Water pressure tanks: Diaphragm type vs traditional

[boybi]

What's the advantage of diaphragm type over the traditional steel pressure tanks?

[ghosthunter]

What's the advantage of diaphragm type over the traditional steel pressure tanks?

For one, no need to periodically drain the pressure tank of water.

Traditional steel pressure tanks depend on air being compressed inside the tank. The trapped air tends to dissolve into the water over time so the volume of air get less and less so the pump turns on/off more often which may result in the pump motor burning out.

[boybi]

How about durability? Won't the diaphragm inside get torn over time? Is this type of pressure tank commonly used in households already?

[ghosthunter]

How about durability? Won't the diaphragm inside get torn over time? Is this type of pressure tank commonly used in households already?

The diaphragm is a concern for me as well if I was buying a new pressure tank. I assume overtime (years) it will develop a leak and need to be replaced. But given the compact size, if you try the same with a traditional steel pressure tank, you will find yourself draining the tank very often. But I haven't used a diaphragm type pressure tank yet.

Anyway, if you are going for the traditional steel pressure tank, just make sure you have it in a sunken portion of the flooring and have adequate drainage.

[oj88]

Not that too often GH. We drain ours every 4 months. Takes around 15 mins to do it. We do this through a faucet+hose near the outlet of the tank. I put the drained water in a drum so nothing is wasted.

The tank is drained of debris through the bottom drain valve once a year, and only after most of the water has been transferred to the drum.

[ghosthunter]

Not that too often GH. We drain ours every 4 months. Takes around 15 mins to do it. We do this through a faucet+hose near the outlet of the tank. I put the drained water in a drum so nothing is wasted.

The tank is drained of debris through the bottom drain valve once a year, and only after most of the water has been transferred to the drum.

The frequency of draining of the tank depends on the amount of use of the pressure tank and size of the tank too.

[boybi]

So will it be wise for me to get the diaphragm type? It costs 3-4x more than the traditional steel pressure tanks.

[yebo]

although the diaphragm type costs 3x more it will last longer. the reason is simple - higher frequency of fluctuating load (fatigue loading). the conventional tank loses air in time, and as it loses air the frequency of pump cycling increases also. this equates to more fluctuating pressure inside the tank over the same time period AND with the same pressure range (amplitude of fluctuation). result is the welds will ultimately give way and the tank will leak at the seams. on a diaphragm type since the air in the diaphragm is not lost (unless the shrader valve leaks, the valve that is the same as the one use to fill air in the tires of your vehicle) then the cycling of the pump is more regular, and therefore less.

you can lessen the effect of fluctuating load by having the pressure settings (On/Off) as close as possible. say instead of On at 15psi/Off at 35psi you can make it On at 25 psi/Off at 35 psi. the amplitude of fluctuation decreases BUT the frequency will increase. the effect is less amplitude but more cycling, resulting to shorter life of the motor and pressure switch. so it will depend on you which is more affordable, a new pump and switch or a new tank.

iwe have only used the diaphragm tank once, that was what we had in the province. never had any problems with it from the time it was installed when i was in grade school until we left when i was in college. but of course that was made in germany, way back in the 70s. as for conventional tanks, i've used these tank for 10 years already, been through 1 stainless and 3 GI tanks in those 10 years. the 4th one is already due for replacement again.

[boybi]

I was told by the salesman that diaphragm type tanks have more water capacity than conventional steel tanks of the same dimension. Is this true?

[ghosthunter]

I was told by the salesman that diaphragm type tanks have more water capacity than conventional steel tanks of the same dimension. Is this true?

true... because conventional steel tanks use the trapped air as the method to create water pressure as compared to the bladder being used to create the pressure.