How to Order Plug Valves
Plug valves are quarter-turn rotary valves that use a tapered or cylindrical plug with a through-port to control flow. They provide tight shutoff, low pressure drop at full bore, and excellent resistance to abrasive and viscous media. Plug valves are widely used in oil and gas, petrochemical, and pipeline applications, particularly where slurries, waxes, or dirty fluids would damage gate or ball valve seats.
The primary design standards are API 599 (metal plug valves for general refinery and chemical plant service) and API 6D (pipeline plug valves for transmission and distribution systems).
Plug Valve Types
| Type | Mechanism | Typical Service | Key Standard |
|---|---|---|---|
| Lubricated (regular) | Tapered metal plug sealed by injected sealant/grease | Crude oil, gas, dirty/viscous service, high-pressure pipeline | API 599, API 6D |
| Lubricated (pressure balance / inverted pressure balance) | Internal pressure balancing reduces operating torque and improves sealing | High-pressure pipeline isolation, large sizes | API 6D |
| Non-lubricated (elastomer or PTFE sleeved) | PTFE or elastomer sleeve wraps the plug, providing self-lubricating seal | Clean gas, chemical, water, moderate-pressure service | API 599 |
| Eccentric plug | Quarter-turn eccentric disc rotates away from seat on opening | Slurries, sewage, pulp, on/off or throttling in dirty service | MSS SP-108 |
Core Attributes
Every plug valve line item in an RFQ or purchase order must include all of the following attributes.
| # | Attribute | Values / Options | Notes |
|---|---|---|---|
| 1 | Design standard | API 599 (refinery/plant), API 6D (pipeline) | API 6D valves carry additional requirements for pipeline integrity (e.g., DIB-1 double isolation and bleed) |
| 2 | Plug valve type | Lubricated (regular, pressure balance, inverted pressure balance), non-lubricated (elastomer sleeved, PTFE sleeved), eccentric | Specify the exact sub-type; “lubricated” alone is not sufficient for pressure-balance designs |
| 3 | Pattern | Regular pattern or short pattern | Short pattern saves face-to-face length; confirm compatibility with your piping layout and spool drawings |
| 4 | Size | NPS | Lubricated plug valves are available NPS 1” through NPS 36”+ for pipeline service; non-lubricated types are typically NPS 1/2” through NPS 12” |
| 5 | Pressure class | 150, 300, 600, 900, 1500, 2500 (lubricated); 150, 300 typical for non-lubricated | Non-lubricated PTFE-sleeved valves are generally limited to Class 300 due to sleeve temperature and pressure constraints |
| 6 | End connection | Flanged RF, flanged RTJ, butt weld (BW) | RTJ is required for Class 900+ and critical hydrocarbon service; BW for welded pipeline installations |
| 7 | Body material | ASTM A216 WCB, A352 LCB, A351 CF8M | LCB for low-temperature service (down to -46 deg C); CF8M for corrosive or stainless-steel piping systems |
| 8 | Plug and sleeve material | Define plug coating (hard chrome, Stellite, ENP) or sleeve material (PTFE, TFM, elastomer type) | For lubricated valves, specify the plug surface finish and coating; for non-lubricated, specify the sleeve material and grade |
| 9 | Port | Full port (full bore) or reduced port | Full port provides unrestricted flow equal to the pipe ID; reduced port has a smaller opening and higher pressure drop |
| 10 | Operation | Wrench operated, gear operated, actuated (pneumatic/electric) | Wrench operation is standard for small sizes (up to NPS 4); gear operator or actuator is required for larger sizes and remote operation |
Optional and Special Attributes
| Attribute | When Required | Details |
|---|---|---|
| Inverted pressure balance design | High-pressure pipeline service requiring tight shutoff with low operating torque | The plug is pressure-balanced by an internal mechanism that equalizes forces, reducing the torque needed to operate the valve |
| Fire-safe (API 607 / API 6FA) | Hydrocarbon service, refinery, offshore | Certifies shutoff integrity after fire exposure; specify the applicable test standard |
| NACE MR0175 / ISO 15156 | Sour service (H2S-containing environments) | Restricts body, plug, and fastener materials; maximum hardness 22 HRC for carbon steel |
| Sealant / lubricant specification | Lubricated plug valves | Specify the sealant type compatible with the process fluid and temperature range; food-grade or non-toxic sealant for potable water or food processing |
| Lift plug mechanism | Large lubricated plug valves requiring reduced operating torque | Mechanism lifts the plug slightly before rotation, reducing friction and torque; specify if required |
| Certificates | Almost always required | EN 10204 Type 3.1 (MTR) minimum; Type 3.2 for critical services; specify PMI if needed |
| Anti-static device | Flammable fluid service | Ensures electrical continuity between plug, body, and stem to prevent static charge buildup |
| Locking device | Safety-critical or lock-out/tag-out applications | Specify padlockable handle or gear operator |
Example Line Items
Correct
3 pcs - Lubricated plug valve, API 599, NPS 8, Class 300, FL-RF, regular pattern, ASTM A216 WCB body, full port, gear operated, NACE MR0175, MTR EN 10204 3.1
This line item defines: quantity, valve type, design standard, size, pressure class, end connection and flange face, pattern, body material, port size, operation method, sour service compliance, and certificate requirement.
Incorrect
3 - Plug valve 8 inch
This is missing: the design standard, valve sub-type (lubricated vs non-lubricated vs eccentric), pattern, pressure class, end connection, body material, plug/sleeve material, port size, operation method, NACE compliance, and certification. The supplier cannot determine whether this is a low-cost PTFE-sleeved valve or a high-pressure lubricated pipeline valve.
Common Pitfalls
| Pitfall | Why It Matters |
|---|---|
| Not distinguishing lubricated from non-lubricated | These are fundamentally different products. Lubricated valves require ongoing sealant injection and are designed for dirty/high-pressure service. Non-lubricated PTFE-sleeved valves are maintenance-free but limited in temperature and pressure. Specifying the wrong type leads to premature failure or unnecessary cost |
| Omitting the pattern (regular vs short) | Regular and short pattern valves have different face-to-face dimensions. If the spool drawing assumes one pattern and the other is delivered, the piping will not fit without rework |
| Specifying non-lubricated for high-temperature service | PTFE sleeves have a maximum continuous service temperature of approximately 200 deg C (260 deg C intermittent). Above this, the sleeve degrades and loses sealing ability. Lubricated or metal-seated plug valves are required for high-temperature service |
| Missing sealant specification for lubricated valves | The sealant must be compatible with the process fluid. A hydrocarbon-based sealant in oxygen service can cause ignition. A standard sealant in H2S service may degrade. Always define the sealant type in the purchase order |
| Forgetting to specify full port vs reduced port | A reduced port plug valve in a pipeline application increases pressure drop and may not meet pigging requirements. Full port must be explicitly stated for pipeline and piggable service |
| Ordering Class 600+ for non-lubricated PTFE-sleeved valves | Most non-lubricated designs are rated to Class 300 maximum. Requesting Class 600 for a PTFE-sleeved valve will result in either a rejection from the manufacturer or a substitution with a different valve type |
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