Expansion - HVAC Tanks
Wessels manufactures three expansion tank designs: Compression, Bladder and Diaphragm. Each tank style has models that are either ASME or Non-ASME coded. Tanks range in size from 2 to 10,000 gallons. Most of Wessels pressure vessels are designed using a pre-pressurized vessel with an internal bladder or diaphragm to manage fluids under pressure. The majority of Wessels products are standard catalogue models, with over 6,000 tanks in inventory for immediate shipment. Custom tanks are produced to customer specifications, for high pressures and/or special materials for severe duty applications.
What are Expansion Tanks?
Expansion tanks are required in a closed loop heating or chilled water HVAC system to absorb the expanding fluid and limit the pressure within a heating or cooling system. A properly sized tank will accommodate the expansion of the system fluid during the heating or cooling cycle without allowing the system to exceed critical pressure limits. The expansion tank uses compressed air to maintain system pressures by accepting and expelling the changing volume of water as it heats and cools.
Some tank designs incorporate a diaphragm or bladder to isolate the expanded water from the pressure controlling air cushion. As water is expanded, it is contained in the bladder to prevent tank corrosion and water logging potentials. The pressure controlling air cushion is pre-charged at the factory and can be adjusted in the field to meet critical system requirements. This design and operation of this style of expansion tank allows the designer or specifying engineer to reduce tank sizes up to 80%.
Compression tanks are designed to absorb the expansion forces and control the pressure in heating/cooling systems.This tank is the oldest style that has been used in this systems. It works well when the air is controlled and kept in the tank, not in the system.
Removable bladder expansion tanks are designed for use in Hydronic heating/cooling systems to absorb the expansion force resulting from the changes in temperature of the heating/cooling fluid.
The diaphragm tank has been developed to allow the systems air cushion to be separated from the systems water. No waterlogging of the tank can occur as the air is held between the tank wall and the outside of a bladder placed inside the tank, while the system water is contained inside the bladder.