Water heater, check valve, accumulators revisited

[Lepke]

The need for an expansion tank depends on the water heater size and the amount of plumbing lines it serves. Water expands with heat. W/o a check valve on the cold incoming line some hot water will push into the cold line. Again depending on the tank size and piping length.
When the water expands it increases the pressure on your plumbing. Most yachts have small water heaters so won't see much hot invading the cold line or need an expansion tank. But if you're fighting water leaks, that could be the problem.
I have a 50 gallon water heater, no expansion tank, and about 70' of hot and cold plumbing and I don't have expansion problems.

[AKA-None]

Originally Posted by a64pilot

Water does expand when heated, that is of course why we have expansion tanks on our engines, but if you look, it doesn’t expand much, and the old way if you left just an inch of air in the radiator, it was all that was needed.
So there is expansion as water heats, but water lines do expand slightly, and if you ever open any water outlet whether hot or cold, it releases the excess pressure if any.
Water is not compressible of course so very little water would need to be released.
<snip>

Actually water is compressible which is one of the reasons you don't want it in a hydraulic system. It's compressible as it can carry quite a bit of gas.

[sailorchic34]

Originally Posted by Lepke

The need for an expansion tank depends on the water heater size and the amount of plumbing lines it serves. Water expands with heat. W/o a check valve on the cold incoming line some hot water will push into the cold line. Again depending on the tank size and piping length.
When the water expands it increases the pressure on your plumbing. Most yachts have small water heaters so won't see much hot invading the cold line or need an expansion tank. But if you're fighting water leaks, that could be the problem.
I have a 50 gallon water heater, no expansion tank, and about 70' of hot and cold plumbing and I don't have expansion problems.

If you have an accumulator installed after the pump, that is an expansion tank. Same thing different name.

[sailorchic34]

Originally Posted by AKA-None

Actually water is compressible which is one of the reasons you don't want it in a hydraulic system. It's compressible as it can carry quite a bit of gas.

Ah, no. Water is not used in hydraulic systems as it has a low boiling point, and a high freezing point. Gases can get trapped in the spaces formed between different molecules of H2O. (since the H atoms are tiny and the O atom is fair size). Water is one of the few substances that can exist in all three phases (solid, liquid and gas) at the same time under the right conditions. Which makes it less then ideal as a hydraulic media..

But water is not really compressible at normal pressures most folks deal with. Elasticity, Elastic Properties

[Cadence]

Originally Posted by sailorchic34

Ah, no. Water is not used in hydraulic systems as it has a low boiling point, and a high freezing point. Gases can get trapped in the spaces formed between different molecules of H2O. (since the H atoms are tiny and the O atom is fair size). Water is one of the few substances that can exist in all three phases (solid, liquid and gas) at the same time under the right conditions. Which makes it less then ideal as a hydraulic media..

But water is not really compressible at normal pressures most folks deal with. Elasticity, Elastic Properties

Or expandable. I hadn't opened up a pressure cooker lately so I might be wrong. Seems it turns to steam?

[US1Fountain]

I chose to not reinstall the check valve. 1 less thing to go bad. I do have the small accumulator after the pump, so any expansion will be handled by it. Water heater is a small 6 gal. The times we use the water heater, its only turned on for that use, then turned off. So if the cold water lines get warm, a few seconds of running and the warm water will be flushed out. I'll see how it goes, and then either leave it as is, or put it back in.

Thanks

[Jlp0217]

My experience: I replaced my Raritan 12 gal water heater a few years ago. Raritan recommended an input check valve so I installed one even though the old one didn't have one. Whenever the water was heated from cold, after being out for more than 1 night, a small amount of water would be released into the bilge through the TP valve. After this happened several times, the seal in the TP valve began failing, first a slow leak, but growing until I replaced the valve. The new TP valve also leaked when heating water from cold, so I removed the check valve. No more problem.
Raritan' reason for the check valve was so that if the plumbing leading to the WH input failed, the tank wouldn't drain and then burn op the heating element. But I find it difficult to drain the tank, so don't believe that's a big concern.




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[a64pilot]

Originally Posted by Jlp0217

My experience: I replaced my Raritan 12 gal water heater a few years ago. Raritan recommended an input check valve so I installed one even though the old one didn't have one. Whenever the water was heated from cold, after being out for more than 1 night, a small amount of water would be released into the bilge through the TP valve. After this happened several times, the seal in the TP valve began failing, first a slow leak, but growing until I replaced the valve. The new TP valve also leaked when heating water from cold, so I removed the check valve. No more problem.
Raritan' reason for the check valve was so that if the plumbing leading to the WH input failed, the tank wouldn't drain and then burn op the heating element. But I find it difficult to drain the tank, so don't believe that's a big concern.




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House water heaters add and remove water from the top for exactly this reason, lose water pressure to the house and the heater remains filled.
A mobile home’s water heater has the water coming in from the bottom, presumably so that it drains automatically when the home is moved, you have to add a check valve to a mobile homes water supply or it may burn out the element if water supply is lost.

If I remember correctly my marine water heater has both hoses in the middle of the box? So that it may drain half way?
Or is that the hoses from the engine I’m thinking about?
I don’t have a check valve myself.

[Mike Banks]

If you do not like check valves vented overboard, then you will need a chamber capable of accepting two litres of displaced water, which means at least twice to three times that size--and this pressure needs to be the pressure of normal mains supply or greater.

Fortunately the tank can be anywhere on the vessel--as long as the pipe connecting to it is clear of bends or kinks. The two litres I have calculated was based on roughly 100 litres of water at ambient temp of 25 Celsius heated to boiling point--so it is on the over-zealous since the hot water service is seldom even seventy degrees.

Anyway--lots of luck. I used a gas heater Bosch type--worked like a charm and never gave a moment's trouble--turn on the tap and it lit up every time. No storage--heat what you use.. If I were to fit a storage type it would be solar.77

[boatpoker]

Says in the Bosch installation manual

"Not approved or designed for :
-Manufactured (mobile) homes, boats or any mobile installation. "

[boatpoker]

Originally Posted by sailorchic34

Ah, no. Water is not used in hydraulic systems as it has a low boiling point, and a high freezing point. Gases can get trapped in the spaces formed between different molecules of H2O. (since the H atoms are tiny and the O atom is fair size). Water is one of the few substances that can exist in all three phases (solid, liquid and gas) at the same time under the right conditions. Which makes it less then ideal as a hydraulic media..

But water is not really compressible at normal pressures most folks deal with. Elasticity, Elastic Properties

Will also cause corrosion in hydraulic steering systems.