Many packing failures are due to faulty packing installation methods. The importance of proper packing installation cannot be over emphasised.
The following steps should be followed.
Remove old packing
Clean the stuffing box and shaft thoroughly and check for wear or scoring. Replace shaft or sleeve if wear is excessive as the packing cannot act as a bearing.
Cut the rings
Never wind packing into a stuffing box. Always cut coil or spiral packing into separate rings.
For pumps and agitators, cut rings with skive or butt (square) joint. The best technique is to cut rings on a mandrel the same diameter as the shaft or sleeve. Do not stretch it on the mandrel. Test the first cut ring in the stuffing box to make sure it is a tight fit with no gap at the join.
Use the first ring as the master from which the rest of the packing rings are cut. If cutting on a flat surface, ensure that the side of the master and not the OD or ID surface is laid on the rings being cut. This is to ensure that the cutting angles are reproduced.
A good tip
To cut rings from a packing that is unusually soft or has a tendency to fray excessively, apply a small piece of tape at the point where the cut is to be made, then cut through the tape. If the tape is thin, it can be left on the packing ring.
Install one at a time
Make sure that each ring is clean when it goes into the stuffing box and stagger the joints at 90° intervals. Seat each ring firmly with a tamping tool.
Rings used on valves and expansion joint. are generally cut with a diagonal joint. (illustrated above). In preparing diagonal cut 45 degree rings, be sure that the first ring is cut carefully, and then tested on the stem.
The gland follower
When enough packing rings have been seated so the nose of the gland follower can reach them, the gland follower is inserted. Never depend entirely on the gland follower to seat a set of packing rings properly - this practice will jam the last packing rings installed but leave the front packing rings loose in the box. The result will be excessive and rapid wear of the rear rings; erratic packing performance, and sometimes twisting and tearing of the front rings.
After the last packing ring is installed, take up bolts finger tight. Start the pump, and take up bolts slowly until leakage is decreased to not more that 1 drop per second. Stopping leakage entirely at this point will cause the packing to burn.
Let it leak at first
Allowing the packing to "run-in" over the first hour before adjusting to acceptable leakage rates will improve the life of the packing. Adjust the gland nuts with ¼ turns until leakage has reached the recommended leak rate.
Never try to stop leakage entirely, unless Klinger has indicated that it is safe to do so
The gland packing and shaft can be lubricated by supplying lubricant into the stuffing box through the lantern ring. The lubricant may include water, grease or the pumped product. Fittings for lubrication are supplied standard on most pumps.
If the stuffing box has a lantern ring, make sure that the lantern ring, as installed, is slightly behind the fluid inlet so that it will move under the inlet as follower pressure is applied.
Replace packing when leakage cannot be controlled by further take-up on the follower gland
Have enough rings
On both centrifugal and reciprocating pumps, about 70% of wear is on the outer two packings nearest to the gland. However, each additional ring does throttle some fluid pressure. On most machines, there must be enough rings so if one fails, another does the sealing, and the machine need not be shut down.
Below are typical pump gland packings for different operating conditions
Fig. 3 Typical stuffing box when pump suction pressure is above atmospheric pressure
Fig. 4 Typical stuffing box when pump suction pressure is below atmospheric pressure
Fig. 5A Typical stuffing box when pumping slurries
Fig. 5B Another type stuffing box when pumping slurries