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A short video describing how BI-TORQ Valve Automation’s fusible link ball valves (also known as thermal shut-off valves) operate.

Go to https://valves.bitorq.com/ to check out Product Configurator for more information. You can download 2D sales drawings and 3D models upon registration.

Let us consider a scenario where the driver hits the brakes hard on a slippery surface. Without ABS, the wheels will lock up or ‘slide’ and the driver will now have no control over which direction the car takes (since steering now becomes useless) and has no way of avoiding collisions. On a car with ABS, the wheels will not lock up and so the driver can still effectively steer the vehicle and dodge obstacles as he judges fit. A car with working ABS is therefore much safer to drive/control than one without.

An ABS system consists of the following components:

Wheel speed sensors
Brake calipers
A hydraulic motor
Pressure release valves contained in an actuator body.
And a very quick thinking computer (or control module) which coordinates the whole braking process.

Whenever you step on the brakes, your foot is actually pressurising a hydraulic system which causes the brake pads to squeeze against and hold the rotating discs, which effectively causes the car to slow down. If the ABS system (through the sensors located in the wheel hub/assembly) detects that one wheel is slowing down more rapidly than the rest (a symptom of wheel-lock) it automatically reduces the brake pressure on this wheel by opening a pressure release valve in the hydraulic system. When that wheel’s speed matches that of the others again, ABS also has the ability to build the pressure back up to normal via the hydraulic motor. The system reacts remarkably quickly, and compares wheel speeds many times a second.

ABS systems can act on just the front wheels (which normally do most of the braking work) or on all four depending on what car you’re driving. When all four wheels are braking heavily as a result of heavy brake pedal application, and one of them is about to lockup (locally called ‘sliding’) due to a low friction surface such as ice/mud/gravel, the ABS control module detects the onset of a skid through the sensor in this wheel and reacts by ordering the ABS actuator to release the brake pressure slightly by rapidly opening a pressure release valve for only this wheel but leaving all other three wheels to brake as they normally should. This lowers the pressure in the brake pipe going to this wheel which causes the brake caliper to loosen its grip on the brake disc on the locking wheel. Once this corrects the locking wheel, the hydraulic motor will build up the pressure again to the optimum braking force and the valve will revert to the closed position.

Note that ABS does not operate all the time. It only does when you brake harshly in an emergency on a slippery surface. Most of the time, the brakes will operate without ABS interference. If you have driven a car with ABS operating, you will notice that the wheels appear to lock and release in jerky movements, this is because there is such a fine line between grip and traction loss in these conditions, and the system constantly tries to keep the pressure at the point just before lock up (which is the most effective pressure for slowing down).

ABS works best with a firm, steady application of pressure to the brake pedal. During ABS operation you are likely to experience some vibrations, which are the pressure release valves opening and closing and an indication that the system is working correctly. Do not release the pedal until you have safely stopped.

You may have heard that it’s possible to slow down quicker in a car without ABS. This has elements of truth, but in practical terms, the benefits of ABS massively outweigh the slightly longer braking distances. For normal road use, ABS is an absolute must as it will allow you to steer out of the way of unexpected hazards.