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E. Kansas | A pump with 1800 rpm max shaft speed is typically indication it is an industrial pump, and usually not suitable for a mobile equipment application. 1750 rpm is typical rated speed of an electric motor, and 1800 rpm is too slow for most mobile equipment applications. Other pump design factors separate industrial from mobile applications.
I don't understand why the hydraulic shop is saying this pump has a 3000 rpm max shaft speed limit, and the literature you're matching to the pump specifies 1800 rpm as max shaft speed. The pump is going to be ruined quickly by exceeding its max shaft speed.
You're not seeing air in the oil because the pump is cavitating, not ingesting air. The pump rotating group is not filling properly since cavitation is occuring, even with all inlet conditions at pump suction port being within spec. The low pressure voids in the oil are because of the entrained air coming out of solution and then being suddenly compressed (imploding) as they pass into higher pressure areas of the pump rotating group. They exhibit extremely high localized temperatures due to the rapid rate of compression taking place with almost no time for heat to transfer away, eroding the pump. The voids are eliminated and forced back into the oil and will remain in solution since they were pulled out of solution.
Air ingestion can come from many places, such as a bad/leaking shaft seal, leaking inlet fittings, reservoir drawdown level from cylinders extending sometimes causing oil vortexing in reservoir over pump suction port, etc. The air ingested is compressed and driven into solution in the pump, but it will come out of solution whenever the pressure is lowered downstream of the pump, as you would see if looking in the reservoir and seeing air bubbles. Oil can only hold so much air, usually around 13% or so in solution at atmospheric pressure. It will hold more at higher pressures, but the air will come out of solution as the pressure is lowered.
You can have entrained air (basically air bubbles) in the oil if it is not deaerated adequately before it is drawn in by the pump, but this air will come out of solution when the pressure falls. Entrained air is similar to air ingestion in having air bubbles in the oil, but is not always the result of air being sucked in. Sloshing oil in the reservoir, creating air bubbles in the oil, poor reservoir design that does not diffuse the incoming oil and causes turbulence on the oil surface, too fast of oil turnover in the reservoir, etc. can all contribute to entrained air.
I don't think all the problems in the above paragraphs are your primary issues, except for the pump cavitating due to exceeding the max shaft speed limit.
I don't know what your solution will be, since you can't run an 1800 rpm max shaft speed pump on the accessory drive without the engine running quite slow. When you find what kind of pump was used on the tractor initially, you'll be able to determine then if it will meet your current flow and pressure needs. It could have been a special numbered (proprietary) pump for Steiger, but you might be able to cross reference if you know some details about it. Maybe some vintage advertising literature or service manuals might give some pump details you need.
Beyond all that, you may have to consider another location for a pump drive, such as belt-driven from the engine, or a through-drive pump to accept the pump you need, or a double pump. It's too soon to worry about all that until the original pump details are known.
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Steiger Panther hydraulics, losing volume at high RPM
