Shower Pump

22 Jan 2007
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United Kingdom
Hi - my dad lives in an apartment and has a mixer shower linked to a gravity fed water system. There is also an electric pump.

The cold water tank is small perhaps 50 litres and is set just below ceiling height which is only 8ft - this tank only feeds the shower. The hot feed is from the immersion heated tank that sits directly under the cold tank. The hot and cold feed pipes to the shower are 15mm copper pipes.

under the bath there is a recently replaced shower pump. There are two clear glass pipes on the pump outlet so you can see the water flow. The cold outlet is aerating when the shower is on. The hot is fine. This aeration causes pressure in the cold flow to fall and then the shower runs very hot and can not be adjusted.

So, suggestions please . . . how can this be fixed? Many thanks. John
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Hi John - Is the cold water aerating as soon as the pump switches on, or after it has been running a while?
If I understand you correctly, the small tank supplies cold water only for the shower. Yes?
You could increase the cold supply from the tank to the pump to 22mm. What could be happening is that the impeller in the pump is agitating the(insufficient) water, causing the air to separate. You don't get this (so much, if at all) with the hot water because the heating process effectively removes some of the air. This is why many pump manufacturers recommend 22mm hot and cold supplies to the pump, but 15mm is usually satisfactory on the outlet of the pump.
If air is being drawn in by the pump, because the water level in the cold tank drops as far as the outlet to the shower, an additional ball-valve can be fitted to give a faster filling rate.
Thanks for the reply. Looks like you were the only one brave enough to put a suggestion forward on this one! You understood my note correctly, yes the cold water tank only supplies the shower, nothing else.

The aeration happens almost immediately so I'm tempted to change the pipes to 22mm. Not too difficult a job and worth a try.

Thanks for the reply G. Cheers. John

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