What is a valve lockout?

Valves are an integral part of piping systems across several industries. Just like other machines and equipment, they also need to be maintained from time to time to avoid unexpected piping failures. During servicing and/or maintenance, valves need to be locked out and tagged out to prevent accidental opening. Valve lockouts ensure that all valve operating machines remain off during LOTO procedures, thereby preventing unexpected release of energy that may cause harm in the workplace. 

What are the main functions of valves?

What is a ball valve lockout?