We recently had our check valve go bad on a shallow well water pump. The valve was replaced. But ever since we have air on the water lines. My Hubby checked the fitting and found them to be tight. We then decided to replace the 20 gallon pressure tank. (since the pump is new, we put in a new pressure tank. He reinstalled the whole setup from the check valve to the discharge line from the pressure tank to the pvc pipe to the home.
All was tight, secure, the pump was primed and holding, the bladder tank was filled with the proper 28PSI the cut on/ off pressure was set a 30/50. Started up the pump an STILL have air in the lines!
Now there seems to be an additional problem, Pump cuts off at 50, cuts back on at 45?? And gauge drops rapidly back down to 28ish.
Please... any advice..

Since you likely have multiple problems and your husband did much of the work it is hard for us to guess what was done wrong. You may need to hire a plumber to be on site to diagnois

If you mean an above ground checkvalve, then I'd start thinking a leaky wellpipe. If you mean your husband replaced the footvalve in the well, as well as the wellpipe, then there has to be a leak somewhere OR the water level in the well drops enough to allow some air to be pulled in during the pump cycle.

Does the pump hold prime OK?

Yes, the pump holds its prime. That is one reason we are head scratching about this. Also the pressure holds steady when there is no water demand, even over a long period such as over night. The pump does not kick on. I would think that if there is a leak in the well pipe itself, then the pump would not hold its prime. However, I am not sure if there even is a footvalve in the well. Is that a rule of thumb; do all shallow wells have a foot valve? Some additional info... the well is about 30 years old, I believe it is 65 feet, seems shallow but the water table here is 13 feet. It is a 2" PVC pipe, the top of the well sticks out of the ground and has a sealed cap on it. It elbows under that sealed cap, underground approx. 36" deep and then runs to the house. We are using a 1/2 HP Gould's pump and a 20 gallon bladder pressure tank. Yikes, I can't fathom (no pun intended) having to dig up that 36" of dirt to look for a crack in the pipe. Even if I have to dig, how would I determine where the crack would be? Should I look for any visible signs other than the obvious? We were thinking there might simply be a malfunctioning "new" check valve or a malfunctioning "new" bladder tank. Sheesh... I dread calling a plumber for such a simple closed system. I appreciate all of your help so far. Hopefully, this additional info will help with the diagnosis.

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Pump cuts off at 50, cuts back on at 45?

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I think I would check that out first, in slow motion.
Suggest pumping up to 50 lbs. turn breakers off. Remove switch cover. Open faucet and let water out slowly until you see and hear switch points close. Read pressure gauge. Did switch really close with a 5 lb. drop in pressure? How much water did you let out?

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And gauge drops rapidly back down to 28ish.

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How much water do you get before that happens? If everything were functioning properly you should have let out about 5-7 gallons total.

You titled your post

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Water pump, Air in water line

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Yet you say you replaced a check valve. Did you replace the check valve because of air or because of loosing prime.
Is this a jet pump or a centrifugal pump?
Is well a dug well or drilled well?
Do you have air coming out faucets now?

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Suggest pumping up to 50 lbs. turn breakers off. Remove switch cover. Open faucet and let water out slowly until you see and hear switch points close. Read pressure gauge. Did switch really close with a 5 lb. drop in pressure?

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I tried this... I allowed the tank to fill with until the pump cut off (50PSI). Unplugged the pump, then opened a faucet. I could see the pressure gauge drop slowly but didn't hear a "click" in the switch until 30 lbs, just where it should happen. I did not check the amount of water yet... we are as you suggested, going in slow motion. Perhaps the switch is bad??

This all started because I was hearing a (for lack of a better description) a thunk at the end of the pumping cycle. I brought it to hubby's attention. Before he could investigate the pump started cycling like crazy with no water running in the house. He checked it out right away. After turning off the pump and doing some general investigation; he found that the bladder tank was not water logged nor were there any leaks to be found. He concluded that the "thunk" noise was a failing check valve. The valve is located just on the intake side of the pump. I might add this, the tank, pump, etc is in a very tight crawl space under the home. Certainly not for a claustrophobe like me. Anyhow, after removing the check valve he discovered that the valve was nearly disintegrated! Total corrosion to the point where the spring mechanism was popping sideways. Since the pump is many years old, we opted to replace it, as well as the bladder tank and all of the PVC piping. Sounds like a lot of work but would possibly save another trip under the house sooner than later.
This is when the air in the lines started. Of course I though there was an improperly sealed joint somewhere. But he checked and doubled checked. Still no leaks. Now after this gauge went wacky, we have no idea.
BTW.. this is a driven well and it was done by a professional plumber/well driller about 30 years ago. I would love to contact him but he has long since went to be with the Lord. So we are on our own for solutions and answers.
This weekend or sooner if time permits, Hubby is going to completely dismantle things and start from scratch. Working from check valve to line into the home.
We still would covet any help or suggestions. I will update with our finding. Hopefully this forum can help other out there that might encounter this problem. You guys (& gals) are great!

If there is a checkvalve between the tank and the well, then the wellpipe could leak and you would not lose prime.

Not real familiar with driven wells so I wouldn't know if it has a footvalve or not. The checkvalve above ground would serve the purpose.

Everything you said points to a leak in the new pipe which was installed. Even a very small leak could leak enough air into the system overnight to cause trouble.

One thing you can look at. When the pump is off, remove the cap over the wellpipe and see if there is any water in the wellpipe. If there is not, then there is either no footvalve, or it is not functioning properly.

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I tried this... I allowed the tank to fill with until the pump cut off (50PSI). Unplugged the pump, then opened a faucet. I could see the pressure gauge drop slowly but didn't hear a "click" in the switch until 30 lbs, just where it should happen. I did not check the amount of water yet... we are as you suggested, going in slow motion. Perhaps the switch is bad??

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From what you say there, the switch is good. If you repeat that with the power on, then the pump should cut on when the switch clicks, and I would think that would occur at 30#.

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Not real familiar with driven wells so I wouldn't know if it has a footvalve or not.

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Neither am I. I think it is just a pipe with a perforated spear point driven into the ground. Therefore no check valve.

If switch didn't "click" until 30 lbs. the pump shouldn't come on until 30 lbs. With switch cover removed you should be able to see a gap between the points at 50 lbs. And see them close at 30. Pump should not run until points are close.

Update:

Hubby had an idea before completely dismantling the system. He unplugged the pump, then drained the water supply into the house (left the faucet open) until no water came out. Then he drained all of the air from the bladder tank until it was at zero. Then plugged the pump in and filled the house lines up. Of course the pump ran without stopping because there was no pressure in the tank. Then he again unplugged the pump, drained the lines and now filled the bladder tank with 25PSI. Started up the whole system again and guess what?. no air in the line! The only explanation we have come up with was there must have been some sort of air pocket in the new bladder tank. Maybe a distortion or fold in the bladder? Probably will never know. So for now the problem is solved. Hopefully, this new system will last another 30 years... that should make me right about the age where I no longer care... lol.

Thanks everyone! Blessings!

Hooray!

Hubby is a keeper. Congratulations