Posted by John G. Hasler on October 30, 2009 at 07:53:16 from (174.124.36.161):
In Reply to: SA Hydraulics posted by Dellbertt on October 29, 2009 at 15:41:50:
I"m not familiar with the SA but this is normal for machines with constant displacement pumps and two-way open-center valves. When all valves are centered the flow of oil meets essentially no resistance and so the engine does little work. When you just crack the valve to lower the implement slowly the system goes on demand. Pressure goes up but only part of the flow goes through the valve to the cylinder: the rest is bypassed and the power (flow x pressure) goes to heating the oil. Open the valve wide to raise the implement and all the flow goes to the cylinder. Since the implement isn"t very heavy not much pressure is developed and so the engine doesn"t need to deliver much power.
Open the valve wide to drop the implement. Engine won"t load down. Crack it just a little to raise the implement slowly. The engine will load down.
Modern machines usually have variable displacement pumps.
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