causing an air leak. As the pump breaks in, tighten the gland bolts evenly. The gland should never be drawn to the point where packing is compressed too tightly, and no leakage occurs. This causes the packing to burn the shaft, or shaft sleeve, to be scored, and prevents liquid from circulating through the stuffing box and cooling the packing. The stuffing box is improperly packed or adjusted when friction in the box prevents the rotating element from being turned by hand. A packed stuffing box that is operating properly should run lukewarm with a slow drip of sealing liquid. After the pump has been in operation for some time and the packing has been completely run-in, drippage from the stuffing box should be at least 40 to 60 drops per minute. This indicates that there is proper packing, that the shaft sleeve is adequately lubricated, and that it is cooled properly.
Eccentric operation of the shaft, or shaft sleeve, through the packing could result in excess leakage. Correction of this defect is extremely important.
Packing should be checked frequently and replaced as service indicates. Six months might be a reasonable expected life, depending on operating conditions. It is impossible to furnish an exact prediction. A packing tool may be used to remove old packing from the stuffing box. Never reuse old and lifeless packing or merely add some new rings. Make sure the stuffing box is thoroughly cleaned before new packing is installed. Also, check the condition of the shaft, or shaft sleeve, for possible scoring or eccentricity, making replacements as necessary.
New packing should be placed carefully into the stuffing box. If molded rings are used, the rings should be opened sideways and the joints pushed into the stuffing box first. The rings are installed one at a time, each ring is seated firmly, and the joints are staggered so they are not in line. The joints should be kept toward the upper side of the shaft about a 90-degree angle from each preceding joint.
If coil packing is used, cut one ring to accurate size with either a butt or mitered joint. An accurately cut butt joint is superior to a poor fitting mitered joint. Fit the ring over the shaft to assure proper length. Then remove and cut all other rings to the size of this first sample. When the rings are placed around the shaft, you should form a tight joint. Place the first ring in the bottom of the stuffing box. Then install each succeeding ring, staggering the joints as described above, making sure each ring is firmly seated.
Make sure the seal cage is properly located in the stuffing box under the sealing water inlet. The function of the seal cage is to establish a liquid seal around the shaft, to prevent leakage of air through the stuffing box, and to lubricate the packing. If it is not properly located, it serves no useful purpose.
A mechanical shaft seal is supplied in place of a packed stuffing box when specifically requested. Mechanical seals are preferred over packing on some applications because they have better sealing qualities and longer serviceability. Leakage is eliminated when a seal is properly installed, and normally, the life of the seal is much greater than that of packing on similar applications.
General instructions for operation of the various mechanical sealing arrangements are included below. It is not feasible to include detailed instructions for all mechanical seals in this chapter because of the almost unlimited number of possible combinations and arrangements. For more information, refer to the manufacturer's instructions. Mechanical seals are precision products and should be treated with care. Use special care when handling seals. Clean oil and clean parts are essential to prevent scratching the finely lapped sealing faces. Even light surface scratches on these faces could result in leaky seals. Normally, mechanical seals require no adjustment or maintenance except routine replacement of worn or broken parts.
A mechanical seal that has been used should not be placed back into service until the sealing faces have been replaced or relapped. (Relapping is generally economical only in seals that are 2 inches and greater in size.)
Four important rules that should always be followed for optimum seal life are as follows:
1. Keep the seal faces as clean as possible.
2. Keep the seal as cool as possible.
3. Ensure the seal always has proper lubrication.Continue Reading