For Part III in this series we turn to the business of limiting and directing the flow of oil around a circuit. As before, a guiding hand comes from John Liposits, technical trainer at John Deere’s Langar, Notts HQ
Hydraulics explained:
- Part I Principles, pumps, relief valves
- Part II Pumps — gear, vane and piston
- Part III Oil control — pressure
- Part IV Oil control — flow, direction
- Part V Open and closed circuits
- Part VI Load sensing
Slowly and bit by bit, a hydraulic circuit is coming together. Part I of this series covered the basic principles (profi (03/15) while Part II looked more closely at various sorts of pumps — gear, vane and piston (profi 04/15). Now things are on the move, we come to ways to control oil as it hurries from the pump, out to the ram(s) or motor and back to the oil reservoir. This section and next month’s chapter IV will cover the most common options, starting off with a family of valves that, in one way or another, handle pressure.
Pressure in a circuit is decided by resistance to oil flow, up to the point that either the pump’s limit is reached or something breaks or blows. Relief valves operate as the system’s pressure ceiling approaches, usually by diverting oil back to the reservoir; in doing that they protect the circuit and set a limit to the maximum pressure in it.
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