How does a “surge” actuator work?

A surge actuator is a key component in hydraulic trailer braking systems, particularly on trailers designed to carry heavy loads. It uses the forward momentum (“surge”) of the trailer to activate the brakes in coordination with the tow vehicle.

Trailer braking system requirements:

• Federal and state regulations require trailers with a gross weight of 3,000 pounds or more to have a functional braking system.

• On surge brake trailers, the tongue is constructed in two sections:

  • The front section with the coupler that attaches to the tow vehicle.

  • The rear section, which houses the master cylinder that controls brake fluid pressure.

How the surge actuator functions:

1. When the tow vehicle slows down, the trailer naturally moves forward, creating a surge force.

2. This force causes the actuator to telescope, pushing against the master cylinder.

3. The master cylinder then builds hydraulic pressure and sends brake fluid through the lines to each brake drum or rotor.

4. As pressure increases, the trailer brakes engage in synchronization with the tow vehicle’s brakes.

5. An integrated, sealed shock absorber moderates the telescoping action, preventing harsh or abrupt braking.

In summary: As the trailer pushes forward during deceleration, the surge actuator compresses, the master cylinder delivers hydraulic pressure, and the trailer’s brakes apply smoothly and proportionally to the tow vehicle’s braking effort. This ensures safe, controlled stopping power even under heavy loads.