A bicycle without a tube is possible, but not rideable. You should always carry a Schwalbe No. 7 A tube with you as a spare when you are on the road. The correct size is usually indicated on the side of the tire. For the No. 7 A, this is 20". The Blitz DV valve on the No. 7 A is 32 mm long.

Details:
• Wheel size: 20"
• Valve type: Blitz (DV)
• Valve length: 32.0 mm
• Width in inches: 1 1/8, 1 3/8

Information on EU Regulation GPSR 

Name of the manufacturer: Ralf Bohle GmbH
Postal address of the manufacturer: Otto-Hahn-Str. 1, 51580 Reichshof, DE 
Electronic address of the manufacturer: info@schwalbe.com