What are the pros and cons of using a plug valve or a gate valve in a pump station valve pit (in addition to the check valve). I've always used plug valves for my isolation valve, but my new employer always uses gate valves. Is either better than the other?

Either a gate or plug is acceptable in this situation.  I stick w. plugs in WW apps though.

You could argue that debris / solids could settle into the seat of the gate valve.  Moreso w. solid wedge w. nonresilient seat. Manufacturers of resilient seated gate valves will say solids settlment isnt a problem. 

Experience and use of different types will vary according to location and requirements, and product prices.

Typically for for instance US contra Europe (my experience is in Europe with European, US and Asian suppliers):

US: Plug valves more easily commercial available and common in ANSI standards, relatively cheaper than in Europe or in EN-standards.

Europe: Gate valves commercially very low prices, fierce competition, commonly used, often dominating up to 250mm  (10 inches). Above this depending on size and automation degree if knifegate or gate is selected. Seldom: plugvalves.

On types:

A plugvalve of double eccentric type will have a long lifetime, no threaded parts exposed for liquid parts (as common for gatevalves) and possibillities for throtteling and simple automation over gear or direct 90 degrees.

A resilent gate valve will be cheap, but there is much quality variation between makes. A good constructed gate valve will have a very long service-free life, and in smaller sizes up to 10 inches be very much cheaper than a plug valve.

Modern constructions of standard resilient gate-valves have overcome the earlier common defects of poor quality inner surface (thicker and better), corrosion of stem and stem nut (correct material selection) and sticking gate (PTFE guides)

For larger sizes, and if automated, knife-gate valves should absolutely be considered as an alternative. NOTE! Even more quality variation in construction between makes than for normal gate-valves. NOTE: Requires good make, precise mounting and obligatory test runs if standstill more than 3- 6 months, but then very dependable and cheap price/lifetime at least up to 600mm (24 inches). Often (in Europe) cheaper or considerably cheaper than normal gate valves in larger sizes or if automated.

Plug valves - double eccentric: Top quality for lifetime and dependability. To be considered for top critical applications, and generally compared to gate-valves and knifegate valves according to total price/lifetime considerations. In Europe this will lead to limited use of plug-valves.

I have limited experince in sizes above 24 inches, but would recommend also here a simple price/lifetime consideration between gate and plug-valves.

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