If the stuffing box bore on a pump measures 4 inches and the pump shaft is 3 1/4 inches, what size packing should be used?

To determine the appropriate packing size for a stuffing box, it's important to consider the dimensions of both the bore and the pump shaft. The stuffing box bore measures 4 inches, while the pump shaft measures 3 1/4 inches in diameter.

When selecting packing, it is generally recommended that the packing be about one quarter of the bore size. Since the stuffing box bore is 4 inches, a quarter of that amount would be 1 inch. However, the packing must also account for the space needed to properly seal around the shaft.

In this case, the effective shaft size is slightly larger than half of the bore size, and therefore, the packing needs to have a size that allows it to fit comfortably in the stuffing box while providing an effective seal. A packing size of 3/8 inch is common practice because it allows for proper compression without being overly large. This size captures the balance between creating a sufficient seal and allowing for the movement of the shaft.

Choosing 3/8 inch packing ensures that it will adequately compress around the shaft, forming a secure seal that prevents leaks, while also fitting within the dimensions of the 4-inch stuffing box bore effectively.