FLOW-MONITORING DEVICES

FLOW-MONITORING DEVICES low-flow switch is normally found in the secondary cooling system to monitor the overall coolant flow. It Most systems incorporate one or more types of is electrically connected to a common alarm circuit to devices to monitor the flow of distilled water through warn personnel when the system flow rate drops the system to ensure that the electronic equipment is below a specified minimum value. A typical cooling supplied with an adequate flow of distilled water. A system low-flow switch is shown in figure 2-15. Figure 2-15.—Cooling system low-flow switch. The main operating parts of the cooling system low-flow switch 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, which 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 to activate the low- flow alarm. A small flow switch is used in electronic equip- ment to monitor the flow to individual components. The flow of water through the orifice causes a pres- sure drop across it. This pressure drop causes the diaphragm to move against the spring. When the dif- ferential pressure (pressure drop) is sufficient, the microswitch activates to indicate that the switch has the proper flow through it. You should be sure that the flow switch is defective before overhauling or replac- ing it, as the problem could be a partially closed supply/return valve, an obstruction in the coolant line, an insufficient coolant pressure, or many other things. By using the coolant system pressure gages and/or the installation of a permanent or a temporary in-line flowmeter, you should be able to correctly isolate the problem. In the secondary cooling system, a full-flow sys- tem flowmeter is provided to enable you to monitor the total system flow rate for troubleshooting pur- poses. Three types of system flowmeters are installed aboard ships; all of which monitor the coolant-flow rate. They are the venturi flowmeter, the orifice flow- meter, and the rotameter. Most systems incorporate one secondary coolant flowmeter and one or more smaller flowmeters to ensure that the electronic equip- ment is being supplied with an adequate flow of cool- ant. A typical equipment-flow switch is shown in figure 2-16. 2-17