Feed and Vent fun :DDDDD

[ShaunCorbs]

does the feed and vent need to onto the flow pipework, i have a situation where is would be better if it could go on the return pipework

something like below

i think it does due to the vent

reason for this its an 8m pump and he wont seal it

 

[rpm]

Edit; see below.

 

[ShaunCorbs]

Shaun what have I told you about laying off the sheep dip.

but its a friday

 

[rpm]

does the feed and vent need to onto the flow pipework, i have a situation where is would be better if it could go on the return pipework

something like below

i think it does due to the vent

reason for this its an 8m pump and he wont seal it

View attachment 33931

What have I told you about laying off the sheep dip.

 

[Best]

[I know it is hot weather and around holiday season, but what has happened this forum? Where has everyone gone?]
Re the question, - Vent would be on the positive side of the pump unfortunately if you did it like in your diagram.
But I wouldn’t be sure if it would pump over

 

[ShaunCorbs]

[I know it is hot weather and around holiday season, but what has happened this forum? Where has everyone gone?]
Re the question, - Vent would be on the positive side of the pump unfortunately if you did it like in your diagram.
But I wouldn’t be sure if it would pump over

The thing is it would suck air in if I flipped them round to make feed first

Really wish he would seal the bloody thing 25+ rads

 

[king of pipes]

Come on Shaun you know the answer here bud cold feed and vent needs to be before the pump as the far right diagram you will have air issues and pumping over if not at a push cold feed can go in the return but could still pump over , seal it mate your the heating engineer fit and set a PRV on the filling loop so the system can never be over pressurised is my advise. Cheers kop

 

[ShaunCorbs]

Come on Shaun you know the answer here bud cold feed and vent needs to be before the pump as the far right diagram you will have air issues and pumping over if not at a push cold feed can go in the return but could still pump over , seal it mate your the heating engineer fit and set a PRV on the filling loop so the system can never be over pressurised is my advise. Cheers kop

Technically it is before the pump

And he won't seal it due to him thinking it won't take the pressure

 

[Gasmk1]

convince him to seal it and use an auto filler set at 1 bar or just below with blow off at 2 bar.

 

[fixitflav]

The thing is it would suck air in if I flipped them round to make feed first

Really wish he would seal the bloody thing 25+ rads

View attachment 33932

Ideally, should be boiler - open vent - cold feed - pump. That's the best arrangement to vent air, which is most likely to come from the boiler, specially on initial commissioning. Also as the cold feed sets the reference pressure for the system, gives lowest risk of anywhere being below atmospheric pressure, as you obviously don't want inward air leaks.
But there shouldn't be a problem putting both on the return as your original sketch, if the height between the boiler outlet and the F/E tank is adequate. The point of minimum pressure is then boiler discharge, and = static pressure from the F/E tank minus boiler headloss, so likely to be well above atmospheric with usual boiler headloss figure. 8m seems high for the pump, but if the complete system does have this friction loss, most of that won't be across the boiler.
Your 3 pump positions diagrams would be more useful if the locations of the boiler and rads were shown. Comments shown are correct, IMO.
No.1 is poor because the minimum pressure is F/E tank static pressure minus total system loss, so if loss is 8m, could be below atmospheric.
No.2 is a non-starter as there will be over-pumping if the pump head is above the height from F/E tank TWL to the top of the vent pipe, typically 0.45m, as it almost certainly will be.
No.3 is OK, could be either of your original options, depending on whether the boiler is to the left of the open vent or between the cold feed and the pump.