Air venting for power shower

[beinerts]

Hi all,

I'm no expert plumber, so excuse the stupid questions/comments. I've got a shower pump that is fed from a hot water cylinder and the cold water tank above it (i.e. hot and cold have the same head of pressure).

There is a gradual build up of air on the hot water side which doesn't seem to get vented through the hot water cylinder, which affects water pressure. My father in law has fitted a manual valve that we open periodically (every month or so) to vent the built up air. It is vented back into the cold water tank.

My question is: is there a kind of automatic air vent we could fit instead of this, to avoid the bother? I suppose it would need to be open under normal positive pressure and then closed under negative pressure, when the pump starts sucking, to stop air being sucked into the pump through the vent.

I hope that makes sense. Thanks in advance for any comments/answers.

 

[Fluffster]

Your pump hot feed from the cylinder should have a surrey/essex flange to prevent air being drawn in and causing the pump to cavitate.

Have you one of these or is it just teed off?

Pete

 

[beinerts]

There's an essex flange on the inside. Not sure where the air is coming from TBH, there isn't any traces of water anywhere to suggest air is getting in somewhere else.

 

[GPlumb]

See if there is a surge down the vent when the pump is started. Put you hand over the end (make sure the water isn't hot first).

 

[beinerts]

Hi, do you meant the vent my FIL put in to let us vent the built up air? There is no suction through that vent when the pump is on...

 

[Fluffster]

Graham means the vent pipe which dischrges into your cold water tank if as he suggests there is a suction when the shower pump activates you can either lower the pump speed if possible or raise the vent pipe higher to prevent air been drawn in.

However your essex flange should prevent this.

How powerful is the pump what bar flow rate?

Pete

 

[beinerts]

Thanks for all the replies. I will try checking the vent pipe. I don't know the exact power or bar flow rate, but I will check tonight and post them up.

 

[Richard C]

It sounds as if you have the pump below the hot water outlet which is fine but does the hot water feed from the pump loop up & over, back down to the shower head? If you have up & over feeds, you must vent the pipes at the highest point or residual air missed by the Essex flange will build up in the top of the loop over time affecting the flow to a point where it could stop altogether. All you need to do is to tee off at the highest point & provide an open vent above the cold water tank or tee into the existing vent at high level.

 

[beinerts]

Thanks for the reply. No, the feed from the pump goes straight up, with the shower head being the highest point. I think any air on that side of the pump would be vented through the shower head.

 

[Richard C]

Thanks for the reply. No, the feed from the pump goes straight up, with the shower head being the highest point. I think any air on that side of the pump would be vented through the shower head.

Sorry, I should have said the shower mixer valve & not the shower head so it wouldn't vent through the head; is it still the case?

 

[beinerts]

No problem! Yes, it goes (diagonally) up to the shower mixer valve and from there straight up to the shower head.

 

[Richard C]

Strange, has it always been like it? Are you sure it’s an Essex flange & not just a flange fitting? Is it correctly installed with an upturned curved pipe on the inside? I’m assuming you have got an open vented system? I don’t really understand why air isn’t venting through the top of the cylinder, have you checked the outlet isn’t blocked with lime scale?

I have an Essex flange which I fitted into a new cylinder & it works perfectly serving 2 showers simultaneously; I also have the further complication of a solar heating system & even this doesn’t cause any air problems. Unless it’s recently started playing up, my guess is it’s to do with pipe layout; have a look at this guide it might give some clue as to what's wrong;
http://www.salamanderpumps.co.uk/Download/instructions.pdf

 

[beinerts]

It's always been like it. The cylinder is quite new, which would rule out lime scale. It was delivered as a single unit, with cold water tank and hot water cylinder joined, with a vent going back into the cold water tank. It also came with two flanges, one for normal hot water and one essex flange for the pump feed.

The layout seems to be fine, looking at the salamender link. I have wondered whether the vent between the hot water cylinder and cold water tank is working. Does anyone have any ideas on how to do this, given as I can only really access the vent pipe exit into the cold water tank? How about blocking the vent exit for a very short time while my wife has a shower? Then, once she's finished, I should get some air bubbles when I unblock it again?

Two strange symptoms to mention:

1) Sometimes, a few minutes after one of us has got out of the shower, there is a trickle of water out of the showerhead. It starts from nothing and then stops. Not a great deal of water, I might add.

2) The built up air doesn't even go back into the hot water cylinder. It's only when we open the valve my FIL put in (on the shower input feed, venting back into the cold water tank) that the air vents.

I realise that while this valve I mention cures the symptom, it doesn't really help to determine the cause.