Jet pump loss of pressure

"Hi"Im new here.This is a complicated post to explain,but here goes.
I have a dug well 18 ft,approx 80 ft from my mobile home.I have a jet pump in bathroom.This past few months,(after coming home one day),i turned pump on .(i always turn pump off when i go away for a few days).When i turned pump on,it ran,built up pressure,stopped and then ,after about 15 sec,started up again,built pressure to 40 lbs,shut off,and started this over and over till i shut it off.When i turn it on,the water is "right there" seems like and no problem,then it shuts off after i use what i need,and then starts up again. Its not muddy .

If it runs like this on /off a few times then it seems to get "air" in the system ,and will run ,about 3 min trying to get water and finally does,after a lot of air comes from the taps,and a large "whooosh",then all is good again.
As i say,if i use it to just run a bit and not cycle too often,its ok,but if it cycles too often then it loses the water ,and after blows out air ,then it ok....well cycling

If it was my foot valve i would lose all my water back in the well...and it wouldnt be able to draw it up all that way ,,would it? I see no where there is an underground leak,no wet spots on the lawn where pipe is buried.This happened while i was away for a few days . Sorry for the long post.
The pump is about 2 years old.The foot valve in well and pipes are about 12 years old.I checked air in my tank,,its 18 lbs and the shut off pressure is 40 ..do it need more air?
Thank you,,,please ...............i need help with this

 

So ,if i understand correct.Even though my well is about 80 ft away and 18 ft deep,,my pump will pump water right away..its like it is right there .Then sometimes after a lot of use like this it will get air and be very slow in dragging up the water....till it blows out air,then its good,till its used again too often,,etc? This is complicated for me,and i want to know for i dont want to dig up all that underground pipe.A foot valve problem is simplier than all that work lol....thanks

 

i wonder if hitting the pipe that goes down th well would loosen an dirt etc that may be keeping the foot valve open?

 

No my well is almost full.It will only start pumping air after i use the pump with it going on and off for some time (i have to use it this way ,for now).Then it will have no water,and pump will run,and then all of a sudden a big whoosh comes up through the pipe,and then,theres water.Till the next time i run pump a lot ,with it shutting on/off.
If i go away ..even for two weeks,and come home,start the pump,there is water right there....funny.But,use it a lot with it shutting on /off on /off and air goes into it

 

Update on my water pump.The shut off pressure is 40 lbs,and i checked the air pressure in the tank and its only 18 lbs (i would assume i need more air added?) .
Also i unscrewed the primer nut on top of pump,and almost had it turned out when i lost my prime,i heard a sucking and water going out of the pump,,,and had a heck of a time getting the pump primed again.It did after a while and opening up a faucet and then after a large gush of air came out,it primed.Still cycling on /off every time i use it .

 

No. If your pressure switch is set for 20/40, with a jet pump you would usually have about 16 psi. The symptom of too much precharge air pressure would be a stutter in water pressure when the pump starts.

With a jet pump, you usually would want the air pressure to be 4 or 5 psi lower than the cut-on pressure of the pressure switch. A jet pump takes a while to get the pressure going. Maybe with such a low pressure, a smaller differential could be OK since the jet pump can develop about 20 psi without the jet.

 

I dont know,,im at a loss here. I understand nothing about a pump,and water line.Maybe it has a leak in the pipe under the ground?,,or like you said,the foot valve is bad.If i change foot valve,how will it prime up to the mobile home from deep in the well,after the line is empty? I know when i first installed the system,it took another pump connected to my water line to draw the water to the home,from the well.I dont know what to do,where to start,,etc.Dont want to dig up water pipe if it isnt that,

 

Pump the well to where the pump shuts off. Close the valve to the house. What does the pressure do?

You could fill a container. If you make that high enough, you could move water with a siphon hose. For a container, you could line a waste container with a couple plastic bags (for redundancy). The bags let the dirty waste container not contaminate the well.

There is a troubleshooting technique that I have not seen discussed. I may have missed that. But anyway, it involves using a combination vacuum+pressure gauge. If the problem is a leaky foot valve or under-water leak, I would expect the pressure to drop through zero into a vacuum. The amount of the vacuum would depend on how far down the leak is, but only to the water surface in the well.

So if it is a leak at the same altitude of the pump, expect the pressure to drop to zero. If the water surface was 20 ft below the pump, expect the vacuum to drop to about 8 psi of vacuum. This presumes a single leak. If you have a leaky air valve and you have a vacuum leak, then expect zero vacuum. If the vaccum leak is small compared to the water leak, you might get a 7 psi vacuum that then moves to zero as air leaks in.

I have not tried this. It seems like it should work.

 

I have no shut off valve from pump to house,(i assume that you mean so the water will stay in tank and not go back to well)? ,only ones that shut flow of water to various taps throughout the house.There is no check valve on my pump to pipe to well.I am going to try the easyest,cheapest way first,,,change foot valves i think

 

You assumed incorrectly.

If you consider changing the foot valve to be easy, good deal.

 

In my mobile home,,the kitchen ,and bathroom are two rooms side by side,the pipes are all right there ,,,no leaks.I dont know whats going on then .

 

my pipe (that comes from house)i n the well is about 5 ft down and its easy to get at as it comes in from the side,it has a angle fitting then i take off the clamps holding the pipe with the foot valve ,and haul it up,change valve ,plunge the pipe up and down till water comes from top of pipe,and re connect to where pipe goes to home.......maybe it isnt that easy,,but it is not leaking inside,,all my pipes are exposed in the house.

 

and i have no idea what to do lol

 

It sounds as if you are describing a pitless adapter. That would indeed make changing the foot valve easier.

However that offers an additional point of possible leaking. Possible does not mean that is where your leaking is.

First confirm that you have a pitless adapter. What follows presumes that you do. The next time you pull it, take a photo of the part that you remove, including any symbols or words.

It would probably be a good idea to replace the o-ring on the pitless. Also, each time you put the pitless back, you want to lightly lubricate the o-ring. I like Molykote 111.