Which of the following is not an automatic check by the stacker?

The correct answer is that turning up the pressure value of the oil pressure safety valve is not an automatic check performed by the stacker. In hydraulic systems, the oil pressure safety valve is designed to prevent excessive pressure from causing damage to the system. Adjusting this value is typically a manual task that should be performed by a qualified technician during routine maintenance or troubleshooting rather than an automatic function of the stacker.

In contrast, checking battery voltage, monitoring lifting height, and testing brake function are typically automated checks integrated into the stacker's operational protocols. These checks are essential for ensuring safe operation and optimal performance of the machinery. For example, monitoring lifting height helps prevent overloading and potential tipping, while regular brake function tests ensure that the stacker can stop effectively when needed. These automatic checks are crucial for the safety and efficiency of forklift operations, while adjusting the pressure valve requires specific knowledge and manual intervention.