Which of the following is a stacker brake device?

The brake lever is a crucial component of a stacker, as it is designed specifically for controlling the braking system of the equipment. This device allows the operator to apply and release the brakes, ensuring safe stopping and control of the stacker when lifting or lowering loads. It is essential for preventing accidents and maintaining stability during operation, especially when handling heavy materials or navigating tight spaces.

The other options, while part of the overall vehicle system, do not serve the same direct function. For example, a diversion steering wheel is more related to directing the stacker rather than controlling its speed or stopping it. Wheels serve as the means for movement and support but do not have any braking capability. An ignition device, on the other hand, is responsible for starting the engine and does not play a role in the stopping mechanism of the vehicle. Thus, the brake lever stands out as the specific device that enables the critical function of braking in stacker operation.