Can a Floating Ball Valve be installed in any direction, is there a perfered direction for flow? I am under the impression that a Floating Ball Valve is Bi-Directional. I was told that I must use a Trunnion Ball Valve for Bi-Directional service. There are no indicators on the valve body as to the direction of the flow. I have looked at many manufactures and NONE of them have a perfered direction. My valve is a 4" 150#, C/S, R/F F/P to the design standards of API-608. I am of the understanding that a Trunnion valve per API-6D is designed for Double Block & Bleed and it too can be installed in any direction. HELP me please with this question.  

Floating ball valves are bidirectional.  The right-hand seat is identical to the left-hand seat so going to the left is just the same as going to the right.  In very low dP application I prefer vertical down to vertical up, but I have installed hundreds of small floating ball valves in vertical-up vent service with less than 3 psid that have worked very well with leaks being rare so this is probably more "fear and superstition" than a real data point.

In my interpretation of the OSHA definition of double-block-and-bleed, a trunnion ball valve satisfies the requirements.  I do work for several companies that adamantly disagree with my interpretation.  At the end of the day, company policy determines whether a trunnion ball valve satisfies their risk tolerance for DBB.

A double block and bleed is in my opinion constructed to block any amount of fluid ,including gas increasing pressure by higher temperature, caught in the room between the seals on both sides and the ball, from escaping to the pipeline both (and either) upstream or downstream.

Bleed construction only if equipped with bore (bore may be plugged by threaded plug or equipped with drainage valve or contraption) to bleed off extra fluid and/or pressure in room above.

Trunnion mounted in itself is no guarantee for either. On the other hand it has to be a trunnion mounted construction to fulfill the requirements.

The description of block and bleed should always be followed by detailed description (not only a norm) of how the end user require this to work (fluid, pressure, lifetime, operation mode, other details and norm etc. etc).

There ARE floating ball valves that are unidirectional.  
One example:  the severe service types such as Mogas or VTI.  Upstream is basically an energizer and the ball floats into a lapped seat for shutoff.  

Other unidirectional ball valves are chlorine or cryo valves that have a relief hole to vent liquid gas upstream from the cavity if it warms to above its saturation pressure and vaporizes.  It is inadvisable to vent downstream because when the ball floats against the downstream seat with shutoff differential, it can unload the upstream seat.  If the upstream seat leaks, then the relief hole completes the leak path if pointed downstream.  

The vast majority of floating ball valves have identical construction upstream and downstream and are fully omnidirectional.

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