We have a design on an influent pump station at the start of a wastewater treatment plant that uses Check and Plug Valves on the discharge side of the pumps. I need to know why plug valves are better for this operation versus using gate valves?

The only calim to fame a plug valve has, is that it is the only valve design that can be in-line adjusted to stop through leakage. Barring this requirement, plug valves are very hard to turn ball valves in disguise.

A plug valve is a 1/4 turn operation, as a posed to a gate valve, where you'll have to turn the hand wheel a number of times to get it closed (something operators like!). You could replace the plug with a ball valve ...they might be a bit less expensive than a plug. Comparing cost of gates and balls are pretty close up to about 4".

Although you can certainly get away with using a traditional Jamesbury or whatever ball valve for throttling service IF it's properly selected, sized, and installed.  I see it done successfully all the time, in installations that have run for 10-15 years or more.  Just like anything else you have to weigh the trade-offs: cost vs. serviceability vs. process criticality.  Obviously in a critical throttling service you would never use an el cheapo ball valve.

I run into lots of plug valves on older installations all the time.  You see them a lot in old gas plants, oilfields, and old LPG/NGL terminals.  I think it's because 50 years ago there were no PTFE seals, so if a 1/4 turn valve was wanted, you used a plug valve.  I'm with all you guys - they are usually stuck open or closed and they frequently leak by when closed.  A plug valve is not acceptable by most plant owners for use in double block and bleed service, for example.  We replace them routinely nowadays with some other valve.  I don't know of anyone who specifies them for new installations.

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