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