Gravity system

[Moggyman]

Hi I have a gravity system two large cold water tanks in loft a pump in bottom of airing cupboard feeds the en suite shower been working fine for years pump is fitted correctly with feeds as should be in 22 mm copper special flange in top of hot water cylinder so I recently added another shower room and fitted another pump in loft which is digital with an integeral pump I took it of the domestic hot water about six inches under the tea for the house hot water and another feed from cold tank in loft this shower works fine with no problems but about every two weeks the existing pumped shower gets an air lock on the hot side I?ve done all the checks for cavitation etc but all seems ok any ideas ?

[Brian Gaff]

Very difficult to read this post as it seems to have no punctuation. However are we to assume that one shower runs the cold feed from the mains while the other from the tanks in the loft?. Is there any way for the higher pressure feed of the cold to get back up the pipes to the place the hot of the other old system is connected? Brian

[harry]

em-1257187-.htm

Your new pump may be sucking air into the system. Down the expansion pipe is likeliest.

Cavitation bubbles are water vapour BTW and disappear when the cause is rem oved

[Fredxx]

I'm wondering what these checks are for cavitation, apart from an audible test?

An airlock suggests air is being pulled into the pipework. You mention your 'flange' being at the top, can you say how close it is to the top?

It's a simple matter to predict pressure drop you would get from the cold feed pipework, I assume 22mm, using your pump flow figures. You might find the head of water you have is less than this pressure drop in your 22mm pipe and elbows etc?

How high is the cold water tank above the HW tank? And what is the expected flow rate?

[Brian Gaff]

I'm still wondering what a digital Shower might be... Brian

[damduck-egg]

Just does the Fingers and Toes.

G.Harman