A question for plumbers … or any other people knowledgeable in this area.
When you turn on a hot water tap, generally what happens is:
a) The water starts coming out at a reasonably high pressure, but cold.
b) After some time, all the cold water in the pipes has come through, and the water starts to get warm
c) At this point, the water pressure drops, sometimes dramatically (sometimes almost to nothing)
Why does it do this? I’ve noticed this in basically every hot water tap I’ve ever turned on, so I presume it’s not to do with any particular configuration of the pipes.
The hot water is coming out of your hot water heater. The cold water is coming out of the towns water tower. The difference in hieght that these are to each other is called Head. Head determines water pressure. Your hot water heater is probably not at the same pressure level as your cold water because of some valve disconnecting it from the souce (ie. the water tower).
This has been discussed before. The washer is rubber and when cold will keep it’s shape better. With the faucet closed it is under much compression. Open the faucet and it still keeps the shape but as soon as it heats up it expands and blocks the water. The cold water faucet will do the same over a much longer period of time.
My hot water pressure starts out low and stays that way. I was told it was because of a combination of the tank and mineral deposits in the pipes.
Maybe the washer in your faucet swells when it gets hot.
Peace,
mangeorge
Rubber does not expand that much due to the change temperature to choke off your pipes as significantly as he is desribing. He proably lives in an apartment complex and has a more complicated plumbing arrangement than people who live in private homes. Just my view of the facts, no dis intended Sailor.
By the way, the inner diameter of a washer gets bigger as it warms up, not smaller. The outer diameter also increases and the thickness increase. This would create a tighter seal and benifit flow.
sailor You explanation makes some sense to me, except… wouldn’t the pipe heat up and expand as well? This is what puzzles me - I would have thought that both the pipe and the ‘flow blockage device of whatever sort’ (a washer, apparently) ought to expand together, leading to the cross section of the flow actually being greater. Or, if the pipe’s metal and the washer’s not, the pipe ought to expand more.
This is a standalone house I’m talking of at the moment, but I don’t necessarily think that’s significant - I’m pretty sure I’ve noticed more-or-less the same pattern in every hot water tap I’ve ever turned on.
If it’s been discussed before, maybe I should go beat the hamsters till they tell me where…
Um, jaybee, you want to see a video of my hot water faucet? I’ll make it if I have to. It is so annoying I have taken time to study it. And how do you explain the following:
It only happens with the hot water faucet, and not the cold.
It only happens if the water is hot. Turn off the heater and it behaves just like the cold water faucet.
Remove the rubber washer and it does not happen (of course the faucet does not close tightly either and it drips).
Take a vise and compress a rubber washer on a very cold day. See if it regains thickness faster when you put it in cold water or in boiling water.
Mangeorge, your situation, obviously, has a totally different cause.
sailor is correct for one of the main causes of this. If you replace the rubber washer with a hard plastic one you will also see a decrease in the effect.
I find it very aggravating to have to open the hot water, wait a bit and then open some more. If I open too much at first it splashes all over so I have to wait a bit. I tried replacing the washers with harder plastic but they did not last because my guests have peanuts for brains. Their MO is “turn faucet until water stops flowing and then 1/4 turn more” which works fine with elastic washers but not with the harder ones which are just destroyed if you overtighten the faucet. So, between the aggravation of arguing with girlfriend over the need to tighten the facet so much or the aggravation of dealing with a stupid faucet I chose that I had better chances against the faucet and I went back to regular washers.
So right now in the kitchen you oen the hat wate faucet one turn and water flows for a few seconds until the hot water arrives and then the flow goes down to absolutely zero and you have to open the faucet again after you had already picked up something to wash. argh
Sailor’s answer is correct here in the US. Jaybee’s answer makes me think he lives in the UK (or some such place) were the plumbing setup is different (but his profile doesn’t give a location). I think, from previous threads, they tend to have a seperate hot water holding tank with a lower pressure. Here in the US, Hot and Cold are both fed from the same source, and so have the same pressure, apart from flow restrictions like mangeorge is apparently experiencing. Aspidistra is from Australia, but from the description in the OP, I bet the setup is more similar to the US than to the UK.
mangeorge, your problem could be as simple as one of the valves on the pipes near your hot water heater not being opened all the way.
On-demand water heaters are a different kind of abomination, also common in Europe. I believe we have also had threads about them. I hate them. They are an abomination and the invention of the Devil himself.
I think our “full” hot water pressure is basically the same as the cold - but in any case any pressure differential between the hot water system and the cold (if such a differential existed) is irrelevant. The cold water tap isn’t on - the cold water that gushes out of the tap for the first few seconds is in fact water from the hot water system (which has been sitting around in the pipes for ages and gone cold).
And thinking about the differences between my current setup and ones in the UK (where I lived for a number of years) has got me thinking… Next time I’m futzing around with the tap for five minutes trying to get the flow right I can just say to myself ‘maybe this is annoying … but you could still be living in a top-floor student-flat in Edinburgh with miserable weedy water pressure that’s barely enough to power a shower-head, and an overnight heating system that gets all used up by four in the afternoon.’
(But of course, if you’ve got English plumbing, there’s no solution. Rest assured, however, that it will give you loads of patience, if you persevere.)
A nonexpanding washer should work on most faucets. Mine has a particular shape. The seat against which the washer closes, rather than flat is kind of sharp and will cut into the washer if you put too much pressure on it regardless of the type of washer. It is just that expanding washers have more give and people tend not to tighten so much. But non-expanding washers should work on other, better-designed, faucets.