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- CommentAuthorSi.min
- CommentTimeApr 14th 2012 edited
HI
I have 100m of 1/2 inch qualpex pipe fitted in my bungalow, 8 double rads 1m by 60cm to run off a CH coil looking to get energy saving Alpha 2 12-50 pump but not sure of expansion vessel size 18 L too big ? The thermal store is in attic space 1800 in height with top of water level of EXpansion Tank 1m above cylinder- Plan is to fit pump next to central heating manifolds in downstairs utility. Any comments appreciated
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- CommentAuthorCWatters
- CommentTimeApr 14th 2012
I believe you need to aim for the expansion vessel to be around 10% of the volume of water in the circuit. 18 L is on the large size for most ordinary gas central heating systems. It musn't be too small but I don't think it matters if it's too big. If too small it will run out of room as the water expands, the pressure will then shoot up and allow water out of the Pressure Relief Valve. -
- CommentAuthorPeter_in_Hungary
- CommentTimeApr 14th 2012
Posted By: Si.minThe thermal store is in attic space 1800 in height with top of water level of EXpansion Tank 1m above cylinder
Expansion tank - not pressure vessel? So is it an open vented system?
Either way CW is right 10% of system volume it the normal calculation, if its too big - no problem. If its too small on an open system water dribbles out of the overflow when the system is hot. BTW you can get away with less than 10% on an open system because you don't need additional space for the pressurised air on the other side of the rubber diaphragm that you don't have. -
- CommentAuthorSi.min
- CommentTimeApr 15th 2012
Hi thank you for your comments ! I shall aim for 10 percent I have literature for rads so litre content not hard to work out but not so sure of water content of 100m of half inch pipe long time since had to use pie r squared ?? Mathematics. In error I included the details of the expansion tank above vented store did not need to do this as central heating is running from its own independant coil thanks again -
- CommentAuthorCWatters
- CommentTimeApr 15th 2012 edited
I think 1/2" (eg Imperial) pipe is 1/2" Internal Diameter so the volume works out at about 130cc/meter (=0.13 Litres per meter). So 100m is 13 Litres.
Modern copper pipe is usually 10, 15 or 22mm Outside Diameter and google says wall thickness is either 0.6 or 0.7mm so the internal diameter of 15mm pipe is around 13.8mm. Gives a volume of about 15 Litres for 100m. -
- CommentAuthorcrusoe
- CommentTimeApr 16th 2012 edited
10% is masses. Not sure wheher expansion tank or vessel from your comments. Is all your pipework 15mm? That's unusual unless you have a very central manifold. -
- CommentAuthorSi.min
- CommentTimeApr 16th 2012
Thanks CW and Crusoe - I can work it out from that. All pipework is half inch im in Ireland - imperial sizes are used here - I thought the olives could transfer from 22mm to 3/4 or 28mm to 1 inch pipe but there is a big difference. Using new Olives and Metric compression fittings seems to works ok. Radiator cirucit is all 1/2 inch to a central manifold :)
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