Fiberglass Pressure Tank

[Sandpiper]

My steel pressure tank has once again rusted and leaked. I live in Alaska and have a drain-back system (with a hole in my well pipe and a snifter valve downstream) so that water always drains from the line between the house and well and does not freeze. Hence I cannot use a bladder or diaphragm tank (as I understand it). Is there any disadvantage to going with a fiberglass tank instead of steel? I am considering a Flex-Lite FLS 40D (https://flexconind.com/wp-content/uploads/2021/09/FLS-Dual-Port-Spec-Sheet-LR.pdf). The obvious advantage is no rust, and less sweating would also be nice. Also, it's getting harder to find traditional tanks without bladder/diaphragm to replace every 10 years. But would it significantly outlive the 10 years I'm getting from a steel tank? I do let my house go cold and freeze hard during the Alaska winter - would that be detrimental to the tank (I would of course drain it). As a side question, is there any way I could actually use a bladder tank with a drain-back hole and snifter valve?

 

[Valveman]

A brass bleeder orifice is all you need to drain the system. Using more than one will drain it faster. A vent/vac valve before a check valve at the tank will let air in and out as needed. The problem is that it will take 30 seconds or so for the air to be pushed out and the water refill the line. Your pressure tank will need to continue supplying the water needed until the pipe is refilled. I think you will need a tank that holds at least 10 gallons of water (44 gallon size tank, 86 would be better) or you will run out before the water gets to the house. Even then it will need a much lower than usual air charge. Tanks with a 40/60 switch need an air charge of 38 PSI normally. I would start with 20 PSI air and see if there is any hesitation in water supply. Then yes you can use a diaphragm tank.

But there is nothing wrong with the fiberglass tank except that the air volume control comes out the top instead of the sides.

 

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[Reach4]

Those Flexcon tanks are good, but expensive. Plus they might be hard to get unless you are a plumber or water treatment specialist.

Are you prevented from moving the water line below the frost line because there is rock you would have to dig through? It is possible to have portions of the water line above the frost line if you add some XPS/EPS insulation to increase the path of heat loss in the high spots. The insulation would have to extend to the side quite a bit. I don't have numbers.