Standard Components
Operation
The Combination Pressure Reducing and Sustaining ACV with
Downstream Surge Control Feature is designed to automatically reduce
a fluctuating higher upstream pressure to a constant lower downstream
pressure regardless of varying flow rates, throttles to sustain a minimum
upstream pressure, and will quickly modulate toward a closed position
if downstream pressure suddenly becomes greater than the desired
regulated setpoint. The quick closing action prevents possible damaging
high inlet pressure from passing through the valve to downstream pip-
ing. Pressure Reducing action is controlled by a normally open, pressure
reducing pilot designed to: 1) Open (allowing fluid out of the main valve
cover chamber) when downstream pressure is below the adjustable
setpoint, and 2) Close (allowing fluid to fill the main valve cover cham-
ber) when downstream pressure is above the adjustable setpoint. A
decrease in downstream pressure causes the valve to modulate toward
an open position, raising downstream pressure. An increase in down-
stream pressure causes the valve to modulate toward a closed position,
lowering downstream pressure.
1
X
X
X
Y/FC
1
P/L
5
2
3
4
CLOSES VALVE
OPENS VALVE
FLOW
(AOS)
Start-up of an automatic control valve requires that proper procedures be followed. Time must be allowed for the valve to react to adjustments
and the system to stabilize. The objective is to bring the valve into service in a controlled manner to protect the system from damaging over-
pressure.
1. Prior to installation, flush line to remove debris.
2. Install valve so the flow arrow matches flow through the line, and gauges to monitor valve inlet and outlet pressures. A Position Indicator
can be installed to provide visual indication of valve position and operation without disassembly.
3. Install isolation valves upstream and downstream of the main valve.
4. Open the isolation ball valves in the control tubing if so equipped. Failure to open these will prevent the valve from functioning properly.
5. Install pressure gauges at locations upstream and downstream of the valve.
Note:
If using butterfly valves, ensure valve disc does not contact the main valve.
6. Provide adequate clearance for valve servicing and maintenance. Refer to valve servicing dimensions on next page.
7. Avoid installing valves 6" and larger in the vertical position (main valve stem horizontal). Automatic Control Valves (ACVs) are designed for
horizontal in-line installation, with the cover facing up (main valve stem vertical). Slow operation or premature stem and guide wear may
occur if valve is not installed according to factory recommendations. Consult factory for detailed engineering review prior to ordering if valve
is to be installed other than horizontally in-line.
8. If valve is equipped with a pilot control system, extra precautions should be made during installation to protect the piping circuit from dam-
age. Only remove the pilot control system from the valve if necessary. Tubing and fittings should be kept clean and replaced exactly as
removed. Consult appropriate hydraulic schematic to ensure proper re-assembly.
9. After installation, vent entrapped air from valve cover and pilot system by following instructions on Technical Bulletin.
The normally closed sustaining pilot remains open when upstream pressure is above the adjustable setpoint, and modulates toward a closed
position if upstream pressure falls below the setpoint. As the sustaining pilot closes, fluid is directed into the main valve cover chamber, allowing
the valve to modulate toward a closed position, raising upstream pressure. Normal pressure reducing operation resumes when upstream pres-
sure is above the sustaining pilot setpoint, and downstream pressure is below the reducing pilot setpoint.
If downstream pressure suddenly becomes greater than the desired regulated setpoint, the normally closed surge control pilot opens and rapidly
admits higher inlet pressure into the valve cover, increasing rate of valve closure. Normal pressure reducing operation resumes when downstream
pressure decreases below the desired regulated setpoint.
1 - Main Valve (905GD - Single Chamber)
2 - Pressure Reducing Control
3 - Downstream Surge Control
4 - Pressure Sustaining Control
5 - Fixed Orifice
X - Isolation Cocks
Installation
912GD-11 (Globe) Pressure Reducing and Sustaining Control
Valve with Downstream Surge Control Feature
2 IOM-A-ACV-912-11_612-11 2115
EDP# 1917038
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