Combining Mains and gravity fed system

[davedemi]

Hi all,

Is it possible (has anyone tried) to combine a gravity fed system (tank in attic) together with the mains.

Basically by passing the tank though putting a non return valve on the outlet of the tank.

This I hope will add the pressure of water up to the mains pressure without need of pumps (noise + electric consumption).

The only worry I have is that the water in tank will never be used thus creating stagnant water in tank.

The only thing I can think of is reducing the mains pressure so it comes to the same pressure of the tank and therefore have double power.

Hope someone can answer.
Cheers

 

[Bernie2]

Hmm!

The mains pressure would force the water back toward the tank. Probably explode the hot water cylinder if its gravity fed, depending on mains pressure. Cause the hot water to back flow and discharge out the vent pipe into the tank making it overflow. In short you could get in a right mess if you tried to do it. And probably breech quite a few water regs. If the water main went off the tank contents would flow back down the main causing possible contamination, water after all is a food stuff.

 

[washer]

No you cant do it

You could replace your gravity cylinder for an unvented cylinder which provides hot water at mains pressure

 

[plumbster3456]

ha ha I have heard it all now.

 

[Gray0689]

This has to be a wind up lol

 

[helpsy]

Yeah go for it!!!!LOL
Let us know what happens.
Maybe it's a trial for the TV show Mythbusters.

 

[davedemi]

Right guys,

I should have explained a bit more.

Our house has got not heating attached to the system as we use geothermal energy combined with solar heating.

The only hot water vessel is a 60l emergency Wall Hung Unvented Stainless Steel Hot Water Cylinder.

As with regards to regs, this is no issue as the connection will have a non return valve on either part of the y junction so no water will be forced back towards the tank and no water will be forced back towards the mains(in the event that the mains water is closed)

The air vent is not a problem as this will have a air release valve rather than being open.

The system has been designed for max 16bar.

The theory works.

 

[Bernie2]

Problem is nrv's can lock up in the open position and you have two unequal pressure mixed water systems coupled together. If the stored water stagnated and became a breeding ground for bacteria, then the mains water went off, the stored water could so easily discharge back into the mains water supply contaminating it.

If you notice many combis have a loose filling loop which should be removed for that reason as well as others, even though they have nrv's on the filling main.

You may get away with it if you used a potable cold water storage tank instead of a cistern of course.

 

[Toddyplumb]

As is said above NRV is not acceptale. See if your local library has a copy of "water Regulations Guide"
I take it with your set up the current cylinder is unvented ?
You are just looking for a back up if you loose mains ?

 

[davedemi]

Hi all,
Thanks for thoughts. I didn't consider the fact that nrv might fail.

The current system is vented with a closed potable tank. The problem is that the cold water given by the tank is not powerful compared to the hot water. I find it a bit of a waste installing a pump when there is so much pressure in the mains. I had considered first of eliminating the tank and running everything off the mains but the problem is that the mains water is not so reliable. It cuts off about once every month and that will mean no water thats why I'm hesitant to eliminate the tank.

I've been looking through the internet and have seen something about a pressure vessel. Anyone knows if this really will increase the pressure without a pump?

 

[Gray0689]

The only way to do it is a booster pump if you don't want to do away with cold water storage

 

[Centralheatking]

Can you post a diagram of the system as it is ? We can all look then. I would like to help.

centralheatking