Compressor Fill Rate Challenge...
- I have been on a 4 year quest to bring the fill rate of my RIX SA3-E up to the 3.0 cfm that it is supposed to be achieving. The first big jump came when AntiqueDiver Bill helped me discover that it had the wrong size pulley/sheave and was running the compressor at about half of its specified 2300 rpm. A bigger pulley increased the fill rate noticeably. Later I rebuilt the cylinder heads and re-ringed the pistons. Then I got an RPM meter and discovered I still wasn't running at 2300 rpm. So I got an adjustable sheave and was able to dial the rpms up to 2250.
- At this point, it was filling tanks pretty fast and since most tanks still have something left, I was estimating and thought I was filling at about 2.9 cfm.
- Well, somewhere in the winter boredom of waiting for the lakes to unfreeze, I stumbled on the AireTex compressor site and read a method to measure the true fill rate and not an estimate. Apparently it has become acceptable for compressor companies to quote an "SCFM" fill rate that is based on filling an 80 cf tank from 500-3000 psi and counting it as a full 80 cf fill. This is not accurate.
- With the AireTex method, you have to fill a tank from completely empty, ZERO pressure. And you put a stop watch on how long it takes to reach a known pressure/volume. You hook up an empty, 0 psi tank, open the valve but keep the fill whip valve shut. Then you turn on the compressor and pump everything up until the fill whip reads the same pressure as you're going to fill the tank. (You don't want to count how long it takes to pressurize the compressor, moisture separators, filters, and fill whip). Then you open the fill whip valve and start the stop watch.
- Long story short, my RIX SA3-E filled that tank from 0-2200 psi at a rate of 2.7 cfm. I emptied the tank and tried it again to get the same result. So, that method is consistent and true. And I may not be getting the full 3.0 cfm rate, but 2.7 ain't bad and my RIX is running perfectly.
- BUT, I wasn't this sensible about it right away. I thought about adjusting the rpms higher to achieve the elusive 3.0... I could get that thing screaming just to save a few minutes of filling time. I talked to Sea Hunt Jerry about it and I think he got the bug and tried measuring the rate on his Bauer compressor... It was supposed to be 4.9 and I think he said he got 3.3 cfm. "It took FOREVER to fill that HOG TANK up to 500 psi!" We were BOTH upset about our less than expected fill rates... But we're okay now. The truth has set us free!
- TAKE THE CHALLENGE!
Have you measured the true fill rate of your compressor from 0-full psi? Do you DARE?
After all it may be disappointing. It's almost guaranteed to be a lower fill rate than you THINK you're getting. Good luck and please post results here!