strange flow behaviour from cold water tap.

My cold water supply to the kitchen is 15mm copper, reasonably straight with no tees, for the 6m or so that I've seen. The remainder to the connection with the main, maybe another 5m, I've never seen but have no reason to suspect it's any different.

There is a stopcock under the sink which isolates the cold tap and a supply to the combi boiler. This is not fully open, I backed it off to just before the point at which it affects the flow through the combi. We have reasonble mains pressure and this stops the cold tap running like a fire hose.

I have a new Pegler tap fitted with conventional washers. When the cold is turned on it starts just fine then dwindles away to nothing in about

5s. Further opening of the tap restores the flow.

Any idea what could cause this? Is it likely to be the tap washer and/or is my tinkering with the stopcock setting ill advised? I even wondered if it was a design feature of the tap, attempting to give a consistent flow across variable mains pressure, and failing.

Reply to
urchaidh
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Possibly it's just something inside the tap mechanism contracting and reducing the flow as the cold water cools the body of the tap down. I have something similar with a hot tap which slows to a trickle as it gets hot.

-- Dave Baker

Reply to
Dave Baker

I've had the same but a Dave says, "Only with a hot tap". Why not check the actual water temperature with a thermometer. I think that ought to be a good indicator of ground temperature too, providing you do not flow too fast.

I don't see why you shouldn't get the same phenomenom witha cold tap.

Chris.

Reply to
mcbrien410

I've has a similar problem. The washer sits in a cup attached to the "jumper":

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Reply to
Chris Bacon

Either the water pressure is too low or more likely it's the o ring sealing the spindle to the tap upper body which is either displaced or hanging up due to lack of lubrication. If the flow changes when you either press down or lift the tap handle then this is usually a good indication of this type of fault. A strip down and application of some silicone grease to the o ring should get it working properly.

Reply to
Matt

I think it could be due to the reduced flow set by the stop tap. The pressure is the same and the whole system is acting as a pressure vessel. When the tap is opened this initial pressure is released - you are then down to relying on the reduced flow rate set by the stop tap.

Reply to
john

The pressure in a hydraulic system is the same at all places. There can't be an initial surge of pressure over and above whatever is being supplied all the time by the mains pipe.

-- Dave Baker

Reply to
Dave Baker

I think he's suggesting that there may be some compressibility in the system - acting like a small accummulator, and that this is charged up to mains pressure and provides some initial flow. Once the stored energy has been released, the remaining flow is limited to what the partially-closed stoptap can deliver.

Reply to
Set Square

I hope not!! Water is pretty much uncompressible so for the above to be the case there would need to be something pretty weird going on in my pipework.

Thanks for all the advice though, will have a look at the tap washer and a tinker with the stopcock this evening.

Reply to
urchaidh

Washing machine or dishwasher hose is good at this :)

Lee

Reply to
Lee

I had something with similar symptoms on a hot bath tap. The flow from the hot tap was much less than the flow from the cold.

It turned out to be a bit of foam insulation from the hot water storage cylinder inside the pipe. The foam floated on the hot water and obstructed the inlet to the tap. However, on isolating and draining the hot water in the kitchen below, the water level dropped and the foam vanished from sight. Many others had tried in vain to find the mystery blockage.

I only found it because my first attempt failed. I only drained it at the adjacent basin, so there was still a trickle of water coming from the tap when I dismantled it again and the foam was still visible.

This sounds like it might be something that sinks and is normally lying in the horizontal run below the sink. On turning on the water, the flow lifts the blockage until, about 5 seconds later, it obstructs the tap. I'd disconnect the pipe, connect it to a large bore pipe or hose and blast some into a bucket.

Then again, it might be something completely different.

Reply to
Aidan

Water may not be compressible - but trapped air is. Besides which, there can be stretchy bits - like washing machine hoses - as someone else has pointed out.

Reply to
Set Square

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