Two ballcocks on main cold water tank - why?

[captainnemo]

I've just moved to a new house and I noticed an overflow leaking from the loft.
In the loft I can see the main cold tank is overflowing and there are two ballcocks installed in the same tank, one of which is leaking.
Luckily each has an isolation valve, so I thought as a quick fix I would just turn off the leaking one and fix it when convenient.

Have I compromised the system in any way and why are there two ballcocks? - not just for dual redundancy surely?

The house has a power show, an electric shower and 3 loos, so maybe the tank needs to fill faster than normal??

Any thoughts?

Cheers

 

[JCplumb]

You answered your own question there.
It's not going to make a massive difference but having 2 piped supplies to the tank will probably help it fill a bit quicker so it doesn't run out as quickly if you're using the power shower.

 

[Dotty]

You haven't two different water supplies have you? One from a well for example.

 

[PriestyUK]

I have seen this in commercial buildings like hospitals or flats, the reason in this case was if one failed you had a backup until the faulty one could be replaced, both would not run at the same time, one would be just sat there ready to go incase it was needed like a super sub lol

Because float valves like this arnt off the shelf and not cheap:

Aylesbury Keraflo K Type SF 2" - 50mm Delayed Action Float Valve | Tanks Direct Ltd

 

[thompsonbrown]

Ive seen this before when the tank was to small for the property and the plumber thought installing 2 fills would alleviate the problem.

 

[Ray Stafford]

One of several ways people used to bodge up for the fact that they were pumping a 25 gall tank, in order to save replacing it with something larger.