Jordan Valve Mark 6127 Series Pressure Reducing Valves - Manual (Page 2)

M
ark
6127 S
erieS
P
reSSure
r
educing
V
alVe
-2-
t
heory of
o
peratIon
(Refer to Schematic Diagram)
A. Pressure- Reducing Action
To understand how the Mark 6127 operates, it is best
to start with the EJECTOR. Due to the orifice in its
upstreamport, the ejector creates a pressure drop
proportional to the flow through it. The flow through the
ejector is in turn controlled by the degree of opening
of the PRESSURE REDUCING PILOT. The wider the
pilot opens, the greater the flow through the ejector
and the lower the pressure downstream of the orifice.
Conversely, the more the pilot closes, the lower the
flow through the ejector and the greater the pressure
downstream of the orifice.
Now note that the diaphragm chamber of the MAIN
VALVE is connected to the branch port of the ejector
and is thus downstream of the orifice. In this manner,
the pressure in the diaphragm chamber of the main
valve is in fact controlled by the pressure-reducing
pilot. As the diaphragm pressure decreases, the main
valve opens; as the diaphragm pressure increases, the
main valve closes.
Putting it all together, as downstream pressure tends to
increase above the set point of the pressure-reducing
pilot, the pilot moves further closed. This results in an
increase in pressure in the diaphragm chamber of the
main valve. The main valve then closes slightly to
restore the downstream pressure to the set point.
Conversely, as downstream pressure tends to decrease
below the set point, the pilot moves further open. This
results in a decrease in pressure in the diaphragm
chamber of the main valve. The main valve then opens
wider to bring the downstream pressure back up to the
set point. The net result of all this is a constant
modulating action by the pilot and main valve and a
downstream pressure which remains constant despite
fluctuations in demand or inlet pressure.
B. Pressure- Sustaining Action
Action of the pressure-sustaining pilot is very similar
to that of the pressure-reducing, except that normally
upstream pressure is higher than the sustaining pilot's
set point. The pilot is therefore full open and has no
effect on the operation of the valve.
However, if demand should increase to such a point that
supply pressure should fall to the pilot's set point, the
pilot will begin to throttle, or modulate, and further close
the main valve to keep the pressure from falling any
further. Note that when this action occurs, downstream
pressure will necessarily fall below the set point of the
reducing pilot. Simply stated, the sustaining pilot is
there to protect the pump or supply system from too
low a pressure, and will come into effect only when
called upon to do so.
I
nstallatIon
The 6127 is furnished fully factory-assembled and
ready for installation at the appropriate point in the
system. The user is referred to the Main Valve section
of this manual for full installation details.
Startup and Adjustment
The following procedures should be followed in the
order presented in order to effect an initial startup of the
Mark 6127:
1. Install pressure gauges of the proper range
upstream and downstream of the Mark 6127.
2. Remove the plastic cap from the pressure
reducing pilot, and loosen the adjusting screw
jam nut. Turn the adjusting screw clockwise to
a full stop.
3. Remove the plastic cap from the pressure
sustaining pilot, and loosen the adjusting screw
jam nut. Turn the adjusting screw clockwise to
a full stop.
4. Turn the adjusting screw of the flow control
valve fully clockwise, then back it off three
full turns.
5. Start the pump, or otherwise start the system
flowing. The main valve will at this time be
either fully closed or open only a very small
amount.
6. Carefully loosen one of the pipe plugs in the
main valve bonnet until fluid appears around
the threads. When only clear fluid (no air) is
discharging, retighten the plug.
7. Open downstream valves to give as much
demand as possible.
8. Slowly turn the adjusting screw of the pressure-
sustaining pilot counterclockwise until
upstream pressure falls to the desired minimum.
9. Check downstream pressure. If it is lower than
desired, close downstream valves as required
to build pressure to a value higher than desired.