844K and 854K Wheel Dozers and 990K, 992K, 993K, 994F and 994H Wheel Loaders Powered Access Stairway Caterpillar


Powered Stairway System

Usage:

854K 221
The system is composed of an electro-hydraulic pump and double acting hydraulic cylinder. Which is attached to a crank and shaft creating rotary action that drives the rotation of the stairway up and down.

At the top of the stairway rotation an inductive proximity sensor, that picks up the presence of metal, triggers the latching system to power the retention pin into the latch receiving block attached to the stairway. The switch must be held in the raise position until the latch is full extended. As an extra indicator, the PAS alarm will also turn off once the latch is fully extended and the switch is still in the raise position.

In the lower switch direction, the machine begins by retracting the pin from the receiver block in the stairway and turning on the PAS alarm to warn of movement. Once the pin is fully retracted, the system will engage the pump to lower the ladder until the stairway rest against the front plate of the Powered Access Stairway platform cover. Seat the stairs against the cover to prevent any movement while the stairway is being used for machine access.

The Powered Access Stairway is not to be used during emergency exits. The state of power on the machine may leave the stairway in an inoperable due to power and system requirements.

Schematic



Illustration 1g06072226
(1) Secondary relief valve
(2) Position sensor
(3) Cylinder
(4) Main relief valve
(5) Reservoir
(6) Manual release valve
(7) Solenoid valve
(8) Pump

Location of Components



Illustration 2g06073504
Powered stairway components (typical example)
(1) Secondary relief valve
(2) Position sensor
(3) Cylinder
(4) Main relief valve
(5) Reservoir
(6) Manual release valve
(7) Solenoid valve
(8) Pump

Operation

The oil reservoir (5), pump (8), solenoid valve (7), and main relief valve (4) are all contained in the same component as part of the pump group. Secondary relief valve (1) is mounted inside the platform group. Manual release valve (6) is mounted inside the platform group and connected to an externally accessible quarter turn ball valve.

Raise



Illustration 3g06072204
(1) Secondary relief valve
(3) Cylinder
(4) Main relief valve
(5) Reservoir
(6) Manual release valve
(7) Solenoid valve
(8) Pump

When the raise stairway has been activated, pump (8) begins to pull oil from oil reservoir (5). The oil is pumped to the head end of cylinder (3). Cylinder (3) begins to extend which pushes a crank that is splined to a shaft. The shaft is splined onto two hubs that bolt to the stairway. As cylinder (3) extends, the stairway begins to raise.

A position switch (2) is located in the platform group. When the stairway has been raised, the crank on the shaft triggers the position switch (2) to engage the latching mechanism while the operator is holding the raise stairway switch until the latch is fully extended and the stairway alarm is deactivated. The pump will continue to run until the switch is released.

Lower



Illustration 4g06072260
(1) Secondary relief valve
(3) Cylinder
(4) Main relief valve
(5) Reservoir
(6) Manual release valve
(7) Solenoid valve
(8) Pump

When the lower stairway switch activates the latching mechanism to retract from receiver activating the stairway alarm. As the operator continues to hold the switch the latch will fully retract and then engage the stairway pump (8) and begins to pull oil from oil reservoir (5). The oil is pumped to the rod end of cylinder (3). Cylinder (3) begins to retract which pulls a crank that is splined to a shaft. The shaft is splined onto two hubs that bolt to the stairway. As cylinder (8) retracts, the stairway begins to lower.

The pump will continue to run until the switch is released.

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