? Trunnion mounted or floating ball valve

Hi people,
I'm familiar with design of ball (floating and trunnion mounted)valves. But, how can I decide which one should be used in specific situation? Which factors have main significance for such consideration?
Student

 

[Hush]

The higher the pressure or larger the bore the greater the seating force on floating balls. At some point the valve would become impossible to operate. Trunnion ball valves 'eliminate' this factor.

 

Thank you Hush!!
I think both these valves are covered with API Spec 6D, but I don't have one. Where is the border between these two valves regarding the pressure and the ball size?

 

[Hush]

API 6D doesn't specify, i.e. manufacturers discretion. Generally the deciding factor is will it function in its intended usage.

 

[visitor]

?check valves, purpose of use?

 

[Hush]

Essentially they are used to prevent backflow. As an example they are used on wellheads where injection of steam or other fluid into the wellbore is required. The check valve prevents any wellbore fluids from flowing back into your injection line.

 

[Hush]

As an adder, there are numerous types of check valves both in design and operation. One way checks which allow fluid to flow in only one direction, two way checks which prevent flow in both directions unless mechanically opened, There are check valves which will only open when a required pressure is reached and check valves which only close when a required pressure is reached. The simplest design is a ball check where the pressure force from one side forces a ball against a seat. The one thing check valves have in common is they are "normally" intended to be used as on/off devices.