气压保持

根据机车车型的不同，有两种控制制动管压力的方法：自动保持和较旧的手动保持。

Self-Lapping

在自动保持系统上，制动管压力会自动调节。司机可以直接将列车制动手柄设置到任何位置。向“应用”方向设置得越近，制动力越强，反之亦然。该阀门会根据手柄的位置自动处理制动管的排压或加压。

Non-Self-Lapping

The non-self-lapping control valves are older. With them, the control lever manipulates the brake pipe pressure directly, and the process is more hands-on. The lever has a few fixed positions. Two of the positions, called “release” and “service” can be thought of as adding and releasing the brake pipe pressure, respectively. The position in-between them, called “lap”, is used to maintain whatever pressure is in the brake pipe. The furthest position, called “emergency”, releases pressure at the fastest possible rate.

By controlling the brake pipe pressure, you indirectly control the cylinder pressure, and thus, brake application.

Auxiliary reservoirs are partially drained whenever brakes are applied. When brakes are then released, it takes some time for the reservoirs to be recharged. The lap position, however, functions only if the auxiliary reservoirs are full. So, to stay in full control over non-self-lapping brakes it is recommended to not release when knowing that moments later braking may be needed again. Calculated, infrequent moves are advised instead.

Monitoring

With both control valve types it is crucial to monitor the brake pipe and cylinder gauges to fully understand the current brake state.

Conflicts

In case a train contains multiple motorized vehicles their control valves are in conflict. The conflict can be even more severe if there are mixed self-lapping and non-self-lapping valves in the train. To ensure safe operation it is necessary to cutout all excess control valves, other than the one intended to be used.