The primary function of a Reverse Lock Out Solenoid is to prevent brake fluid pressure from reaching the brakes while the vehicle and trailer are reversing. While drum brakes often don't require a solenoid due to their inefficiency in reverse, disc brakes can generate braking power in both directions. Therefore, disc brakes require either a manual lockout or an electrically activated solenoid to function properly.

Types of Reverse Lock Out Solenoids:

1. Stop Flow Solenoid:

   • The stop flow solenoid is the most commonly used type and can be installed on almost any hydraulic actuator. It features two fluid openings and is installed at the master cylinder, with the brake line or hose connected to its rear. The solenoid's electrical wire connects to the tow vehicle's reverse lights.
   • Operation: When the tow vehicle is put in reverse, the solenoid is activated, stopping the flow of brake fluid to the brakes, allowing the vehicle and trailer to reverse smoothly.
   • Advantages: Easy to install and compatible with most hydraulic actuators.
   • Disadvantages: If the tow vehicle stops on an incline and is put in park or out of reverse, the solenoid can allow pressure to reach the trailer brakes due to the trailer leaning into the tow vehicle. This can cause the brakes to lock if backing up continues.

2. Reverse Flow Solenoid:

   • This solenoid has three fluid openings and requires actuators to be pre-drilled and tapped to accept a return line. All Tie Down Engineering actuators are compatible with a reverse flow solenoid, but it is essential to verify that your actuator has the return port before purchasing this type.
   • Operation: Connecting the reverse flow solenoid is similar to the stop flow solenoid, but includes an additional tube connected to the master cylinder's return port. The solenoid's electrical wire is connected to the tow vehicle's reverse lights. When the reverse lights activate the solenoid, it redirects the brake fluid back to the master cylinder instead of the trailer brakes.
   • Advantages: This design resolves issues related to backing up on an incline, as it prevents pressure from reaching the trailer brakes. Additionally, if a reverse flow solenoid malfunctions or becomes clogged, it typically results in no pressure reaching the trailer brakes, rather than causing the brakes to drag, as could happen with a stop flow solenoid.