If of any interest, would also mention that pump efficiency pass/fail specs depend on the pump design. (we use external gear, no piston or geroter pumps. Only the transaxle TRW motor uses an internal gear geroter design)
An external gear type, minimum and typical efficiency would be 80-85% gpm delivery at 2500 psi approx, compared to the theoretical and maybe the actual gpm delivery at 0 psi with an inlet head pressure ( flooded inlet at atmospheric psi 14.7#). The pump has a delivery drop off curve whereby at a threshold rpm, 0 psi, the gpm will drop off, meaning the capacity of the pump has been attained and will quickly drop from overspeeding by the engine or input shaft. When testing a pump on tractor, a flowmeter will measure efficiency of clean, unaerated, correct viscosity oil under this condition at governed WOT.
The search for a new replacement pump should be gpm rated nearly at or slightly below engine governed speed (typ. 3600 rpm) since CCI's are direct crank mount. Look for the pressure loaded efficiency rating at a mfr tested rpm and gpm delivery. If the pump is above 85%, you have a really good used, or typical new performing pump. If the pump is below 80%, then overheating of the oil will rapidly deteriorate the pump as the oil is only recirculating inside the pump itself (internal gear slippage). Its probably time to think about a new one because oil seals in the pump and related downstream components don't like hot oil above around 200F. Cast iron center section pump bodies offer the highest resistance to wear, aluminum is cheaper and will not tolerate contamination as well. Most everyone will be buying an aluminum pump as the lower gpm units are price rated. Cast iron is for industrial equip, typically.
If a hyd system is properly maintained, designed for optimized flow without causing backup restrictions(funneling), and has a relief valve set to factory spec. it will last many years. Maintenance, oil spec, overspeeding, contaminated hyd components, and wear are the enemies of our tractors. Which is true of any hyd sys. Albeit, most of us don't have flowmeters, a hyd shop would likely or an ag or ind. equipment dealer, and perhaps they'd check it on the tractor (cheaper maybe than bench test). I used to have a flowmeter and I miss it but had to turn it back in when I left a previous job.
A lot of blah blah blah, but I love hydraulics and what it can do for you.... I used to teach industrial back hyd. years ago.... Here's one for you to remember...You can't have a good sys unless you have 2 things: Flow AND pressure. Pressure alone will not give you system performance. So, what is PSO? (pressure squirting out).... Have fun! And thanks Hy for the :thumbsup: (I'd be happy to help anyone learn hydraulics, anytime...) :wink: