保壓

依動力車輛不同，可以見到兩種控制軔管壓力的司軔閥系統：「自動保壓」和較舊式的「非自動保壓」。

Self-Lapping

在「自動保壓」司軔閥上，軔管壓力是由閥件自動決定。司機員僅需將司軔閥手柄移動至一定範圍內的任意位置。愈向「緊軔」方向推動施加的軔力愈強，反之愈弱。該閥將根據手柄的位置自動釋放或增加軔管中的壓力。

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.