цементировочный клапан обратного давления(a special coupling device, inserted one or two joints above the bottom of the casing string, that contains a check valve to permit fluid to pass downward but not upward through the casing. The float collar prevents drilling mud from entering the casing while it is being lowered, allowing the casing to float during its descent and also decreasing the load on the derrick. The float collar also prevents a backflow of cement during the cementing operation. (Bab GofPI) – АД MichaelBurov)
