Table 1-1.—Operation of a Boiler Circuit

The ELECTRODE PROBE TYPE of feedwater control (fig. 1-9) and low-water cutoff consists of an electrode assembly and a water level relay. The electrode assembly contains three electrodes of different lengths correspondin g to high. low, and burner cutout in the boiler drum. To understand the operation of a boiler circuit, refer to figures 1-9 and 1-10 as you read the information in table 1-1. Although this information is not complete. it is presented here to acquaint you with the operation of the electrode type of boiler water level control. Try Cocks The location of the try cocks is shown as item 6 in figure 1-6. The purpose of the try cocks is to prove the water level in the boiler. You may see water in the gauge glass. but that does not mean that the water level is at that position in the boiler. lf the gauge glass is clogged up. the water could stay in the glass giving a false reading. The try cocks, on the other hand, will blow water. steam. or a mixture of steam and water out of them when they are Figure 1-9.—Electrode type of water level control. manually opened. When steam is discharged from the lowest try cock, you have a low-water condition. Table 1-1.—Operation of a Boiler Circuit Operation A c t i o n Results When the feed pump switch The feed pump motor is The feed pump will operate under control of the is in the auto position. energized. water level relay (item #6 in fig. 1-10). When the water level in the The circuit through the All of the CONTACTS labeled #6 change position. boiler reaches the level of electrode is grounded and this The three feed pump contacts that are normally electrode #3. completes the circuit. closed, i.e., 6-1, 6-2, and 6-3 open, and contact 6-4 closes which maintains the grounded circuit through electrode #2. When the water level falls The circuit through relay #6 This de-energizes relay #6, so all of the CONTACTS below electrode #2. will no longer be grounded labeled #6 return to their normal positions. Contacts because the water is not in 6-1 through 6-3 close and 6-4 opens. The feedwater contact with the electrode. pump is energized and water is pumped into the boiler. When the water level rises Relay #6 will energize again. The cycle continues and the water level in the boiler again to electrode #3. is maintained. When the water level falls Relay #5 will be de-energized. CONTACT 5-1 will open. This action de-energizes below electrode #1. the entire control circuit. The boiler is now shut down and the low-water alarm is sounded. 1-11