flow through partially open gate valve

[wra]

Is there a good table or equation to let me estimate the amount of flow passing under a "cracked" open gate valve? This is located between two pressure zones with about 100' head differential. I could simply use an orifice equation, but wonder about the best Cv and the area. (and I know this is the wrong way to use a gate valve)

THANKS

 

[77JQX]

See if you can get your hands on a copy of the "Handbook of Hydraulic Resistance" by Idelchik. Or, this site lists K values for part open gate valves:

http://www.engineeringtoolbox.com/minor-loss-coefficients-pipes-d_626.html