12" Water Main Leak

[xcavate]

I have a job were another crew installed 400' of 12" ductile water line. The line is leaking out about 8 trash barrels of water in about 30 min.It leaks only from 200psi to 150psi then stops. It holds static pressure. So a pretty sizeable leak. The boss had the leak detectors come out with there high tech gadgets and cant find the leak.

I am left with the task now of trying to repair this thing. We have the leak isloated between two gate valves and there is one mechanical joint in the run. I have already dug up one of the gate vavles and had to put 8 turns on the bolts noone tighten them but that wasnt the leak. Then i dug up the 3 bells behind it and the 45 bend and still no leak. The other gate is located in the middle of the street and I did that tie in. First bell is on the shoulder of the road so it will be tough to dig up.

The leak detector think it might be a split in a length a pipe and thats why he cant pick it up.

I dont want to remove the dirt from the whole main at once due to it might buckle and blow the joints apart. So do I dig the rest of the bells up and hope its a rolled rubber or expose the whole thing a lil at a time and hope i find it. I have a pump on hand to keep at 200 psi while we look for it.

Any suggestions?

 

[RollOver Pete]

Check out the bells first.
It's much easier than digging up the whole thing.
But pay attention to what you are digging up.
Your leak will travel along the bottom of the main.
When you dig out a bell, a little extra effort digging to the bottom may show you which direction to go.

 

[xcavate]

Im just surprised with about 200 gallons leaking out it hasnt surfaced anywhere. The pipe is in sand and we havent even found a spec of water yet.

 

[danhoe]

Dig up the mech. joint first, if you already had to tighten up one joint chances are that the other one needs to be snugged up. A rolled rubber on 12" was pushed home with the hoe and the operator would have felt it. How many gallons are you loosing ? how many times have you pumped it up, are there a bunch of dips in the line you might need to work the air out, when you bleed the line out of a hydrant or corp if the water is milky that is a sign of air in your line. pm me if you want I will check in the morning leave me your mobile I will call you and get your problem solved. Dan

 

[stumpjumper83]

I dont know if any companies in your area are simlarly eqquped, but a company named Abel recon, a division of abel construction in mountville, pa. Has a camera crawler that can go down the pipe and have a look see. They may have other technologies that might help too.

 

[dayexco]

any hydrants inline? if so, can you isolate it? sometimes the "guts" of a hydrant won't hold pressure, and they'll pee up to the bleeder hole, if you have rock around the hydrant, and never expose themself

 

[xcavate]

Well I have pumped it up about 10 times. The water line is pitched up hill. The main was filled slowly and bleed to the water comes out clear. No hydrants inline and I already dug up the mechanical joint. Its either a split piece of pipe, rolled rubber or some out the gate vavle might be back feeding which I doubt. I have cranked down on the gates and I dont hear any bypass and the correlator didnt pick up anything.

It takes about 8 trash barrels to pump up to 200psi and it all leaks out. So somewhere in between 200 and 300 gallons.

The correlator guy thinks its a spilt peice of pipe. He says if it was a rolled rubber he would have picked up on it.

 

[xcavate]

The second time I pumped it up it held 200psi for 50 min before leaking. The first time and every other time I have lost the amount of water described above. This just stumps me.

 

[dayexco]

ductile? my bet's on a rolled/torn gasket. haven't seen many split ductile pipes in my 40 yrs.

 

[PipeGuy]

does the line pressure always stop at 150 psi? What is the pressure on the main from the city? I would lean towards the MJ fittings to look for the leak. If you have much deflection on your bells look there next, for instance if your water main goes up and down a hill and you just deflected the bells instead of using fittings.
A couple of years ago we had a watermain with a leak and we bact tested it and left the main live. The main was on for about 4 months and the leak never surfaced and it also was in sand.
I still would say you best bet is the MJ fittings then dig the bells.

 

[xcavate]

City main is at 85 psi or so. The main always stops leaking within 15 psi of 150psi.

 

[JimBruce42]

Sounds familiar... I was on a job this spring, where we had a leak during the pressure test for a new 16" ductile iron run. The guy with the fancy "thingamabobs" came out, went to the far points, and started to narrow it down, but couldn't without getting on the pipe. So we had to dig holes, here, and there eventually we got it to a T-joint and hydrant, but that wasn't it either, went a little further up from it to the joint, nothing, next joint nothing, but the sensor guy was able to say we were within X feet.

Long story short (too late), turns out that it was a split about 6" long in the pipe itself. The sensor guy said that if it had been a joint or a valve he would have been able to narrow it down in a flash, but a crack in the pipe apparently is a lot trickier to narrow down without digging.

We didn't have any water bubble up either, the pipe run was all shot, so we figure the water was finding a seam in the rock and just following it out.

 

[Dwan Hall]

I don't know what I am talking about here but have you ruled out one of your valves not seating? Could go back to the next valve on bath end and test those sections at the same time. may be worth a try.

 

[dayexco]

I don't know what I am talking about here but have you ruled out one of your valves not seating? Could go back to the next valve on bath end and test those sections at the same time. may be worth a try.

that is a GREAT idea!....could have existing valve that's bleeding back on you.

 

[xcavate]

Well we think we found the leak..... We have it isolated to the first length of pipe off the street. In the middle of the length is the testing corp. We are thinking maybe the corp was screwed in crossthread.

 

[tylermckee]

Only time we ever get leaks is on the saddle/corp, or on flanged fittings where someone didnt keep the flange faces clean. And we never trust valves, new or old they dont always seal 100% at 200+ PSI.

 

[mjd37]

I had a similar problem last fall, and it turned out to be the new valves we installed. The submittals were approved for valves with a pressure rating of 150psi. Didn't work too good on a 250psi test.

 

[xcavate]

Its not the gate valve backfeeding. I have water coming out from under the road. There are no bells under the road. So its either the megalug on the gate or the testing corp which is a direct thread no saddle. It goes from 200 psi to 150 psi in less then 20 min.

 

[AtlasRob]

Its not the gate valve backfeeding. I have water coming out from under the road. There are no bells under the road. So its either the megalug on the gate or the testing corp which is a direct thread no saddle. It goes from 200 psi to 150 psi in less then 20 min.

Sorry cant help, but am intrested in your terminology.
Gate valve, Ok no prob.
Bells ? ( push joints on lengths of pipe, male one end, female (bell )on other ?
Megalug ?
Testing Corp ?

 

[dayexco]

first pic is of a mega-lug...it's a joint restraining device for mechanical joint pipe

can't find a pic of a corp valve handy....it's just a valve attached to the watermain...for typically a home service connection.