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  1. FluidPowerUser

    Piston motor speeds

    Yes, if the displacement is limited to 50% of the standard motor, the power and the torque will be reduced by the same amount.
  2. FluidPowerUser

    Piston motor speeds

    I was the hydraulic engineering manager at Caterpillar before moving to BR. Yes, they could very well have changed the swash angle to limit the displacement. Internals of the A10 motor are like this. Swash plate is fixed at an angle to give the relevant displacement. Piston diameters are...
  3. FluidPowerUser

    Piston motor speeds

    I used to work at Bosch Rexroth and now I work at a distributor for Bosch Rexroth. Try the link below. https://www.boschrexroth.com/en/gb/search.html?q=R902495615&origin=header You had said 5cc/rev for the motor displacement, I was just checking. Yes, the motor could have an anti cavitation...
  4. FluidPowerUser

    Piston motor speeds

    Are you confident on that number? The minimum displacement on those A10 motors is 10.6 cc/rev. If this is the motor that is fitted, then the max speed is dictated by the mechanics of the swash plate and the reciprocal motion of the piston. The statement on the data sheet is pretty clear: ▶...
  5. FluidPowerUser

    Piston motor speeds

    A pump pushing oil through a motor will continue to do so until the pressure at the inlet of the motor goes above the max pressure. The motor will run at a speed that is proportional to input flow and the displacement. A pump of the same displacement would be speed limited by it ability to...
  6. FluidPowerUser

    Piston motor speeds

    The speed limit is set by the shaft seal and bearings. High speeds will limit the bearing and seal life.
  7. FluidPowerUser

    Adding load sense to a plain valve

    If the load sense signal is draining across an orifice, the flow will vary depending on the pressure differential across the orifice. If you use a compensated flow control valve, you can set the total flow to 0.2 GPM and it will remain at that flow independent of the pressure in A and B. Using...
  8. FluidPowerUser

    Adding load sense to a plain valve

    Yes, that’s basically the right idea. The check valve isn’t required as there will be no pressure from the LS port. Is it safe to assume that the P,T and LS are on the back of the tractor? You don’t need the solenoid valve. If you want to make sure your load sense drains down, you use a...
  9. FluidPowerUser

    Adding load sense to a plain valve

    Hello Andy Your load sense line needs to go on the A and B line, with shuttle valve between them so that the highest pressure is sent back to tractor to increase the flow. With no signal back to the pump, via the LS port, it will stay at the standby pressure 250 - 290 PSI. The pump will try...
  10. FluidPowerUser

    Hydraulic Hose Dash ID OD standards

    The dash size refers to the bore of the hose and that is always given as nominal bore size as an approximate diameter. The OD of the hose depends on the number of layers of wire and the outer sleeve thickness as per the application for the hose. A multi spiral hose with abrasion resistant outer...
  11. FluidPowerUser

    hydraulic breaker repair

    Possibly A derivative can be found on Wikipedia. I’ve used it in 1D simulations like Amesim and Matlab.
  12. FluidPowerUser

    low hydraulic pressure problem CAT 988K loader

    It's not just a line relief, it's also a make up check valve to allow the cylinders to pull oil in if there are external loads acting on them. It does look like cavitation damage, which suggests that the cylinder has been subject to frequent external loads. The damage to the external surface...
  13. FluidPowerUser

    hydraulic breaker repair

    Aim for 0.008mm radial clearance. Equation for leakage is Q = [πR (R-r₀)3/ (6 µ L )] (1+ 3/2ε²) ∆p where ε =e/ (R-r₀) R is bore radius rois spool radius μ is oil viscosity L is sealing length Δp is pressure drop e is eccentricity
  14. FluidPowerUser

    low hydraulic pressure problem CAT 988K loader

    The noise from the piston pump would be the first indication that the charge pump was struggling to fill the piston pump. Also, the charge pump is a gerotor type pump, centrifugal pumps don't lend themselves to applications where the speed varies.
  15. FluidPowerUser

    low hydraulic pressure problem CAT 988K loader

    We are looking for something that is related to the speed of the pump. The servo piston on the pump is balanced between the pump outlet pressure + spring force versus the pilot pressure that is controlled by the proportional valve. The angular velocity of the pump will apply additional force on...
  16. FluidPowerUser

    low hydraulic pressure problem CAT 988K loader

    Does the same thing happen when you stall the lift cylinders in both directions and also when you rack back and tilt forward? The 10% reduction in the pump displacement is a big clue about what's going on here. If you see the same pressure reduction on all implement movements, then it suggests...
  17. FluidPowerUser

    low hydraulic pressure problem CAT 988K loader

    Could be an electronic issue. The pump displacement is controlled by a proportional solenoid. The spools for the implements are all electro hydraulic too. Might seem like a strange question, but are you sure that it’s not meant to back the pump displacement off at high idle to limit the power...
  18. FluidPowerUser

    pump unloading schematics question

    It’s valve 1 that’s too small to handle the flow from P1, not the highlighted valve as I said before. The pilot flow is very small. There is a control orifice in the highlighted valve to make sure there is a good pressure differential. Otherwise the valve will be unstable when the P2 pressure...
  19. FluidPowerUser

    pump unloading schematics question

    As a former employee of Bosch Rexroth I can confirm the following. The highlighted valve is not big enough to handle the flow. It’s a small pilot valve that vents the main stage at the required pressure, as set on the spring in valve 1.
  20. FluidPowerUser

    Sawmill parallel cylinder lift issues

    The issue here is the load differential across the cylinders. The flow divider will do its best to compensate for the pressure differential, but one leg of the flow divider will see higher leakage around the gears and it may also be spilling oil across the relief valve and that is why the...

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