California Code of Regulations
Title 8 - Industrial Relations
Division 1 - Department of Industrial Relations
Chapter 4 - Division of Industrial Safety
Subchapter 7 - General Industry Safety Orders
Group 20 - Flammable Liquids, Gases and Vapors
Article 146 - Piping, Valves and Fittings
Section 5611 - Valves

Piping systems shall contain a sufficient number of valves to operate the system properly and to protect the plant. Piping systems in connection with pumps shall contain a sufficient number of valves to control properly the flow of liquid in normal operation and in the event of physical damage. Each connection to pipe lines, by which equipment such as tank cars or tank vehicles discharge liquids by means of pumps into storage tanks, shall be provided with a check valve for automatic protection against backflow if the piping arrangement is such that backflow from the system is possible. [See also Section 5596(b)] .