When it comes to choosing the style of a BALL VALVES, piping engineers face a difficult decision.  If the pipeline is 2” or over, and when the ANSI pressure class is 600 and above, do they accept a floating ball style or trunnion style? Both designs have their strengths and weaknesses.

When making this decision consideration has to be given to the proposed pipeline media.  The worst-case scenario is a dry media, such as gas, which will remove any of the lubricants that are applied during the assembly, thus increasing the co-efficient of friction between the ball and the seat and so dramatically increasing the operating torque.

Trunnion mounted valves are upstream sealing and floating valves are downstream sealing which means the forces applied by the pressures of the pipeline media on the seats are vastly different.  This greatly affects the operating torque, with the floating design having the largest torque at full differential pressure.
Oliver Twinsafe have carried out an extensive research and development program in both trunnion and floating ball valve designs for this undoubted dilemma of which style is best when it comes to Double Block and Bleed pipeline ball valves and we have designed our products accordingly.

We ensure our floating ball valves for the pipeline sizes have strengthened stems and levers or handles to cope with the increased torque that can occur, particularly within a ‘dry’ pipeline environment. The floating ball design is available up to 3” bore.

Trunnion ball design valves can be supplied with lever operation (for lower ANSI pressure classes) but as the bore diameter or ANSI pressure class increases a more practical option is to opt for gearbox operation which is supplied as standard.

Both options can be supplied in the ASNI B16.10 and API 6D length which means existing single isolate valves can be replaced with an Oliver Twinsafe Double Block and Bleed Valve without any expensive pipe work modifications.

So which is best, floating or trunnion mounted?  There is no industry official standpoint on the subject but our research has told us that if you want a large bore, high pressure class or metal seated valve then trunnion mounted is probably your best choice. If not and your valve needs a 3” in smaller bore then the floating design should be top of your list.