Figure 14-19.--Bleeder bomb.
expelled. The brake bleeder valve is then secured, and
the bleeder bomb hose is disconnected.
This method of bleeding should be performed
strictly in accordance with specific instructions for the
Figure 14-18.--Bleeding brake system (top-down method).
aircraft concerned. Although the bleeding of
individual systems presents individual problems, the
cover the end of the hose. The air-laden fluid is then
following precautions should be observed in all
forced from the system by applying the brakes. If the
bleeding operations:
brake system is a part of the main hydraulic system, a
portable hydraulic test stand may be used to supply the
1. E n s u r e t h a t t h e b l e e d i n g e q u i p m e n t i s
pressure. If the system is an independent master
absolutely clean and filled with the proper type
cylinder system, the master cylinder will supply the
of hydraulic fluid.
necessary pressure. In either case, each time the brake
2. Maintain an adequate supply of fluid during the
pedal is released, the bleeder valve must be closed or
entire operation. A low fluid supply will allow
the bleeder hose pinched off; otherwise, more air will
more air to be drawn into the system.
be drawn back into the system. Bleeding should
3. Continue bleeding until no more air bubbles are
continue until no more air bubbles come through the
expelled from the system and a firm brake pedal
bleeder hose into the bleeder container.
is obtained.
BOTTOM-UP METHOD.--In the bottom-up
4. Check the reservoir fluid level after the bleeding
method, the air is expelled through the brake system
operation is completed. With brake pressure on,
reservoir or other specially provided location. Some
check the entire system for leaks.
aircraft have a bleeder valve located in the upper brake
line. In this method of bleeding, pressure is supplied
Overheated Wheel Brakes
by a bleeder bomb. A bleeder bomb (fig. 14-19) is a
portable tank in which hydraulic fluid is placed, and
In the event an aircraft has been subjected to
then put under pressure with compressed air. The
excessive braking, the wheels may be heated to the
bleeder bomb is equipped with an air valve, air gauge,
point where there is danger of a blowout or fire.
and a connector hose. The connector hose, which
attaches to the bleeder valve on the brake assembly, is
NOTE: Excessive brake heating weakens tire and
provided with a shutoff valve. Normally, the hose is
wheel structures, increases tire pressure, and creates
connected to the lowest bleed fitting on the brake
the possibility of fire in the magnesium wheels. When
assembly. With the brake bleed fitting opened,
the brakes on an aircraft have been used excessively,
opening the bleeder bomb shutoff valve allows
the fire department should be notified immediately,
pressurized fluid to flow from the bleeder bomb
and all unnecessary personnel should be advised to
through the brake system until all the trapped air is
leave the immediate area.
14-17
