I'm after some advice from any plumbers on here. (Again)

I've just fitted a thermostatic shower valve and have installed a shower pump. For some reason, I seem to be getting air in the system when I turn the shower off. This air prevents the shower from working when I next turn it on.

The shower pump has a dedicated feed from the HW cylinder using a Salamander Flange. The cold feed is direct from the storage tank in the loft. The outlets from the pump flow to the valve and up to the shower head like the crap picture below.



Shower

I suspect that the crank in the pipe which connects to the shower head is causing the problem and somehow allowing air back into the pipe. If I bang this pipe to disturb the air, the water flows and the pump fires up again. Can any plumbers confirm that this could be the problem????

Phil

Wheres the pump in relation to the Cylinder Phil??

About a meter away, behind the bath. The HW feed comes from the top of the cylinder, down, underneath the floorboards and up and into the pump.

Phil

That could be you problem. YOuve got a drop from the cylinder into the floor, then horizontal, then back to the vertical and up past the pump, then horizontal again and then a drop into the pump.

Ideally you want to drop from the cylinder into the pump, because you havent try fitting a non return valve just in front of the pump.

The installation literature states Do not install a non-return valve, or devices
which contain non-return valves, in the
suction (inlet) pipework to the pump. The
pump must be free to vent to the supply
tanks at all times

It would be extremely difficult to plumb the pump in directly below the cylinder.

Phil

Put it in immediatly after then, shouldnt cause any harm on the pressure side but should stop any air being drawn back in.

Edited to add that Ive never fitted a pump where Ive read an instruction that the pump needs to vent back to the tank. Thats a new one for me......

[Edited on 8/2/09 by iiyama]

I have been having a very similar problem with a modern pump I recently fitted to replace an old worn out one...


Annoyingly.. the old one worked amazingly well without any special pipework etc... but the new one just wont work...

Great advance in technology you stupid pump designers!


So I am repairing the old pump and will have to re-install it.... Not ideal... I cant believe its so hard to get it right!

The pump is fitted similar to the diagram below. Only difference is the HW feed which is as mentioned above. Again, the installation manual states - It should be positioned as close to the water source as possible, having a
minimum flooded suction head of 0.5 metres at all times Which it does......

Phil


Shower Install

Here is a detailed picture of the pipework in my application. Any more opinions/ideas as to how air may be getting into the system??

Phil
[img][/img]

you get this sorted Phil?

Sort of. The pump manufacturer reckons that the system is fine and suggested that living in a hard water area, the bottom of the cylinder may be lined with chalk, to a depth which restricts the flow of cold water entering the bottom of the cylinder. This could possibly cause the shower to pull air from the vent/expansion pipe.

The cylinder is about fifteen years old at most, so I suspect this may not be the cause.

I've been checking the shower for the last week or so (without the pump switched on) and every time I turn it on, I do get flow, so maybe the air is no longer there. Or maybe it will return when I run the pump?

One thing that concerns me though is that I've read on the web somewhere, that the hot water take off from the cylinder should be horizontal for at least 450mm before tee-ing into the vent pipe, which mine isn't. Is this the case and if so, could it be drawing air from the vent/expansion pipe?

I've got a feeling the problem may return when I run the shower pump for a period of time.

Phil

[Edited on 15-2-09 by Hellfire]

I have a power shower with just over the minimum recommended head of water (and like yours the HW feed goes from the tank, under the floor and then back up to shower), but if I crank the flow up past 1/2 way on the control knob it starts sucking in air and the motor revs it's nuts off. I suspect it's sucking it in through the hot water tank vent/overflow pipe, but not sure how I can fix that.

EDIT: My outlet pipe is also a bit shorter than 450mm before joining the vent pipe, not sure why that would make a difference though.

[Edited on 16/2/09 by MikeRJ]

The chalky deposit theory sounds like b0ll0x. Does the thermostatic valve switch the shower pump off and stop the water flow ? I'd say it's letting the water run back down the pipe and the air is pulling into the cranked section as you first suggested.

quote:

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Originally posted by Peteff
The chalky deposit theory sounds like b0ll0x. Does the thermostatic valve switch the shower pump off and stop the water flow ? I'd say it's letting the water run back down the pipe and the air is pulling into the cranked section as you first suggested.

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There SHOULD be a 450 run from the tank to the vent, in practice this is often not the case.

There may be a calcium build up in the bottom of the cylinder but I suspect this isnt your problem.

Id fit a couple of non return valves immediatly after the pump, (single check, not double).

quote:

---

Originally posted by iiyama
There SHOULD be a 450 run from the tank to the vent, in practice this is often not the case.

---

Phil as you know in not a plumber!!!! so i may be wrong but can you block the air vent pipe in the loft and run the pump to see if it stops air getting to the pump ?
if it dose stop it that's your answer. it must be the way the pipe work is
but dont leave the air pipe blocked for long

Or am a talking cr*p
Graham

OK, Looking at your diagram again, have you piped the pump directly off the top of the cylinder? Or have you fitted a surrey/warrix flange?

If either of the latter then I cant really see what the problem is, other then the pipework having a natural air trap in it.

If the former then Jacko could well be right. When the pump is fired its pulling down on the water in the vent pipe to the extent that its then pulling air.

To stop this you need to fit a surrey/warrix or essex flange.

If you already have one of these fittings fitted then I would fir single check valves on the pressured side of the pump.