Jordan Valve Mark 5108 Series Back Pressure Regulator User Manual
Page 2
M
ark
5108 S
erieS
B
ack
P
reSSure
regulating
V
alVe
-2-
t
heory
of
o
peratIon
To understand how the Mark 5108 operates, it is best
to start with the Ejector (3). Due to the orifice in its
upstream port, 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 Relief Pilot (2). 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
(1) is connected to the branch port of the ejector and is
thus downstream of the orifice. Therefore, the pressure in
the diaphragm chamber of the main valve is effectively
controlled by the pressure relief pilot in the manner
described above. As the pilot opens, the diaphragm
pressure decreases and the main valve opens; as the
pilot closes, the diaphragm pressure increases and the
main valve closes.
If the Mark 5108 is installed as a pressure relief valve,
the pressure upstream of the main valve is normally
below the set point of the relief pilot. Therefore, the pilot
is fully closed, and so is the main valve. However, if, for
any reason, the pressure rises above the set point, the
pilot will open, and the main valve will follow in turn. The
net effect is that the main valve will open and control
the pressure at the set point, not allowing it to rise any
further. Once pressure returns to normal, the pilot and
main valve will return to the closed position.
If the Mark 5108 is installed as a pressure sustaining
valve, the pressure upstream of the main valve is
normally above the set point of the relief pilot. Therefore,
the pilot is wide open as is the main valve. However, if
system demand increases to the point that the upstream
pressure tries to fall below the set point, the pilot will
start to close and the main valve will follow, throttling as
required to keep the pressure from falling any further.
I
nstallatIon
Figure 1 shows a typical installation of an angle pattern
Mark 5108 in pressure service. Here it will relieve the
startup surges of the centrifugal pump, but this time in
pressure sustaining service. Here it will keep a
minimum back pressure on the pump to keep it from
running off the right of its curve in periods of high system
demand. These illustrations are intended only as rough
guides for valve installation, as indeed there are many
other places in a system where the Mark 5108 can be
effectively employed. However, note the use of isolation
valves. While these do not affect the operation of the
5108, they can be extremely useful if the valve needs to
be isolated from the line for maintenance or repair.
For full installation details, the user is referred to the Main
Valve section of this manual.
s
tart
- u
p
and
a
djustments
The following procedures should be followed in the order
presented in order to affect an initial startup of the Mark
5108. Note that the procedure differs somewhat between
a pressure relief valve and a pressure sustaining valve.
Procedure A. Pressure Relief Valve
1.
Install a pressure gauge of the proper range
upstream of the Mark 5108. The unused inlet
side port in the main valve body may be
used for this purpose if there is no
convenient location in the upstream piping.
2.
Remove the plastic cap from the pressure relief
pilot (2) and loosen the adjusting screw jam nut.
Turn the adjusting screw clockwise to a full stop.
3.
Loosen the adjusting screw jam nut on the flow
control valve (4) (closing speed control). Turn
the adjusting screw clockwise to a full stop, then
counterclockwise three full turns.
4.
Make sure both pilot system isolation ball valves
(6A and 6B) are open.
5.
Start the pump or otherwise start the system
flowing. The main valve at this time should
be fully closed.
6.
Carefully loosen a pipe plug in the main valve
bonnet until fluid begins to discharge around
the threads. When only clear fluid (no air)
is discharging, retighten the plug.