What Is a Plug Valve?

Quick Answer

A plug valve controls flow by rotating a tapered or cylindrical plug with a through-hole 90 degrees inside the body. Lubricated plug valves inject sealant between the plug and body for sealing and are standard for pipeline crude oil and gas gathering. Non-lubricated plug valves use PTFE sleeves and suit chemical and clean-fluid applications. Standards: API 599, API 6D.

Details and Applications

Plug valves excel in services requiring frequent operation, tight shut-off, and resistance to abrasive or viscous fluids. They are common in pipeline manifolds, fuel gas systems, and multiport diverter applications. Their ability to handle slurries and erosive media makes them preferable to ball valves in certain dirty-service applications. Plug valves are among the oldest valve types and remain widely used.

Lubricated vs Non-Lubricated

Parameter	Lubricated Plug Valve	Non-Lubricated Plug Valve
Plug shape	Tapered (conical)	Tapered or cylindrical
Sealing	Sealant injected between plug and body	Elastomer sleeve or PTFE liner
Lubrication	Required (grease injected via fitting)	Not required
Maintenance	Regular sealant injection needed	Low maintenance
Operating torque	Low (lubricated surfaces)	Moderate to high
Max temperature	Up to 350 degC (depends on sealant)	Up to 200 degC (PTFE) / 260 degC (special liners)
Fire safe	Yes (metal-to-metal backup)	Depends on liner material
Dirty service	Excellent (sealant flushes debris)	Good (liner protects surfaces)
Standard	API 599, API 6D	API 599, API 6D
Pressure classes	Class 150-2500	Class 150-300 (typically)
Sizes	1” to 36”+	1/2” to 12”
Cost	Moderate	Lower
Typical application	Pipeline, crude oil, gas gathering	Chemical, corrosive fluids, clean service

Lubricated Plug Valves

The tapered plug sits in a matching tapered body cavity. Sealant is injected through a check valve and grease fitting on the top of the valve. The lubricant fills the space between plug and body, providing both sealing and corrosion protection. Regular re-lubrication is required; without it, the plug can seize.

Lubricated plug valves are standard for pipeline block valves in crude oil and natural gas gathering systems. They handle waxy crude, sand-laden production fluids, and high-pressure gas without the seat damage that would degrade a ball valve in similar service.

Non-Lubricated Plug Valves

A non-lubricated plug valve uses a polymeric sleeve (PTFE, PFA, or other fluoropolymer) between the plug and body. The sleeve provides both sealing and low-friction operation without the need for sealant injection. The trade-off is a lower temperature and pressure limit, dictated by the liner material.

Non-lubricated designs are preferred in chemical plants, pharmaceutical facilities, and any application where sealant contamination of the process fluid is unacceptable.

Comparison with Ball Valves

Feature	Plug Valve	Ball Valve
Sealing element	Plug surface + body/sleeve	Ball + seat rings
Dirty service	Superior (sealant flushes, no cavities)	Good (but cavities can trap debris)
Maintenance	Lubrication required (lubricated type)	Minimal
Multiport options	3-way, 4-way, 5-way	3-way (limited)
Weight	Heavier	Lighter

Pro Tip

For multiport applications (diverting flow between multiple pipelines), plug valves with 3-way or 4-way ports are more compact and cost-effective than multiple ball valves with a manifold arrangement.

Plug valves comply with ASME B16.34 pressure-temperature ratings and are dimensioned per ASME B16.10.

Read the full guide to valve types