Looks like the specifications are in the manual and I must have quit caring about them when we got a tractor that could handle most any hydraulic requirements. I am just going to type this up as a direct quote from the Deere 1910 manual: Tractor Hydraulic System Requirements: Operation of the hydraulically driven fan requires tractor to have either a load sensing hydraulic system or a closed-center hydraulic system with flow control. These types of hydraulic systems usually have large oil reseroirs and increased oil cooling capacity. They deliver the oil flow needed for the fan motor to maintain fan speed at the selected RPMs without surging. Tractors with open center hydrualic systems are not recommended. Hydraulic system requirements
Number of SCV's (min.): 1 - Fan/Auger
Gallons-per-minute: 17.3 to 26.6 GPM - Fan Important: In addition to these requirements, tractor MUST be equipped with a low-pressure drain line connection for the fan motor case drain. Prevent fan motor damage. Sump pressure MUST be less than 25 psi. Note: See Recommended Tractors and Tractor Hydraulic Compatibility for further information. Verify tractor hydraulic system meets all requirements. After all of this there is a chart. I'll try to put some of the important stuff in here in a manner that is readable, but it's not going to be as nice as the chart in terms of formatting: For single shoot: If you have 5 primaries and require 3500 RPM you'll need 17.3 GPM @ the SCV and 1130 pounds of pressure at the SCV If you have 6 primaries and require 4000 RPM you'll need 20.7 GPM @ the SCV and 1350 PSI at the SCV If you have 7 primaries and require 4200 RPM you'll need 22.2 GPM & 1440 PSI at the SCV If you have 8 primaries and require 4500 RPM you'll need 24.6 GPM & 1590 PSI at the SCV For double shoot: If you have 5 primaries and need 4200 RPM you'll need 21.8 GPM & 1720 PSI at the SCV If you have 6 primaries and need 4500 RPM you'll need 24.2 GPM & 1810 PSI at the SCV If you have 7 primaries and need 4750 RPM you'll need 26.0 GPM & 1900 PSI at the SCV If you have 8 primaries and need 5000 RPM you'll need 26.6 GPM & 1930 PSI at the SCV Important: Marginal tractors would perform better at lower rates and lower operating speed. | 
Hydraulic GPM to run fan on large air seeder?
