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same sample which indicates
Figure 10 weak fluid. The sampling hose and pump should also be checked.
The filter yarn, Figure 9, in the sampling hose should be replaced whenever noticeable discoloration takes place. This will also provide easier pump operation.
The entire hose assembly, Figure 10, should be checked periodically.
The easiest way is as follows: With finger placed over inlet side or filter side, depress pump. Pump should remain depressed until vacuum is released. With finger over outlet or instrument side, apply moderate pressure to the bulb. If it cannot be depressed, the bulb and hose are all right.
For greatest accuracy when using CO2 indicators, allow them to reach room temperature. If they are cold, experience has shown that readings will be slightly high. Also, when servicing C02 indicators be cautious with the red absorbent solution. It is potassium hydroxide, which is a poison and acidic and can cause severe burns. Always avoid contact with skin, eyes and clothing.
Checking the stack thermometer: The thermometer should be checked for obvious damage and / or a bent stem. If the instrument appears in good condition, the following tests can be performed to check accuracy:
Boiling water test; insert thermometer in boiling water. If instrument reads 210-215 ° F, instrument is okay.
Thermotest; check thermometer against a thermocouple or good mercury thermometer.
Another good test is comparing temperature in a warm air furnace plenum against either of these two instruments.
If, when using a Bacharach thermometer, it is found that the instrument has wandered, it can be recalibrated by securing the hex-shaped nut on the back of the Tempoint ® and by rotating the black dial to correspond to the correct temperature setting.
When using any of these instruments, care should be taken to handle them properly. Analyzers should be vented of all samples and be in an upright position when stored. Also, instruments should be at room temperature when in use. Under adverse conditions, disregard first CO2 test as a warm-up / cool-down procedure. Proper use especially hinges on the proper insertion depth of sampling tubes.
The tubes should end at roughly the center of the pipe to trap the hottest and most highly concentrated flue gas samples. The thermometer’ s bimetal is at the end of the probe and in the case of electronic instruments, the thermocouple is also at the end of the sending tube. One manufacturer’ s use of spring clips is especially conducive to obtaining the desired insertion depth, Figure 11( Dwyer # A357).
When using most thermometers, most of the units found in the manufacturer’ s kits have stem lengths of 5 inches. This allows for accurate temperature readings for up to and including a 10-inch diameter fluepipe. When taking temperature readings on a larger pipe, a longer stem on the instrument is preferred. Bacharach makes a thermometer with an 11-inch stem, and this longer stem will properly accommodate up to a 22-inch fluepipe.
Temperature of flue gas has always been,
Figure 11
and still is, one of the single most important tests we perform on heating plants. From knowing that a 1 % CO2 change will affect temperature 25 ° F, we can make burner adjustments with accurate thermometers very easily. So, it is very important that we use and maintain the equipment to the best of our ability.
Finally, in this discussion about the basic use of instruments, the calculators or slide rule charts and tables should be touched upon. Some tables are temperature compensated at 50 ° F, but others require the subtraction of ambient temperature, i. e. the average temperature of the basement or boiler room. Subtraction of 100 ° F
22 FEBRUARY 2026 | FUEL OIL NEWS | www. fueloilnews. com