Installing a wet tap into a City water main in NYC is performed by highly trained and skilled DEP field forces. Specialized tools and equipment are used to install a wet tap connection for a water service line. More specifically a tapping machine (typically a Mueller B101), an electric generator to operate the tapping machine, and hand tools are required.
In the skilled hands of a properly trained DEP tapper less than a gallon of water is lost in the process of installing a typical tap. There are various steps to successfully install a tap, and distinct components that make up a tapping machine. A typical tap takes only about 20 minutes to install by an experienced tapper.
Cleaning the main properly
The first crucial step before a wet tap on a water main is installed is cleaning off the main properly. If it is an old city water main a hammer is used to bang off layers of corrosion and dirt. Then a pipe scraper is used to clean any remaining scale or dirt.
The main must be cleaned completely around so the tap machine fits on snugly and securely. If the machine shifts while work is in progress it can have severe implications. In some cases a section of the City water main must be shut to reset the tap machine.
Installing a saddle on the City water main
The next step is to install the saddle. There are different sized saddles for each size of city water main. The saddle has a gasket that provides a water-tight fit for the tap machine.
Installing the tap machine
The actual tap machine is then placed on top of the saddle. This part of the machine contains a flapper valve. When this valve is open a shaft can go from the top of the machine to the water main. When it is closed it prevents pressurized water at the bottom of the tapping machine from reaching the top. This allows a cap to be taken off the top of the tapping machine after a hole has been drilled in the main without any water coming out.
A chain is placed around and underneath the city main and attached to either side of the tapping machine . When tightened the chain makes for a water tight seal between the tap machine and the saddle.
Drilling through the City water main
Depending on the size of the connection to be installed a bit is selected. This combination drill and tap bit is attached to the end of a shaft. This is a threading tap and should not be confused with the tap or corporation stop that will later be screwed into the water main to provide the connection for the water service. This smooth shaft goes through a water tight seal in the cap that will be screwed onto the top part of the tap machine. The flap in the body of the tap machine is in the open position. The cap is then screwed on to the machine that is already chained to the water main, and the shaft pushed down until the bit contacts the main.
An electric drill then turns the part of the shaft that extends outside of the machine. After the drill part of the bit penetrates the side of the water main it is forced further in until the tap part of the bit contacts the main and creates pipe threads. It is important to use carefully maintained tools and drill bits. Otherwise an improper or poorly threaded opening can be drilled, and leaks can occur for a variety of reasons.
Inserting the wet tap into the City water main
The shaft of the tap machine has a flap that creates a chamber inside the machine. It is similar to a periscope on a submarine. After the threads are created the shaft is rotated in the opposite direction so that the bit can be pulled up out of the main. Once the bit is above the flapper valve, the flapper is closed. The cap and shaft are removed from the tapping machine.
The bit is then removed from the shaft. The top of the tap/corporation stop, which is in the closed position, is screwed onto the shaft. The cap is then screwed back onto the top of the machine and the flapper valve is opened. The shaft is then pushed down until the threads on the bottom of the tap contact the threads on the hole drilled in the main. The tap is screwed into the water main.
The connection between the tap and shaft is designed so that when the shaft is turned in the opposite direction the shaft separates from the tap as opposed to unscrewing the tap from the main. After the tap is screwed in hand tight, a hand wrench is then used. A skilled and experienced tapper ensures that the tap is not installed overly tight. Because a wet tap has tapered threads it is very important not to over tighten the tap. Over tightening could result in splitting the city water main.
Removing the tap machine
Removing the tap machine is the easiest of all steps. Once the shaft is separated from the tap the cap is screwed off. The chain that holds the machine to the water main is removed and the machine removed from the main. Incredibly only about a gallon or so of water is lost in the whole process. Most of water is lost after the tap is installed because the water drains out of the inside of the machine when it is lifted off the main.
Who is allowed to install wet taps on City water mains?
When a new wet tap is needed on a city main none but DEP field forces are allowed to perform this work. While some NYC water main contractors own their own tapping machines and tools, they are used exclusively for private work inside private property, and only when approved by code. Obviously working on a public water supply main is sensitive work, and requires none but skilled and approved personnel.