A trunnion-mounted ball valve is a valve design in which the ball is fixed by trunnions (support shafts). Its core structure consists of a valve body, a ball, trunnion supports, a valve seat, and an actuator. Unlike traditional floating ball valves, the ball in an imported trunnion-mounted ball valve is fixed by upper and lower trunnions and rotates only around its axis to achieve opening and closing. This design significantly reduces operating torque and improves sealing reliability under high-pressure conditions.
What are the parts of the trunnion ball valve?
The structural design of a trunnion-type ball valve revolves around "stability" and "sealing." Its core components include the ball, trunnion, valve seat, valve stem, and valve body:
Ball: The ball surface is machined with a circular through-hole, the diameter of which matches the pipe's inner diameter, ensuring minimal fluid resistance when fully open. The ball is typically made of stainless steel, carbon steel, or a corrosion-resistant alloy to suit different media requirements.
Truncuse: Symmetrically positioned support shafts (trunnions) on both sides of the ball are connected to the valve body via bearings, forming a fixed structure. The trunnions not only restrict the ball's axial displacement but also reduce operating torque through rigid support, allowing the valve to open and close easily even under high pressure.
Valve Seat: The valve seat employs a spring-loaded design, automatically compensating for wear and maintaining sealing pressure. Some high-end models have lubrication ports around the valve seat, allowing lubricant injection to reduce friction during closure and extend service life.
Valve Stem: The valve stem is connected to the trunnion via a key, transmitting the rotational torque from the drive unit (manual, pneumatic, or electric). The valve stem seal utilizes a stuffing box structure with a spring-loaded design to effectively prevent media leakage.
Valve Body: The valve body is typically a one-piece cast or forged structure, with a material matching the ball to ensure pressure resistance. Its internal flow channel design is optimized to reduce fluid turbulence and lower pressure drop.
Trunnion Ball Valve Dimensions
trunnion mounted vs floating ball valve
| Feature | Trunnion Mounted Ball Valve | Floating Ball Valve |
|---|---|---|
| Core Structure | Ball fixed by upper/lower support shafts (trunnions). Seats are floating, typically spring-loaded. | Ball has no fixed support, only connected (often loosely) by the stem. Ball "floats". Seats are fixed in the valve body. |
| Working Principle | 1. Sealing: Closing pressure pushes floating seats against the ball. 2. Torque: Lower & more consistent operating torque (especially under high pressure) due to fixed ball position. Friction mainly at seat/ball interface. |
1. Sealing: Closing pressure pushes the floating ball against the downstream seat. 2. Torque: Higher operating torque, especially for large sizes/high pressure. Torque increases significantly with pressure due to ball/seat friction. |
| Key Advantages | High Pressure/Large Bore: Robust structure. Sealing force generated by media pressure. Suits high pressure (Class 600, 900, 1500, 2500+), large bore (DN100+). Low Torque: Easier operation (critical for large valves), extends actuator life. Bidirectional Sealing: Typically designed for bidirectional sealing. Less Seat Wear: Minimal seat/ball friction during operation. |
Simple & Compact: Fewer parts, easier manufacturing, often lower cost (small sizes/low pressure). Excellent Low-Pressure Seal: Good seal at low pressure/vacuum via preload. Lighter Weight: Generally lighter than trunnion valves at same size. |
| Key Disadvantages | Complex Structure: More parts (trunnions, bearings, spring seats), higher cost (especially smaller sizes). Larger Size/Weight: Generally bulkier/heavier than floating valves at same size. |
Pressure/Size Limits: Limited for high pressure (>Class 600 typically) or large bore (>DN150 typically). High sealing force causes excessive torque, ball distortion, or seat damage. High Torque: Requires large actuators under high pressure. Mainly Unidirectional Seal: Usually designed for flow in one direction. Weak bidirectional sealing. More Seat Wear: Higher seat/ball friction during operation. |
| Typical Applications |
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Trunnion mounted ball valve in stock
