Combines Dan about our hyd quiz

tbran, if you can't figure this one out, what hope for the rest of us! I am bound to be way off the mark but will toss in a couple of suggestions while trying to use the principle of Occam's razor, ie. the simplest explanation is likely to be the right one! First the obvious points; 1 _ An hours running needed so the oil had to reach a certain temperature and therefore a certain viscosity and therefore flow rate. 2 _ The pump was delivering a bit below full capacity. Flow rate again. 3 _ Half throttle re-established hydraulic function so it seems related to flow rate again. 4 _ An R40 so the flow rate is lower through what I assume is the same size hydraulic valve block as the larger R60's and etc. 5 _ Hydraulic function restored when combine attitude was changed. My first guess would be that it is related to the hydraulic oil reservoir and perhaps very closely related to the actual physical level of the oil in the tank including full tank conditions. Under a very specific return flow rate into the oil reservoir and a very specific viscosity, possibly with the return valve problem contributing the last straw, the internal design of the reservoir may have caused a vortex to form around the tank intake when flow rates and viscosities were set up for this to happen. This would have sucked air into the system and would account for the time taken to re-establish hydraulic functions and also account for the non operation at full throttle as with the higher flow rate the vortex would again be re-established in the tank. A slight change of the tank tilt in a specific direction would possibly be enough to shift the oil levels and trigger points in the tank to stop the vortex forming so everything goes back to normal. I would check the tank filter and the tank breather as the condition of the tank filter may be critical to this problem. And I would consider changing the hydro oil and maybe even a different viscosity rated oil. I also have another possible explanation which involves the fluid flow within the valve block behaving in a manner that involves laminar flow of liquids and some fluid dynamic flow regimes but I don't think this explanation is applicable to this case. I will really be interested in other possible and simpler explanations than the above.

Aiming downhill would of created slightly more head pressure at pump intake and slightly more head pressure on return from valve. How this would be enough to give you them problems is beyond me. Things that pop into mind is pump shaft seal or suction hoses taking on air causing foam in tank which could shut you down until foam settled out. Vortex deal could make sense and a guy could of unfastened tank to tilt accordingly to give that a test if it was still bothering. Might want to try that if it bothers again. I know he had pulled screens and oil to bypass that as problem. It's hard to believe that relief valve would be sensitive enough to the slightly higher return pressure. Was this the main system relief valve that you polished shimmedIJ I thought that was screw adjustable. I believe you said you had replaced that valve earlier. It wasn't the spool in steering priority valve your talking about was itIJ I think there was a problem with that spool being just a bit tight in housing many years ago thus they come with undersize but that would give jerky steering symthoms not loss of flow beyond steering. I don't know but I'm glad it was you and not me with that problem. Best of luck

laminar flow of liquids Do I detect some training in engineeringIJ

None! lots of work on air movement in machine fan systems plus a life long interest in the physical sciences such as astrophysics plus 2000+hours as a glider pilot plus 600+hours in power aircraft. I am just a broke old farmer with some mechanical know how. Cheers!

Suction hose has a crack sucking air under or right on edge of clamp because of overtightening. Had this on my old tractor after R_R on hydraulic system. Was a bit hard to find cause of Ahh no pressure on suction lines .