Water system accumulator tank

[jelmore]

While putting in a new hot water heater, I had to deal with the water pump and associated connections and parts. The system has an accumulator tank and my understanding is that the pressure in that tank provides the instant water pressure and supply for the coach and then the pump kicks in when the system pressure drops to the cut-in setting of the pump. The accumulator tank specs call for the pressure in that tank to be 2psi below the pump cut-in setting.

While the tank was out of the coach, I checked the pressure in the tank and there was 0. I think it's been that way since we bought the coach. I aired it up to 38psi and it was reinstalled. I can tell a difference in the water the water delivery acts and it all works as described above. I can tell when the pump kicks in.

The water pump specs, a Headhunter Mach 5, say the system can work either with or without an accumulator tank. The pump will get to full speed and pressure instantly on demand without the tank. With the tank, it will do the same but only when the system pressure drops to 40psi.

With no air in the tank, we've never had any issues at all with water pressure. It's always been instant at full pressure.

So, what is the value of the accumulator tank in this system?

[jack14r]

When something like an icemaker needs water,the pump will not come on if the accumulator is aired up correctly.

[Jon Wehrenberg]

An accumulator tanks has several purposes. It lengthens the pump run cycle time. Instead of the pump kicking on as soon as water is drawn, it allows a certain amount of water to flow before the pump kicks in. The accumulator if plumbed properly will provide a big volume of water in a short period of time, such as to flush a Headhunter toilet. Finally, if you have a closed water system and no expansion that an accumulator tank provides, as water in the HW tank expands, such as it does from heating, you can experience hydraulic pressures if there is no place for that growth of water to go.

Your HW tank failed because the accumulator tank had no air cushion, the relief valve was failed closed, and each heating cycle of the bus from normal HW temps, to those created by engine coolant expanded the water and over time the tank grew and grew. Had the relief valve functioned, or the accumulator bladder been pressurized, the excess pressure would have been relieved.

[jelmore]

Your HW tank failed because the accumulator tank had no air cushion, the relief valve was failed closed, and each heating cycle of the bus from normal HW temps, to those created by engine coolant expanded the water and over time the tank grew and grew. Had the relief valve functioned, or the accumulator bladder been pressurized, the excess pressure would have been relieved.

Having read the instruction tag attached to the pressure/temperature relief vale, I now know that they specify the valve should be checked annually. Thanks Jon for the explanation.