Rotating Head 2 : A rotating pressure-sealing device used in drilling operations utilizing air, gas, foam, or any other drilling fluid whose hydrostatic pressure is less than the formation pressure. (RP 53)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}