APA

American Petroleum Institute A., . (2003). Specification for drill string non-return valves. Washington: American Petroleum Institute, API.

Chicago

American Petroleum Institute API, . 2003. Specification for drill string non-return valves. Washington: American Petroleum Institute, API.

Harvard

American Petroleum Institute A., . (2003). Specification for drill string non-return valves. Washington: American Petroleum Institute, API.

MLA

American Petroleum Institute API, . Specification for drill string non-return valves. Washington: American Petroleum Institute, API. 2003.