Accumulators and Expansion Tanks

Leaky Pressure Relief Valve on your Calorifier?

If so, it may be due to the water in the calorifier expanding as it heats up. If it has nowhere to go the pressure builds until the pressure relief valve does it’s job and releases a small amount of water to bring the pressure back to a safe level. 

One way to prevent this in a safe way is to install an Expansion Tank on the hot outlet side of the calorifier and to set it just above the maximum pressure of the pump but below the pressure of the pressure relief valve (PRV). 

• For example, if the maximum pressure of the pump was 30psi and the PRV was set at 45psi you would set the expansion tank at around 35psi. This will mean only water which is being expanded by heat will get into the expansion tank, rather than that from the pressure of the pump.

An accumulator works alongside the system, but it serves a different purpose to the expansion tank. It is usually installed on the cold side near the pump, and acts as a pressure buffer. Inside, it contains a pocket of compressed air that smooths out pressure changes when taps are opened or closed. 

While an accumulator can absorb some minor pressure fluctuations, it is not designed to handle thermal expansion from heated water. That’s why an expansion tank is still needed on the hot side of the calorifier.

When choosing a tank to absorb thermal expansion, pick one sized at around 8% of the calorifier’s capacity. This ensures there is

 enough diaphragm movement to compensate for the expanding hot water.
Some tanks, like certain Surejust models, are rated for both hot water expansion and can also function as accumulator tanks for smoothing pump flow. However, a standard cold-water accumulator alone is not suitable for this purpose.

When used as an accumulator on the cold water side, they should be set at approximately 12–13 psi, just below the cut-in pressure of the pump, to maximize diaphragm movement. This helps prevent rapid pump cycling and prolongs pump life. 

All Surejust accumulator/expansion tanks come complete with mounting brackets and a 13 mm hose spigot. Most are rechargeable, and larger tanks have replaceable rubber membranes. They are suitable for potable water, with stainless steel flanges on selected models.