The air-laden fluid is then forced from the system by applying the brakes. If the brake system is a part of the main hydraulic system, a portable hydraulic test stand may be used to supply the pressure. If the system is an independent master cylinder system, the master cylinder will supply the necessary pressure. Bleeding should continue until no more air bubbles come through the bleeder hose into the bleeder container. In the bottom-up method, the air is expelled through the brake system reservoir or other specially provided location.
Some aircraft have a bleeder valve located in the upper brake line.
In this method of bleeding, pressure is supplied by a bleeder bomb. The bleeder bomb is equipped with an air valve, air gauge, and a connector hose. The connector hose, which attaches to the bleeder valve on the brake assembly, is provided with a shutoff valve. Normally, the hose is connected to the lowest bleed fitting on the brake assembly. With the brake bleed fitting opened, opening the bleeder bomb shutoff valve allows pressurized fluid to flow from the bleeder bomb through the brake system until all the trapped air is expelled.