US Patent 7845401 Telescoping wiper plug

A wiper plug has a telescoping feature to allow it to be shorter while in a lubricator so as to reduce lubricator length as compared to an extended length for proper propulsion past off center openings such as side pocket mandrels in the string. The wiper has a telescoping feature that allows it to extend when dropping or being pumped from a lubricator. Once extended, it can lock in the extended position so that it doesn't collapse on the way down the string. Centralizers can optionally be used between an upper and a lower wiping section.