do we have an airlock?..if so how can we fix this...cows have no water....how can we tell if we have an airlock?

 

You could close everything off the valve and hook pressurized air up to the pipe anywhere down stream.
If the valve is bypassing the air, there will be bubbling in the cistern. Open and close the valve and see if the amount of bubbles changes. That way you can tell if the valve is working and sealing off.

 

How many water hydrants did you have open at the beginning and how many are now open?

I'm wondering if you didn't initially exceed your flow rate and sucked air back through an open hydrant and air locked the system.

If it is air locked your going to have to get the air and water in the pipe to move some how either using pressure or vacuum.

 

they didi try opening and closing the gate valve...it did burp a little....but we still have only a trickle down lower...they are thinking they will cut the pipe midway or where the steep decent ends....see if water flows freely there....??? this seems crazy...2300 feet of pipe...

can we blow air from below back toward the cistern?....how much pressure?

 

Nearly 8 football fields long?

While my first thought was a kink in the pvc line, I'm thinking it could be air in the line. While it is generally look at as a gravity system, in rolling terrain it is also a syphon system.
You need to fill the pipe with water. I can't imagine how you'd force water into the pipe from the cistern, so how about you try to suck water from your hydrant? Shut off all the hydrants, except one. Hook up a suction pump at the open hydrant. Once the air is cleared, it should flow.

 

It's to early to read your question over and over, but do realize the gate of a gate valve can come loose, drop and cut off your water supply. May a rag was left in the piping while preforming repairs...My 2 cents

 

You have a blockage someplace. Is there a screen on the cistern outlet? You may have been better off to have used a larger size polyethylene pipe leading to a clean out box farther down with the smaller lines coming off that. A larger size would pass debris easier. A clean out box with a sump would allow debris to settle.

 

yes, there is a screen on the outlet pipe....the idea of a cleanout box is great....

so they cut the pipe below where they just installed the new pipe....almost washed them away...good flow...no blockage to that point....so gate valve, all the two inch pipe and into the inch and a half are good....they will repair where they cut.....and open a hydrant beyond and turn the water on again...any air should be pushed forward....I think....

if there is not any water pressure beyond this new repair point then we have to deal with that...there could be a blockage in there, but at least we know the new pipe is all good down the steepest part....flowing from cistern....that is the first 1200 feet from cistern....now to deal with the rest of the system...

 

on roling terain there is a chance there is an airlock in one of the high points ive had i where the pressure from the cistern was not enough to push against the buoyancy to push the bubbles out what i did there was fill a barrel with water then attach a pump up to the last hydrant last hydrant on the line this way the pressure from the pump and the buoyancy are heading in the same direction this had helped me clear airlocks in gravity systems many a time.

 

Does the initial gush of water, and then drastic slow down, happen every time you open it? Meaning, if you close the valves, wait 20 minutes, and open back up, does it initially gush out, then slow down again?

If that's the case I'd say you have a partial blockage for sure, be it valve, or some other obstruction.

My other thought is friction loss through the pipe. Did you downsize the pipe when you went to pvc? That's a good length of run. Do you have any idea what the difference in elevation between the hydrants and the water level in the cistern is? That would help determine how much pressure you should have. Friction losses would slow you down a lot over a long run. Specially since you say you kept reducing the size of the pipe.

The air lock is a decent thought too. That would be easy enough to push out with a pump. Drop a submersible pump in the cistern and route the discharge into your piping. It should only take a slug of water to get that siphon going.

 

update on water system:...

it was a combination of blockage and air lock....we are up and running now, wiser for having worked through all of this...we just replaced a couple of frost free hydrants...easier than taking them apart....and used the second story of the house to 'burp' the house lines.....and most important of all......we learned a lot about what not to do if there is ever a next time...

 

gwithrow,

HI...I maintained a gravity feed domestic water supply to a dated farm house located in the rolling hills for a lady. She shared the many issues with the system when her now deceased husband cared for the system. Days were spent attempting to get the system back up according to her. My solution to get rid of the air pockets in low spots was to use a vacuum cleaner on the final point of use piping to suck the trapped air/water from the lines. A 55 gallon barrel was used to hold the vacuum and catch any surge of air mixed with water to prevent flooding the vacuum cleaner. This fix certainly beat climbing the small mountain to get to the spring and avoided me having to make the 78 mile trip one way.

 

We have a spring that supplies our house and 20 head of Dexter cattle with water.

It's about 600 feet from the house.

The spring is mentioned in the deeds for the property going back to the early 1800's.

The line goes under the road and when the town was repaving they dug a nice trench for me and I put in a new spare section 'just in case'.

When they were digging they uncovered several of the 'really old' lines from the past.

One was even made out of wood.