Mr. BobH. If there is a "plug" at the top of the upper pump I would guess this is where you would add the fluid. I've been told that it is IMPORTANT to add the appropriate type of fluid. Some systems use ATF (automatic transmission fluid) while others take a specific hydraulic fluid. If your units have a makers name or mark you may be able to search their website to ascertain the recommended fluid. Mixing the wrong types could do some damage.
That being said, unless you can see what the current level is, it will be difficult to top up the pump without getting fluid all over the place. If there isn't a dipstick attached to the plug, remove the plug and insert a small dowel of wood to determine the existing level. Get a pump type oil can and fill with fluid.
** Squirt enough fluid to almost fill the pump and leave the plug out.* Check and note the fluid level.* Go to the lower station and crank the steering wheel fully left and right.* Do this numerous times (maybe 12-15).* Have someone standing by at the filler plug in case fluid flows out during this procedure.* Check fluid level again.* If the level has remained the same, you can be fairly confident that no air is in the lower pump.* Repeat turning regime for the upper wheel checking the fluid level after every 3-4 rep's and adding just enough fluid to keep the level just below overflowing.* During the first few rotations, keep a sharp eye out for fluid overflow (any entrapped air may cause overflow).** Keep repeating this turing process until level in pump remains constant.** You should be good to go.
-- Edited by RT Firefly on Tuesday 27th of March 2012 10:02:03 AM