2
IOM-1078
NOTE:
The sense chamber is not a dead-ended cham-
ber. In addition to the main flow and pilot flow when the
valve is open, there is also a very small flow from the
pilot valve into the vessel through the sense connec-
SECTION IV
IV. START-UP
Operation of the Model 1078 is automatic once the set
pressure has been established. (The set pressure is
usually bench-set at the factory prior to shipment.) The
set pressure may be approximated on the bench or set
after the valve has been installed. If the set pressure is
to be made after valve installation, the adjusting screw
should be backed off before applying inlet pressure to
the valve.
NOTE:
The set pressure is defined as the
pressure at which the valve should be fully closed on
increasing tank pressure.
Refer to applicable drawing dependent on sensing
style. Temporarily keep valve A closed. Use an
appropriate pressure indicating instrument for G2
to measure the pressure in the vessel. (For external
sensing open valves C and E, then valve B.) Now very
slowly open valve A while watching gauge G2. NEVER
SLAM OPEN VALVE A! The Vacu-Gard should close
when the tank pressure reaches the set pressure of the
pilot. To adjust the set pressure, remove the hex cap
at the top of the pilot and loosen the jam nut around
the adjusting screw. Clockwise rotation of the adjusting
CAUTION
A pressure/vacuum relieving device large enough to
vent excess pressure and to serve as an emergency
vacuum breaker must be installed to protect the tank.
CAUTION
DO NOT overtighten threaded connections since
damage or breakage may result. Wrap all NPT threads
with TFE tape. Apply anti-seize compound on bolt
threads.
CAUTION
DO NOT exceed the maximum inlet pressure on the
nameplate, as the valve may not open in time. Likewise,
the minimum nameplate pressure must be maintained,
otherwise the valve may not open.
screw will increase the set pressure. Counter clockwise
will decrease the pressure provided there is a manual
valve to vent the excess pressure. Do not set the set
pressure beyond the nameplate range. Tighten the jam
nut after adjustments are made and replace the hex
cap.
In the event that the adjusting screw is backed out
eliminating the spring compression, intentionally or
unintentionally, the valve will begin to open when the
tank pressure reaches about 1” w.c. vacuum.
VACUUM SET VALVES:
For valves that are set to
open and close on vacuum - a clockwise rotation of
the adjusting screw will set the valve to open closer
towards atmospheric pressure (less vacuum).
SECTION V
V. SHUT-DOWN
Refer to drawings on page 3. Close inlet block valve A. Remove plug D slowly from the body to allow any pressure
that maybe trapped in the body to vent to atmosphere. If installation has remote sensing, close valve B and valve
E. The Model 1078 can now be removed from the system or repaired while in place.
tion. Therefore, the sense tube must be large enough
so that the flow will not be restricted. Premature closing
of the valve may occur if excess pressure builds up in
the sense chamber due to a sense line that is too small
.
CAUTION
Follow your company’s safety procedures to avoid
injury to personnel or damage to equipment.
