It really depends on the type of pump the OP has got. For example The Mitsubishi EP series don't have an air tank, they have an accumulator (Mitsubishi's term for a small presure tank with a diaphragm)
The WP series does have an air tank.
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Water pressure tank 06-03-2016 10:17 PM Dapper You're a religious dogmatist but I don't believe you're a fraud
Right and wrong, not a fraud-----correct, yes I am thoroughly convinced of my Christian beliefs but not a dogmatist, at least not according to the definition.
Actual pressure tanks of 40-75 gallons or so with a bladder are available. I purchased mine in Mukdahan, actually made in USA. I have my own well and test the water about annually and it is drinkable, no microbacteria , etc. The advantage of a closed system like this is the water remains clean as it's not open to the atmosphere, and water pressure is fairly constant. My 75 is connected to a 20 GPM submersible well pump. I know of at least 2 shops here selling these, some from US, others from a Thai supplier. I have also found them in Udon, and awhile back I saw some stainless type at Global, but didn't seem that well made. The larger tank capacity allows a longer on and off run time.
So, what's been going on, Khun Peters, update please.
I have been to busy to address the issue,getting ready to go to the states for six months. When I get back in October I will secure and install a different type of pump and pressure tank, with an adjustable pressure switch to start and stop the pump.as I am going to change the system so I am going to increase the volume also.