Figure 1-20.-Cooling system flow switch.
spring is allowed to force the diaphragm downward
releasing the tension on the rocker arm, and the inlet
pressure opens the valve. The outlet pressure increases
to the preset level, and the static control chamber
pressure balances the valve spring to maintain a
regulated downstream pressure to the served equipment.
You should take the following precautions with this
type of valve. Ensure that the locknut is loose before
you adjust the adjusting screw; otherwise, you could
strip the threads of the brass spring chamber. If water
should start leaking out of the vent, the valve should be
serviced for a leaking diaphragm. This should be done
before it ruptures. The vent should never be plugged or
painted over. Either would inhibit its operation.
If you should remove a flow regulator or a pressure
regulator, make certain that you reinstall it correctly,
because it can be installed backwards. Look for an
arrow for direction of flow or the inlet and outlet
stamped on the body of the device. Pipe-joint sealant
should be used only on the male pipe threads and not
closer than one thread to the open end to seal the device.
Improper use of anti-seize tape can result in the tape
being cut loose and circulated in the cooling system,
which could plug up a small component.
FLOW MONITORING DEVICES
Most systems incorporate one or more types of
devices to monitor the flow of distilled water through
the system to ensure that the electronic equipment is
supplied with an adequate flow. A low-flow switch is
normally found in the secondary cooling system to
monitor the overall coolant flow. It is electrically
connected to a common alarm circuit to warn personnel
when the system flow rate drops below a specified
minimum value. A typical cooling system low-flow
switch is shown in figure 1-20. The main operating
parts consist of a hermetically-sealed reed switch and a
permanent magnet attached to an internal shuttle. With
the proper flow of coolant, the shuttle moves the magnet
up and away from the reed switch. This keeps the reed
switch contacts open, When the coolant flow drops
below the minimum for a flow switch, the shuttle is
forced down by the spring to a balanced condition
against the flow of the distilled water. The magnetic
field is now close enough to cause the reed switch to
close and activate the low-flow alarm.
A much smaller flow switch is used in electronic
equipment to monitor the flow to individual
components. Atypical equipment flow switch is shown
in figure 1-21. The one depicted contains a fixed orifice.
The flow of water through the orifice causes a
pressure drop across it. This pressure drop causes the
diaphragm to move against the spring. When the
Figure 1-21.Equipment flow switch.