Problem encountered in connection of 2 water tanks with different volume

[darren72]

Hi All,

I have a doubt on the water level balancing between 2 water tank of different volume which i sincerely hope that you can enlighten me on that.

In view of additional water demand in one of my upgrading projects, I have to increase the effective water storage capacity of the existing water tank from 84 m3 to 136 m3. Current tank size is 10m(L) x 4m(W) x 3m(H) with center partition. However, in view that the operation requirement of the building, existing water tank need to be in operation for 24/7. Hence, a new tank is to added on beside the existing tank to meet the new water demand.

A tank size of 5m(L) x 5m(W) x 3m(H) will be sufficient to meet the new effective water storage capacity.

My question are as follows:

a. If the 2 tanks are linked up by a balancing pipe , will this cause overflow at the smaller tank? If yes, how to mitigate this problem as both tank will need to be connected to a set of water pumps before going out to the fittings.

b. Alternatively, if the tanks are not linked up, will there be any problem if the outgoing pipes from the 2 tanks be linked up together before connection to the pumps.


Your help is very much appreciated.

Thanks

 

[Resolute]

In answer to a I think you'll be fine, as long as the larger tank doesn't have a higher fill level then the smaller one it shouldn't overflow.

As to b, I wouldn't want to link both tanks and use a pump in case the smaller tank emptied quicker and then draw air in.

I'm sure someone with more experience can give a better answer though!

 

[PlumbBobBob]

i think overflowing would only be a problem if the smaller tank were lower than the larger one.

 

[darren72]

Hi Resolute,

Thanks for your reply. Just to further clarify:

In answer to a I think you'll be fine, as long as the larger tank doesn't have a higher fill level then the smaller one it shouldn't overflow.

Can i understand as as long as i set the ball valves of both tank to the same level, i will be able to achieve the respective water capacities of each tank but wth the same effective water height?

As to b, I wouldn't want to link both tanks and use a pump in case the smaller tank emptied quicker and then draw air in.

So will there be any problem if i use the existing outlet pipe from existing tank to pump with the 2 tanks linked up as though the pump is drawing water from one big tank?

 

[stevetheplumber]

Just raise the smaller tank to make the water levels match

 

[Resolute]

Hi Resolute,

Thanks for your reply. Just to further clarify:

In answer to a I think you'll be fine, as long as the larger tank doesn't have a higher fill level then the smaller one it shouldn't overflow.

Can i understand as as long as i set the ball valves of both tank to the same level, i will be able to achieve the respective water capacities of each tank but wth the same effective water height?

As to b, I wouldn't want to link both tanks and use a pump in case the smaller tank emptied quicker and then draw air in.

So will there be any problem if i use the existing outlet pipe from existing tank to pump with the 2 tanks linked up as though the pump is drawing water from one big tank?

I might of mis-understood you. Are you bridging the two tanks? If so then you only need one fill valve and 1 draw off?

If tanks are staying separate then where are you planning on joining them up?

If you bridge the tanks then you need the overflows to be the same height or else neither tank can be filled higher then the lower of the overflows (hope that makes sense).

 

[secret squirrel]

Hi Resolute,

Thanks for your reply. Just to further clarify:

In answer to a I think you'll be fine, as long as the larger tank doesn't have a higher fill level then the smaller one it shouldn't overflow.

Can i understand as as long as i set the ball valves of both tank to the same level, i will be able to achieve the respective water capacities of each tank but wth the same effective water height?

As to b, I wouldn't want to link both tanks and use a pump in case the smaller tank emptied quicker and then draw air in.

So will there be any problem if i use the existing outlet pipe from existing tank to pump with the 2 tanks linked up as though the pump is drawing water from one big tank?

I don't understand, if your linking both tanks why have two ball valves, I'd have just the one, with the demand pipe being on the tank that isn't being fed by the ball valve. This will prevent any water stagnating.

 

[LegionellaSlave]

I've never liked the one ball valve method as the tanks without ball valves get a lot of scum on the surface.
Also the two ball valve method is difficult to balance on low demand.

What sort of building is it?
You might have responsabilities to conform to like water regs and legionella.
:icon10:

 

[secret squirrel]

I've never liked the one ball valve method as the tanks without ball valves get a lot of scum on the surface.
Also the two ball valve method is difficult to balance on low demand.

What sort of building is it?
You might have responsabilities to conform to like water regs and legionella.
:icon10:

Whenever possible, I try and put in one big coffin tank. I normally find that this does the trick. If I do have to join two I only use one ball valve.

 

[Resolute]

Whenever possible, I try and put in one big coffin tank. I normally find that this does the trick. If I do have to join two I only use one ball valve.

Same here, but you explained it better then me! I've never tried using two ball valves and tried to balance the tanks.

The original post mentions needing to keep the tank in use throughout, would it be possible to put in a larger tank alongside the existing one and then swap the connections when it was in place?

 

[secret squirrel]

There going to be without water for a short time no matter what. Just by linking the two tanks there going to have to be drained off. A bit of an inconvience but I don't see being able to avoid it.

Also depends on room in the loft, too many variables

 

[Gray0689]

I've never liked the one ball valve method as the tanks without ball valves get a lot of scum on the surface.
Also the two ball valve method is difficult to balance on low demand.

What sort of building is it?
You might have responsabilities to conform to like water regs and legionella.
:icon10:

I totally agree
One big tank or 2 tanks with separate feeds

 

[LegionellaSlave]

The tank in the OP is a big-un.
Why cant it cope?

 

[Gray0689]

Just re read op that is a commercial tank what are you feeding with it???

 

[LegionellaSlave]

Current tank size is 10m(L) x 4m(W) x 3m(H) with center partition. However, in view that the operation requirement of the building, existing water tank need to be in operation for 24/7. Hence, a new tank is to added on beside the existing tank to meet the new water demand

What is the building mate?

Why do you need another tank for 24/7 use?

 

[BLOD]

You might have responsabilities to conform to like water regs and legionella.
:icon10:

I agree -
tanks this size will more than likely have a whole list of regs to follow.
I'd think that each
tank will need it's own fill valve and overflow to enable it to be isolated from the other tank for draining/cleaning etc.

 

[BLOD]

I agree -
tanks this size will more than likely have a whole list of regs to follow.
I'd think that each
tank will need it's own fill valve and overflow to enable it to be isolated from the other tank for draining/cleaning etc.

While allowing for good movement of water through both tanks when in use.

 

[SimonJohns]

That's alot of stored water

We are encroaching on major water regs here

The tanks will have to have balanced feeds going to a comman header

Inlet valves opposite to outlet

And alot more to boot BUT in the op you said both tanks will be3m high. So in theory you won't have a problem. But you will need to get your auk3 gap. And get the valve to work correctly.

What valves u thinking of using, Keraflow or standard 1212-1?

 

[WaterTight]

perhaps some sort of mermaid for general maintenance?

 

[easyt]

Obviously I am not aware of water regs in this situation without research (being a diy type). I would have thought it best however to have the inlet on one tank and the outlet on the other to ensure circulation in general use. If I was worried about cleaning out the tanks I would have an inlet and outlet on both but would valve off the inlet on one and the outlet at the other. What I would be wary of is one tank doing all the filling and emptying and the other doing very little water changeover.

As I said - not an expert.

 

[Ian10261]

Inlet and outlet on both tanks with the outlets joined together (this is the way i've always done it) is best practice as water is drawn from both tanks simultaneousley and hence much less chance of stagnation. Also as you said a valve on each outlat will make maintenance easier as you can keep one in service whilst working on the other.

 

[darren72]

Hi All,

Really thanks you guys for the overwhelming response.

Perhaps i may not have explain clearly on the problem. Hence, i would like to reiterate the problem as follows:

Current site situation

Existing Cooling tower make up water tank size is 12m(L) x 6m(w) x 3m(H) with an effective capacity of 172 m3. The tank is connected to the cooling tower basins via a set of pumps and pressure pressel. No disruption of water supply to existing cooling tower from cooling tower tank is allowed as the building is 24 hours in operation.

Upgrading requirements

In view that building expansion, new cooling tower is added. Hence the cooling tower make up tank need to upsize to an effective cap. of 198m3. The possible ways are as follows:

1. To provide a brand new tank to meet the new cap.

2. To add a new tank beside to meet the new cap.

Opt 1 is obviously too costly which leaves us with option 2. My questions are as follows:

1. Will the 2 tanks achieve water level equilibrium eventually if i linked the tanks together with a balancing pipe but using back the existing outlet pipe to serve cooling tower basins?

2. any other alternative solutions?



Looking forward to your contribution from you guys. Many thanks.

 

[stani]

just read through this for the first time now, been off for few days, its great when you look and then re-read the posts, specially; Also depends on room in the loft, too many variables , especially when you see that the amount of water is to be increased form 84cu/metres or 84 tonnes to 136 cu metres or 136 tonnes, can you imagine that in the loft. lol

 

[darren72]

There is no problem as the existing structure loading is sufficient and space is not a problem as the tanks are located at an open yard dedicated for MEP equipments.

Just want to clarify if i add a new tank of size of 4m(L) x 3m(W) x 3m(H) beside the existing tank size of 12m(L) x 6m(W) x 3m(H) (with exactly the supporting height from floor level) to make up the additional 26m3 of water, can i rely on the ball valves at the existing tank to control the water level of both tank to achieve the new effective capacity if both new and existing are linked up by a balancing pipe? Will there be any possiblity of overflow problem at new tank due to one tank is smaller than the other.

Looking forward to constructive advice and suggestion from the floor.

Many thanks.

just read through this for the first time now, been off for few days, its great when you look and then re-read the posts, specially; Also depends on room in the loft, too many variables , especially when you see that the amount of water is to be increased form 84cu/metres or 84 tonnes to 136 cu metres or 136 tonnes, can you imagine that in the loft. lol

 

[Gray0689]

What is this for (cooling tower)