The power for this unit either can be applied separately or through any digital indicator having a 24Vdc transmitter supply (Manas also can supply this product). They are temperature compensated to take care of any drifts due to temperature. It is a blind two-wire field mounting type transmitter, taking inlet of draft signal in pneumatic form and delivering two-wire 4-20 mA output. MANAS offers two types of draft measuring instruments. The basic principle is based on measurement of differential pressure (very low pressure) using proper techniques and then converting the signal to standard process instrumentation signal like 4-20mA or 0-5 Vdc etc. Digital Draft Gauges and blind Draft transmitters. When most of the boiler manufacturers & users were using analog (Mechanical) draft gauges, from that time, for 20 years, “MANAS” has developed and has been supplying one of the most accurate & economical drafts measuring instruments viz. In this system, one of the fans is selected to control the combustion air to suit the fuel feed and the other is assigned to take care of the proper furnace draft.įinally, all this is necessary to maintain a continuous supply of air through the fire bed for proper combustion of fuel and to exhaust the flue gases to the atmosphere after their energy content is given at the required region.įor efficient control and monitoring purposes, fairly accurate measurement of drafts at various places as mentioned above is very important. In boilers using the balanced draft technic, slight negative pressure is maintained at a furnace. This combination of FD, SA, and ID fans is called balanced draft fans. Secondary Air Draft for a high-pressure boiler.Ĭombustion air to steam boilers is supplied (force draft) through FD fan & Secondary air fan (pressure fan at the inlet of boiler) or using ID fan (suction fan at boiler Chimney) or by using both FD, SA, and ID fans. ![]() ID Fan Inlet (Range between -140 to -150 mmwc). Air heater Outlet (Flue Gas) about -100 mmwc. Economizer Outlet ranging between -70 to -80 mmwc.į. Boiler Outlet (Flue Gas) about -30mmwc.Į. Furnace Draft (It should be ideally zero but kept slightly negative, the measuring range required is +/- 50mmwc)ĭ. ![]() Air Heater outlet (Hot Air, usually between +130 to +140).Ĭ. FD fan outlet (Cold Air)/Air heater inlet (The usual range is about 150 to 200mmwc).ī. There are different points of measurement of boiler drafts & it’s approx. It is thus extremely important to measure and control the boiler drafts. Uncontrolled draft causes poor, non-efficient operation of a furnace (poor combustion efficiency), unstable pilot flame, build-ups of highly toxic gases like carbon monoxide, soot accumulation due to varying air-fuel ratio. Measuring and controlling the furnace draft is important for two reasons. Here we are talking about Boiler applications. In two main applications draft measurement and control is essential. This signal, in turn, is amplified to standard values like 4 – 20 mA, 0 – 5.0 Volts, etc., and then used for display as well as control.Īpplications of Draft Measurement and control: It is measured with the help of a transducer that converts this small differential pressure to a small electrical signal. ![]() The word draft is usually used for very low-pressure differentials up to 1000 mmwc. Draft means a difference in pressure or differential pressure.
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