Flexibility Concerns when Connecting Watermains to Appurtenances

[BernieH]

Could someone also advise me on joint flexibility?

I understand a mechanical joint has some flexibility to it. So connecting an appurtenance such as a gate valve to a watermain using a mechanical joints is probably straightforward.

But a flanged joint is rigid, so if a gate valve is connected to a watermain using a flange, then some kind of flexible connection must exist immediately up and downstream of the valve, right? Could a push-on pipe joint be considered flexible enough? If so, how close would it have to be to the flange?

How about a hydrant lead connected to a main using a welded retainer gland. A rigid connection, but not a significant concern?

Thanks

 

[bimr]

Several of the ductile iron pipe manufacturer’s recommend that only flexible joints be buried i.e. Mechanical Joint.

For ductile iron pipe, push-on or mechanical joints are the most common joints used for buried water main service. These pipes allow some flexibility (2 to 5 Degrees depending on pipe size) at the joints. Except in certain soils, the joints are not required to support the weight of the pipe.

 

[cvg]

flanges are buried all the time, especially on valves. A push on joint is considerably more flexible than a mechanical joint. There is no need to have a flexible joint immediately next to a welded or flanged joint. In fact there is not necessarily any need for flexible joints at all, there are literally 100's of miles of welded steel pipelines which function quite well without any mechanical joints.

 

[rconner]

While it is certainly true flanges have long been used, I believe it is also true some joint flexibility is now generally regarded as beneficial in underground connections of pipelines (and maybe flexibility is particularly important when pipelines connect to structures, and I guess other pipelines can be considered as such!) I also agree most ductile iron pipe and steel etc. manufacturers are probably in agreement with verbiage in numerous AWWA (incidentally consensus) standards regarding these matters, including AWWA C600 for ductile iron pipe, and incidentally also AWWA Manual M11 for steel pipe. I would recommend a read of the past thread e.g. at

http://eng-tips.com/viewthread.cfm?qid=164171,

and I suspect other disccussions that would be accessible with some keywords and the "search" feature of these forums.