What is a trunnion on a ball valve?

A trunnion is a short shaft that anchors the ball at the bottom, with the stem anchoring it at the top. The ball rotates on these fixed points instead of floating between the seats, so line pressure loads the trunnion bearings rather than the seats.

What is the main difference between a floating ball valve and a trunnion ball valve?

In a floating ball valve the ball moves downstream and line pressure presses it into the seat. In a trunnion mounted valve the ball is fixed and the seats move onto it. Trunnion designs need less torque at large sizes and high pressure classes.

How does a trunnion mounted ball valve work?

A quarter turn of the stem rotates the fixed ball between open and closed. Springs keep the seats in contact with the ball at low pressure; at higher pressure the line pressure adds to the seat load on the upstream side.

What is a Class 600 valve?

Class 600 is a pressure class defined in ASME B16.34. For material group 1.1, such as WCB or A105, the shell rating at −29 °C to 38 °C is 102.1 bar (1,480 psi); the allowed pressure falls as temperature rises.

What is the pressure rating of a Class 1500 valve?

For material group 1.1, such as ASTM A216 WCB or A105, ASME B16.34 allows 255.3 bar (3,705 psi) at −29 °C to 38 °C. The allowable pressure falls as the temperature rises, and the seat and seal materials can set a lower limit than the shell rating.

What does 600 CWP mean on a ball valve?

CWP means cold working pressure: 600 CWP is a 600 psi rating at ambient temperature, usually marked on small threaded valves. It is a different rating system from ASME Class 600, which allows 1,480 psi at ambient temperature for group 1.1 steel.

Draft page. The factory document pack for this page is still under review. Values marked “To be confirmed” have not been verified yet.

Trunnion mounted ball valves

Ball valves · API 6D

A trunnion mounted ball valve holds the ball on a fixed shaft at the top and bottom, so line pressure is carried by the trunnions instead of the downstream seat. Spring-loaded seats seal against the ball. The design keeps operating torque lower on large bores and high pressure classes, which is why pipeline specifications usually call for it.

Who makes this valve

Signed panel factories with API 6D in force4

How licences are checkedExpiry date in the API Composite List, not the “Active” flag

Registry checked8 Nov 2026Next check 8 Feb 2027

Manufacturer and licence no.Named in your quotation, with the registry link

We publish one number per API specification, never a factory-by-factory row: a row with its licence set and expiry year would point at a single registry entry. One RFQ is quoted by several panel factories, and each quotation names the manufacturer, its API licence number and where to verify it, so you can check the source before you order. How we check licences

How it compares

Trunnion mounted vs floating ball valve: design differences (general, not a partner-factory claim)
Feature	Floating ball	Trunnion mounted ball
Ball support	Held by the seats; moves slightly downstream under pressure	Fixed by upper and lower trunnions
How the seal is made	Line pressure pushes the ball into the downstream seat	Spring and line pressure push the seats onto the ball
Operating torque	Rises quickly with size and pressure	Lower for the same bore and class
Typical use	Smaller bores and lower pressure classes	Larger bores, higher classes, pipeline service
Double block and bleed	Not usually offered	Possible with self-relieving or double piston effect seats (API 6D defines both)

Specification range

Grades listed are common ASTM designations for this valve type. The size and class range offered by the partner factory is confirmed against its datasheet before this page goes live.

Trunnion ball valve specification: size × pressure class × ASTM grade
ASTM grade	Form	Sizes (NPS)	Pressure classes	End connections	Partner factory supplies
ASTM A216 WCB	Cast carbon steel body	To be confirmed	To be confirmed	To be confirmed	To be confirmed
ASTM A105	Forged carbon steel body	To be confirmed	To be confirmed	To be confirmed	To be confirmed
ASTM A352 LCC	Cast low-temperature carbon steel	To be confirmed	To be confirmed	To be confirmed	To be confirmed
ASTM A350 LF2	Forged low-temperature carbon steel	To be confirmed	To be confirmed	To be confirmed	To be confirmed
ASTM A351 CF8M	Cast 316 stainless steel	To be confirmed	To be confirmed	To be confirmed	To be confirmed
ASTM A182 F316	Forged 316 stainless steel	To be confirmed	To be confirmed	To be confirmed	To be confirmed

Pressure–temperature rating (ASME B16.34)

The pressure class sets the maximum working pressure at each temperature for a given body material group. The table shows ASME B16.34 Standard Class values for material group 1.1 (for example WCB and A105) at −29 °C to 38 °C. Seat and seal materials may limit a valve below the shell rating.

ASME B16.34 Standard Class, Group 1.1, −29 °C to 38 °C. Shell rating only; the valve rating can be lower because of seat and seal materials.
Pressure class	Max. working pressure (bar)	(psi)
Class 150	19.6	285
Class 300	51.1	740
Class 600	102.1	1,480
Class 900	153.2	2,220
Class 1500	255.3	3,705
Class 2500	425.5	6,170

Partner factory P-T curve for this valve: To be confirmed

Class 600 flanged and Class 900 RTJ

Class 600 and above are often specified with ring type joint (RTJ) flange faces, where a metal ring gasket sits in matching grooves. Flange dimensions and facings come from ASME B16.5 up to NPS 24; face-to-face dimensions come from ASME B16.10 and API 6D.

Which sizes the partner factory supplies in Class 900 RTJ is still to be confirmed from its datasheet.

What a pressure class number means

The class number is a rating category, not a pressure in psi. ASME B16.34 gives the maximum allowable pressure for each class, material group and temperature. For group 1.1 at −29 °C to 38 °C, Class 150 allows 19.6 bar (285 psi), Class 600 allows 102.1 bar (1,480 psi) and Class 1500 allows 255.3 bar (3,705 psi).

Above ambient temperature the allowable pressure falls with the material strength, so a Class 600 valve does not carry 102 bar at 400 °C. Higher classes also need thicker walls and heavier flanges, which is why the weight step between classes is large.

API 6D or API 608: which specification applies

API 6D is written for valves in pipeline and piping systems and carries a full quality and documentation regime: design, materials, welding, testing, marking and records. API 608 covers metal ball valves with flanged, threaded and welding ends and is often named for general process service.

The two specifications do not test identically, so the purchase order decides. Name the specification, its edition and any additional requirements such as a fire test or a low-temperature test; a quotation against a different specification is not a like-for-like comparison.

Fire-safe design and fugitive emissions

A fire test is a type test of a design, not a test of every valve. API 607 and ISO 10497 burn a valve with its seats and seals and then check that it still isolates; ask for the certificate and check the valve type, size range and design it covers.

ISO 15848-1 covers fugitive emissions from the stem seal, with tightness classes measured before and after mechanical and thermal cycles. A project that specifies low-emission packing should state the class, the test standard and the cycle count in the purchase order.

No fire-test or emission-test certificate for a partner factory valve is published on this page.

Sour service: NACE MR0175 / ISO 15156

NACE MR0175 / ISO 15156 sets material requirements for equipment exposed to wet H2S in oil and gas production. Whether it applies depends on the H2S partial pressure, the in-situ pH and the temperature, so the RFQ should state those values rather than only the word “sour”.

For a ball valve the standard affects the body and trim materials, bolting, welds and hardness limits. A carbon steel valve that is acceptable in sweet service may need a different trim or heat treatment when the same line turns sour.

Testing and documents to request

API 6D specifies hydrostatic shell and seat tests, with optional supplementary tests in its annexes. API 598 is common for general-purpose valves. Ask for the test procedure, the test record for each serial number and EN 10204 3.1 material certificates for pressure-retaining parts.

Datasheet and drawings

Datasheet: To be confirmed

A datasheet, dimension drawing and STEP file will be published here, without factory branding, after the panel factory authorises them. Until then, ask for them in your RFQ.

Prices, lead times and minimum order quantities are quoted per enquiry against the datasheet you send; they are not listed on this page.

Frequently asked questions

What is a trunnion on a ball valve?: A trunnion is a short shaft that anchors the ball at the bottom, with the stem anchoring it at the top. The ball rotates on these fixed points instead of floating between the seats, so line pressure loads the trunnion bearings rather than the seats.
What is the main difference between a floating ball valve and a trunnion ball valve?: In a floating ball valve the ball moves downstream and line pressure presses it into the seat. In a trunnion mounted valve the ball is fixed and the seats move onto it. Trunnion designs need less torque at large sizes and high pressure classes.
How does a trunnion mounted ball valve work?: A quarter turn of the stem rotates the fixed ball between open and closed. Springs keep the seats in contact with the ball at low pressure; at higher pressure the line pressure adds to the seat load on the upstream side.
What is a Class 600 valve?: Class 600 is a pressure class defined in ASME B16.34. For material group 1.1, such as WCB or A105, the shell rating at −29 °C to 38 °C is 102.1 bar (1,480 psi); the allowed pressure falls as temperature rises.
What is the pressure rating of a Class 1500 valve?: For material group 1.1, such as ASTM A216 WCB or A105, ASME B16.34 allows 255.3 bar (3,705 psi) at −29 °C to 38 °C. The allowable pressure falls as the temperature rises, and the seat and seal materials can set a lower limit than the shell rating.
What does 600 CWP mean on a ball valve?: CWP means cold working pressure: 600 CWP is a 600 psi rating at ambient temperature, usually marked on small threaded valves. It is a different rating system from ASME Class 600, which allows 1,480 psi at ambient temperature for group 1.1 steel.

Standards cited

ASME B16.5: Pipe flanges and flanged fittings, NPS ½ to NPS 24.
ASME B16.10: Face-to-face and end-to-end dimensions of valves. Edition quoted to: ASME B16.10-2022.
API Spec 6D: Pipeline and piping valves: design, manufacture, testing and documentation of ball, gate, plug and check valves.
ASME B16.34: Valves with flanged, threaded and welding ends: pressure–temperature ratings by material group and pressure class. Edition quoted to: ASME B16.34-2025.
API Std 608: Metal ball valves with flanged, threaded and welding ends.
API Std 607: Fire test for quarter-turn valves with non-metallic seats: a type test of the design.
ISO 10497: Fire type-testing requirements for valves: test procedure and acceptance criteria.
ISO 15848-1: Fugitive emissions: measurement, test and qualification procedures for valve stem seals, with tightness classes from a type test.
NACE MR0175 / ISO 15156: Metallic materials for use in H2S-containing environments in oil and gas production: material selection, heat treatment and hardness limits for sour service.
API Std 598: Valve inspection and pressure testing (shell, backseat and seat).
EN 10204: Types of inspection documents, including the 3.1 and 3.2 certificates.