilot. Under these conditions,
somewhat greater overpressure may be required to
produce the full flow capacity of the relief valve.