A tap with a mind of its own

Bert Coules used his keyboard to write :

Most likely - the cold water still in the neck, expanding as it warms up, then dribbles.

My electric shower does the same - cold water in the hose warms up to bathroom temperature, then dribbles out of the head.

Thanks; it sounds likely. My only slight reservation is that I'm not sure I'd characterise what happens as a dribble: it seems a little more (and a little more forceful) than that.

I have occasionally noticed my 8 year old bathroom mixer tap (wash hand basin) doing that since new and have always wondered. It's not a dribble, more a very short trickle.

Could it be a combination of limescale reducing the nozzle size slightly and surface tension now being sufficient to hold back some water for a few seconds after turning off?

A bit like the ketchup bottle problem. Neck/nozzle is full of ketchup/water and it hangs there until air can enter the neck/nozzle releasing the ketchup/water.

Tim

Thanks for the thought but I think that's unlikely: this particular tap is fed (on both hot and cold sides) with softened water.

That's quite a good description of what I'm seeing.

Aha, so could you have some blockage in the water softener? Brian

on 08/03/2018, Mr Pounder Esquire supposed :

The skin effect of the water, means it will sit in the neck of the tap, until it expands enough to overflow, once the over flowing begins, close to the entire lump of water will flow out in a trickle. If the trickle repeats, then your tap is passing/ leaking.

Thanks for the thought. It's possible I suppose but would that cause the effect I'm seeing?

Also, the same softener feeds two other taps, two cisterns, a shower and a washing machine and I've never noticed any problems with any of them.

It has been doing that since new.

It is only the tap over the wash hand basin that does this. I've never seen the bath, shower or the kitchen tap do this. We live in a soft water area.

Reading these replies, I wonder if it could be, in my case at least, because the tap has a particularly lengthy spout which rises almost vertically from the body of the tap and then curves forward and slightly down. When the tap is turned off there must be a reasonable amount of water still in that spout and if the suggestion is right that it expands then wouldn't it produce exactly the effect I described?

Your spout is just as I suspected. I think the water between the highest part and the exit is held there by air pressure provided no air can get in, but probably after one or two drips of water, sufficient air can tunnel in behind the suspended water which then falls out.

Maybe the o-ring that seals the nozzle swivel is worn and is allowing air in.

Tim

Have you had your prostate checked?

I was going to, but I thought stripes would look better so I went for them.

I have exactly the same issue and your description of the tap matches mine too. It happens about 10 mins after use and only happens once. The heating of the water to room temperature and expanding enough to break the surface tension sounds plausible to me