Installation and Maintaining Compression Packings
Packing the Pump Correctly
The importance of packing the pump correctly cannot be overemphasized. Many packing failures are due to incorrect installation of the packing. The following steps have been devised to ensure effective installation of packings on pumps.
1. REMOVE ALL THE OLD PACKING FROM THE STUFFING BOX. Clean box and shaft thoroughly and examine shaft or sleeve for wear and scoring. Replace shaft or sleeve if wear is excessive.
2. USE THE CORRECT CROSS-SECTION OF PACKING OR DIE-FORMED RINGS. To determine the correct packing size, measure the diameter of the shaft (inside the stuffing box area, if possible) and then measure the diameter of the stuffing box (to give the O.D. of the ring). Subtract the I.D. measurement from the O.D. measurement and divide by two. The result is the required size. CUT… DON?T WIND.
3. WHEN USING COIL OR SPIRAL PACKINGS, ALWAYS CUT THE PACKING INTO SEPARATE RINGS. Never wind a coil of packing into a stuffing box. Rings can be cut with butt (square), skive (or diagonal) joints, depending on the method used for cutting. The following illustration shows these methods of preparing bulk packing. The best way to cut packing rings is to cut them on a mandrel with the same diameter as the shaft in the stuffing box area. If there is no shaft wear, rings can be cut on the shaft outside the stuffing box.
Hold the packing tightly on the mandrel, but do not stretch excessively. Cut the ring and insert it into the stuffing box, making certain it fits the packing space properly. Each additional ring can be cut in the same manner, or the first ring can be used as a master from which the balance of the rings are cut.
If the butt cut rings are cut on a flat surface, be certain that the side of the master rings and not the O.D. or I.D. surface is laid on the rings to be cut. This is necessary to that the end of the rings can be reproduced.
When cutting diagonal joints, use a miter board to that each successive ring can be cut at the correct angle.
It is necessary that the rings be cut to the correct size. Otherwise, service life is reduced. This is where die formed rings are of great advantage, as they give the exact size ring for the I.D. of the shaft and the O.D. of the stuffing box. There is no waste due to incorrectly cut rings.
4. INSTALLATION ONE RING AT A TIME. Make sure it is clean, and has not picked up any dirt in the handling.
Seat rings firmly (except PTFE filament and graphite yarn packings, which should be snugged up very gently, then tightened gradually after the pump is on stream). Joints of successive rings should be staggered and kept at least 90 degrees apart. Each individual ring should be compressed 25% with a tamping tool. When enough rings have been individually seated so that the nose of the gland will reach them, individual tamping should be supplemented by the gland. Utilize a bushing at the bottom of the box to reduce the rings to 5 or 6.
5. AFTER THE LAST RING IS INSTALLED, take up bolts finger tight or very slightly snugged up. Do not jam the packing into place by excessive gland loading. Start pump, and take up bolts until leakage is decreased. Make sure gland bolts are taken up evenly. STOPPING LEAKAGE ENTIRELY AT THIS POINT WILL CAUSE THE PACKING TO BURN UP.
6. ALLOW PACKING TO LEAK FREELY STARTING UP A NEWLY PACKING PUMP. Excessive leakage during the first hour of operation will result in a better packing job over a longer period of time. Take up gradually on the gland as the packing seats, until leakage is eliminated.
7. IF THE STUFFING BOX HAS A LANTERN RING, install in the bottom of gland or remove.
8. REPLACE PACKING WHEN LEAKAGE CANNOT BE CONTROLLED BY FURTHER TAKE-UP ON THE FOLLOWER GLAND. DO NOT ADD MORE PACKING RINGS.
9. ON BOTH CENTRIFUGAL AND RECIPROCATING PUMPS, about 70% of wear is on the outer two packings nearest the gland. However, each additional rings does throttle some fluid pressure. On most pumps, there must be enough rings so if one fails, another does the sealing, and the pump need not be shut down. In an eight ring set-up, the first five rings do the majority of the sealing, the bottom three do little sealing, but are needed to fill the available space. The advantage of using fewer rings is less rod wear. Also, the stuffing box design is simpler and takes less material.