Pump sucking in air

[stevethejoiner]

I have converted a none residential building for habitation and have had a problem with water pressure and flow rate to a shower.

Set up is as follows.

Gravity, open vented, with indirect cylinder, with woodstove for heat source.

Some of the pipework to what is now a bathroom was already in place and run in 15mm so is not ideal for a shower on gravity system with poor head.

Also I found we had fantastically high pressure on the incoming water main and with poor flow on the hot side the shower was useless so I installed a pump on the floor at the bottom of the cylinder to the hot supply.
I chose a Stuart Turner universal single 3 bar

The problem is the pump is pulling air in from the open vent. Turner,s technical just said bleed the pump, which I did but still have the problem. The water comes through in spits and spats, like you get when you first turn a tap on after you have had the water off, but unlike a temporary supply interruption it does not clear itself, it continues all the time. I have confirmed it is air from the expansion as I have TEMPORARILY installed a valve so I can isolate the expansion, and when I do this, the pump works beautifully, open the valve again and the hot flow is rubbish again.

I am thinking I can replace this TEMPORARY valve in the expansion and install a one way valve so air cannot come down but it will still work as it should in the event of cylinder overheat. But I know this is not normal practice and there may be a cause that I cannot identify.

Untitled

• stevethejoiner
• 27 Dec 2011
• 1

I could not find a way to add text to the drawing so to clarify:
The pump is on the ceiling on the left hand side of the drawing. Pipework to and from the wood stove is 28mm. The supplies to and from the Turner pump is in 22mm but this reduces to 15mm when it drops through the ceiling into the original hot flow pipework.

 

[Dan Robinson]

That would be incredibly dumb.

Read the pump's manual and fit a surrey or Essex range to the cylinder and do things properly.

 

[stevethejoiner]

That would be incredibly dumb.

Read the pump's manual and fit a surrey or Essex range to the cylinder and do things properly.

Thank you for your response.

But can I first say, being incredibly dumb would be doing something you do not have knowledge about without asking, I am asking for advice, so actually quite sensible.

I would read the manual, but pump purchased 2nd hand without a manual, thus the phone call to Turner's technical department.

And your recommendation of surrey/essex flange is a good one, thank you.

 

[Dan Robinson]

I wasn't implying that you were dumb...merely that doing as you wanted would have been.

It is always a good idea to download manuals for things like this then it maks things easy.

 

[dcawkwell]

chuck the pump and get an unvented cylinder

it sounds as if the pump is drawing water faster than the header tank can supply it hence pulling in air

 

[alex444]

An open vent is no longer open when you fit a valve to it and close it, it may make your pump work properly but it then blocks the route of expansion.

Best way to avoid air problems is just to have a read through shower pump instructions and tick off each point on installation, as Dan said, using for example a surrey flange would most likely sort it.

Alex

 

[stevethejoiner]

chuck the pump and get an unvented cylinder

it sounds as if the pump is drawing water faster than the header tank can supply it hence pulling in air

You did not read all of my post or realise that a wood fired appliance requires a vented set up. But it certainly is drawing air faster than the water it requires.

 

[stevethejoiner]

An open vent is no longer open when you fit a valve to it and close it, it may make your pump work properly but it then blocks the route of expansion.

Best way to avoid air problems is just to have a read through shower pump instructions and tick off each point on installation, as Dan said, using for example a surrey flange would most likely sort it.

Alex

I did not fit a valve to solve the problem, it was an experiment to find out if the air was coming from the expansion pipe, and is certainly not left closed, so the system still is vented. And as Dan say's, I shall install a Surrey flange.

Thank you.

 

[Dan Robinson]

Good man.

 

[Boilerman2]

Try isolating the cold feed to the cylinder and then open a hot tap with a non-return valve in the open vent watch the cyliner colpase -still its easy to transport it to the scrapyard afterwards!!

 

[stevethejoiner]

Try isolating the cold feed to the cylinder and then open a hot tap with a non-return valve in the open vent watch the cyliner colpase -still its easy to transport it to the scrapyard afterwards!!

Brilliant reply.
You see, asking questions and waiting for replies before you act (especially ones which explain the consequences of what could happen with your theory), makes sense.

Thanks.

 

[dcawkwell]

to be honest although i am sure someone will correct me i cant see the point of the expansion pipe since even if this wasnt there any expansion would simply go back up the cold feed pipe so i would keep the valve closed if that is working for you

 

[gaswizzard]

to be honest although i am sure someone will correct me i cant see the point of the expansion pipe since even if this wasnt there any expansion would simply go back up the cold feed pipe so i would keep the valve closed if that is working for you

...........and if the cold feed got blocked/shut off/frozen? , cylinder would collapse.

The other point to remember is if the pump is drawing off more water than the cold feed can deliver the cylinder WILL collapse.

Another point being if the cold feed were to be issolated then cylinder could explode due to expansion upon heating.

 

[Dan Robinson]

to be honest although i am sure someone will correct me i cant see the point of the expansion pipe since even if this wasnt there any expansion would simply go back up the cold feed pipe so i would keep the valve closed if that is working for you

Oh dear....

 

[dcawkwell]

to be honest although i am sure someone will correct me i cant see the point of the expansion pipe since even if this wasnt there any expansion would simply go back up the cold feed pipe so i would keep the valve closed if that is working for you

...........and if the cold feed got blocked/shut off/frozen? , cylinder would collapse.

how? if cold feed is frozen then there can be no flow of water except the few litres in the pipes below the cylinder. cant see that collapsing a cylinder. even then the movement of expansion in coldfeed due to heating is likely to make this less likely
lets revise it and say have the valve open just ever so slightly
that should cure the problem. but whatever works.
oh for modern systems instead of dark ages stuff