High Pressure Vented Ball Valves

Please, attach a symbol for your valve. Is it a 3 way? The simple statement that it is a ball valve and vented does not make sense. If it's a shutoff valve, there will be 2 ports, and one is always pressurized, so, no vent at all.

If it's a 3 way (the vent being the 3rd way), it may be oppened to atmosphere, or you may be able to connect it to some line.

Please specify better. I don't think I understood your question fully.

The vent goes on downstream side to permit relieving pressure on the downstream piping and equipment.

Upstream pressure, as in a boiler, requires a major shutdown of the whole shebang!

If you had a vent on the high side it could create a problem in and of itself.

Yes, and this is actually a 3 way valve, one way venting downstream to atmosphere and upstream closed, and upstream and downstream connected and vent closed to the other position.

making hole on upstream side.