Man what a pain and mess.
I first used 2 1/2 quarts. Then I capped it off and charged the piston. Now there was air trapped in the fluid side of the tank and I wanted to make sure there was none at this time.
I slowly opened up the plug to allow air to escape, tilting the pump back and forth. This was an unsafe way to do this, I think having a slow-down valve instead of a plug is much safer.
I was using a 250 pound crack pressure check valve at this time and only about 80 pounds of air pressure.
Question: What way makes more sense to get all the air out of the fluid side after fluid was added? Do you put a light charge on the gas side and hope that the pistons o-rings are not too tight and that the piston will move just enough to push out the air from the fluid side. But you might blow some fluid along with gas out to the cylinders.
Answer: don't have the piston all the way in, allow enough room for about 2 1/2 quarts of fliud. Then keep adding until all the air is replaced by the fluid. Then cap and connect everything before you charge up the gas chamber.
I say 2 1/2 quarts, but this is a ball park guess. What you want to do is have the right amount of area for the gas to safely compress with pressure. Not too much room, not too little room. Having a pressure guage on the gas side will help to find this magic combination.
If you want to move the piston be VERY CAREFULLY, the best way might be to take out the schradder valve and push down with a blunt rod. Yes you could use air pressure to blow it out. Not my first choice, not very safe if the piston shoots out. If I had to shoot it out, I might aim the open end of the tank away form anything and anyone. Maybe into a large body of water. Maybe not, I should ask Ron how he does it and report back.
