Ships and marine technology – Graphical symbols for technical documentation – Part 3: Shut-off parts, control parts and regulating parts; Text in German and English
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 05/01/2017

Ships and marine technology – Graphical symbols for technical documentation – Part 3: Shut-off, control and regulating parts
standard by Deutsches Institut Fur Normung E.V. (German National Standard), 08/01/1998