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」。

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。

On non-self-lapping systems, 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”, will release pressure at the fastest possible rate.

Auxiliary reservoirs are being drained when braking. When the brakes are released, it takes some time for auxiliary reservoirs to fill up again. The lap position, however, functions only if the auxiliary reservoirs are full. To stay in full control over braking it is recommended to not release non-self-lapping brakes when knowing that moments later braking may be needed again. Calculated, slow moves are preferable when releasing the non-self-lapping brakes.

With both brake types, the driver can see exactly how much braking force they are applying by looking at the brake pipe and brake cylinder gauge needles.

兩種系統都相當易於操作，但「自動保壓」系統對初學者來說可能更為直觀。更為簡化的說法：「自動保壓」系統依據司軔閥手柄位置選擇目標軔力，壓力由閥件自動調整；「非自動保壓」系統則靠著操作司軔閥手柄直接增減壓力、軔力。

In case a train contains motorized vehicles with both self-lapping and non-self-lapping brake valve types, only the self-lapping ones will be functional when operating the brake. For that purpose, vehicles are also equipped with brake cutout valves, which can be used to isolate certain vehicles from the brake system and resolve this conflict.