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 applications 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.

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.  

Re DBB and trunnion mounted valves:

A trunnion mounted valve can be fitted with a cavity bleed valve that enables that the seat tightness can be tested. Some valve vendors will efer to this as DBB (using only one valve). It is however NOT true DB since the valve seats on is tight if there is high pressure on both sides of the vave. So if you have a significant pressure difference upstream/downstream and you close the bleed and the HP side fails - the it will push the LP seat open. If the reason for requing DBB is that you have opened the line then downstream pressure will be atmosperic and then you wont have DBB at all - open or closed bleed.

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