Before attaching a pressure regulator to a compressed gas cylinder, _______.

The correct action before attaching a pressure regulator to a compressed gas cylinder is to blow the valve for a moment. This procedure helps to clear the valve of any dust or debris that may have accumulated in it. Clearing the valve ensures that the connection is clean and reduces the risk of contamination or improper function of the regulator once it is attached.

Ensuring the valve is free from particulates is essential for safe and effective operation, as any residue could interfere with the flow of gas, potentially leading to hazardous situations or equipment malfunction. This practice promotes both safety and reliability when handling pressurized gas systems.

Using a petroleum-based solvent to clean the regulator threads or adjusting the regulator to check output before attachment may actually introduce risks or not be relevant to the proper setup procedure. Additionally, doing nothing does not address the need for cleanliness and preparation prior to making such connections.