Excelsior Unvented HW Cylinder.

[Johntheo5]

Has anyone any experience of these which have a venturi to maintain the internal air gap?.

 

[muggles]

I've got a customer with one. Doesn't seem to work any better than any other type of air gap cylinder - still needs the air gap recharging every year

 

[Johntheo5]

My fear was that it might pull in too much air resulting in the air gap increasing and causing problems if it got close to the dip tube HW outlet.

 

[Nigel L]

I had one of these installed thinking it was a good idea but unfortunately the venturi device does not draw in sufficient air to keep the air gap replenished. After several months I find the vent pipe outside is dripping when the tank is being heated and I have to shut off the cold inlet, fit a hose to the drain cock and run off about ten litres of water to replenish the air gap. I am going to get an expansion vessel fitted next time the system is serviced which will solve the problem. However, these tanks are supposed to eliminate the need for an expansion vessel which was why I opted for it. I did wonder at the time why these cylinders were not more commonly used if they were as good as they are claimed to be. If something is too good to be true then it probably is not all it seems. Maybe if you run lots of hot baths and there is prolonged rapid water flow the venturi will perform adequately but for showering and hand washing it is definitely inadequate. It would be better if it over performed as that would only cause a small amount of problems air to be pushed out of the hot taps along with the water and it would be a reassuring sign that the air space was being maintained. My advice is to stick with a conventional unvented cylinder and have an expansion vessel fitted on the cold inlet between the non return valve and tank. That will need less maintenance than this supposedly maintenance free system.

 

[Nigel L]

My fear was that it might pull in too much air resulting in the air gap increasing and causing problems if it got close to the dip tube HW outlet.

If it did pull in too much air then the worst it would do is spit out air bubbles along with the hot water. Maybe a bit messy if the water splashed a lot when this happened but the opposite problem is more likely and you end up with insufficient air in the tank and the pressure gets too high when the water is heated. If air in the hot water was a problem it could always be overcome with an automatic air vent.