Trunnion Mounted Ball Valve (TMBV for short ) is a type of ball valve where the ball is fixed in position (supported by trunnions at the top and bottom) and does not float like in a floating ball valve. Instead, the seats move toward the ball to create sealing. This design is widely used in large-diameter, high-pressure pipelines.

Description

1. Structure of Trunnion Mounted Ball Valve


Ball: Supported by trunnions (upper and lower shafts) to keep it fixed.
Seats: Spring-loaded or pressure-activated seats move against the ball to achieve sealing.
Operation: Quarter-turn (90°) via gear, lever, or actuator.
Standards: Designed to API 6D / API 608, fire-safe to API 607 / API 6FA.

2. Features of Trunnion Mounted Ball Valve


Fixed Ball: Ball does not shift under pressure, reducing operational torque.
Double Block and Bleed (DBB): Can provide upstream and downstream sealing simultaneously, allowing cavity pressure relief through bleed valves.
Low Operating Torque: Since the ball is supported, less torque is required for operation compared to floating ball valves.
Emergency Sealant Injection: Many designs allow seat and stem sealant injection in case of leakage.
Fire-Safe & Anti-Static: Meets fire-safe requirements; anti-static devices discharge static electricity.
Wide Range of Sizes & Pressures: Suitable for large-diameter and high-pressure pipelines.

3. Advantages of of Trunnion Mounted Ball Valve

Handles High Pressure & Large Sizes :Preferred for Class 600 and above and sizes typically DN150 (6”) and larger.
Reduced Seat Wear:Because the ball is fixed, pressure loads are absorbed by trunnions, not the seats.
Longer Service Life:Less deformation and wear on seats, especially under high pressure.
Safe and Reliable Sealing :Double block & bleed capability allows maintenance or testing without removing the valve.
Automation Friendly:Lower torque makes it well-suited for electric, pneumatic, or hydraulic actuators.
Versatile Applications: Can handle gas, oil, water, slurry, and corrosive media.

4. Typical Applications of Trunnion Mounted Ball Valve

Oil & Gas pipelines (long-distance transmission, high-pressure service).
Petrochemical plants (critical shutoff for process units).
Refineries (safety isolation).
Underground & subsea pipelines.
High-temperature & high-pressure steam or gas service.

4. Expanded View of 3 Piece Trunnion Mounted Ball Valve 
expanded view of trunnion mounted ball valve
Bill of API 6D Trunnion Mounted Ball Valve materials 
 

No. name of Part Materials
1 Body A350 LF2 A182 F316 ASTM  A105
2 Closure A350 LF2 A182 F316, A351, CF8M ASTM  A105
3 Stem A350 LF2+ENP 316 SS, 17-4 PHSS, 410 SS A182 F6a
4 Seat Ring A350 LF2+ENP 316 SS, 410 SS ASTM  A105+ENP
5 Ball A350 LF2+ENP A182F316, A351, CF8M, 410 SS ASTM  A105+ENP
6 Seat Insert Devlon, Nylon, PEEK, RTFE
7 Trunnion A350 LF2 316 SS, 410 SS ASTM  A105
7-1 Trunnion Block A350 LF2 316 SS, 410 SS ASTM  A105
7-2 Trunnion Block Pin 410 SS 316 SS, 410 SS ASTM  A105
8 Gland A350 LF2 316 SS, 410 SS ASTM  A105
9 Adapter Plate A350 LF2 316 SS, 410 SS ASTM  A105
10 Stem O-ring/ Lipseal Low Temp HNBR /Viton AED
Low Temp HNBR /Viton AED
Low Temp HNBR /Viton AED
Low Temp HNBR /Viton AED
Low Temp HNBR /Viton AED
Low Temp HNBR /Viton AED
Low Temp HNBR /Viton AED
11 Stem O-ring
12 Gland O-ring
13 Seat O-ring/Lipseal
14 Seat Subseal
15 Closure O-ring
16 Trunnion O-ring
17 Backup Ring PTFE
18 Gland Seal Low Temp HNBR /Viton AED
19 Body Seal Low Temp HNBR /Viton AED
20 Trunnion Seal Low Temp HNBR /Viton AED
21 Stem Packing Graphite
22 Seat Spring Inconel X-750
23 Bearing PTFE, Carbon Steel PTFE, 316SS PTFE, Carbon
24 Thrust Washer PTFE, Carbon Steel PTFE, 316SS PTFE, Carbon
25 Sealant Fitting Carbon Steel, SS Ball Check 316SS, SS Ball Check Carbon Steel
26 Socket Bolt A320 L7M A193 B8/B8M ASTM A193-B7
27 Socket Cap Screw A320 L7M A193 B8/B8M ASTM A194-2H
28 Stud Bolt A320 L7M A193 B8 ASTM A193-B7
29 Hex Nut A194 7M A194 8 ASTM A194-2H
30 Grounding Pin Stainless Steel
31 Grounding Spring Inconel X-750
32 Key Carbon Steel Stainless Steel Carbon Steel
33 Dowel Pin Carbon Steel Stainless Steel Carbon Steel
34 Relief Plug Carbon Steel Stainless Steel Carbon Steel
35 Drain Plug Carbon Steel Stainless Steel Carbon Steel
36 Mounting Plate Carbon Steel Stainless Steel Carbon Steel
37 Gear Operator Ductile Iron Case, Carbon Steel Worm Gear
38 Hand Wheel Carbon Steel, Ductile Iron
note: Materials also available in F321, F347, F51, F53, monel, inconel, incolloy and hastelloy.  Metal-to-metal seated ball valve designs are available upon   request.

note: Additional materials available upon request.


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