Good Morning,
  The manufactures name plate should spec out how many CFM your compressor can produce. From here you can size the drier accordingly. For example I run two 200hp VSD at 1000cfm each and my drier is rated from 1600 cfm we sized it according to the maximum amount that could ever be put across it at one time. Make sure you consider prefilters and after filters on your drier it will exstend the life of you drier. Our previous compressor and drier lasted 25 plus years and we have just replaced and upsized this past fall.  If you are still having problem tell me what size hp your compressor is and I'll work the math and show you as well.

2571

thank you 2571. i have 2 50hp hydrovanes, they are both 10 plus. i appreciate your reply.
thax again?

I'm not sure what you mean by 10 plus, please explain. But your hydrovane are a british design and they calculate in metric so here what I have so far. A 50 horsepower hydrovane generate about 7 to 7.2 m3/min so to convert to American Standards take 7 for example and multiple by 35.31 this gives you cubic feet per min (CFM) or 247 CFM. Looking forward to helping.

2570