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Difference Between Floating Ball Valve & Trunnion Ball Valve.
Datetime: 2016-06-18    Visit: 776

The key difference beteween a floating ball valve and a trunnion mounted ball valve is how each achieves a line seal. Trunion mounted ball valves are uses a spring mechanism and/or line pressure assistance to drive the upstream seat against the stationary ball. The surface area exposed to the pressure through the relatively small passageway is actually just the back of the seat.

 

The floating ball valve utilize natural line pressure to press and seal the ball against the downstream seat. The line pressure is exposed to a greater surface area - the entire upstream face of the ball, which is an area equal to the actual pipe size.

 

A floating ball valve is a valve with its ball floating (not fixed by a trunnion) inside the valve body, it drifts toward to the downstream side and tightly pushes against the seat under the medium pressure 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. Due to unavailability of high performance seat material, floating ball valve is mainly used in middle or low pressure application.

 

Design FeaturesReliable Seat Seal

The structure design of double-beveled sealing ring has been adopted to reduce the friction between the ball and the sealing ring to achieve lower operation torque.  When the medium pressure is low, the ball has smaller contacting surface with sealing ring, which introduces higher sealing pressure to ensure the sealing reliability. When the medium pressure gets higher, the contacting area between ball and sealing ring increases accordingly. Larger contact area reduces the sealing pressure to avoid the deformation of sealing ring.

 

Fire Safe Design

In case of fire, non-fireproof material for packing and seat will be burnt-out and considerable medium leakage may possibly cause fire spread. CRV adopted metal to metal seal as auxiliary structure to prevent medium leakage in case of fire as shown in figures. The fire safe design confirms to the requirements of API607, API 6FA and BS 6755.

 

Ball of trunnion ball valve is fixed, it does not move with medium pressure. Trunnion ball valve has floating seats.  The seats move with the medium pressure to tight the ball and seal ring to ensure sealing reliability. Bearings could be mounted in top shaft and bottom shaft, which reduces operation torque. This is widely used in valves with high pressure and big sizes. To decrease the operation torque and increase sealing reliability, lubricated ball valves are adopted in recent years. A special sealant is injected between sealing faces of lubricated ball valve to create a layer. This increase the sealing reliability while decreasing the operation torque, which is better for high pressure, big sized ball valves.

 

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.

 

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.

 

Anti-static Design

Except for the anti-static features floating ball valve has, the trunnion ball valve has more. The ball of the trunnion ball valve gets close contact with each other through the trunnion, adjusting cushion, and down-end cap, the passage of static electricity thus forms together with the valve, which may lead the static electricity caused by sparks generated by friction between the ball and seat during on and off performance to the ground to prevent the possible  risk of fire or explosion.

 

Fire Safe Design

With the valve heated in a fire application, the nonmetal material parts such as seat sealing ring of PTFE,O ring for the stem, and sealing gasket for body and bonnet, might be damaged due to high temperature. CRV's special design of auxiliary metal to metal or the graphite seal is designed for the trunnion ball valve to effectively prevent both internal and external leakage of the valve in case of fire As required by customers, CRV's fire safe design for the trunnion ball valve meets the requirement of API 607, API 6Fa and BS 6755.

 

Design Feature: 
Trunnion Mounted. Side Entry/Top Entry. Independent Ball & Stem
Full Bore/Reduced Bore. Cast 2pcs Bolted Body /Forged 3pcs Bolted or Welded Body
Soft Insert Seat/Metal–to-Metal Seat
Anti-Blowout Stem. Fire Safe Design to API 6FA/607. Anti-static Device
Double Block & Bleed Function. With Vent and Drain Hole
Grease Injection on Stem & Seat . Extended Bonnet or Stem Optional

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