This truck application required sequencing of extension and jack cylinders so that the jack legs extended to full width before the jack cylinders lowered the legs to lift the vehicle. When raising the jacks, the reverse scenario was required: jack cylinders up, and then jack legs retract. In this application, the customer wanted to be able to see and feel the pressure rise when the jack legs first contacted the ground. Although the original dual sequence package performed 'as advertised', high internal mechanical friction plus the small bore of the extension cylinders, required a high pressure setting for the sequence valve, thus causing the jack cylinders to lower at a much higher pressure than was needed. This resulted in incorrect 'feedback' for jacking pressure to the operator, along with wasted horsepower when lowering the four jack legs.
The simplified solution
Although kick-down sequence cartridges do open at a preset pressure, they differ from standard sequence valves in that they shift and stay open (much like a 2-way directional valve) and do not maintain the sequence pressure in the primary circuit. By changing the original Sun Hydraulics RS*C-*** valves to SQ*B-*** kick-down sequence cartridges, the jack legs lowered at only the pressure needed by the jack cylinders. This made it easy for the operator to detect ground contact, and meant that the pressure shown on the gauge while lowering the jacks represented the jack pressure, not the sequence pressure setting.
Hydraulic circuit showing kick-down valves in place
NOTE: If a circuit requires a minimum primary circuit pressure to be maintained (eg clamp and drill circuit), a kick-down sequence valve will NOT work, and a standard sequence valve should be used. The Sun kick-down sequence valve is not available with a built-in reverse flow check, therefore do not try to exchange an SC*A-*** with an equivalent kick-down cartridge, if reverse flow is required.
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