Why do big trucks use air to brake instead of brake fluid like a normal car?

Question

Basically the title.

In: Engineering

Answer 1

Trailers are often disconnected and reconnected.

If you spill some air, no big deal. If you spill some hydraulic fluid, that’s somewhere between a mess and a pollution standards violation.

If you need more air, it’s free. You just pump it out of the atmosphere. If you need more hydraulic fluid, that’s $20-50 per gallon.