214 & 224 WHEEL-TYPE EXCAVATORS Compressed Air System Caterpillar

Compressed Air System
1.1. General
2.1. Standard Compressed Air System
3.1. Antifreeze Position
4.1. Summer and Adding Position

Fig. WH 191


The compressed air system installed in the 214. 224 supplies the brake system and switches the hydraulically blockable swing axle stabilizing system.

Standard Compressed Air System

(1) 106 cm3 compressor

The air compressor takes in air from the combustion air line behind the dry-type filter for the diesel engine (as clean air is taken in, no intake filter is required). The compressed air is available at the pressure connection. The compressor is pressure-oil lubricated, i.e. it is connected to the diesel engine lubrication circuit. Avoid starting up dry before initial startup of machine or after repairs, i.e. fill compressor crankcase with oil first.

(2) Pressure control valve

The pressure control valve is an automatic reversing valve which maintains the prescribed pressure in the air tanks. When the system has reached maximum air pressure, the control valve switches the compressor to idle, i.e. zero delivery. If the pressure in the system drops too low, the control valve switches the compressor on again.

Cut-out pressure of control valve: 7.3 bar (730 kPa)

Cut-in pressure of control valve: 6.6 bar (660 kPa)

The tire inflator connection is also on the control valve. Reduce pressure of compressed air system below cut-in pressure of control valve, 6.6 bar (660 kPa) (open drain valves on air tanks), as no air is delivered during idle running.

(3) Antifreeze pump

The antifreeze pump allows injection of antifreeze and prevents freezing-up and formation of ice in the air tanks, tubes and valves. Access is by opening the rear lefthand door.

For adding antifreeze and checking level (as well as in frost-free months) the pin with the T-handle should be pressed in against the housing. Then lower stop and lock with a 90° turn. The plug with dipstick can then be slackened and methylated spirit (ethyl alcohol) poured in as antifreeze.

When the plug is removed, air may be heard to escape through a pressure compensation hole. Fill through a funnel, which should be raised enough for the air to escape from the filter. Close filler neck again and place pin with T-handle in antifreeze position.

Antifreeze Position

During winter, 5°C and below, pull up T-handle.

Summer and Adding Position

Press T-handle down against stop and turn through 90°.

(4) 20 liter air tank for service brake

(5) 10 liter air tanks for handbrake (parking brake) and other actuators (continuous locking of service brake and swing axle stabilizing valve). The first of these brakes is for the handbrake.

(6) Drain valves

Located at the lowest point of the air tanks for draining off water. In winter conditions, they should be operated daily by pushing to the side.

(7) Overflow check valve

When the pressure in one air tank has reached 6 bar (600 kPa), the overflow valves permit air to flow into the next tank. They also prevent the first tank from being filled from the subsequent tank (no return flow).

(8) Brake valve

The brake valve is used for operating the service brake. By means of a pedal, an amount of compressed air determined by pedal travel is driven out of connection Z1 and reaches the single-chamber brake cylinder, item 13, by way of the 2-way valve, item 10, and the swivel (connection 3), item 17. The single-chamber brake cylnder is connected to the main cylinder (hydraulic), item 15. The force produced in the single-chamber brake cylinder is transmitted to the main cylinder, where it is converted into hydraulic pressure. This then acts on the wheel cylinders of the four wheel brakes.

The connection for the brake light switch (pressure switch), item 14, and for the double air pressure gauge, item 9, are also on the brake valve.

(9) Double air pressure gauge

Indicates supply air and air discharged for the service brake.

(10) Two-way valve

Needed for alternative operation of either the service brake or the continuous locking of service brake with 3/2-way directional valve, item 11.

(11) 3/2-way directional valve

a. Activation of continuous locking of service brake.

b. Activation of swing axle stabilizing valve (automatic pilot valve), item 19.

(12) Pressure switch, 3 bar (300 kPa) setting

From 0 to 3 bar (0 to 300 kPa) air pressure, the pressure switch energizes a fault light on the instrument panel and at the same time a hydraulic electromagnetic valve, which is integrated in the pilot-control line from the running gear control valve to the left valve block.

NOTE: Handbrake locked when spring brake cylinder, item 18, vented. Fault light in cab and running gear blocked.

(13) Single-chamber brake cylinder

Supplies force to main hydraulic cylinder, item 15, by means of compressed air discharge.

(14) Pressure switch, 0.5 bar (50 kPa) setting

At a braking pressure of 0.5 (50 kPa) bar and above, the brake lights receive current (turns on).

(15) Main cylinder

Conversion of pneumatic force into hydraulic pressure for the wheel cylinders. The compensating tank, mounted directly on top, supplies the main cylinder with brake fluid.

(16) Handbrake valve

When the line to the spring brake cylinder, item 18, is vented the handbrake is on.

When the line is aerated, the compressed air reaches the spring brake cylinder, item 18, via the swivel (connection 1), item 17, and releases the handbrake.

NOTE: See explanation for pressure switch, item 12.

(17) Hydraulic swivel for three compressed air passages.

(18) Spring brake cylinder (single-acting cylinder)

Release pressure: 3 bar (300 kPa)

(19) Swing-axle stabilizer valve

For blocking the swing axle (front axle). An air cylinder switches the hydraulic part of the valve.