Cold water shower question

[Bobbie54]

Just curious as to the cause of this: using the shower, hot and cold turned on to a desired temp. I use the handle to shut the water flow off. When I turn it back on I get a spurt of cold water, then hot mixes in. Why? Is it because the cold is currently under pressure (hookup) and the hot under less pressure?

[rubicon327]

Yes. You are correct. Better than hot scalding you but you can probably fix it if you really want to.
https://www.thefitrv.com/rv-tips/how...our-rv-shower/

[kavm]

Thanks for posting this. We also experienced this… I thought this was an unadvertised bonus hydrotherapy feature

Dave - Watched that video. Very interesting, though we will not try this at home…

[Brian B-P]

Originally Posted by Bobbie54

Why? Is it because the cold is currently under pressure (hookup) and the hot under less pressure?

That might explain it, but why would they be under different pressures? Water to both faucets starts in the same place (at the city water inlet or onboard pump discharge) at the same pressure, and when there is no flow (shower paused) there is no loss of pressure in either side of the system due to flow restriction. There should only be a significant pressure difference if one side has some sort of inline regulator (not just a restriction) that the other one doesn't have.

The water in the hose cools off during the pause, but the should only be noticeable after an extended pause.

Water-saving pause valves in shower heads are normally designed to allow a trickle to continue to flow, to avoid these problems (primarily the possibility of crossover flow to other faucets).

[Bobbie54]

I don't think it does it on the pump, which would suggest it has to do with pressure. But I'll check next time.

Easy fix- I handhold the showerhead anyway, so I just let the cold part come through. But it surprised me.

[flynfrfun]

I went ahead and ordered the parts from the video. I get a pretty long shot of scalding hot water. Also, I dislike wasting water and hearing the pump cycling while it's dripping. I hope it works.

[kavm]

Originally Posted by Brian B-P

That might explain it, but why would they be under different pressures? Water to both faucets starts in the same place (at the city water inlet or onboard pump discharge) at the same pressure, and when there is no flow (shower paused) there is no loss of pressure in either side of the system due to flow restriction. There should only be a significant pressure difference if one side has some sort of inline regulator (not just a restriction) that the other one doesn't have.

The water in the hose cools off during the pause, but the should only be noticeable after an extended pause.

Water-saving pause valves in shower heads are normally designed to allow a trickle to continue to flow, to avoid these problems (primarily the possibility of crossover flow to other faucets).

We have observed this behavior in non-hookup situations as well.

[MVA]

I have observed this problem also.

Background - The high water system is fed by the hot water heater. The heater likely has as small air pocket in the top. This air pocket will be a damping function to the hot water system. This is similar to the anti-water hammer air tubes plumbed in your home (if you have them). The cold water system is confined to the piping without an air pocket. Water is nearly incompressible at these pressures; air is clearly compressible at these pressures.

Likely cause - When you open the valve on the pressurized system on the shower, the cold water will flow quickly. There is no air accumulator to account for the pressure drop caused by the open valve. The hot water will not initially flow as quickly as the pressure drop caused by the open value can be accommodated by the air space. It will only take a second or two for the pressure to equilibrate in the hot system. Hence the initial cold surge.

--2 cents

[kavm]

The YouTube video shared by rubicon327 is excellent, even though I do not have the confidence to tackle the solution there.

[Bea]

We have also experienced this, so last year we found and watched a different video that talked about the same issue (differing hot and cold water pressures affecting the water temp) so all we did, was install a simple shut off value. (https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 ). But this video rubicon327 shared was much better! Thanks!

Our shut off valve works, stops the water completely and when camping 'off grid' - every drop matters! Right?? Thankfully, now we don't feel rushed when taking a shower, when soaping up. But did the shut off valve help with the cold water blast, after turning the water back on? Maybe just a little?

However, we did not install a check value, only a shut off value, so that's probably why. But I installed our shut off valve, right next to the shower head. Hummm.... Now I am tempted to switch the location and attach it at the beginning of the hose (on the faucet itself), instead, and see if the cold blast warms up a bit? James, in this video made me realize that the cold water might be pushing its way up into the hose when it is in the 'shut off' mode?? I will report if the new location helps at all.

Not sure if we'll go to all the trouble of installing a check value, under the sink, since we are now conditioned to point the shower head away from us every time we turn the shut-off valve back on. The right temp comes back very quickly so not a big concern but it's always fun to think about future mods. And with that... there might even be a better place to install a water check valve on the hot water line, like closer to the water heater...hummm. Will have to take a closer look at the hot water lines next time we venture out. Thanks for starting this thread Bobbie54! -Bea

[cityofdestiny]

Originally Posted by Bobbie54

Just curious as to the cause of this: using the shower, hot and cold turned on to a desired temp. I use the handle to shut the water flow off. When I turn it back on I get a spurt of cold water, then hot mixes in. Why? Is it because the cold is currently under pressure (hookup) and the hot under less pressure?

We experience this when hooked up, but not when dry camping (pulling water from the fresh tank.)