Wet "Live" Tapping or Dry Tapping? 2

[mikezal14]

On a newly installed watermain in a subdivision (8") is it better to wet tap or dry tap the services onto the main?( right now the main has no water in it) and why?

 

[RWF7437]

If the main "has no water in it" you can ONLY dry tap it.

 

[mikezal14]

sorry i should give more details.

The main is empty right now, would it be better to dry tap then charge the main, swab, pressure test, chlorinate and sample. Or charge the main, wet tap then swab etc.

i've always thought wet taping was better because it was easier to check for leaks on the main stop, check that the main stop was on (see water come out the curbstop) and it pushes the fillings out of the pipe.

Does anyone see it a different way?

 

[GoldDredger]

I read the following passage in one of my college books I saved:

Wet and Dry Taps

"Connections can be made either when the main is empty (dry tap) or whe the pipe is under pressure (wet tap). Dry taps are made only during the installation of a main. Most tapping done today, whether on a new or existing mains, is wet tapping. This method is preferred when adding a service connection to an existing main because it allows the connection to be made without turning off the water and interrupting service to existing customers. There is also less chance of contamination, since the pressure in the main tends to expel any foreign matter"

Intro to Water Distribution, AWWA 1986, vol 3, pp 94

 

[rconner]

[see also

http://books.google.com/books?id=7L...&hl=en&sa=X&oi=book_result&resnum=1&ct=result

]

 

[coloeng]

In our water system,when a contractor is installing a water main for a new subdivision, we require them to dry tap all of the service connections, install the service line to the meter yoke and connect to the meter yoke. They then do the flushing, disinfection and pressure test. Our reasoning for this is that all of the service connections will be pressure tested as part of the water system as a whole. I know that other systems wait until the main has been pressure tested to install the service connections.

On main line connections we almost always wet tap them.

 

[bimr]

Most systems wait until the water main has been pressure tested to install service connections.

Most then use wet taps.

The line item costs for wet or dry taps is the same.

If you do a wet tap, you will also be able to locate a leak at the time of the tap, rather than have to track down the problem later.

 

[rconner]

I generally agree with the published guidance pointed to in this thread, and particularly perhaps when directed to what I suspect are common very small service connections to e.g. a small diameter distribution water main (like 8” as the original inquiry). I will make the comment, however, that if is desirable to make a significantly larger (e.g. originally unanticipated) tap into e.g. a much larger new transmission main, I would think there could be a rather significant difference in logistics and/or cost to make the connection depending on the method chosen. In the case of a “dry” connection, it might be possible to simply cut a sizeable hole in the pipe with common tools, assemble a tapping sleeve or saddle over the hole and around the pipe (as may be required for structural strength/reinforcement etc.), then lay the branch piping (also with common, simple tools/equipment) not much unlike other pipe work. In the case however of a larger branch size wet tap under pressure, this of course requires quite heavy, complex, and specialized equipment and expertise that may not necessarily be as readily available to all contractors and utilities.

Also, e.g. if small taps and corp stops/service lines etc. are installed in the dry and prior to pressure tests, the pressure rating and capabilities of all elements/appurtenances then under pressure in the eventual test should probably be considered (I have heard that some modern mains and joints etc. are capable of, and now sometimes being subjected to, very high pressure acceptance tests, that can be well beyond e.g. the seat rating of at least some valves or corporation stops, etc.)

 

[coloeng]

Tap saddles for service connections are typically rated at 200 psi and corporation stops rated at 300 psi. As long as you don't exceed those pressures when you test, there shouldn't be a problem.

Shouldn't all elements/appurtenances of your water system be capable of handling the pressure that the system is normally operated at plus some factor of safety? Typical test pressures are 1-1/2 times normal operating pressure or 150 psi, whichever is greater. Unless you operate your distribution system at pressures above 130 psi, you shouldn't have any issues. You should take the pressure rating of all appurtenances into consideration if you require testing above 200 psi.

 

[rconner]

While I am admittedly not in the service valve, curb stop, nor corporation stop businesses, I believe AWWA Standard C800, Underground Service Line Valves and Fittings , contains the minimum requirements in Sec. 4.2 General Design , "4.2.2 Normal pressure. Normal-pressure service line valves and fittings shall be suitable for use with water at 100° F (38° C) and 100 psig (700 kPa) for 1-in.
(25.4-mm) and smaller sizes, and 80 psig (560 kPa) for 11/4-in. (31.8-mm) through 2-in. (50.8-mm) sizes.
4.2.3 High pressure. High-pressure service line valves, fittings, service saddles, and meter setters shall be suitable for use with water at 100° F (38° C) and 150 psig
(1,050 kPa) pressure."

I guess if you are instead buying service valves that are good for 300 psi seat test/service, there would be no obvious problem testing against same, of course as long as the pressure was that much or less. You are of course correct one should take the pressure rating of all appurtenances into consideration, as "a chain is only as strong as its weakest link" (this is basically what I ws trying to say).