FLOW SENSE SEQUENCING:
Sequencing of hydraulic cylinders is traditionally done with pressure activated sequence valves. While in most instances this system works well there are a few limitations. It is not possible to use full pressure during cylinder movements or the sequence valves will “fire” early. Like wise if the equipment being sequenced is being moved around at the same time it is possible to get spurious pressure peaks that will also cause premature firing. A typical problem and solution is outlined below.
When ploughing the plough needs to be turned over each time the tractor reaches the end of the field. To make full use of the timed control valve the turning has to be controlled with one actuation of the spool valve. Large ploughs can weigh in excess of 2 tonnes making it necessary to fold the plough before turning to reduce the inertia.
To sequence a Turnover plough through four Cylinder movements with one movement of the spool valve.
Traditional sequencing using pressure triggered sequence valves proved unreliable as unexpected pressure peaks were experienced due to uneven and sloping fields, (the turnover takes place while the tractor is turning round) and the erratic build up of heavy soils on the plough bodies. The Pressure system also requires 3 progressive pressure settings.
HAC developed with Dowdeswell Engineering a valve that sequences by monitoring the oil flows to and from the cylinders. When each cylinder stops moving the next cylinder movement is triggered. The Flow Sense system has the advantage that full pressure is available for each cylinder movement.