Shower pump and air locks

[pricelesspete]

Hi Guys

Have recently had a loft conversion built which will contain bedroom and new en suite. Everything has been installed in en suite but we are experiencing problems with the hot water supply to the bathroom in that it keeps getting air locked.
A new negative head shower pump was fitted to feed the supply. It is in the eaves of the loft directly over the hot water cylinder. Unfortunately I could not fit a Surrey flange to the head of the cylinder as the original fitting could not be shifted so teed off from hot water outlet pipe . I am aware that this is probably the reason for the air but need to know if there is a way of clearing the problem without tampering with teh cylinder. Did try fitting an air vent at the highest point but that has not really sorted it.
Would it help if I repositioned the shower pump so that it is sited at the base of the cylinder cupboard so that the hot water is feeding down into the unit and it then only has to pump up to the bathroom? Hope this makes some sense to you experts

 

[Richard C]

In installations where the pump is above the HW cylinder, a side entry Essex flange with an anti-gravity loop should be used, these are usually preferred by pump manufacturers anyway; top entry flanges are not really suitable in this situation let alone no flange at all. Feeding aerated water directly into the pump will continually cause problems, considerably shorten the life of the pump & invalidate your warranty. I suspect what your actually experiencing is cavitaion rather than air locking. Cavitaion is a phenomenon caused by small air bubbles in the water & these can generate so much heat on the surface of the impeller it can actually burn holes in it; difficult to imagine in all that water I know but true. I don’t know your pipe work layout but you must also avoid inverted loops in the feed before the pump.

You may get away with moving the pump to the base of the cylinder & fitting 45 degree angled feed from the top vent (look here page 3, figure 2):
http://www.salamanderpumps.co.uk/Download/instructions.pdf
Personally, I’d go with the Essex flange.

The above link also gives other useful info that will help you design the pipe work layout, this is not specifically unique to Salamander pumps & will generally suit any make of pump.