Air Block in Cold Water System

[sylviansghost]

I wonder if anyone out there can help me!! I'm not a plumber but an electrician. (probably doesnt help!! hehe)

Replaced my wash hand basin in the bathroom today. Isolated the cold water main and outgoing supply from the loft cold water tank.

Changed it all over but on reconnecting the water supplies I have lovely hot water coming out but the cold water just trickles as so does the tap from the bath.

I checked the valve in the loft and it is open, tank nice and full.

Water does come out in spurts!! I know this isnt a heating problem but can you also get air locks that could be causing this problem??

Any help would be much appreciated.

Regards

 

[MANDATE]

It's not clear if your cold water is fed from the tank or direct off the mains, I'm assuming the tank. However you will not have an air lock. An airlock is created when air is trapped in a pipe and there is no escape route for the water even though there is some pressure trying to force the water along. This happens mostly in filling up heating systems because the pipes fill from the bottom trapping air which you can't move because is compresses before it will move.
A pipe could be blocked with sludge but I would not suspect that unless the water tank had been drained and sludge disturbed
I can only think the valves have not been fully opened assuming these were the only items involved. If by chance it is fed off the mains then recheck the main stop cock.
I'm not a plumber either or an electrician.

 

[neilmcl]

Have you managed to fix the problem yet, if yes, please let be know
how as I have a similar problem after replacing the sink in the kitchen,
the bath cold water tjust trickels out. All the other cold water up stairs
& down stairs works ok.

 

[croydoncorgi]

If you have a shower mixer, try this:

- unscrew flexible hose taking care not to lose the rubber washer;

- turn on hot and cold taps;

- place thumb over open end of shower feed;

- switch on shower for 5 - 10 seconds;

- switch back to 'taps mode'

- turn off hot tap and see if cold continues to run.

I beg to differ on the subject of airlocks. It's VERY easy to airlock either / both cold and hot supplies from a storage tank. This trick will often clear it (by forcing the air back to the tank) if only one of them is locked.

 

[oilman]

It's VERY easy to airlock either / both cold and hot supplies from a storage tank

I don't see how either. You have an open outlet, and you have some pressure feeding the inlet, so unless the pipe comes out of the tank and goes up above the level of the water in the tank it will flow out of the tap. Won't it?

 

[croydoncorgi]

All you need is a pipe that's dead level or slightly rising for a short distance, or goes down then up again. Once it's full of air, the pressure of water from a tank will often be too low to shift it.
Believe it - it happens!

 

[MANDATE]

Looks like we will have to agree to differ.
The 2 things about air locks are:
1 How does the air become locked?
2 Why won't it move ?
A pipe that goes down then up again will never have a air lock, but a pipe that goes up then down again may have depending whether or not there is an escape route. An inverted U pipe getting filled from both ends is bound to trap air and form an air lock and this is what happens when heating systems are filled
A level pipe will not have an air lock.
A slightly rising pipe will not have an air lock, not unless it forms part of an inverted U.
The truth is that all air locks can be moved but some are harder than others. It depends on the pressure trying to move it and the resistance offered at the outlet.
The difficult ones are in the heating system because the pump pressure is not that high and there is considerable resistance.
You don't need to move an air lock from pipes from a water tank because I don' t believe one can be created in the first place as there is no resistance if the taps are open.(other than sludge/faulty valve)

 

[croydoncorgi]

Of course I meant 'up then down'! In other words, a high point where air can collect witn no escape route.

'High pressure' tank feeds and 'low pressure' CH systems?? For example, a Grundfos 15/60 CH circulator can pump 0.25 litres per second against a static head of 5 metres. That ain't low pressure compared with a tank-fed outlet, which on the top floor of a building can't have more than 2 metres head (how could it, unless you've got the tank on stilts above the roofline! (Of course, this ignores the probability of air in the pump itself - part of the problem which means it will get nowhere near its rated performance.)

You don't have to believe anything you don't choose to. Let's wait to hear what the problem was and / or what solution fixed it.
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