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Had a real head scratcher with this Gehl skid steer hydraulic system

The customer was complaining that the hydraulic system was operating slower than it should. Initial diagnosis after flow testing the auxiliary pump was that the pump was down on performance.
So we removed the Vickers ADU series piston pump and found it was not far from a major failure.

In trying to source a replacement pump found that Eaton had built a special for this machine manufacturer, they had fitted an 80cc rotating group into the next size down housing. This was to enable a high flow function on the skid steer to be able to operate implements with high flow requirements like road surface profiling implements.

We were able to get Eaton to build this special for us, but could not get a full code breakdown to be sure that all pump specs were correct. On fitting up the new pump to the machine we found that we were not able to get the full flow characteristics as stated in the machine specs.

After much heartache diagnosing, further testing seemed to indicate a problem with the load sensed directional valve. Having found that some contamination from the pump failing had made its way back to the return filter, we believed that may also be causing issues with the valve. We finally discovered that the main issue was the new pump had a bleed down orifice that was causing a loss of the load sense signal.

Once we finally diagnosed this, removed the pump again and plugged the orifice in the controller, we gained another 20 odd litres per minute flow rate, or roughly an extra 20%, plus a more positive pressure response to all functions.



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