Tech Tips

Special Tip from Bill Hobbie

What is the basis for the time tested rule of thumb used for sizing boiler feed receiving tanks? We all know the formula: Capacity of receiving tank = boiler horsepower x 0.069 GPM x (15 to 20 minutes)/0.80 How is this arrived at? First, remember that it takes 970 BTU of latent heat to change one pound of water to steam. Now divide 33475 BTU/hour/boiler h.p. by 970 BTU/pound of water = 34.51 pounds of condensate/hour/boiler h.p. To convert to pounds/minute, divide this by 60 minutes/hr = 0.575 pounds/minute/boiler h.p. Realizing that 1 gallon of water = 8.33 pounds, dividing 0.575 by 8.33 = 0.069 gallons/minute/h.p. which is the volume of water lost per minute the boiler is steaming per h.p. How is the 15 to 20 minutes arrived at? This is the lag time for typical steam systems. To determine your specific time, cold start the boiler and when the pressure gauge needle leaves the post, start the timing. Stop the timing when you hear condensate sloshing back in the returns. This measured time is how long water was "missing" from the boiler. Dividing by 0.80 increases tank size, reflecting the need to keep some water in the tank at all times to keep the pump primed so only 80% is usable. So, to illustrate, a 40 h.p. boiler with a 20 minute time lag requires a 69 gallon receiver capacity (40 x 0.069 x 20/0.80) It is as simple as that!

Sight Glass - Jeff Krawic

Probably the coolest AND the most positive method of proving air leaking into fuel-oil suction lines, is to install a refrigerant SIGHT GLASS ONLY (Not a moisture indicator type glass) into the suction line as close to the fuel oil pump as possible. Preferrably the type with "See Through" glass on 2 sides. Combine a vacuum gauge with the sight glass and very often the answers to your fuel supply questions will be made "clear" as you observe the glass and gauge. NO bubbles should be present. "Let's be safe out there."

Natural Draft - Jeff Krawic

Each heating season, we receive a number of questions regarding "Natural Draft" issues. There are only 3 things you need to remember about natural draft. 1.) The HIGHER the chimney, the stronger the draft. 2.) The COLDER the outside temperature, the stronger the draft. 3.) The HOTTER the gases inside the chimney, the stronger the draft. That's about it. The height of the chimney is fixed so we are left with only 2 true variables. The gas temperatures and the always changing outside temperature. The greater the temperature difference between the outside air temperature and the exhaust gases, the stronger the draft of the chimney. "Let's be safe out there."

Testing thermocouples - Jeff Krawic

Thermocouples MAKE electricity!!!! Yup, it is based on 2 factors. Dissimilar metals, (electrolosis) and "Hot Junction-Cold Junction" The two ends of the sensing tip have dissimilar wires, crossing each other and making contact. The HIGHER the temperature difference between the tip, (usually immersed in the fire) and the base, the stronger the voltage output of the thermocouple. Thermocouples can and SHOULD be tested before you replace them. If I had a dime for every good thermocouple I have found discarded................. The outside copper casing of the end that connects to the gas valve, and the silver bulb protruding from the inside, are the 2 places to test with your meter. The meter MUST be capable of reading "MILLIVOLTS" and the range should be near the zero to 50 Millivolt area. Standard thermocouples produce aproximately 30 millivolts. Powerpile bulbs produce in the area of 750 Millivolts. Thats 3/4 of a volt!!! Not bad for making electricity from fire!! Test your thermocouples before discarding them as failed. "Let's be safe out there."

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