Teeing into a water main

To supply water to a new subdivision, it was necessary to not only add a junction to the water main but to also join up two dead-end segments serving two separate halves of a loop road. The work was to be done in two phases, which would involve temporarily interrupting water service to different groups of abutters on different days. The subdivision road happened to connect near the end of one of the lines, so the developers decided to do that part first and get their connection into the new neighborhood-to-be finished.

As that segment also serves my house, the water would be off most of the day so I was ready with bottles and buckets filled up.

[Each image links to a larger version that shows more detail.]

Hole in the ground at road edge  

The water department guys came by with an electronic locator to mark about where the main ran before the construction crew arrived. They got a little bit of a late start on the digging, but it went quickly and by the time I got enough coffee into me and wandered outside to look there was already a big hole in the ground. Meanwhile the muni guys had gone up the street to shut off the valve to this segment, and were letting it drain from the hydrant at the end of the line.


(Who's that old guy?)

There's the old water main The backhoe driver got the hole down close to the pipe but obviously didn't want to hit it. A bit of hand digging exposed the old pipe and cleared the dirt away underneath it, leaving it bridging across the hole over about 9 feet of length.

The soil in this area is very uniform and sandy, and the entire operation was almost like they were playing in a big sandbox. It was clear just from watching that the guy running the backhoe was very good at it, like the massive machine was an extension of his own body and capable of very delicate, artistic movements.

Scraper tool to clean off pipe They ran a chain tool with little flat teeth around to scrape the pipe clean, as they'd have to attach leakproof fittings to some parts of its outer surface. It seemed surprisingly easy; I expected that the pipe would be much more rusty and rough but this looked in fine shape for fifty-plus years in service. The black iron was still black.

Spraying out from saw cuts They needed to cut a section out, so the guy began sawing and soon found where the water was. Most of the section is up a slight hill from here and hadn't drained all the way down, especially since pit level was a few feet below the hydrant outlet, so quite a bit of water spritzed out of here before it started to calm down. It soaked promptly into the highly permeable soil and just vanished.

Perseverance Undercutting pipe
Our saw-wielder persevered, working on this cut and the closer one hidden behind the pit edge in parallel. I gotta hand it to him -- he held steady against some of the awkward angles that would tend to make the saw kick back, to bring the cuts around underneath the pipe. And no safety glasses for most of it.

The abrasive-grit blade goes through some interesting singing resonances as it speeds up and slows down, which finally explained all the odd ringing noises I had been hearing in recent weeks from farther back in the subdivision site.

Pipe finally falls away Finally the section fell away with a thump, and they huffed it up out of the pit. The poor guy was totally soaked at this point, but I guess they're quite used to this sort of thing.

Not only was the old pipe in good shape on the outside, it was almost pristine on the inside too. Roman aqueducts aside, for a vintage-1956 or so installation in cast iron that's kind of amazing. No inordinate deposits or corrosion, and likely no concerns about future capacity with a healthy six-inch main feeding relatively few houses along this stretch. And they were about to join up *two* six-inch mains around the loop which would then both combine to feed the subdivision, increasing the net capacity to this point and adding redundancy to the system as well.

Joint ring and gland ready They prepared the incoming end for a new coupler, adding a ring and compression gland. Here's why the outside of the old pipe had to be nice and clean.

The pipe kept drooling water pretty much the entire time. The muni guys evidently couldn't get the old gate valve up the street to close quite all the way, but this didn't seem to faze anybody. Happens all the time. The backhoe operator dug a small sump in one corner of the pit, so the water would run to there and not puddle up under the plumbing operations.

Installing reducer Industry standard for neighborhoods of this scale appears to be eight-inch mains these days and that's what they had been installing around the site already, so they had to adapt the six-inch up to eight-inch to match all the rest of their stock. Besides, two 6" inside-diameter pipes at a total of 56 square inches cross-section would be feeding the single eight-inch at 50 square inches, so the engineering worked out nicely.

He did the initial tightening of the compression ring with an impact wrench, but finished up by hand-torquing the joining bolts to a rated spec. While it needs to be tight, you can't just wail on these things without risk of overdoing it and ruining the gland.

Tee assembly brought by backhoe They had already pre-assembled the tee and three new valves in eight-inch pipe, which the backhoe now floated over from somewhere back in the site.

Extra nipple added To align the stem of the tee with where they needed the subdivision supply pipe to go, they added a two-foot nipple before going into the valve.

Tee won't quite fit But they hadn't cut the removed section quite wide enough, as the other end of the tee banged into the old pipe [arrow] and they had to stop and cut a little more off that before the tee would align right.

Leveling tee assembly Then they could seat the connection and start tightening it up, checking that everything was level as the weight of the new assembly settled onto the earth. Someone mentioned that the gate valves needed to be dead vertical or they'd get cantankerous over time.

Take note of all the little blue knobs sticking off the couplers at a slight angle.

New valve assembly in place And the tee was in! Despite it being a fairly heavy assembly, a few blocks of wood and the tightened connection were enough to hold it in place for the moment.

The blue knobs are actually breakaway nuts that drive diagonal wedges down between the compression ring and the pipe, locking the joint and pipe together with just the right calculated force -- after which the thin shaft under the nut shears off and that's as far as you go. They did that to all of them, finalizing all the joints including the ones in the tee assembly itself, and just left all the broken-off nuts in the pit.

Thrust block is simply a big rock Any time a high volume of liquid makes a turn in a pipe system, reaction force is created. In water systems, this is counteracted with a thrust block to resist the force and keep the pipe from moving or coming apart. In this case it was a thrust *rock*, lowered carefully in and set against the back of the tee and thumped down just a little bit with the backhoe bucket. Then they backfilled around the rock a bit to lock it in. Not exactly a precise concrete wedge poured against undisturbed earth, but it would do.

Attaching tapping tool Dual-purpose drill and tap bit
The guys spent some time laying one or two more pieces of pipe off the stem of the T toward the subdivision site, and connecting to the run they'd already installed up there and backfilling most of that. Then they came back to the pit here to continue. Since they weren't connecting to the other remaining part of the old pipe they simply capped that valve opening off for the moment, thus disabling the nearby hydrant completely -- they intended to remove and replace it with a new one when the rest of the loop went in, but weren't ready to do that part yet. However, there was one more house tied in beyond the cut and they needed to restore water service to that.

They decided to bring that home's service off the middle of the T since it was handily exposed here, using a fitting called a corporation stop. This would be a nice demo of how subscribers typically get tied into a water main. A drilling jig is chained around the pipe, which guides a special bit that drills and taps a hole in one operation.

Air-powered corporation drill This drill is air powered, and turns the tap bit and an advancing screw through a gear train in a precise ratio to advance the bit at the right rate to bore through the side of the pipe, and then cut tapered pipe threading into the edge of the hole as it gets expanded.

Threaded hole ready Once that was done and the jig removed, the result was a nice clean threaded hole through the pipe wall. I'm guessing a certain quantity of drill shavings landed inside the pipe and they made no effort to retrieve them, but that would probably get flushed out later anyway.

Adding corporation stop The corporation stop was then threaded in to an appropriate point, leaving the valve fitting pointing upward. A little teflon tape gave some versatility on how tight it needed to be; one turn more or less wouldn't make too much difference but as with anything else in plumbing, it's entirely possible to overtighten and break these things.

Roll of copper service line Water back on, flushing system
They attached a piece of copper service line temporarily and had the town water guys turn the street back on, and used the new tap to do a basic air flush on the line. With only a one-inch or not much larger opening at the downhill end of a longish run it took a while, but ran clean. Then they could close that first valve in the tee and continue working downstream of it. At that point my water was technically back on, but I didn't reopen my own main valve and flush the inside plumbing until quite a bit later.

As much as I've objected to this overall subdivision project, this was all interesting from an infrastructure standpoint and the guys didn't mind me hanging around asking questions and snapping away, so I was pleased with how much I could learn in a day of just watching this stuff happen.

The next challenge was to find where the extra house's service came in, which involved digging to the old pipe closer to the hydrant. They eventually found it, and decided that simply removing the rest of the old main piping would make things generally easier.

Pulling hydrant and the rest They dug out a little more and cut the house service line back out of harm's way, and then chained up to the hydrant and simply yanked the entire mess of old pipe and anything else attached right out of the ground.

Hydrant and old pipe out The backhoe dragged this assembly away and laid it aside, and the guys ran a new piece of service line from the new corporation and joined it up to the existing feed with a union. Then they could backfill all of this for the moment until they were ready to build the rest of the loop connection, which would happen the next week.

All of the old iron from today and whatever else would come out of the job was slated to be recycled. Yes, I asked.

_H*   131018