Pipe stoppers, or pipe plugs as they are sometimes known, are used to temporarily seal the end of a pipe or opening for many different testing applications. Pipe stoppers are mainly used to seal off from water, gases and foreign objects in newly laid pipes, or pipework systems that are under repair.
Pipe stoppers are available in a number of different styles to suit many applications for pipe sizes from 11/2in to 24in and larger on request. Special Pipe stoppers are also available for pressure testing.
Standard pipe stoppers are fitted with a natural rubber seal, but silicone, nitrile, neoprene, or Viton can be supplied if required.
A central spindle/shaft on which two plates are fitted with a natural rubber tyre (ring) between them, a wing nut on the shaft moving the two plates together compressing the tyre and making the seal in the pipe. These stoppers can also be supplied with a hollow shaft version for screwing on standard hose connections or for using fixed or free nipple caps.
Source (partial): TAG-PIPE