When my sprinkling system is running the gage on the pressure tank will spike to 70 psi and then go to 0 psi. What can cause this?

Depends. If it is happening fairly quickly, in just several seconds, then your tank might be waterlogged. Depress the valve stem on the air valve towards the top for a few seconds. If water comes out, then you have found your problem.

However, if it happens over a minute or two, then it would seem the pump is not cutting on. You would need to remove the grey cover off the switch and see if the points are closed or not. They should be once the pressure gets towards zero.

Check that out and get back to us.

It does happen very quickly. I pressed the air stem and nothing but air came out. I removed the cover but everything is electronic in there. I did not see any points. When the pump kicked on it ran the pressure up to 95 PSI. The pump is a vairable speed pump which can pump 25 gallons per minute if that helps. There are no red lights on the control panel to indicate a problem.

The grey covered box is a pressure control switch. They are usually set in the factory. It turns your pump on and off. In side the grey cover it will show u how to adjust it and what the pressure was set at.

If the pressure switch is not shutting off at 60PSI, I would replace switch. The switches are set to go on and off at following PSI. 20/40, 30/50, or 40/60.

With cover off, look at the center of the electronics. U will see 2 stationary bars with 4 small round contacts and in front of that 2 movable bars with 4 contacts that will mate with stationary when PSI reaches turn on pressure.

If u are going to replace pressure switch, be sure to turn breaker off for pump.

Chuck

A variable speed pump... that changes things. The setup for one of those if different. And at 25 gpm, that is a really good pump. While it does sound like the switch might be bad, I'd call the pump manufacturer and see if I could get some help from them.

With I knew more about those pumps, but I don't.