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Expansion vessels for Thermal Stores

Expansion vessels are needed when you have a sealed, or pressurised, heating system. Most new heating systems in the UK are sealed and indeed most boiler stoves and biomass boilers are installed on sealed systems on the continent. Over here there are now a growing number of boiler stoves suited to sealed systems and hence expansion vessels are needed. When a thermal store is involved the volume of water in the system becomes rather large and hence the expansion vessel volume also needs to accommodate.

An expansion vessel is essentially a metal tank, as you can see, with a balloon/membrane inside. As it warms up the water in the system expands and pushes into the balloon/membrane. When installing the system your heating engineer pumps air into the other side of the balloon/membrane to pre-charge this part of the tank. This pre-charge pressure is dependant on the height of your heating system. Essentially the higher your house is the higher the pressure will be at the base of your heating system because all that height of water is pressing down. By pre-charging the air on the other side of the membrane you ensure that there is somewhere for the water to expand into, otherwise the water would just fill full of water the moment it was connected.

The size of the expansion vessel is determined by the static pressure of the system (so the height of the whole heating system) and, most importantly, the maximum operating pressure. The maximum operating pressure of the system is decided by the element in the system with the lowest maximum operating pressure. As the water in the system heats up it expands and compresses the balloon in the expansion vessel. As the balloon compresses the air pressure in the balloon increases. We have to calculate the overall expansion vessel volume so that when the water has fully heated the pressure in the balloon is a little less than the maximum operating pressure of the system.

Our heating engineers can calculate the right size of expansion vessel for your system. You will need to tell them the total system volume, the height of your system from the lowest point to the highest point, the maximum operating pressure (so the element in the system with the lowest operating pressure), and whether the system is filled with anti-freeze. They can then do the rest.

Model Fitting Units Diameter Height Pressure Rating Nominal Heat Output Fitting Type Volume Price
Flamco Contraflex
FLAMCO CONTRAFLEX EXP VES 18/0,5 3 BAR Inch 286mm 381mm 3bar G, M 18 £99.96 inc. VAT
FLAMCO CONTRAFLEX EXP VES 35/1,5 (3bar) Inch 396mm 435mm 3bar G, M 35 £151.07 inc. VAT
FLAMCO CONTRAFLEX EXP.VES. 50/1,5 [6BAR] Inch 437mm 493mm 6bar F 50 £234.97 inc. VAT
FLAMCO CONTRAFLEX EXP.VES. 80/1,5 [6BAR] Inch 519mm 534mm 6bar F 80 £335.75 inc. VAT
FLAMCO CONTRAFLEX EXP.VES. 100/1,5 [6BAR] Inch 550mm 630mm 6bar G, M 100 £617.82 inc. VAT
FLAMCO CONTRAFLEX EXP.VES. 150/1,5 [6BAR] Inch 550mm 837mm 6bar G, M 150 £704.50 inc. VAT
FLAMCO CONTRAFLEX EXP.VES. 200/1,5 [6BAR Inch 484mm 1300mm 6bar R 200 £870.54 inc. VAT
FLAMCO CONTRAFLEX EXP.VES. 300/1,5 [6BAR] Inch 600mm 1330mm 6bar R 300 £1,121.39 inc. VAT
FLAMCO CONTRAFLEX EXP.VES. 400/1,5 [6BAR] Inch 790mm 1180mm 6bar R 400 £1,340.63 inc. VAT
FLAMCO CONTRAFLEX EXP.VES. 500/1,5 [6BAR] Inch £1,366.88 inc. VAT
Flamco Flexcon
FLAMCO FLEXCON PREMIUM 18/0,5 [6BAR] Inch 286mm 405mm 6bar R 18 £135.22 inc. VAT
FLAMCO FLEXCON PREMIUM 25/0,5 [6BAR] Inch 25 £194.69 inc. VAT
FLAMCO FLEXCON PREMIUM 35/0,5 [6BAR] Inch 396mm 435mm 6bar R 35 £249.79 inc. VAT
FLAMCO FLEXCON PREMIUM 50/1,0 [6BAR] Inch 437mm 493mm 6bar R 50 £362.69 inc. VAT
FLAMCO FLEXCON PREMIUM 80/1,0 [6BAR] Inch £591.41 inc. VAT
FLAMCO FLEXCON EXP. VESSEL 110/1,5 [6BAR] Inch £625.78 inc. VAT
FLAMCO FLEXCON EXP. VESSEL 200/1,5 [6BAR] Inch £952.27 inc. VAT
FLAMCO FLEXCON EXP. VESSEL 300/1,5 [6BAR] Inch £1,233.13 inc. VAT
FLAMCO FLEXCON EXP. VESSEL 600/1,5 [6BAR] Inch £1,814.59 inc. VAT