FLOW MONITORING DEVICES

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. 1-17