Combined F&E

Trapeze

Iv'e been reading through some old threads here and I see that @John.G has a combined F+E pipe. I understand the benefits of such a piping arrangement. But I'm at a loss to understand what use the hook-over piece of pipe is. It seems to me that it has no use in such an arrangement. Can anyone explain it to me please?

John.G

Strictly speaking, only required if there is a isolating valve on the cold feed but I feel it does serve a purpose when filling the system after drain down, the system requires filling very slowly, I have a isolation valve on the F&E tank filling line before the ballcock and I just crack this open while refilling as I feel that the water can slowly trickle down the common pipe and the air can vent upwards through the same pipe, I have never had a problem with using this method, some do when refilling too rapidly, but slow filling without any vent might achieve the same results. My system was installed with the combined system 50 years ago and I have never had a problem.

Trapeze

Thanks for replying, but I fail to see what having a valve before the ball cock has to do with the f+e. What am I not understanding here. 😕

Edit, I understand the reason for that valve at ballcock (let's you know if you have a leak) but I don't see how it makes a difference to the combined f and e .

John.G

The difference it can make is when the system is being refilled after drain down, when refilling a lot of air has to be pushed out of the system, if the filling is very slow then it gives the air a pathway up through the common vent&feed pipe while the water is slowly trickling down through the same pipe, if the system is allowed to fill unrestriced then the air can't vent resulting in days of venting the rads continuously otherwise, to vent the air.