Circulator (Pump)
The circulator (circulating pump) in a hot-water space heating sys- tem operates in a sealed piping circuit (loop) and is always filled with water. Recommendations for their service, maintenance, troubleshooting, and repair are contained in Chapter 10, “Steam and Hot-Water Line Controls” in Volume 2.
Air Separator
When a hot-water heating system is filled with cold water, the water contains some air dissolved in solution. The air emerges from solution when the water is heated and moves rapidly through the pipes and radiators making noises in the pipes and radiators. In some cases, air pockets become trapped in the farthest radiators, which prevents them from heating. An air separator is used to trap, separate, and remove this trapped air from the water before it enters the system.
Some systems use inline separators installed in the piping close to the boiler. The inline separator shown in Figure 15-71 consists of two chambers slightly wider than the pipe. Water containing trapped air enters the separator and slows down slightly as it expands into the first chamber. The slowing down of the water causes the air trapped in it to separate, form bubbles, and float to the top of the first cham- ber. The water, free of the air, passes into the second chamber and then into the system piping. The air tapped at the top of the first chamber is vented out of the system through an automatic air vent (installed in the tapping on top of the air separator) or passed into an expansion tank.
The air separator shown in Figure 15-72 is screwed into the boiler supply tapping. The separator traps the air in the top of the boiler section, where the water is hottest and where it travels a long horizontal path at low velocity, permitting the air bubbles to separate. The trapped air escapes through a 3⁄4-in tapping into an
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air-cushion expansion tank or through an automatic float vent on systems using diaphragm expansion tanks.
An air separator can only expel air that reaches the boiler. However, sometimes air pockets remain trapped in the piping or radiation, thereby impeding the water flow and reducing the heating performance of the boiler. Such air pockets can be eliminated by installing several different purge fittings in the heating system. A manual air vent is installed on the highest point of the system (automatic air vents are not generally required); see the following section.
Some boilers are constructed with built-in air separators, which make the addition of an external unit unnecessary. Figure 15-73 illustrates the working principles of one of these integral units. In this design, the air is diverted to an automatic air vent. A variation of this design provides for the diversion of air to an expansion tank. The manufacturer refers to this device as an air eliminator. Its
function is similar to the air eliminator used on pipelines, but it dif- fers in design and construction.