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
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 ;-)