Pressure Balance hole in ball Valve 1

[MA123d]

As per API 6D 25th Edition, the design of the pressure balance hole, when equipped, shall have a ratio between the length of the hole
and the hole diameter of less than 10 (L/D < 10).

How / Why this ratio is provided ?

 

[jmec87]

The intention was to minimize the risk of the hole getting plugged and then no longer providing the pressure balance functionality during service. A hole with a high L/D ratio is more susceptible to plugging due to fouling.

The specific ratio (L/D < 10) was arbitrarily chosen.

The 6D task group has recognized that this could result in undesirably large pressure balance hole diameters on large valves. There is an addendum in progress (planned to go to ballot this week) that would limit the maximum required hole size to 0.5".

 

[bryansonnier]

Just a thought, if you need a smaller diameter but have a long run, could you use a stepped hole so that at no point it would violate the rule?

So instead of a hole 6" long x .5" diameter L/D = 12 you could have a first hole 3" long x 1" diameter L/D = 3 and a second hole 3" long x .5" diameter L/D = 6.