R_O_M
Guest
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.