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surveyor1 10-24-2009 08:16 PM

Shower is hot/cold
 
Just bought a '88 sundeck trawler (Hi, Dave).
The shower in the aft stateroom works o.k. except the water comes out intermittently too hot and too cold, cycling very rapidly between the two as if in time with the pulsations of the pump.
I'm wondering if anyone else has encountered anything similar or should I just plan on replacing the pump?* Is it normal for them to cycle rapidly ? Are there some brands that are smoother ?

thanks

Marin 10-24-2009 09:06 PM

Shower is hot/cold
 
Not knowing anything about your plumbing we can only relate your problem to the systems we have on our own boats. In our case, the fresh water pump applies pressure via an accumulator tank to the water coming from the water tanks. The pump runs as it pressurizes the accumulator tank and then shuts off until the pressure in the tank has dropped to a certain point and then the pump kicks back in. The cycle rate varies with the water demand. With a low demand, say a sink tap on at a fairly low flow, the pump is on for about 2 seconds and then off for about 2 seconds. Or maybe a bit faster. But under high demand, like a shower, the pump simply stays on. The accumulator tank is there to keep the water flow to the system at a fairly constant pressure instead of pulsing as the pump cycles.

On our boat the pressurized water is fed to the cold water taps and to the hot water heater. So turning on a hot water tap reduces the pressure in the whole system which starts the pump going which pressurizes the system and forces hot water out of the hot water tank and through the hot water hoses to the sink taps and shower. So on our boat, at any rate, I cannot think of any way the pump could cause a cycling between hot and cold water in the shower head. It's simply pressurizing the whole system.

Now I suppose it's possible for a partial hose blockage or something to prevent the full pressure from reaching the hot water tank, so when the pump cycles off when the accumulator tank (assuming you have one) is up to pressure, I suppose it might be possible for the lesser resistance in the cold side of the system to over-ride the reduced pressure on the hot side until the pump kicks back in again. But I'm speculating here and this theory could be total BS.

Perhaps if you could describe the actual pump and plumbing layout in your boat someone on this forum with more water system experience than me could suggest some causes of the problem you're experiencing.

-- Edited by Marin on Saturday 24th of October 2009 09:12:25 PM

Marc1 10-25-2009 04:02 AM

RE: Shower is hot/cold
 
Quote:

surveyor1 wrote:

Just bought a '88 sundeck trawler (Hi, Dave).
The shower in the aft stateroom works o.k. except the water comes out intermittently too hot and too cold, cycling very rapidly between the two as if in time with the pulsations of the pump.
I'm wondering if anyone else has encountered anything similar or should I just plan on replacing the pump?* Is it normal for them to cycle rapidly ? Are there some brands that are smoother ?

thanks

88' sounds like fun, congratulations!

It seems you pressure tank is water logged. (Wild guess)
If your pressure pump has a tank next to it with a pressure switch on top of it, the tank is supposed to be clear of water in order to have a volume of air that can be pressurised and act as a shock absorber of sorts. Air gets slowly pumped away with the water and the tank get's filled with water to a point that the pump reaches maximum pressure as soon as it starts, yet if you are using water, the pressure drops instantly and so the pump switches on and off again and again. No good.
Solution is simple, drain the tank. If it does not have a drain tap, you will have to undue one of the houses at the bottom. Make sure it does not leak when you tie it up again. Better to change the two bit of hoses and SS clamps whist at it. Good luck!
*

Phil Fill 10-25-2009 01:12 PM

RE: Shower is hot/cold
 
I dont think its the pump going off and on that is making the water going hot and cold?* We do not have an accumulator tanks but a straight pump and our water does not go hot to cold with the pump cycling.* I dont see how an accumulator would correct the problem as pressure on a liquid is distributed the same though out.**
So what else might cause the water temp to go hot to cold?*****

Keith 10-25-2009 05:34 PM

RE: Shower is hot/cold
 
Sounds like either the hot or cold circuit is more restricted than the other. If it gets colder as the pressure increases, I would suspect the hot water circuit is restricted, and vice-versa.

Mine will change temperature when something else draws hot or cold water, but when the pump is working, it's just fine. I have a diaphram pump with an accumulator.

Marin 10-25-2009 11:39 PM

RE: Shower is hot/cold
 
Quote:

Marc1 wrote:
If your pressure pump has a tank next to it with a pressure switch on top of it, the tank is supposed to be clear of water in order to have a volume of air that can be pressurised and act as a shock absorber of sorts. Air gets slowly pumped away with the water and the tank get's filled with water....
Some accumulator tanks--- the one on our boat is an example--- simply have a diaphragm in the middle.* There is x-amount of air pressure on one side of the diaphragm and the other side has water coming in from the water pump and going out to the fresh water plumbing.* The diaphragm acts as a shock absorber to keep the water from pulsing in the lines, but the only thing shutting off or turning on the pump is the pressure in the water system downstream of the pump acting on the pump's own pressure switch.* There is no pressure switch on the tank itself.

*

wingspar 11-15-2009 10:29 PM

RE: Shower is hot/cold
 
The accumulator tank is disconnected. The hot water tank is located in the bow. Try using only the FORWARD water tank as it is close to the hot water heater. The valve is under the lower step. The rear tank is right by the water pump and differences in pump pressure can be magnified do to differences in plumbing lenghts.

Dave

surveyor1 11-16-2009 08:53 AM

RE: Shower is hot/cold
 
Thanks Dave,

I removed the broken accumulator tank and replaced the pump with a variable pressure model that does not require a tank. That seemed to help.
Also, did you see the response to my query re: the mystery board ? I think the person that said it is a support for the keel of an inflatable nailed it. Sounds reasonable.

Rob W.


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