Converting close coupled to combined feed & vent
- Thread starter nairb999
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I know all responses are with best intentions but I have 2 conflicting bits of advice on changing my closely coupled vent/feed arrangement
One solution is to convert to combined vent/feed and dispense with vent. The other solution it lower the t into the pump.
Can anybody mediate ?
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Recommendations from technical design publications have generally said the feed pipe should be of sufficient capacity to hold approximately 3% of the system volume...the reason being the system water does not get "expanded" up into the F&E cistern each time the system heats up.
However, this is often impractical (unless surge tanks or very oversized feed pipework is used) especially where the cistern is only just above the connection point.
Did you bale out the F&E cistern before you initially drained down, otherwise allsorts of muck could be in the system.
The H pattern you have is a perfectly acceptable setup...I suggest you cut out the vent tee section and check this is clear. Also check the vent pipework is clear. Does the vent pipe rise vertically and then bend over the cistern, perhaps it runs up to the roof and then dips lower before looping over the cistern. This would allow water to act as a trap and inhibit proper venting. An image of the F&E pipework in the roof would be useful including the inside of the vessel showing float level etc.
Have you also checked the gland nut on the pump inlet valve is tight. Did you use PTFE tape or copperease grease on the pump union threads to ensure the fitting is sufficiently tight. Sometimes air can be drawn in through valve stems etc.
However, this is often impractical (unless surge tanks or very oversized feed pipework is used) especially where the cistern is only just above the connection point.
Did you bale out the F&E cistern before you initially drained down, otherwise allsorts of muck could be in the system.
The H pattern you have is a perfectly acceptable setup...I suggest you cut out the vent tee section and check this is clear. Also check the vent pipework is clear. Does the vent pipe rise vertically and then bend over the cistern, perhaps it runs up to the roof and then dips lower before looping over the cistern. This would allow water to act as a trap and inhibit proper venting. An image of the F&E pipework in the roof would be useful including the inside of the vessel showing float level etc.
Have you also checked the gland nut on the pump inlet valve is tight. Did you use PTFE tape or copperease grease on the pump union threads to ensure the fitting is sufficiently tight. Sometimes air can be drawn in through valve stems etc.
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Yes
When I fitted the new 22mm feed pipe I cleaned out the black lining in the pipes that were put back. All the pipe down the left hand side is new
I wrapped the olives in PTFE tape but not the treads. Air has always been a problem with this 10 year old system hence why I was opting for combined feed/vent option
Is he suggesting linking the vent pipe into the feed pipe
The "close coupled" feed and vent is so called because the two pipes are connected very close close together (hence the recomended maximum of 150mm) and their connections are therefore under virtually the same pressure.
I would be surpirised if going for a combined feed and vent makes any difference. Are you sure the vent pipe rises vertically all the way? It looks from your images that this is old pipework - ie painted, have you confirmed there is no blockage/partial blockage in the pipe.
Combined feed and vent don't always vent particularly well especially when initally filling. You could though cap off the vent pipe just above the tee, then tee in a new vent pipe near the feed outlet of the cistern.
How high was the water level set in the F&E vessel, it is often set too high (the float arm is not bent down) resulting in serious corrocion as water is expelled through the overflow when the system expands in volume.
I would be surpirised if going for a combined feed and vent makes any difference. Are you sure the vent pipe rises vertically all the way? It looks from your images that this is old pipework - ie painted, have you confirmed there is no blockage/partial blockage in the pipe.
Combined feed and vent don't always vent particularly well especially when initally filling. You could though cap off the vent pipe just above the tee, then tee in a new vent pipe near the feed outlet of the cistern.
How high was the water level set in the F&E vessel, it is often set too high (the float arm is not bent down) resulting in serious corrocion as water is expelled through the overflow when the system expands in volume.
The vent pipe is definetely clear as I managed to rig up mains water to the vent pipe and at very low pressure water was entering the expansion tank. Also I have done the jam jar test at start up and watched water sucked up the pipe for a second before returning to normal level. The vent pipe rises nearly a meter above the tank before dropping down to just under the tank cover whcih is a very tight fit
I think this is what Agile was recommending. What do you think about installing a bleed valve when I cap off
Water level is 175 mm .
Sticking mains pressure water through a pipe is NOT the same as checking the pipe is clear...use a lenght of hose pushed through. Mains water could easily pass through a 5 mm squared hole, a lot different than 300 mm cross section of a 22mm pipe.
Forget the jam jar test...not really telling you much. An initial small surge is normal. As the pump starts it will have a tendency to pull down water via the F&E feed and expansion pipes especially if there is air trapped in the system. The positive pressure from the pump outlet will compress the air initially before circulating the water.
Ideally the water level should be perhaps 50mm above the feed outlet allowing plenty of expansion capacity.
You could stick a vent on the "capped pipe"...use a 1/2" standard radiator vent plug fitted to a 1/2" female iron ccoupling. All the other vents merchants sell are carp.
Forget the jam jar test...not really telling you much. An initial small surge is normal. As the pump starts it will have a tendency to pull down water via the F&E feed and expansion pipes especially if there is air trapped in the system. The positive pressure from the pump outlet will compress the air initially before circulating the water.
Ideally the water level should be perhaps 50mm above the feed outlet allowing plenty of expansion capacity.
You could stick a vent on the "capped pipe"...use a 1/2" standard radiator vent plug fitted to a 1/2" female iron ccoupling. All the other vents merchants sell are carp.
fortunately I used a number of compression joints so I can easily split the vent pipe above the t and try the "pipe" test. if no problems I could try combined vent/feed method as you suggest.
Will also change tank level
thanks for your input and that of all other forum members
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