Piston pump issues

Hi all,
I have a Duro dual piston water pump, I am having issues with air in the water and low water pressure.
I have checked all the suction line coming in for leaks. The pump didn't seem to be pulling well, so we tore the pump down and found 2 broken springs on the bottom side, replaced them and got better pull with it. I am still getting air, and low water pressure after the pump runs for a bit. Air spurts from the taps and toilet.
Pressure switch is set to 30/50 and tank charged to 25 lbs - I know it should be 28 and am wondering if I should drain it and add the extra 3 lbs?
My main concern is the air at the pump, I can release the air through a valve there so I know the air is getting in before the cold water tank. The tank is a couple years old but holds air pressure steady and no water comes out air valve.
Water is from a spring with a huge cement cistern, water level doesn't seem to be dropping below the foot valve and drawing air there.

Kind of at a loss, anyone got suggestions??

Thanks
Crimson

You have an air leak somewhere, and it would be somewhere between the footvalve and where the pipe screws into the suction port of the pump. Piston pumps have a more positive lift than an impeller type pump, so air is easier for them to get if there is a restriction. I don't know what kind of restriction you can have in a cistern unless the footvalve is plugged up.

bob...

I have a piston pump and have had two problems in the past. The first was a hole in the galvy draw pipe just below the water level so the pump would work fine for a few minutes and then start drawing air... My second problem was with the packing and packing nut on the piston arm. Adding some packing and keeping the nut tight, (once a season ) solved that problem. Both problems I rebuilt the piston first and found out it was not the problem.

Keeping the nut too tight will also wear out the shaft which will eat packing quicker. The nut should be adjusted so the pumps packing is allowed to drip ever so slightly. This lubricates and cools the shaft.

bob...

speedbump said:

Keeping the nut too tight will also wear out the shaft which will eat packing quicker. The nut should be adjusted so the pumps packing is allowed to drip ever so slightly. This lubricates and cools the shaft.

bob...

Click to expand...

Yes, my pump requires some drip for lubrication and i watch that closely.

Hi
New foot valve installed about a month ago and no leaks there that we can find, cistern is sunk partially in the ground and pipe buried from cistern to where it comes into the house, no leaks we can find in the house???
The air seems almost gone so I figure it was just from them installing new foot valve.
There is a shut off between the pump and tank and when you shut that, pump builds up to shut off pressure and kicks out perfectly.
Checked the packing and it seems ok, I keep the nuts just so they drip a wee bit too LOL
Still puzzled ..
Now the men are downstairs checking the holding tank etc.

Crimson

There should never be a valve between the pump and tank.

I still say you have an air leak somewhere, otherwise there would be no air.

bob...

The air is mostly gone now, a small spurt occasionally last couple days but thats all, water pressure upstairs is still lower but consistent.
We had found a connection at the wall the first time I posted that was *possibly* sucking air.
Whats the best way to test for air being pulled in, when there is no water leaking out?
And why shouldn't there be a valve between pump and tank? Just curious -- plumber we know said it wouldn't hurt the system to put a ball valve in there, that it wouldn't cause any restrictions.
Thanks Bob I appreciate your advice!
Crimson

There really isn't any way to find an air leak, unless it's large enough to hear it. Then you wouldn't have any water. It doesn't take much of an air leak to stop a pump from priming.

If it's almost stopped now, you may have found it in the wall connection.

bob...