Final answer:
Components like the pressure relief device are not connected directly to the service valve on a DOT cylinder; these are typically connected to the cylinder body to release gas if pressure exceeds safe levels.
Step-by-step explanation:
When discussing the components connected to the service valve on a DOT cylinder, it's important to understand that the service valve is the primary means of controlling the flow of gas in and out of the cylinder. While many parts are associated with the cylinder and valve assembly, certain components like the pressure relief device, also known as a safety or relief valve, are not directly connected to the service valve. Instead, the pressure relief device is typically connected to the cylinder or the tank body itself to ensure safe operation by releasing gas if the pressure exceeds a predetermined limit. This prevents potential hazards that could arise from overpressure, such as the cylinder rupturing due to thermal expansion or overfilling – scenarios mentioned in the provided context point to the fact that the gas is not leaking out, and the cylinder does not change size-at least not significantly as it warms, indicating a stable system where the pressure relief device's role is to mitigate unforeseen pressure increases.