Cold water tank sizing??

[RayPlumb]

I looked at a job reciently and cleint (commercial wearhouse) reports no hot and cold water throught gravity fed taps. Suspected air lock.. I flushed air out with mains pressure. Client says happening for about 3 years on and off, more common (every 3-4 days) in summer.
I changed a clogged ball valve on cold water tank. Got good pressure 5 bar. 4 days later same again. I suspect they are running it dry, as 28mm feed from tank.
How do I work out how big a cold water tank they need. They have
10 wc's
2 urinals
20 basins taps all off gravity cold tank ( inc. hot cylinder).
The tank at the moment looks about 650lts tank.
Is the tank too small or am I missing somthing??
Thanks
Ray..

 

[mrlennie]

Could you possibly reduce the flow so that all the cisterns fill up slower giving the ball cock time to do its job?

Or if there is space simply add another tank?

Interesting question.

 

[WHPES]

Use of spray type taps will reduce water consumption.

 

[tamz]

Doubt very much if it will be running dry. What size ballcock? Should be an 1" valve on that size tank.
Even if it did run dry, it would rectify itself overnight and be running in the morning. Easy checked. Turn everything on and watch the tank.
Factories and the like usually have a peak period. Lunch / break times. Be there at those times and watch it.
Check outlet pipework has a constant fall as someone may have had a clamber over them making a dip and causing an airlock. A gravity system needs correctly graded pipes to work.
Things that have been in for years working perfectly until a couple of years ago don't just develop a i need a bigger tank symptom.
Use you head and think about it. Think about what has changed. Same number of employees, same usage, same water pressure etc except somebody maybe hit the pipes with a forklift a couple of years ago!
Check the pipes.

 

[WHPES]

What size is the float valve? I assume it's bigger than 1/2"?

 

[oldplumber]

bung the cold feeds onto mains pressure, got asked to do this for a local factory once and it was because their storage tanks were massive 3 x 7500litres and they were going stagnant!!! shouldnt be an issue as not all the loos etcare all used together, unless they have formal t breaks and p breaks

 

[RayPlumb]

Thanks for the replys. The tank is fed from 15mm pipe and standard 1/2" part 2 valve. The air lock develops between the tank and the Hot water cylinder. Behind breeze block wall and above faulse ceiling. I have slowed the supply down to all the taps, hopefully giving the valve time to catch up enough and not to let air in feed pipe.
Will see how it goes. If it doesn't work then will try hunt down where the air lock trap is in the pipe.

 

[WHPES]

See if you can locate the high point where the airlock is happening and fit an automatic air vent to fix the problem.

 

[justlead1]

Hi. Once you have confirmed its shortage on demand. Try an equilibrium ball valve. The flow rate is 10 fold that of a standard bs1212. And a lot easier than changing cisterns. Good Luck

 

[WHPES]

In the warehouse I guess everyone will have their break times at the same time so all the sinks and loos will be going together at various times during the day.

You could increase the size of the valve to 3/4" which will let more water through faster.

 

[stoker122]

Should be sorted by now

 

[RayPlumb]

Warehouse now closed. another buisness gone under. So not a problem anymore.