Many buses and motor coaches are fitted with parking and emergency brakes that do not use a large spring in the brake chamber. This type of chamber is called a DD3 Safety Actuator. Although similar to a spring brake chamber, a DD3 brake chamber has three air line connections instead of two. Internally, these chambers have a mechanical means of locking a brake in the applied position. A control valve similar to the one used in conventional spring brake systems applies the emergency and parking brakes. Releasing the spring brakes requires operating the control valve and then pressing the brake pedal for three to five seconds.