Lenght Of Vent Pipe to Prevent air intake on pump start up ?

[dannyo]

My hot water vent pipe rises 200mm above the HW in pipe going into the 3 port valve.

Is this long enough?

I have recently installed a new Grundfos 15-60 pump (for 8 rads) however I think it is sucking in air on start up due to pump inertia and I suspect it is coming down the manual bleed valve on the vent pipe.

Can anyone tell me how long a vent pipe should be to prevent air intake on such a pump. The manual bleed valve is a total of 600mm in height above the pump.

My pump works great as long as I bleed it after start up. I am thinking of extending the length of the pipe as well as adding an automatic bleed valve?

I would really appreciate any input as I am a novice!

 

[chrishutt]

It all depends on the general arrangement of your system. Can you describe the location of boiler, F&E pipe and tank, vent pipe and rads in relation to the pump?

 

[namsag]

Standard 8 rad system should only have a 15/50 fitted .If using larger pump speed 1 or 2 should be used.

 

[dannyo]

Thanks for response.

Boiler is downstairs. Hotwater tank is in airing cupboard on level 3. Pump is just above floor level in airing cupboard with h/w pipe feeding into tank through a 3 port valve. Other port goes off to heating. Vent pipe is located after 3 port valve next to water tank. Radiators are on 3 levels and there is 8.

I fitted a Grundfos 15-60 as this was the same rating as the pump that I took off. I have it running on speed one.

Hope you can make sense of what I describe?

 

[dannyo]

Would really appreciate some advice on the above problems if possible!

 

[doitall]

What you are saying sounds all wrong to me.

Look in my profile and email me a drawing or photo.

 

[dannyo]

sorry but I do not know how to look into your profile.

What in particular do you think sounds wrong?

 

[chrishutt]

You have not said where the main vent pipe and the F&E tank and connection is in the circuit, even though you were asked to do this .
The 200mm vent pipe you refer to is just a stub with a manual opening cap at the end - that's not the vent pipe.

 

[dannyo]

Sorry I did not understand the question as I a novice.

Can you give me a bit more information on what the main vent pipe and the F&E tank and connection are and I will find out hwere they are for you?

 

[chrishutt]

Check out this and then answer the above questions.

 

[dannyo]

I will have a look today although I will struggle to draw a full diagram as I am a plumbing novice.

Could you answer me one quick question - would it do any harm to change the manual bleed valve to an automatic bleed valve so that any air sucked in on pump start is is blown back again straight away? Or should I consider extending the length of the bleed pipe I am not sure if this would help.

Can you advise?

 

[ChrisR]

L:eave the bleed manual for now. Automatic ones can let air in.

If you have MS WORD try a sketch in that, then email it to one of us. If you go up a level from here and click on our name it'll show our Profile.


You can send us the .doc file, or Save As html and you'll get a subdirectory with a jpeg in it, which you can send us or stick in an online photo repository like photobucket.

 

[chrishutt]

You can send us the .doc file, or Save As html and you'll get a subdirectory with a jpeg in it, which you can send us or stick in an online photo repository like photobucket.

Might be a bit techy for our novice.

Dannyo, you don't need to draw a diagram. Just follow the pipework from the boiler up to the pump. Are there any pipe branches on this? If so, where do they go?

Alternatively, have a look around in your roof space or other high places for the Feed & Expansion tank. It's usually a black plastic effort, about 400 x 300 x 300 with 3 pipes connected to it. The one that ends above it, pointing downwards, is the vent pipe. Follow these pipes back to see where they join the system.

 

[dannyo]

Here goes and apologies if this makes no sense!

Tank in loft of 3rd floor, pump in airing cupboard on 3rd floor and boiler down stairs.
2 large pipes and 1 small pipe going from boiler to airing cupboard.
Description of airing cupboard area.
Small dia pipe from airing cupboard to loft, large dia pipe from airing cupboard floor to pump with a split going to join small dia pipe.
Pipe from pump to 3 port valve + split to small dia pipe going upto loft. From 3 port valve to rads and water tank and manual bleed valve pipe.
Pipe from bottom of tank joins small pipe to loft and also a large diameter pipe which I think is carrying cold water.

Hope the above makes sense and would really welcome any suggestions.

 

[chrishutt]

We need to know where the various branches (tees, splits, whatever) are in relation to the pump. It sounds like there is one before the pump and one after the pump, which might explain why you have a problem.

Also you haven't followed the pipes through to the loft to see which does what. If you can't be bothered to do this properly you'd better just call in a heating engineer.