Hydraulics provides an effective, compact, and economical means of extending sliding sections of recreational vehicles. In addition, a new bidirectional hydraulic power unit accomplishes the task without using a directional control valve.Of course, not all RVs have this multitude of amenities, but for those that do, it can be difficult to fit all these creature comforts into a vehicle narrow enough to travel standard roads and still have living space. These luxury RVs have slide-out sections that nearly double the width of living space. Even if these sections could be pulled out manually, luxury demands that they extend and retract with just the flip of a switch.
Smaller RVs — about 6500 lb or less — with slide-out sections use electromechanical assemblies for extension and retraction. Larger, heavier vehicles, require the power of hydraulics because electro-mechanical systems would be larger, heavier, and more costly than a hydraulic system. Furthermore, the hydraulic system's power unit can be used not only for the slide-out section, but for powering cylinders of a leveling system as well. So instead of requiring an electric motor for every electromechanical function, the hydraulic solution can use a single electric motor and pump for all functions by using valves to route hydraulic power to the appropriate actuators.
High force from hydraulics
The slide-out units and leveling systems are actuated by double acting hydraulic cylinders, which typically have bores of 3¾ in. and strokes of 12 to 30 in. The systems generally operate at pressures from 1750 to 2250 psi. Depending on system pressure and bore, each cylinder can generate 12,000 to 63,000 lb of force. However, stroke speed is relatively slow — roughly 10 in/sec. This means the hydraulic power unit (HPU) for the system need only deliver about 1 gpm of flow, but at high pressure.
Once the sliding section is fully extended, either hydraulic check valves or mechanical latches secure it in place. Leveling systems generally work by depressing a rocker switch to extend the cylinder. When the switch is released, a load-holding check valve secures the cylinder in position. More sophisticated systems incorporate level sensors for automatic leveling. However, whatever the setup, the leveling systems can use the same HPU as that used for slide-
load-holding check valve secures the cylinder in position. More sophisticated systems incorporate level sensors for automatic leveling. However, whatever the setup, the leveling systems can use the same HPU as that used for slide-
63,000 lb of force. However, stroke speed is relatively slow — roughly 10 in/sec. This means the hydraulic power unit (HPU) for the system need only deliver about 1 gpm of flow, but at high pressure.
Once the sliding section is fully extended, either hydraulic check valves or mechanical latches secure it in place. Leveling systems generally work by depressing a rocker switch to extend the cylinder. When the switch is released, a load-holding check valve secures the cylinder in position. More sophisticated systems incorporate level sensors for automatic leveling. However, whatever the setup, the leveling systems can use the same HPU as that used for slideout sections because the two functions do not have to occur at the same time.
Compact HPU keeps it simple
