I have a newly installed centrifugal water pump at home with a 72 gal tank. The problem is that t pump/motor always run after using just few amount of water. I investigated its cycle and found out that it went off when pressure reached 30 psi and goes on when it is at 20psi. Have seen its diagram on prv cover saying that I can only adjust the off cycle but not the on (20 psi). What I wanted is to make it on at 10 psi, is that possible?

Possible? Yes. Smart? No. At 10 psi, you will only get a dribble in the house. It sounds like you have a water logged tank, meaning that there is very little air in the tank. Is this a bladder tank? Sounds awfully big for a bladder tank.

What you referred to as a prv is more likely the switch. What make/model switch do you have? Also, how many adjustment nuts do you see under the cover?

Thanks, have already tried 10psi by unplugging the pump/motor and observing up to what pressure can water go out. At 10 psi(based on gauge attached, I assumed its working well), shower and lavatory faucets can still be used but with low pressure only.

What is a bladder tank by the way?

Yes I mean the switch (prv). I forgot its brand/model. I'll check it when I got back home. If I'm not mistaken it has 2 adjusting nuts inside

The unit is Pumptrol, Square D. How can I make the adjustment, say make it 15psi before it would run again.

Turn the large, center nut clockwise to increase both cut in and cut off pressures. Turn the smaller nut to increase the cut off pressure only. Most people look for 20/40 or 30/50. Mine is at 40/60. Obviously, turn off power to the switch before adjusting unless you just like risking a good shock. It is trial and error. I can tell you that a half-turn accomplishes next to nothing. Think of turning the nut two or three revolutions at a time when you are trying to ratchet up the cutin/off pressures. Then turn power back on and observe the cut off point. Turn off the power, drain the system through a faucet, then try it again. As I said, it's trial and error until you get where you want it.

BTW, you would like to have a twenty pound or so differential between the cut in and cut off points.