Why a stuffing box is necessary in PCP drive heads?

Progressive cavity (PC) pump drive heads require a stuffing box to seal crude oil from leaking onto the ground where the polish rod passes from the crude oil passage in the wellhead to the drive head. Because crude oil typically contains fine sand particles, alignment between the stuffing box and the polished rod is imperfect, and PC drive heads run continuously, it is very difficult make stuffing boxes that last as long as desirable by oil production companies. By using a flexibly mounted standpipe in various configurations, around which is a bearing supported shaft carrying the sealing means, long term durability of the stuffing box can be achieved. By using a pressurization system such that the pressure output exceeds the pressure at the flow line, stuffing box seal life can be extended and external leakage from the stuffing box can be eliminated. A double wall standpipe may be provided in some applications as part of the pressurization system. In some cases pressurization of the stuffing box is sufficiently advantageous that a floating standpipe is not economically warranted.