Position of expansion vessel on unvented cylinder...

[Stroker]

I acquired a G3 certificate just a few months ago, so haven't yet had exposure to many different installations. One I came across last week: Gledhill 210 StainlessLite tank, the expansion vessel is plumbed directly into the Secondary Return port. There is a specific port available on the expansion relief valve, which is still plugged (from factory). Has anyone seen this configuration before? Any reason why one would use the SR port in preference to the ERV port?

 

[hard-work]

If the secondary port is half way up the cylinder it does make sense. Many have the vessel on the cold feed which is right at the bottom. Many do not like the vessel on the hot water draw-off as it is exposed to heat. The cold feed is away from the parts that matter at the top. The secondary port further up is a good compromise.

 

[Stroker]

Thanks. I'm wondering if there is an increased risk of legionella with this set up...the water in the vessel being relatively static and warmed (largely by conduction through the pipe from the cylinder)?

 

[hard-work]

As long at the water coming out of the draw-off has been at 60C all is OK.

 

[Gasguru]

The port on the expansion PRV might be for the balanced cold take-off...you'd need to ascertain where the non return valve is located, sometimes they are located within the expansion valve manifold.
I've seen a few cylinders where the vessel has been plumbed in such a way and is upstream of the non return valve and therefore ineffective.
The vessel should be on the cold cylinder inlet side.

 

[hard-work]

Some are on the hot. As is this. White vessels can be on the hot and blue only on the cold.

 

[muggles]

White vessels can be on the hot and blue only on the cold.

That's an interesting theory. What about green ones?

 

[hard-work]

Prefer pink and yellow polka dot myself.

 

[Madrab]

MI's are what you want to follow. The manufacturer will specify where on the system the EV should be placed - most ask for the EV to be cut into the cold feed to the cylinder after the NRV and combi valve.

A lot of installers will use the hot outlet side of things as it's easier to pipe and locate within the confines of a cupboard where a lot of cylinders are located.

Ultimately, in either orientation, the EV carries out the same function of protecting the cylinder from expansion when heating.