expansion tank for solar thermal

[richardbeckett]

hi everyone, i represent a company manufacturing expansion tanks and would like to know what happens if the expansion tank loses its pre charge ?. Thanks

[offthegridandy]

Pump it up with foot pump?

Andy

[micko]

If you are looking at the problem from the other way the water pressure will rise and then vent through the overflow valve.

[richardbeckett]

Thanks, in fact I just want to know what would happen IF the expansion tank lost its pre charge. I assumed the primary system would relieve due to pressure and I was wondering if anyone had experienced this ??.

[shajazzi]

The expansion vessel may fill with fluid (depending how it is sited). If the system is filled whilst the expansion vessel is deflated and the system builds pressure then something may give and you want to hope that its the pressure relief valve and not the coil in the tank or some other weak point.

shajazzi

[wookey]

If the vessel loses pressure after the system is filled/commissioned then system pressure will drop from the usual 1.4bar to <1. That reduces the boiling point of the system so it's a bit more likely to stagnate. In normal operation this won't do any harm.

On stagnation, so long as the system hasn't been topped up to normalise the pressure, things will remain as-designed and water will move into the expansion vessel and no fluid should be lost. If the diaphragm has actually died then water may get stay stuck in the vessel and I'm not sure what happen when the steam volume reduces. I guess the air that was the other side of the diaphragm will move to a local high point.

If the system is topped-up after pressure is lost, to restore the guage to the desired setting then probably on on normal heating, and certainly on stangation, fluid loss will start to occur from the PRV. (At which point someone will notice there is a problem).