Fun with Water Heaters!

[s/v Jedi]

That's it, bookmarked for future reference, tnx Chris ;-)

And look at that manifold on the page you linked, a work of beauty! The only metal is the nails in the clips that fasten it to that beam.

ciao!
Nick.

[Strygaldwir]

I have the Sharkbite fittings. The ones I have are metal. They appear to be brass. I used a tee and a coupling. VERY easy to install and after a couple weeks, they appear to be holding (A couple of weeks is not an endorsement, yet )

[varekai]

My hot water tank gets up to 180 degrees when I run my engine at 2000 rpm through the heat exchanger in the water tank. The problem is that the pressure release valve opens up. Is there a way to automatically by pass the feed from the engine heat exchange once the water temp in the hot water tank reaches about 160 degrees?

[witzgall]

Varekai,

Have you looked into pressure release valves that can handle the 180 degree water? I am not sure if they are available, or safe, but it sure would be easier....

Chris

[varekai]

I would not want the water over 180 degrees. It could blow like a bomb

[Cheechako]

A little surprised the valve vents that low.. May be defective...? You could try putting a valve in line to the heater and running with it partially closed. (only if the heater is on a "side loop")

[varekai]

I put a new one in thinking the old one was defective. I was going to make up a manifold with ball valves to by pass the water tank but was hoping for something easier and automatic.

[CeesH]

Originally Posted by s/v Jedi

Exactly, that's what I called "open up the hot-water line". However, this will cause the system to drain at the point of failure. The waterpump will keep the pressure up and that pressure will be the highest pressure in the system (the line is open to the atmosphere during failure).

So, let's look what happens when a hot water line starts leaking: the fresh water pump will try to keep pressure up so all hot water will flow out of the burst. The checkvalve is irrelevant to this mode of failure.

Next is a leak in the cold water line: the fresh water pump will try to keep pressure up so cold water will flow out of the burst. Without a checkvalve, hot water from the heater will only backrun into the cold line until the pressure inside the waterheat is down to the same level as that of the pump. Vacuum in the hot water line prevents it from further discharge. Apart from a small amount of hot water (from the coldest part from the tank), a checkvalve is irrelevant to this mode of failure too.

However, if we start to perform maintenance on the system, we might open up both hot and cold water lines with the pump switched off. When the pump is switched off, we enter a new game. Now, the hot water can flow back into the cold lines. But a closed valve at the hot water output of the heater prevents that as good as a checkvalve. Also, checkvalves tend to fail over time and have no visual sign of proper operation, making this less safe than a hand operated ball valve.

Pls. elaborate. My view is that the thermal expansion valve protects the tank against too much pressure and will provide that protection regardless of a checkvalve. The only difference is that without a checkvalve, the whole system is at the same pressure while a checkvalve partitions the system and the tank + hot water lines can have a higher pressure than the cold water lines. The primary function of the expansion valve is to protect the tank and that mode of operation isn't affected by having a checkvalve or not.

Also, the waterpump has a checkvalve so the water can't run back into the tank.

Pls elaborate. The tank will only explode when it's internal pressure becomes higher than it's designed maximum. Even with a checkvalve (which still works) installed, the hot water lines and faucets are at that same pressure level. Before the tank explodes, the thermal expansion valve opens and reliefs the pressure. No explosion and no destroyed boat.

In short: the checkvalve does not prevent explosion or enable the relief valve to work. The relief valve (thermal expansion valve) works on pressure.

The only major accidents I am aware off are caused by propane water heaters.

cheers,
Nick.

In Europe it is not allowed to press hot water, due to expansion, back in the cold water system, the IN of the heater MUST have a non-return valve and the OUT of the heater (we call it a boiler) MUST have a thermal expansion valve with a drain attached to a dispose line. Pré-mixing is not allowed and must happen at the tap. That's the reason why almost all kitchen and shower taps in Europe are from the thermostat type (to protect for burning).

PS. In the public domain most hot water systems are terminated with a small diameter return line and a pump to the water heater to guarantee the minimum hot water temperature.

CeesH

[CeesH]

Nothing better then a picture, the green line is the over-pressure line.