Posted by: @saf1973

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the exact model number 1100001955 is not listed in the manual and they do have "vertical and Horizontal" models.   But to me this one looks like it should be Vertical as it has a wall brace.

Anyone else have this installed or experience of these?

Thanks for including a photo @saf1973

I have five expansion vessels of differing sizes and orientations.
But it has much to do with me having a well and no mains water supply!  😎 

All of these are self-installed, and I've had to replace one due to a failed membrane.
Three are for potable (treated) water, and the others for expansion in heating circuits.

The good news is that I therefore have the experience you're looking for!

The quote from the Zilmet site "Expansion vessels should always be installed in a vertical orientation with the water connection at the bottom" needs context.
It is not always the case.

Domestic well-pumps are often supplied with a horizontal expansion vessel beneath them - for which Zilmet is one of the manufacturers!

Nor is a welded bracket an indication of the preferred orientation.

Different models of expansion vessel are required depending on the 'type of water' in the system they are connected to.

Potable water, suitable for drinking, is usually connected to a vessel painted blue if it is made with cast mild steel.
But it can be left unpainted if stainless steel is chosen.

If the fluid contains system inhibitor chemicals, such as that which runs through radiators, then the vessel manufacturer may recommend that the internal rubber diaphragm is evenly in contact with that fluid.
That would occur in a vertical orientation such as you describe.

Each vessel is different, which is why it's important to select the correct one for the application.

Over time (years) there will be 'leakage' of air across the membrane.
That which enters a heating circuit will be eradicated through the air-release valves.

But the slow migration of air (gas) molecules will reduce the pressure in the expansion vessel.

This pressure is restored by using a car foot-pump to add air through the schrader valve beneath the black cap at the opposite end to the water connection.

It's tricky to do that whilst squeezing yourself into a kitchen cupboard!

Moreover, to obtain the required pressure, it's usual to have a shut-off valve on the water connection.
Otherwise you're pushing the foot-pump against the entire water circuit!

In tight situations I have two shut-off valves on the flexible connection to the expansion vessel.
By shutting both, I can remove the entire vessel from the circuit, whether it has any pressurised water inside it or not.
I can then take it outside and re-pressurise it with ease.

In most cases a pressure vessel should be oscillating around the half-full position.
If it's completely full of water then the pre-pressurised air part of the vessel needs pumping up.
You can deduce this by placing the vessel on a set of bathroom weighing scales.
1 litre of water has a mass of 1Kg.

Does that help?

@transparent thanks for the post!

Mine is connected to the combination valve which sipplies the cold feed to the DHW tank and balanced cold to the house, so from your post it would see that it does not matter it's orientation so much?  Also, this is a white vessel so is it the wrong type?

I am thinking that if it is on its side any sediment would build up under the membrane and potentially rub against it with the friction eventually bursting it.  If it is vertical the sediment would remain at the bottom of the vessel and not touch the membrane.  Fortunately I do have a whole house filter so sediment should be minimal.

I had a similar unit in my previous property where I maintained it, i had to release the water pressure in the system to be able to pump up the diaphram.  In one instance i replaced it as the diaphram had burst.  It was wall mounted but i cannot remember if that was for Potable water or the heating system.

i've just found this good YT video that explains a lot and shows a vessel in horizonal orientation...

Posted by: @saf1973

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... from your post it would see that it does not matter it's orientation so much?  Also, this is a white vessel so is it the wrong type?

I don't think you can deduce that much from what I've said!

Zilmet will specify the orientation for each design which they offer.
It depends on a number of factors, including the composition of the butyl-rubber membrane, and the type of lacquer which may have been applied to the internal walls.

There are more combinations of features than can possibly be described by the colour which is used to paint the outside.

It is no longer the case that all manufacturers use blue to identify suitability for potable water.
As that YT video demonstrates, the new vessel chosen by the presenter is coloured white, but he introduces it as suitable for potable water!

I too have had difficulty finding the Zilmet specification sheet for your particular vessel.

However Advanced Water's site does have a document you can download which allows you to calculate the pre-charge pressure and the required total capacity you need.