2-pc Cast Trunnion Mounted Soft Seated Ball Valve

The 2-piece cast steel trunnion mounted soft seated ball valve as a quarter-turn isolation product for pipeline, refinery, petrochemical and power service. The defining feature is the trunnion support: instead of a ball that shifts under line pressure, the ball is anchored and the seats are spring-loaded toward it. That single design choice changes how the valve seals, how much torque it needs, and where it is the right choice.

Soft seats give a tight, bubble-tight shutoff across the common service temperature band, while the cast two-piece body keeps the valve economical across a wide size and pressure range. The following sections explain the working principle, the body and seat options, isolation arrangements, dimensions, materials, testing and the information needed for a quotation.

How a Trunnion Mounted Ball Valve Works

In a trunnion mounted valve the ball carries integral upper and lower trunnion shafts. These shafts ride in bearings housed in the body, so the ball is held at the centre of the cavity and cannot move laterally under line pressure. The line thrust is taken by the trunnions and bearings and passed directly into the body, not into the seats.

The two seats are annular assemblies backed by disc or coil springs. At low pressure the springs provide the initial sealing force; as line pressure rises it adds a self-energising force behind each seat, pressing the seat against the stationary ball. Because the seats carry only the contact stress needed to seal, seat loading stays roughly constant and operating torque does not climb with pressure.

With both seats independently loaded, the valve can seal against pressure from either direction. This is the basis of its bidirectional capability and of the double block and bleed (DBB) or double isolation and bleed (DIB) function described below.

Design Standards

Design features

1. Double sealing system of packing, and firesafe design
2. Stem with emergency grease injection
3. Integral anti-blowout design structure of the stem
4. Floating preload seat ring design to ensure good sealing under Iow pressure
5. Double block and bleed function (DBB)
6. Double isolation and bleed function (DIB)
7. Anti-static function
8. Low torque design
9. Top flange self-limited design

2-pc Cast Trunnion Mounted Soft Seated Ball Valve drawing

Material of Construction

Note: Materials listed in the table are general. When ordering, please contact GNEE sales or technical team to confirm the details.

Dimension & Weight

CLASS 150 Full Bore

CLASS 150 Reduced Bore

CLASS 300 Full Bore

CLASS 300 Reduced Bore

CLASS 600 Full Bore

CLASS 900 Full Bore

CLASS 900 Reduced Bore

CLASS 1500 Full Bore

CLASS 1500 Reduced Bore

Trunnion Mounted vs Floating Ball Valve

The two designs solve the same isolation task differently. This comparison explains where a trunnion mounted valve is the better fit; for the full discussion see the floating vs trunnion comparison.

Testing, Fire-Safe and Safety Features

Each valve is subjected to pressure testing per the governing specification: shell test at 1.5 times the rated pressure and seat test at 1.1 times the rated pressure. Seat leakage for soft seats is accepted to ISO 5208 Rate A; testing is performed per API 598, ISO 5208, EN 12266-1 and API 6D as applicable.

Fire-safe design per API 607 / API 6FA, with a metal-to-metal secondary seal and graphite fire seals so the valve retains shutoff after soft seats are exposed to fire.

Anti-static device per API 608: a spring or contact path keeps the ball, stem and body electrically continuous; the resistance is verified not to exceed 10 ohms.

Blow-out-proof stem with a shouldered or integrally retained head that internal pressure cannot eject.

Emergency sealant injection ports on the stem and seats (optional per API 6D) allow temporary sealing if a seat is damaged in service.

Cavity self-relief on SPE arrangements prevents over-pressurisation of the trapped body cavity.

ISO 5211 actuator mounting pad for gear, pneumatic, electric or hydraulic actuation; ISO 15848 low-emission packing available where specified.

 

 

 

 

Provide the following to receive a quotation: nominal size and pressure class, end connection (RF / RTJ / BW), seat material, applicable standard edition, DBB or DIB requirement with SPE/DPE arrangement, actuator type, inspection and documentation requirements, and delivery destination with requested schedule. A data sheet or drawing helps confirm the specification.

Request a Quotation

Applications

Oil and gas transmission pipelines - mainline block valves, station isolation

Refinery and petrochemical units - crude, process gas and product isolation

Power generation - high-pressure utility and feed systems

Tank farms and terminals - manifold, loading and pig-launcher isolation

LNG and cryogenic systems where the body and trim materials are specified for the temperature

Suitability depends on design pressure, diameter, medium composition, temperature, corrosion control and the project specification. A trunnion mounted valve is selected where large diameter, high pressure or frequent automated operation makes low, stable torque and bidirectional isolation decisive.

FAQ

What is a 2-PC cast steel trunnion mounted soft seated ball valve?

It is a quarter-turn isolation valve with a two-piece cast steel body, a ball anchored by top and bottom trunnions, and spring-loaded soft seats. The fixed ball and moving seats provide bidirectional sealing, low and stable operating torque, and suitability for large diameters and high pressures.

How does a trunnion mounted ball valve differ from a floating ball valve?

In a trunnion mounted valve the ball is fixed by trunnions and line load is carried through bearings into the body, while spring-loaded seats move toward the stationary ball. A floating valve has a free ball that is pushed against the downstream seat by line pressure. Trunnion mounting gives lower, more stable torque and is preferred for larger sizes and higher pressures.

What do DBB and DIB mean for a trunnion ball valve?

DBB is double block and bleed: both seats block independently and the cavity between them can be vented. DIB is double isolation and bleed. DIB-1 uses double-piston-effect seats on both sides (DPE x DPE); DIB-2 uses a single-piston-effect upstream seat and a double-piston-effect downstream seat (SPE x DPE). The choice follows the isolation requirement of the service.

What are SPE and DPE seat arrangements?

SPE is single-piston effect: cavity pressure above line pressure lifts the seat off the ball and relieves to the low-pressure side. DPE is double-piston effect: line pressure acts on both the upstream and downstream seats so the valve seals against pressure from either direction. These arrangements determine whether the valve provides DBB or DIB isolation.

Which standards apply to 2-PC cast trunnion ball valves?

Design and manufacture follow API 6D, API 608, ISO 14313 and ASME B16.34. Face-to-face dimensions follow ASME B16.10 and API 6D. Flanged ends follow ASME B16.5 (up to 24 in) and ASME B16.47 (26 in and above); butt-weld ends follow ASME B16.25. Testing follows API 598, ISO 5208, EN 12266-1 and API 6D. The applicable edition is defined by the purchase order.

What soft seat materials are available and what temperatures do they cover?

Common soft seats are PTFE (about -29 to +200 degC), RPTFE (about -29 to +230 degC), PEEK (up to about +260 degC), Nylon (about up to +120 degC) and Devlon (about up to +220 degC). These ranges are indicative and depend on pressure, medium and specific grade. Soft seats seal to ISO 5208 Rate A.

What sizes and pressure classes are available?

Typical supply is NPS 2 to 48 (DN50 to DN1200) and Class 150 to 2500 (PN10 to PN420), in full or reduced bore, with flanged (RF/RTJ) or butt-weld ends. Larger sizes and higher pressure classes are evaluated per inquiry against the purchase order.

What information is needed to request a quotation?

Provide the nominal size and pressure class, end connection, seat material, applicable standard edition, DBB or DIB requirement with SPE/DPE arrangement, actuator type, inspection and documentation needs, and delivery destination with schedule. A data sheet or drawing helps confirm the specification.

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