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

 

[64degrees]

I’d go with a robokit and pressurise the system, never seen it cause the pipework to fail, and if it stays open vent the air in the system will cause bigger problems in time.

 

[king of pipes]

Normally no inserts used

Seen that happen Shaun quite a few times bud i had the same issue with the Worcester classic system I posted on here couple of months a go pipework was poorly installed cast your mind back I sealed it but as I said the working pressure was set to a bar not much more than a open vent system worcesters dont work on a pressure switch so you can run it on low system head low as 0.5 bar worth considering bud good luck kop

 

[Best]

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

I do a lot of plumbing repair jobs, and you are correct about pumps lasting on the return much longer. I noticed over the years that pumps on oil boilers fitted to the return where lasting 20 or more years and their rubber washers weren’t perishing.

 

[ShaunCorbs]

Nice rads kop

 

[fixitflav]

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

That wasn't one of your original options, but that would be OK.
Should then be open vent - cold feed - pump - boiler. You definitely don't want the cold feed on the discharge side of the pump or there's a good chance there will be negative pressure somewhere, if pump DP is 8m.
As I'm sure you know, the open vent and cold feed should be no more than 150mm apart to avoid risk of over-pumping, but where they are in the circuit relative to other kit is irrelevant.

 

[fixitflav]

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.

I would guess they are old systems. I bought 1st house in 1972 which was piped like that, but it was going out of favour vs boiler - open vent - cold feed - pump then or shortly after, due to the issue of seesawing causing aerated water entry. I modified it, and piping was simpler as the cold feed point was then directly below the F/E tank.

 

[ShaunCorbs]

That wasn't one of your original options, but that would be OK.
Should then be open vent - cold feed - pump - boiler. You definitely don't want the cold feed on the discharge side of the pump or there's a good chance there will be negative pressure somewhere, if pump DP is 8m.
As I'm sure you know, the open vent and cold feed should be no more than 150mm apart to avoid risk of over-pumping, but where they are in the circuit relative to other kit is irrelevant.

No it wasn't as it would be under neg pressure

Can't get the vent and feed before pump unless it's on the return as it's an ab roof, which isn't the best as it won't vent if the boiler boils

It's a bloody catch 22

 

[fixitflav]

as it would be under neg pressure

Not sure I understand that. It won't be under negative pressure if the cold feed is on the pump suction pipe.

Can't get the vent and feed before pump unless it's on the return as it's an ab roof, which isn't the best as it won't vent if the boiler boils

Hard to say without knowing the details. You've clearly looked at lots of options so it's unlikely I can add anything, but I'm game to try if you want, no doubt others here will too.
The bit about the boiler boiling - is it solid fuel? I didn't think boiling was an issue with gas or oil, as there are control and limit-stats.

 

[ShaunCorbs]

Not sure I understand that. It won't be under negative pressure if the cold feed is on the pump suction pipe.

Hard to say without knowing the details. You've clearly looked at lots of options so it's unlikely I can add anything, but I'm game to try if you want, no doubt others here will too.
The bit about the boiler boiling - is it solid fuel? I didn't think boiling was an issue with gas or oil, as there are control and limit-stats.

it would go

pump on return pushing into boiler
feed on flow
vent on flow

there is an always risk in certain circumstances eg if a stat goes bad etc

 

[fixitflav]

pump on return pushing into boiler
feed on flow
vent on flow

I'd be a bit nervous with that arrangement. I did sketch below based on some assumptions:-
Pump DP 8m, total system loss 8, 3m across boiler, 5m across rads and pipework
TWL in F/E tank 3m above fill point on pipe
Boiler, pump and rads are all at same level
Shows pressure -2m after the rads. The assumptions won't be spot on and it could be refined to allow for different levels, so it might be OK in practice, specially if it's a tall building so plenty of head from the F/E tank. On the other hand, it might be worse.

there is an always risk in certain circumstances eg if a stat goes bad etc

What precautions are normally taken which you can't do on this job? I'm curious because it might apply to my house!

PS I hope you're charging the customer double time!

 

[ShaunCorbs]

tbh these days seal the system unless its ropy like the one im doing

and some boilers have flow switches in dont fire unless theres flow

 

[Vee]

Why not seal without pressurising. Use the header as top up, with gate and non return fitted. Sealed system controls as required with heat only or system boiler ( Worcester Cdi used to not need minimum pressure to operate, but check with them).

 

[ShaunCorbs]

Why not seal without pressurising. Use the header as top up, with gate and non return fitted. Sealed system controls as required with heat only or system boiler ( Worcester Cdi used to not need minimum pressure to operate, but check with them).

thats not a bad shout would the non return open tho also would need a prv

 

[Vee]

Non return is to stop the water backing up into the header. Therefore system controls required, i.e PRV and expansion vessel required either external or internal to boiler (system). Doesn’t need filling loop as header acts as top up vessel. Works a treat without stressing existing pipe work. As the system is sealed and there is no open vent non return will stay shut as for air to get in water would need to get out.

 

[ShaunCorbs]

Non return is to stop the water backing up into the header. Therefore system controls required, i.e PRV and expansion vessel required either external or internal to boiler (system). Doesn’t need filling loop as header acts as top up vessel. Works a treat without stressing existing pipe work.

yea but would it open under gravity and not stick

 

[Vee]

See edit above.

 

[Vee]

yea but would it open under gravity and not stick

Have got two systems like this operational now in their sixth year and no problems.

 

[ShaunCorbs]

Have got two systems like this operational now in their sixth year and no problems.

head of the tanks vs the position of check?

 

[Vee]

Top of system for header. Followed by gate or lever in downfeed, so you can turn system of and for easy replacement of check valve. I positioned them in airing cupboard. Check valve can be anywhere between isolation valve and where it tees into the system.

 

[ShaunCorbs]

Top of system for header. Followed by gate or lever in downfeed, so you can turn system of and for easy replacement of check valve. I positioned them in airing cupboard. Check valve can be anywhere between isolation valve and where it tees into the system.

Trying to work out how much head you have

 

[Vee]

Trying to work out how much head you have

Not sure how to read that?

 

[fixitflav]

Use the header as top up, with gate and non return fitted.

Does the gate valve stay open in normal operation?

I can't see how this differs from just having an expansion vessel, but with pre-charge pressure somewhat lower than normal.
Still need to put the expansion vessel connection in the right place, to avoid having negative pressure somewhere.

 

[fixitflav]

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.

I converted mine about 20 years back. Old cast iron floorstanding boiler, gravity HW, pump next to boiler, pumping downwards. No controls. Cold feed to boiler return.
Scrapped the boiler and installed wall-mounted condensing. Moved the pump to the airing cupboard, added diverter valve (system W), open vent, cold feed and DV in the airing cupboard. Added cylinder and room stats. Re-used the gravity 28mm pipes as pump suction and cylinder return.
Still working OK.

 

[Vee]

Does the gate valve stay open in normal operation?

I can't see how this differs from just having an expansion vessel, but with pre-charge pressure somewhat lower than normal.
Still need to put the expansion vessel connection in the right place, to avoid having negative pressure somewhere.

Gate valve stays open. Ans yes you can just seal, add vessel and PRV and have virtually no pressure. Its just convenient using the existing header instead of a filling loop if its already there.

 

[fixitflav]

Gate valve stays open. Ans yes you can just seal, add vessel and PRV and have virtually no pressure. Its just convenient using the existing header instead of a filling loop if its already there.

OK thanks