Difference Between Trunnion Ball Valve and Floating Ball Valve

A floating ball valve is a valve with its ball floating (not fixed by a trunnion) inside the valve body,the line pressure drives the ball to against the seat from downstream side to ensure sealing reliability. The floating ball valve has simple structure, good sealing performance but the seat material is required to withstand the workload since the sealing pressure is bared by the seat ring. The floating ball valve is mainly used in middle or low pressure application.

The trunnion ball valve has extra stem at the bottom of the ball, the extra stem called “trunnion”. The trunnion ball valve seat is spring loaded,the seat is pushed by the spring against the ball to realize the sealing when the valve is under low pressure rating. When the trunnion ball valve is under high pressure,the line pressure pushes seat again the ball enabling the seal between the upstream seat and ball.

The floating ball valve is normally designed for small sizes,no more than 8 inches. For the pressure rating s, the highest applicable pressure  for the floating ball valve is  as below:
Class 1500 for 1-1/2 inch and below; Class 900 for 2 inch;Class 600 for 3 & 4 inch, Class 300 for 6 inch.

floating ball valve
                                  Floating ball valve picture

The trunnion ball valve is designed for bigger sizes and higher pressure rating,size starts from 1-1/2″, up to more than 40 inch; the pressure rating is from Class 150, up  to Class 2500.

Trunnion ball valve
                            Trunnion ball valve picture

Both the floating ball valves and trunnion ball valves are able to designed with the features of fire safe,anti-static and anti-blow out stem.  Besides,the trunnion ball valves have the following features:

Double Block and Bleed
Trunnion ball valve features the front ball sealing design structure. Each seat of the ball valve can separately cut off the medium at both upstream and downstream to achieve double block function. When the ball valve is closed, body cavity is segregated from both upstream and downstream even there is pressure at both ends. The medium left in the body cavity could increase the pressure to propel the seats. The medium could be bled out through the relief valve to ensure valve safety.

Sealant Injection Device
Trunnion mounted ball valves are provided with devices for Sealant injection, which are on both the stem and seat for the trunnion ball valves of DN>150mm (NPS6), and in the body cavity for the valve of DN<125mm. When the O ring of stem or the body seat ring is damaged due to accident, the medium leakage between body and stem can be prevented by injecting the Sealant through the device.

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