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Adjusting charge pressure on Sundstrand


npalen

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I see in the service manual (Allis 720) where the charge pump pressure can be adjusted by changing shims under the plug on the left side of the hydrostat. I would like to speed up the 3-point lift a little and wondering if anyone might have experience with making this adjustment? I believe there is an access plug in the sheet metal housing (chasis) next to the hydrostat. Thanks Nelson
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There is a plug in the frame for that, But from what I was doing on mine it only set the pressure for the hydrolics, I had to adjust mine up a little bit, did not get any more speed. If you go in there have a magnet and pressure guage that goes up to 1000lbs
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Flow = speed in hydraulics. Pressure = the work that can be done when converting fluid energy into mechanical energy. In this case how much weight you can pick up with the lift. The only way to get more speed is to increase the rpm's of the charge pump, or speed the engine up. The variable here is to check the output of the charge pump as it may be worn out.
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Is it possible that the spring against the relief valve has weakened over time letting the valve crack slightly under pressure? I'm thinking that part of the flow would then go past the relief with the remainder doing the work. The 3P lift seems slow at low RPM but perhaps that's the way they're designed. I realize that the charge pump is not a powerhouse. Thanks for the feedback. Nelson
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