Inside Blowout Preventer 1 : A device that can be installed in the drill string that acts asa check valve allowing drilling fluid to be circulated down the string but prevents back flow. (RP 53)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}