Trouble with single pipe system

[John.g]

(Replying to SJB, post #3)

Its recommended that you pump away from the expansion vessel, if the E.vessel is installed as close to the pump (suction) as possible then the pump will run with a head of E.vessel press+pump press so if pump (differential ) head is 0.5bar and E.vessel is 1.0 bar, outlet side of the pump will run at 1.5 bar, if installed on the discharge side of the pump then the pump discharge will be 1 bar and the suction 0.5 bar which even though unlikely can lead to air ingress if high system head losses and perhaps circulation issues.
This pump is running at 1.0 bar stopped and 1.5 bar running so E.vessel may be installed as recommended. Its interesting that all the rads heat up at 1.8 bar. Also very important with any system is the E.vessel pre charge and filling pressure, the filling pressure should always be higher than the pre charge pressure to give a little reserve so that the cold pressure is always at the required pressure.

Regarding the installed 80 litre E.vessel, if one assumes a average hot system temperature of 70C then a pre charge pressure of 1.0 bar with a filling pressure of 1.5 bar will result in a reserve of 16 litres and a final pressure of 1.84 bar ASSUMING the total system volume is 350 litres (I worked backwards), if the pre pressure is increased to 1.8 bar ( to get all rads circulating) then a filling pressure of 2.0 bar will give a reserve of 5.3 litres and a final pressure of 2.31 bar for the same 350 litres.

One way or the other IMO its vital to check those pre charge and filling pressures.

 

[Single pipe Sean]

(Replying to SJB, post #3)

Its recommended that you pump away from the expansion vessel, if the E.vessel is installed as close to the pump (suction) as possible then the pump will run with a head of E.vessel press+pump press so if pump (differential ) head is 0.5bar and E.vessel is 1.0 bar, outlet side of the pump will run at 1.5 bar, if installed on the discharge side of the pump then the pump discharge will be 1 bar and the suction 0.5 bar which even though unlikely can lead to air ingress if high system head losses and perhaps circulation issues.
This pump is running at 1.0 bar stopped and 1.5 bar running so E.vessel may be installed as recommended. Its interesting that all the rads heat up at 1.8 bar. Also very important with any system is the E.vessel pre charge and filling pressure, the filling pressure should always be higher than the pre charge pressure to give a little reserve so that the cold pressure is always at the required pressure.

Regarding the installed 80 litre E.vessel, if one assumes a average hot system temperature of 70C then a pre charge pressure of 1.0 bar with a filling pressure of 1.5 bar will result in a reserve of 16 litres and a final pressure of 1.84 bar ASSUMING the total system volume is 350 litres (I worked backwards), if the pre pressure is increased to 1.8 bar ( to get all rads circulating) then a filling pressure of 2.0 bar will give a reserve of 5.3 litres and a final pressure of 2.31 bar for the same 350 litres.

One way or the other IMO its vital to check those pre charge and filling pressures.

Yes that is interesting. I would say the total volume would be a fair bit higher and more like 600/700l judging by the size of the rads and length of pipe work.

 

[John.g]

OK then, why don't you increase the E.vessel pressure?, if I've interpreted you correctly you said that 1.8 bar is satisfactory.

A 650 lire system with a 80 litre E.vessel and 70C system temp should give the following:
Pre pressure Filling Pressure Final pressure reserve
1.0bar 1.0bar 1.43bar 0 litres
1.0bar 1.5bar 2.21bar 16 litres
1.8bar 2.0bar 2.70bar 5.3litres

 

[Single pipe Sean]

OK then, why don't you increase the E.vessel pressure?, if I've interpreted you correctly you said that 1.8 bar is satisfactory.

A 650 lire system with a 80 litre E.vessel and 70C system temp should give the following:
Pre pressure Filling Pressure Final pressure reserve
1.0bar 1.0bar 1.43bar 0 litres
1.0bar 1.5bar 2.21bar 16 litres
1.8bar 2.0bar 2.70bar 5.3litres

Yes I shall try that. As if left untouched the boiler will just stay at 1 bar and won’t drop below which is why I’m still doubtful there’s a leak.
Thank you

 

[cr0ft]

It’s very common to have leaks that only happen when above a certain pressure level.

 

[Single pipe Sean]

Hi Guys,
For those of you who are still interested.
Pressure in the expansion vessel has been increased and everything seems to be working perfectly for the last few days, no topping up! Not sure if this has solved it I shall keep an eye on it over the weekend!
Thanks again for all your advice.

 

[John.g]

What is the pressure cold and then hot, if you don't mind?

 

[Single pipe Sean]

What is the pressure cold and then hot, if you don't mind?

1 bar cold and 1.7bar hot (70degrees) which seems to be doing the trick fingers crossed.

 

[John.g]

Thanks, just trying to get a feel for your system contents, based on that and assuming a 70/60C flow/return temp.
The 80 litre E.vessel with a pre charge pressure of 0.5 bar and a filling pressure of 1.0 bar (reserve of 20 litres) with a final pressure of 1.7 bar would mean a system contents of 850 litres. A pre charge pressure is 1.0 bar (no reserve) would mean a system contents of 1125 Litres.

 

[Single pipe Sean]

Thanks, just trying to get a feel for your system contents, based on that and assuming a 70/60C flow/return temp.
The 80 litre E.vessel with a pre charge pressure of 0.5 bar and a filling pressure of 1.0 bar (reserve of 20 litres) with a final pressure of 1.7 bar would mean a system contents of 850 litres. A pre charge pressure is 1.0 bar (no reserve) would mean a system contents of 1125 Litres.

Evening John,
The expansion vessel is at 2.1bar,
What does this mean?