Blancing line on Pig launcer/receiver 1

[Khansahib]

In desinging a pig launcher I have provided a 2" balancing nozzle on the minor barrel which in turn is tied in to the kicker line (downstream of kicker isolation valve) for feeding. In some modles the balance line is tide in between major and minor barrels rather than minor barrel and kicker line. What are the merrit between the two options and which one is more acceptable in the industry.

 

[zdas04]

I'm assuming that "downstream of the kicker isolation valve" means "on the barrel side of the kicker isolation valve"--a valve like the kicker line really doesn't have an upstream or downstream since it is normally shut and when shut "downstream" would be either the barrel side or the pipeline side.

Not sure why this would ever be useful. I have often had problems getting a pig to seat in the minor barrel (also known as the "throat", but "minor barrel" works) solidly enough to launch. A pressure source downstream of the pig might make the process worse and I can't see where it would ever make it better.

I always put a vent on the minor barrel as close as possible to the barrel isolation valve so that if I get some small leakage past the barrel isolation valve I can stop that leakage from pushing the pig out of the minor barrel, maybe the balance line you are talking about is trying to serve the same purpose? If that is the case tying it between the kicker and the throat would by hydraulically similar to tying it between the minor and major barrels, and I don't think that either location would provide much (if any) benefit.

I just put a vent at the barrel isolation valve and another one at the closure and skip the balance line.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

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[Khansahib]

David,
Thanks for the tip, normally, the balance line is provided to keep a little pressure in the front after door closure otherwise there is a possibility of hitting the front of the pig on the valve.