Hot-Water Boiler Valves, Controls, and Accessories
The boilers used in hot-water heating systems are also fit- ted with a variety of valves, controls, and other devices designed to ensure the safe and proper operation. Some are similar to those used on steam boilers (e.g., pressure relief valves and low-water cutoffs). They also share the same measuring and controlling functions described for steam boiler valves, controls, and accessories. Figures 15-48 and 15-49 illustrate their arrangement on a hotwater space heating boiler.
Hot water (hydronic) boilers operate under high pressures and temperatures. To avoid serious injury,
never begin any service or repairs shutoff before taking the follow- ing precautions:
• Wait for the boiler to cool down to 80°F (27°C) or more.
• Wait for the boiler pressure to drop to 0 psi (0 bar).
• Disconnect the electrical power before making any electrical connections.
Principal Hot-Water Boiler Valves, Controls, and Accessories
A hot-water boiler should be equipped with the following valves, controls, and accessories:
• Pressure relief valve: A safety valve used to relieve boiler pressure when it exceeds the maximum safe level.
• Low-water cutoff: A device that automatically switches off the burner if the boiler water level becomes too low for safe operation.
• High-pressure limit switch: A safety device used to turn off the burner when boiler pressure exceeds its preset maxi- mum safe operating level.
• Aquastat: An automatic switching device used to control temperature limits or to operate the circulator (pump).
• Water pressure-reducing valve: A valve used to keep the boiler and system automatically filled with water at the desired operating pressure.
• Air vent: A device that releases air from the system to the atmosphere.
• Expansion tank: A tank used to accommodate the expanded volume of heated water in a hot-water (hydronic) heating system.
• Air separator: A device used to separate trapped air bub- bles and pockets from the water before it circulates through the hot-water heating system.
• Circulator: A pump used to move the water through the hot-water heating system.