Types of expansion tanks
Static expansion tanks
Static expansion tanks are available in a range of sizes to accommodate various system volumes and are supplied to order pre-charged with nitrogen to the pressure required for the intended installation. The pre-charged expansion tanks come in two types.
Diaphragm type, in which the diaphragm which spans the middle of the tank. The water in the tank is in contact with the tank’s metal inner surface and therefore is unsuitable for potable water.
Bladder type, which contains a replaceable butyl bladder. Because the water in the tank is completely contained inside the membrane, the risk of corrosion is avoided and the tank is suitable for systems containing untreated water.
Examples of this type of expansion tank include Duraflex Cobalt.
Regular maintenance required for pre-charged expansion tanks includes complete draining and pressure testing at least annually.
Pump-controlled Pressurisation Systems
Pump-controlled Pressurisation Systems operate as pressure-maintaining stations with automatic water make-up and deaeration. Typically, a pump-controlled expansion tank comprises a tank fitted with a replaceable butyl bladder, a pump and a control panel. This type of system represents a superior method of system pressure management, provides close pressure control, degassing, and water-makeup with BMS interface capabilities.
Pressure control with this type of system is much more fine-tuned and up to 90% of the tank’s capacity can be utilized, compared to less than half that volume with a pre-charged tank (depending on system pressure). This saves a significant amount of plant room space and piping. One pump-controlled expansion tank can be substituted for four pre charge vessels.