Fun with Water Heaters!

[GordMay]

ABYC Standard H-33, Potable Water Systems, specifies the maximum pressure on the vessel not to exceed 80 psi.

Marine Water Heater tanks must be tested to:
up to 15 Gal @ 120 psi
16 - 120 Gal @ 300 psi
over 120 Gal to ASME standards (pressure vessel)

Most shoreside plumbing codes require the use of piping having a minimum 100 psi @ 180 F rating, for both the hot and the cold water portions of the water distribution system.

Crosslinked Polyethylene “PEX” tubing systems are tested to, and can be used with, standard T and P relief valves that operate at 210̊ F (heating applications) and 150 PSIG (1.03 MpA).
A typical Nylon Reinforced PVC Hose for pressurized drinking water systems will be rated at about 150 PSI (1.03Mpa) -to- 175 PSI (1.21Mpa).
"Cheapo" hoses may be rated much less.

[s/v Jedi]

Originally Posted by GordMay

The check valve (or backflow preventor) prevents the expanding water from backing into the municipal water supply, or the boat’s storage tank, thereby relieving pressure.

Ah, another possibility that I didn't think of: connecting the boat to the municipal water supply. We never do that so I missed that one.

This is how it is:

1. There is a check valve in your water pressure pump. Expanding hot water can not flow back to your water tank(s) because the pump (with it's check valve) is in between and blocks that flow regardless if it's switched on or not.

2. Expanding hot water increases the pressure in the water heater and all hot water plumbing. If hoses are used for that plumbing (instead of pipe) a lot of expansion is absorbed by the hoses expanding their diameter under pressure. Also, a failure as a result of too much pressure is just as likely in the hot water plumbing as it is in the heater. The heater's over-pressure relief valve protects the hot water plumbing too, but most boats hot water plumbing will start leaking before the relief valve triggers.
Make sure that a triggered relief valve doesn't spray boiling water where that imposes danger. You can install a hose to this valve to direct this somewhere safe.

3. If the boat is connected to the municipal water supply, this connection is made to the cold water plumbing. The check valve in the water pressure pump (which is switched off) prevents water flowing into the tank(s). The plumbing in most boats can't handle the municipal water pressure and need a pressure reducer installed between shore- and boat-plumbing.
If the municipal water pressure fails, water from the water heater can flow out through the cold water inlet of the heater, possibly burning up the electric element when that is switched on but not completely immersed in water. This is where a check valve mounted to the cold inlet of the water heater comes into play. This check valve is not a safety device, it is to save the electric element.

What I like:

- Schedule 40 PVC plumbing parts. I replaced all those barbed-T's with PVC manifolds. I use the PVC cement to assemble the manifolds. These will last for ever. I use this for pump pick-up pipes, cold and raw water manifolds and sometimes even add the cheap PVC ball-valves (the cement-on type, not threaded). For hot water, I use bronze parts (T's and nipples with Permatex high temperature thread sealant) although high temperature PVC is also available (the cream colored pipe & parts).

- A valve between hot water plumbing and water tank(s) which can be opened momentarily until hot water arrives at the valve. This saves big amounts of water.

- I'm impressed with what I read and see about PEX plumbing, and in particular the pipe-to-fitting connections without metal parts (expand the pipe, put it on the fitting and the pipe's memory crimps it on). I will replace our hose-based plumbing with that when we arrive near a good source of PEX.

- Imagine's shower system for boats with crew or guests who tend to use too much water when taking showers ;-)

ciao!
Nick.

[donradcliffe]

The temperature in my shower tends to fluctuate dramatically as the pressure pump cycles--I get a burst of hot as the pump kicks on. Do the mixing valves respond fast enough to eliminate that fluctuation??

[s/v Jedi]

Originally Posted by donradcliffe

The temperature in my shower tends to fluctuate dramatically as the pressure pump cycles--I get a burst of hot as the pump kicks on. Do the mixing valves respond fast enough to eliminate that fluctuation??

No, I don't think so. Your best course of action is to prevent the pressure changes. The best way of doing that is a non-cycling pump. These pumps have variable speed, so turn slowly instead of cycling.

cheers,
Nick.

[chala]

Gord thanks for the links.
It is interesting to note that fusing plugs are not mentioned in the reports. I have seen them in Oz and in Europe. They are normally fitted to the top center of the vessel.

“ABYC Standard H-33, Potable Water Systems, specifies the maximum pressure on the vessel not to exceed 80 psi.”
It will be interesting to know if Christian P & T valve is rated at 80 psi. I was not able to read the yellow label attached to it.
The disadvantage of a lower psi is that the P & T valve tends to dribble far more.
It also to be noted that the pressure pump when it operate in lieu of the check valve require to be rated to the value of the P & T valve.

Nick you are correct.
“This is where a check valve mounted to the cold inlet of the water heater comes into play. This check valve is not a safety device, it is to save the electric element.”
And also will prevent a built up of pressure in the water supply line and pump.

“Make sure that a triggered relief valve doesn't spray boiling water where that imposes danger.”
The temperature part of the P & T valve will operate and open and stay open at 90oC. If this occurs the valve will be destroyed in the open position and will need to be replaced. It also will mean that both the regulating and safety thermostat will have failed and also need replacing. The temperature will be at 90oC and not boiling. As the water escape the pressure pump should cut-in bringing cold water to the water-heater and keep running until the water tank is empty or some one attend to the fault and switch off the pump.

“These will last for ever.”
PVC when aging becomes brittle and crack. The crack on the T is apparent; the crack on the elbow is along the seam.

Donradcliffe
Have you tried to install an accumulator?
Note: the pressure in an accumulator cannot be higher that the discharge pressure of the pump or it would not work. At 80 psi I do not consider them dangerous.

Legionella.
In the Tropics in the wet season the cold water tap can reach temperature in excess of 30oC. In the forty years I have been in the tropics I do not know of any case of Legionaries disease attributed to the water supply. Of course good housekeeping is necessary.

I did like the threads name “Fun” with water heaters.

[scotte]

OK, so I see where I was confused a bunch of posts back... The heater from the OP mentions a "tempering thermostatic valve", which is a totally different beast than the "temperature control valve" I've seen on Kuumo heaters. I got these two confused.

"Tempering thermostatic valve" mixes cold water in to extend hot water times (and prevent output water from being too hot).

"Temperature control valve" is in the engine coolant loop (not the hot water output) to prevent the water from getting too hot.

[Sailormann]

I replaced our hot water heater and some of the fresh water system on our boat. I used a product I found at Home Depot which is a series of brass fittings that just push on to the ends of plastic or Pex tubing. I was a bit sceptical but tried them and I have to say that they are pretty amazing. Easiest plumbing jo I have ever done and completely leak free.

[senormechanico]

Sailorman,

Can you please post a pic of one of these fittings?

I'd like to try them.

Steve B.

[Christian Van H]

Originally Posted by Sailormann

I replaced our hot water heater and some of the fresh water system on our boat. I used a product I found at Home Depot which is a series of brass fittings that just push on to the ends of plastic or Pex tubing. I was a bit sceptical but tried them and I have to say that they are pretty amazing. Easiest plumbing jo I have ever done and completely leak free.

Hey Sailor! I believe Home Depot sells Sharkbite fittings, which match your description.
http://www.cashacme.com/prod_sharkbite.php

[GordMay]

"SharkBite" Connector Installation Instructions:
➥ http://www.cashacme.com/_images/pdf_...stall_Inst.pdf

[Strygaldwir]

Isn't ridgid pipe that is subject to the vibration of a boat a concern? I thought I read some where (probably in this Forum!) that prolonged vibration could cause the joints or seams to fail.

[Christian Van H]

Originally Posted by Strygaldwir

Isn't ridgid pipe that is subject to the vibration of a boat a concern? I thought I read some where (probably in this Forum!) that prolonged vibration could cause the joints or seams to fail.

Cant say that anyone here is speaking about rigid stuff... PEX is quite flexible.

[Strygaldwir]

I was responding to Chala's pictures. They look like pipe elbows. And Jedi referred to Schedule 40 which if I understand correctly is strictly a rigid pipe standard. Just wanted to make sure my understanding is correct.

[s/v Jedi]

Yes, we're talking about everything at once ;-) The schedule 40 PVC I use is just for making manifolds, not for pipes. I have some 15 year old manifolds aboard that look like new. I don't see these cracking from 45 psi water pressure in a lifetime but the pictures from Chala show failures. To me they look like caused by other factors like mechanical sideways forces you get when using rigid pipe, vibrations etc. PEX is flexible enough to absorb all that... I hope ;-) The wrong thing to use is brass pipe like used in houses. It work-hardens quickly under vibration.

The sharkbite fittings: the ones Chris used appeal much more to me as they have no metal. I forgot their name but Chris will tell us that I think ;-)

cheers,
Nick.

[Christian Van H]

ProPEX system from Wirsbo, now Uponor: Uponor - Plumbing Systems