This system is not the same as the deuce engine but may provide some folks here some ideas. Not sure where to post but the discussion seems to be here now. Suggestions on my OT welcome. PM me or blurt it out.
When I replaced the hydraulic pump on Betty, the dirty old hoe, I added a large hydraulic filter (Ford had designed the system with just a crude suction screen.) The system is open center, meaning the pump is moving 100% of the oil at all times. When it is not doing work 100% is moving back to the tank at very low pressure. The pump is a Vickers vane type rated at 13gal/min at ? rpm (have to look it up). The remote filter base is from NAPA. The by-pass was removed and plugged. The present filter is a 10 micron NAPA #1860. It is classified as a 'hydraulic' filter, unlike the engine oil filters which are in the 'lube' group. It is paper media and has a 40gal/min rating. The oil is a 'transmission type' hydraulic , one spec. is International HyTran-5. It about as thick as hyd. fluid gets, prob. similar to 20W. There is a 60psi gauge on filter base inlet. The base outlet dumps directly to tank thru a 1" I.D line. The gauge should provide a good indication of pressure across the media. The filterand gauge are located by my wrist so over many years I have observed:
Cold oil (40-80*F), moderate (1500-2000) rpm~30psi.
Cold oil high rpm (2300) rpm~50psi (I avoid this)
Cold oil idle (600rpm)~15psi
After a few (2-3) minutes moderate rpm~15psi
Warm oil (30min)moderate rpm~10psi
Warm oil idle ~5psi
Hot oil (1-2 hour) moderate rpm~5psi
NAPA has at least 9 other hyd filters that fit this base. There are 5,6,7,10 and 25 micron medias, and various lengths. All rate 40gal/min. I am using the second largest. I started with the largest, approx 1" longer, a 5 micron glass media, but saw very high pressures, especially when cold (gauge pegged).
Hyd oil, being a single weight prob. thin out more than, say, 15W-40. The oil seems to 'loosen up' a lot in just a few minutes. I did not test the by-pass setting before removing it but feel sure it would have been opening. I think this pump may be moving more volume than the deuce oil pump, even at these moderate rpm(s). Looking in the tank is like watching a toilet flush.Temp and media seem to be a big factors for pressure differential. JimK