For proper system operation, the air cushion (Compression Tank) should be the only air space within a closed hydronic system. This air cushion can then provide adequate pressurization for all fluctuations of the system. Because air can be absorbed in water, some means of restricting the flow of cooler water from the tank into the system is needed without restricting the passage of air into the tank. Compression tank size can be reduced by reducing vapor pressure if this is achieved. The Airtrol can do this by allowing the air to rise in into the top of the tank, but the water flow is restricted by a ball check or trap.
Bell & Gossett is a division of Xylem, a spin off of ITT Industries, and is a leading manufacturer of energy efficient pumps, valves, heat exchangers, and accessories for plumbing, wastewater, and HVAC — including steam and heat transfer — applications. The company sells a variety of products, including centrifugal pumps, hydronic specialties, heat exchangers, condensate handling equipment, valves, rotors and controllers, for use in residential, commercial and institutional buildings. Bell & Gossett is known throughout the HVAC business as the industry’s educator. Their Little Red Schoolhouse, a completely equipped learning center, has trained more than 60,000 engineers, contractors and installers in the proper design, installation, and maintenance of HVAC systems.