The Real Worth of Hydraulic Symbols

hydraulic schematic drawingI am regularly involved in troubleshooting problems with hydraulic equipment. In these situations, there are two things I always do before reaching for my test gear. The first is to conduct a visual inspection of the hydraulic system, checking all the easy things that could cause the problem in question (never overlook the obvious). The second is to ask for the schematic diagram for the machine’s hydraulic circuit.

A schematic diagram is a ‘road map’ of the hydraulic system. And to a technician skilled in reading and interpreting hydraulic symbols, it is a valuable aid in identifying possible causes of a problem.… continue reading »

Hydraulic Cylinder Efficiency and How To Calculate It

Hydraulic excavator boom cylindersWith modern sealing technology, the volumetric efficiency (leakage losses) of a hydraulic cylinder in good condition approaches 100%. But the mechanical-hydraulic efficiency of a hydraulic cylinder varies with seal type and the tolerances between the piston-rod and its wear bands.

Recall that mechanical-hydraulic efficiency refers to the amount of force lost due to mechanical and fluid friction. In a cylinder, these losses are due to friction between the piston-rod and its wear bands and seals, and the friction of the fluid as it’s ejected from the return side of the cylinder at the required velocity. In practice, fluid friction is not significant, provided the cylinder’s ports and its connections are adequately sized.… continue reading »

This Problem Could Be Destroying Your Hydrostatic Transmission

Rexroth A2VSL1000 hydraulic pumpRupert Murdoch, the boss of global media giant News Corporation was a neighbor of ours where I grew up. Not that my family was particularly well off. It’s just that my father’s farm happened to be situated close to a group of “sheep stations” the media mogul owned. And compared to the 300,000 acres Mr Murdoch controlled, Dad’s land holding was modest indeed.

In 1981, just in time for the wheat harvest, Dad took delivery of a new combine harvester. It was one of many he owned over the years, but this one was different. It was the first I’d seen equipped with a hydrostatic transmission for the ground drive.… continue reading »