Some hydronic heating systems use electrically operated valves to control the flow of water into each zone. In these zoned hydronic systems, the valves operate in conjunction with a single circulator. The construction details of a typical electric zone valve are illustrated in Figure 10-62. When the room thermostat calls for heat, an electrical current …
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A flow control valve is used (1) to prevent gravity circulation in a hydronic heating system when the circulator is not operating and (2) to permit the summer–winter operation of an indirect water heater. As shown in Figure 10-61, a flow control valve can be installed in either a vertical or horizontal position. Either location …
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A hot-water heating control consists of an outdoor liquid expansion type bulb connected by a capillary system to a double-ported three-way automatic mixing valve (see Figure 10-59). It is designed to blend the hot water from the boiler with the cooler return water in inverse proportion to the outside water and deliver the blended water …
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Water-tempering valves are used in hot-water space heating systems where it is necessary to supply a domestic hot-water supply at temperatures considerably lower than those of the water in the supply mains. The water-tempering valve automatically mixes hot and cold water to a desired temperature, thus preventing scalding at the fixtures. These valves are designed …
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An electric control valve (regulator) is designed to provide remote electric on-off control in heating systems and steam process applications (see Figure 10-49). The solenoid pilot at the top of the valve is connected to a room thermostat, automatic time clock, or some similar device from which it can receive an electrical signal. When the …
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Temperature regulators are used for many heating and cooling applications, including small-flow instantaneous heaters or coolers (shell-and-tube or shell-and-coil heat exchangers), small storage or tank heaters, and similar installations. The Spirax Sarco Type 25T temperature regulator shown in Figure 10-48 is a diaphragm-operated valve used for regulating temperature in a variety of different process applications. …
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Sometimes air pockets will form in the pipelines of steam or hot water heating and cooling systems and retard circulation. One method of eliminating these air pockets is to install one or more air eliminators at suitable locations in the pipeline. An air eliminator (or air vent) is a device designed to permit automatic venting …
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An undersized expansion tank or one that is completely filled up with water will cause the boiler pressure to increase when the water heats. Because the expansion tank is too small or too filled with water to absorb the excess pressure, the relief valve will begin to drip. The dripping relief valve is only symptomatic …
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The air in a diaphragm-type expansion tank is separated from the water by a flexible rubber membrane (see Figure 10-44). These tanks are smaller than the closed steel tanks and come from the manufacturer precharged with compressed air. When the tank arrives at the site, the diaphragm is fully expanded against its inside surfaces. When …
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The closed steel expansion tank has no moving parts (see Figure 10-43). It is normally two-thirds filled with water and one-third with air. As heated water expands and its excess volume enters the tank, it compresses the air at the top of the tank. The compression of the air in the tank results in an …
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