Weird well pump guage behavior

A friend has a shallow well with a jet pump in the basement. The pump is a Wayne brand. I have done plumbing for years and this one has me stumped, so I thought I'd toss it on this newsgroup and see if anyone can make sense of it. I should note that I rarely run across these jet pumps anymore because most people have deep wells with submercibles these days. But this guy only has a 40' deep well on a rural farm, and gets plenty of water.
He had no gauge on the pump and has been getting air in the lines in the house. Constant spitting and sputtering from the faucets. The well has plenty of water, so I thought there was a leak somewhere in the pipes in the well. That was until I took a closer look at the pump using a trouble light, not just a flashlight. since his basement lights did not work because all the pull chains were broken off. (the guy is not handy in the least).
That's when I noticed that the clamped fitting where the well pipe attaches to the pump was leaking a slow but steady drip. Tightening the clamps did not help, so I replaced the barbed fitting and cut off the end of the pipe which was really torn up from the clamps. That solved the air in the lines.
I decided to put a gauge on the pump while I was doing the job, only to find that every pump I have ever worked on has 1/4" pipe plugs for gauges and other accessories. NOT THIS PUMP. It has 1/8" plugs. The pressure switch is not screwed into the pump, but mounted on the motor and attached to the pump by a tiny hose, with a 1/8" fitting. The pump only has two more plugs. One is above the tiny hose to the pressure switch, the other directly below the inlet pipe from the well, and there is not enough room there to put a guage.
I chose the only workable plug, (above the pressure switch hose) removed it, and using a 1/4' to 1/8" reducer, installed the guage.
The pump was primed and turned on. The guage showed ZERO pressure the whole time the pump filled the tank. I am standing there watching it, knowing by the sound of the pump that it IS pumping the tank full, and wondering why the heck the gauge is still reading zero. Then the pump stopped and it instantly jumped up to about 50lbs of pressure. As I drained water from the tank, the gauge slowly dropped until it reached a little below 30lbs and the pump kicked ON. Immediately the gauge dropped to ZERO.
WTF??????? I have never seen anything like this. Why the heck does the gauge drop to zero while the pump is running and show the actual pressure after the pump stops? This is just too weird.....
Yes, I have considered placing the gauge in the line going to the tank, but did not feel like ripping pipes apart at the time. However, this still leaves me with this unanswered question of why the gauge drops to zero when the pump is running.
Anyone ????
By the way, I did install some new light fixtures so the guy can see in his basement again...
Mark
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snipped-for-privacy@UNLISTED.com wrote:

Apparently you are reading the pressure on the SUCTION side of the pump. Your readings are normal, when the pump stops the pressure equalizes to the foot valve.
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i had somewhat similar situation and it was due to a hard film across the small tube going to the guage. the film apparently was able to transmit some pressure to the guage, but gave false readings.
Nick Hull wrote:

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wrote:

I sort of thought it was something like that but could not explain it. Makes sense...... Guess I need to move it to the piping, or else just leave it since it really does the job where it is. The idea was to determine the start and stop pressure and that it does.
Thanks
Mark
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