Height of vent pipe formula

[PlumBum86]

Does anybody know the formula used to calculate the height of the underside of the open vent pipe to the water level in the cwsc?

Thanks

 

[PlumBum86]

have just found it.....

Height of vent pipe above water level in cwsc = Height (meters of static head) x 40mm + 150mm


For example, let's say that the distance between the static head and the lowest point is 3 meters.

• 3 x 40mm + 150mm = 270mm

270mm would be the height that the open safety vent pipe has to rise above the water level in the hydronic heating system expansion tank when the system is cold.

 

[AWheating]

good to know, thanks! 🙂

 

[tamz]

Clever stuff but the feed and vent is the wrong way around on the drawing you found. Keep looking.
Min 450 is usually adequate for most but if say the boiler was in the loft and the head was 900 above the pump how would you figure that one out?

 

[PlumBum86]

Well noticed with the feed and vent pipe being the wrong way round.

And good question! im not sure?

 

[jase158]

0.9 x 40mm or round up to 1 x 40mm

 

[spanner]

high mate for every metre of the OSV you add an extra 40mm plus another 150mm plus another 200 to prevent any expanded water discharging over into f+e..

 

[fuzzy]

450mm

 

[wickywise]

I am at my wits end trying to solve a venting problem and even though the pipe work has not been changed from when it worked without venting, in desperation I am looking at the height of the vent pipe above the F&E water level. My question refers to the diagram above. When it refers to the "static head and the lowest point", what is the lowest point? Is it the bottom of the lowest radiator or the bottom of the boiler? From the bottom of my radiators it is approximately 6.5 mtr and from the boiler about 5 mtr. The highest point of the vent pipe above the cwsc water level is 350mm. From the formula above it suggests this is about right. Confirmation that this is correct or otherwise, would be much appreciated.

 

[lame plumber]

you need to start your own thread and state exactly what you have been doing to the system to cause an issue, could be just a blockage but give it to us in full then you may get the right answer.

 

[spanner]

Bottom of the hw cyl and f &E if for the hot water system and bottom of the boiler for f &E primaries...:devil::devil:
This is the safety reasons for breakdown or component fail..
However you don't want to be seen discharge of water going through to f&e no matter what orientation of your measurements from top to bottom

 

[sheff paul]

I am at my wits end trying to solve a venting problem and even though the pipe work has not been changed from when it worked without venting, in desperation I am looking at the height of the vent pipe above the F&E water level. My question refers to the diagram above. When it refers to the "static head and the lowest point", what is the lowest point? Is it the bottom of the lowest radiator or the bottom of the boiler? From the bottom of my radiators it is approximately 6.5 mtr and from the boiler about 5 mtr. The highest point of the vent pipe above the cwsc water level is 350mm. From the formula above it suggests this is about right. Confirmation that this is correct or otherwise, would be much appreciated.

Had this problem before ,we always scrap the tank and pressurise the system if the boiler has a overheat stat on it ,which most heat only boilers mid 90's had,you can waste a lot of time trying to stop pump over,remember to change rad valves,and any half rusted rads

 

[wickywise]

you need to start your own thread and state exactly what you have been doing to the system to cause an issue, could be just a blockage but give it to us in full then you may get the right answer.

Thank you lame plumber but being to new to this forum I do not know how to start a new post. But here is what has happened so far:
The problems started three months ago when it was noticed that hot water was venting into the expansion tank. The water level remains the same which suggests the cold water feed is clear.
The pump was suspected to be at fault and was replaced. The venting continued and at the same time the boiler started to performed erratically, sometimes supplying hot water but mostly only warm.
A blockage in the system was suspected near the Aerjet. The pipe work in that area was removed and cleaned. A flushing agent was added and pumped around the system for seven days. The system was then power flushed for eight hours, reversing the flow and flushing each radiator in turn. The ground floor radiators which are fed by micro bore were removed and thoroughly flushed. It is felt now there are no blockages in the system.
The Potterton Suprima 80L boiler has had a new Thermister and new PCB fitted. It is now functioning correctly producing hot water to all sixteen radiators.
However, although the central heating is working well, it continues to vent into the expansion tank but less so when the pump is at lowest speed.
I can confirm the motorised valve is functioning correctly, as is the Hot Water Cylinder. Also an electrician has checked the central heating wiring/thermostats and all are OK. I am checking that 350mm is sufficient height between vent pipe and water level in the CWSC.
Can someone please offer alternative solutions to those already tried. I should add that I have had visits from five different plumbers/heating engineers.

 

[Mike Jackson]

Reading the Suprima manual the suggested configuration for an open vented, fully pumped system is to use a combined feed and vent. This would put an end to any pumping over issues. The diagram is on page 11 of the installation instructions.

 

[lame plumber]

350 would seem to be min clearnace needed. question is was the pump swap like for like or does the new one have a larger head? if everything is done as you state, there would seem to be a blockage causes the pumping over if it never occurred previously. could always follow mj's advice and combine the feed/vent and renew all the pipework in that area. use a magnet to try and see if you can find the blockage (magnetite is magnetic hence why you can trace the blockage in copper pipework)

 

[wickywise]

Thank you very much Mike Jackson and Lame Plumber. Mike, you can obviously see something I can't as the diagram appears to only show a cold water feed. However, you are repeating what one of the plumbers said to me i.e. join the 15mm cold water feed to the 22mm vent pipe and do away with the aerjet. I was reluctant to do this as it seemed strange to discard part of the original installation which has functioned satisfactory for twenty seven years until the latest problem.
I have provided a picture of the area concerned. The 22mm return pipe goes into the aerjet at the bottom. The 22mm vent pipe exits at the top. The curved 22mm pipe from the bottom of the aerjet to the pump has the 15mm cold water feed joined to it with a compression joint.
This is the area of piping that was thoroughly cleaned and there is now a 22mm compression joint just above the aerjet and one further down the 22mm return pipe. Disconnecting the cold water feed and the pump valve makes it relatively easy to remove this section. I don't want to push my luck Mike but would it be possible to explain or give a diagram how exactly I would achieve your suggestion. I understand that measurements could be crucial with this conversion. I should just say that I am unable to bend 22mm pipe but if this is essential I can always get it done.
Reference Lame Plumber's comment about replacements. The plumber who changed the pump (which I believe was an Alpha) said the Apha was not necessary and replaced it with a pump without the faned bit at the top and the variable speed settings. The new pump has three speed settings. I later replaced both valves either side of the pump because one was leaking.
Once again thank you both for your comments and advice.

 

[lame plumber]

you may well find your air separator is sludged up , run a magnet over it to see

 

[Mike Jackson]

Hopefully I've managed to get a screenshot.of the manual.

 

[helpsy]

F&E 450mm
CWSC 150mm + 40mm per metre head

 

[wickywise]

I have decided to follow Mike Jackson's advice and join the cold water feed 15mm pipe to the 22mm vent pipe. Both pipes run parallel from the loft and my only question; is there an optimum point at which the connection should be made. For convenience it would be better to be higher.
I have shown a drawing of my proposed pipe work. The return flow comes up from the floor and is one point five inches behind the line of the pump. The distance between that pipe and the valve to the pump is six point two five inches. This makes it a tight fit to connect the vent pipe but hopefully it will be possible.
It would be easier if the return flow pipe was connected directly to the vent pipe and the feed to the pump teed off it. I feel that if this was done it would encourage water to go straight up the vent pipe rather than to the pump.
Any observations would be much appreciated.

 

[spanner]

I'm bit lost :smile5:!!