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NORA Oilheat Technicians Manual

Figure 13-14: Pump resistance, TACO “00” circulator outward to the pump body. As the water is pushed away it pulls water from the system into the impeller. This movement of water creates “head pressure,” Figure 13-14. Pressure reducing valve The pressure reducing valve allows for the automatic filling and maintenance of system water pressure. This valve takes incoming service water pressure and reduces it to an adjustable pressure. We need pressure to push water out of the boiler and up in the system. It takes one PSI of water pressure to push water 2.3 feet up a pipe. Typical residential systems operate at 12 pounds pressure because that much pressure will push water up 27.6 feet (sufficient height to heat a radiator up in the attic of a two story home). The factory setting of 12 PSI Chapter 13 Heating Systems Figure 13-16: Flow control valve is almost always adequate for residential applications. See Figure 13-15. Pressure relief valve The pressure relief valve Figure 13-15: Pressure reducing valve protects the boiler and system from high pressure conditions. Its discharge should be piped to an area where the released water will not scald the occupants. Relief valves should always be sized to boiler manufacturers’ specifications. Residential hot water boiler relief valves are set to open at 30 PSI. Flow control valve The flow control valve is used to prevent gravity circulation on a forced hot water heating system. It is a check valve opened by the circulator’s force so the heated water can travel through the system. See Figure 13-16. Air elimination or control Water holds a great deal of air in suspension. Cold water holds more air than warm water and as water is heated, the air is released. If air gets trapped in the system it can stop the flow of water to that part of the system and cause a no heat call. Air vents release air from the system and are often installed at the highest point to keep air from accumulating. In addition, most systems, with the exception of the series loop, have air vents installed in each piece of radiation. Series loop systems typically have air removed through “purge valves” located in the return piping. Chapter 13—Heating Systems 13-13 Flow—GPM Total Head—Feet


NORA Oilheat Technicians Manual
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