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.

 

[Best]

If the system had no push fit, then I would try to convince the customer the benefits of a sealed heating system

 

[ShaunCorbs]

If the system had no push fit, then I would try to convince the customer the benefits of a sealed heating system

Already tried won't have it (think it's been diy soldered)

 

[sammathias]

If the system had no push fit, then I would try to convince the customer the benefits of a sealed heating system

I'd like to think pushfit can with Stand 1bar!! Although I dispise the stuff.

 

[Best]

I'd like to think pushfit can with Stand 1bar!! Although I dispise the stuff.

Only reason I mentioned push fit as a risk is I hear of some coming apart.
One customer has the expansion vessel and filling loop in attic and kept the pressure to nearly zero because he said a push fit fitting below his hall floor had once come off. Worry is he had since put hardwood flooring over the hall.

 

[ShaunCorbs]

Normally no inserts used

 

[fixitflav]

But I wouldn’t be sure if it would pump over

Why would it pump over, if the headloss between open vent and cold feed is < height of vent loop above F/E tank TWL? Which it must be anyway to avoid over-pumping, however the system is arranged.

 

[fixitflav]

Technically it is before the pump

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

If the F/E tank and pipework are existing, why go to the expense of changing to an expansion vessel? You would still need to decide where to connect it (ideally between boiler and pump IMO)

 

[Best]

Difficult to say Shaun what you should do. If you combined the feed and vent I think would be wrong as I find that causes systems to corrode.
Pity you can’t install new feed & exp tank and new vent and feed pipework at boiler end.
One solution would be neutral point installed where the feed and vent could then come off it. But am sure you don’t want to do that.
I am actually having the same problem trying to decide how I convert a gravity hot water/pumped rads to all pumped on a very old system, without pump over or corrosion.

 

[Best]

Why would it pump over, if the headloss between open vent and cold feed is < height of vent loop above F/E tank TWL? Which it must be anyway to avoid over-pumping, however the system is arranged.

If you are right, then that is his answer just to go with vent and feed ahead of pump. I would wonder if most of zones are closed, would it still be ok.
Where possible I would seal systems because the cost is very little (if vessel size required is not large).

 

[oilmark]

Open vented system must have vent from flow on boiler before any other connection.

 

[Best]

Open vented system must have vent from flow on boiler before any other connection.

Virtually all open vent systems (except gravity to cylinder) I know of in my area are done with the vent off the flow at cylinder and feed off the cyl return.
Pump is at boiler. They usually work fine, but some factors make it likely to pump over if cylinder is close to boiler and pump on a non zoned system, or where many rads and zones turn off.

 

[Ric2013]

What if you reverse the flow and return under the pump in your diagram and have the pump pushing into the boiler? Also reverse the feed and vent so vent remains the first tee after the boiler? Negative pressure system, and microleaks at rad valves will let air in etc, but would be safer than your diagram.

 

[ShaunCorbs]

ive decided to put the pump on the return and keep the feed and vent to spec if it does pump over will give him the option to leave or seal it

 

[Ric2013]

Excellent!

An old boy told me the pump will last longer if it is running on the cooler return water, hence the old way of doing it with the pump on the return. Don't bleed the rads with the pump running, though

Nos da

 

[ShaunCorbs]

Excellent!

An old boy told me the pump will last longer if it is running on the cooler return water, hence the old way of doing it with the pump on the return. Don't bleed the rads with the pump running, though

Nos da

cyfaill hen nos dda