Abstract: A safety sub is disclosed for retaining drilling fluid in the kelly or equivalent and other components of the mud system located above the drill string when pressure drops in the drill string, such as when the circulation pump is turned off in adding a new joint to the drill string. The safety sub includes a pressurized elastomeric cartridge with an elastomeric closure having an asymmetrical wall thickness, preferably achieved by the removal of a chord of material from its external circumference. When internal drilling pressure drops, the external pre-charge pressure closes the elastomeric material by inwardly collapsing the thinner wall portion of the closure. The metallic end pieces of the cartridge are bonded to the elastomeric material during the molding process.

Abstract: These is disclosed apparatus for monitoring the rotative position of a rotary closure member of a valve, wherein a shaft is rotatably mounted in a housing for connection to a part exterior of the housing which rotates in response to rotation of the closure member, and cam rings are assembled for rotation about the shaft through pinion gears rotatable with the shaft to cause cam surfaces about the rings to engage and activate switches in the housing.