New pressure switch not turning on pump

[imacdad]

I have a submersible pump on 220v with a large diaphragm tank on a 30/50 system. I put in the large tank to reduce pump usage. This past weekend I replaced the pressure switch because the old one was sticking open. The new switch works intermittantly. Works fine for a few days and then when the shower is running, will not kick the pump on when the pressure drops down. The new switch has the cut-off feature built in for low pressure. I noticed yesterday that when the shower is on that the pressure drops down slowly until it gets to about 30psi. Then it drops off like a rock. I believe this is what is causing my switch to not work right, but what causes the sudden drop in pressure? Shouldn't it be more gradual to the cut in pressure of 28psi?

[valveman]

You have too much air in the pressure tank. The point where the pressure drops like a rock tells you how much air is in the tank. If you only have 25 PSI air in the tank, then it will drop from 25 to 0 instantly. You just dont want the bladder to hit bottom and the presure drop like a rock until the pressure switch gets the pump running.

[imacdad]

I will check the pressure again. I set it up at 28psi when I installed it, but my guage may have been faulty.
Thanks.

[valveman]

No two gauges ever read the same. You need to give yourself a little cushion, especially with a low pressure cut off switch. I would go with 20 to 25 PSI air in the tank.

[imacdad]

I'll give it a try. Thanks again.