Can I have two water storage tanks at different levels in gravity system?

zulutango

Would appreciate help from the forum on the following query. I'm helping a friend who is renovating an old house.

There are two small water storage tanks, and he needs to use both. The problem is that they are are different levels. One is in an upper roof space and the other is in a lower roof space at a different side of the building. The difference in levels is about 2 metres.

Can both be tied into the same distribution pipework? Or will the greater pressure from the higher tank push water flow back towards the lower tank? How do I get around this?

John.G

zulutango wrote: »

Would appreciate help from the forum on the following query. I'm helping a friend who is renovating an old house.

There are two small water storage tanks, and he needs to use both. The problem is that they are are different levels. One is in an upper roof space and the other is in a lower roof space at a different side of the building. The difference in levels is about 2 metres.

Can both be tied into the same distribution pipework? Or will the greater pressure from the higher tank push water flow back towards the lower tank? How do I get around this?

Installing non return vaves in any outlets from the lower tank will stop the higher tank overflowing the lower tank if both outlets are teed together but I cant see both tanks supplying water "together", the higher tank will supply all the water until almost empty then the lower tank will start supplying some of the water, but you will then have the higher tank ball cock fully open and the lower tank (and its ball cock) supplying the remainder but you will then probably have problems with air entering the system as you are effectively running with one empty tank (with its ball cock fully open) if the demand is very high,

zulutango

Thanks John.

I was looking at it and was thinking I could use one as the cold feed for the hot water cylinder and the other for general cold water distribution. It would mean I'd have slightly different pressures in the hot and cold pipes, but would that be a problem?

Another thing I was thinking of was having the pipes from each tank run through a pressure equalisation valve like this - http://www.altecnic.co.uk/plumbing-heating/pressure-reducing-valves/19/

Hey presto, all is solved! Or but I'm probably missing something!

John.G

zulutango wrote: »

Thanks John.

I was looking at it and was thinking I could use one as the cold feed for the hot water cylinder and the other for general cold water distribution. It would mean I'd have slightly different pressures in the hot and cold pipes, but would that be a problem?

Another thing I was thinking of was having the pipes from each tank run through a pressure equalisation valve like this - http://www.altecnic.co.uk/plumbing-heating/pressure-reducing-valves/19/

Hey presto, all is solved! Or but I'm probably missing something!

Your first thoughts above of using one tank for cold water supply etc is probably the simplest/best way of doing it. Re the difference in the tank heads, it shouldnt be a problem except that you are using a gravity fed bathroom shower (upstairs) as a 2 meter differential at that level will make a huge difference to the mixed flowrates. I would suggest using the lower tank to supply the cold water as this will be the greater requirement and you will get ~ 10% more flow through its ballcock especially if you have a poor mains supply pressure of say around 1 Bar at attic level.

The pressure reducing valve may do the trick but you just dont know until you try it, if it works as advertised then you will have all the advantages of the two tanks supplying equal amounts of water and thus greater total capacity.