Is the reservoir built into the frame? Regarding the mystery device, maybe a filter with a bypass for cold weather starts or perhaps even servicing the filter with the system live? "Refill valve" appears to be able to divert flow simply back to tank. Dunno why you need that on a splitter? 3.5" cylinder + 16 GPM pump = 8 second cycle time assuming a 24" stroke. Should be PLENTY fast. 22GPM may be a waste/create heat issues depending on line friction. Remember that increasing the GPM of the system is going to generate more heat. I'd take operating temps of the oil in the reservoir before upgrading. If your already over 160 degrees then you might want to consider increasing the reservoir size or adding some kind of cooler. Ideally the oil should never exceed 180 deg. Warmer than that will decrease oil life. This thing needs a new suction hose ASAP by the looks of it. Don't wait for it to leak air/cavitate the pump. Suction hose isn't big $$. Also suction line is kinda small/long for going 16GPM or higher. Build a hyd. log lift for it and name it "SplitZilla". EDIT: If you do modify the hydraulic system I'd ditch that filter setup and plump a regular spin-on into the return line off the valve. Having a filter in the suction line can be restrictive and excessive restriction will cause pump cavitation and that ain't good. The fix ain't cheap either.