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We have a red expansion tank in our building. We have so many problems with this tank. Every 3 months we have to change the tanks tube because the tube is perforated every 3 months.

Now an expert (hopefully) suggests to change the expansion tank with a pressure sensor. He said that this type of sensors is better than the expansion tank.

Now, which one is better and what is the difference between them?

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Is it this sort of tank? What is causing the perforation? Rust? Corrosion? Photos might help. –  RedGrittyBrick Oct 30 '13 at 16:32
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I wonder if he meant a pressure release valve rather than a pressure sensor? In any case, I'd be more concerned with what's making the tubes fail so often, my expansion tank is over 5 years old and I haven't had any problems with it. Maybe you have some galvanic corrosion? Is everything bonded and grounded properly? –  Johnny Oct 30 '13 at 16:32
    
It seems that the room high temperature is the cause of tube perforation. Now we decided to insulate the room to decrease the temperature. –  S.Yavari Nov 1 '13 at 9:17
    
If the expansion tank similar to the one linked to by @RedGrittyBrick above, it is rated for temperatures up to 120C, I don't see how high room temperature could be the cause of the tube perforation since I have never heard of a room temperature exceeding the boiling point of water. How hot is your room? –  Johnny Nov 4 '13 at 6:01
    
Our expansion tank is designed for cold water and has a chinese manufacturer. We changed the tube with a high quality italian tube. I hope that this solve our problem. –  S.Yavari Nov 4 '13 at 8:06

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I would guess from what's here that the expansion tank is on a well pump, and the suggested replacement is a constant pressure controller for the pump.

However, in most cases a constant pressure controller still requires an expansion tank (though it can be a smaller expansion tank, depending on the type of system.)

A standard well pump installation has the pump off, or pumping full-speed. The pressure tank is nearly empty at the pressure where the controller turns the pump on, and holds some gallons/liters of water when the pressure has risen far enough to turn the pump off. The pump cycles on and off repeatedly when water is used for a long time.

There are several approaches to constant pressure control. One of the simpler versions uses a pressure-regulating valve with a slight leak, and the aforementioned type of controller and tank. Starting from the "pump off" condition, this system will run water from the pressure tank until it reaches the turn on pressure for the pump, and then will rise to the pressure-regulator's set pressure (typically halfway in between on and off - so 50 for a system that's on at 40, off at 60) where it will slow down water flow to just what is being used, and maintain that pressure. Counterintuitively (but factually), the well pump actually draws less power and runs perfectly happily "partly shut-off" by the valve. If water use is VERY slight or turned off completely, the slight leak allows the pump to slowly pressurize the tank until the pump shuts off. If water is used for a long time, the pump runs as long as water is being used, until the use rate is very, very low or stops.

More complex (and usually expensive) systems use sensors and a variable frequency drive to actually change the speed of the pump to match water use and maintain constant pressure. Even those still use an expansion tank, though.

If your Italian tank bladder/tube also fails, it's probably time to suspect the poor construction quality of your Chinese tank (possibly damaging the bladders/tubes) and replace it with something better.

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