|To get maximum life from packing and shaft.|
|This information has been in our
office for many years. We don't know where it originated and who to
credit. It's the soundest advice you're likely to find.
The material is reproduced here with original illustrations.
|For packing to be successful in any
application the equipment must be in first class condition. Poor
equipment means poor packing life and, more often than not, poor packing
life is the result of poor equipment rather than the packing itself.
The shaft or shaft sleeve should be in good condition. Run-out of more than .003" should not be accepted. A shaft with whip or runout opens the space between the shaft and the packing, which makes excessive leakage inevitable.
An example of the problem of shaft whip is of interest - In a pump with a 50 lb. impeller running at 3600 RPM, with a shaft runout of .003"; i.e. .006"across the diameter, the shaft will exert a force of 56 lb., 3600 times per minute. Under these circumstances it is virtually impossible for the packing to seal against the shaft, excessive leakage will occur. The packing is generally blamed for the failure.
One item of pump condition often overlooked is the state of the stuffing box. Rough or pitted surfaces make for difficult sealing on the O.D. and prevent proper adjustment of the gland, due to excess 'hang up' of the O.D. of the packing.
|Remove all old turns of packing,
clean the stuffing box thoroughly, avoid scratching the shaft. Check
for shaft run-out and the condition of the stuffing box. Measure
shaft and stuffing box, to determine the correct size of packing required.
The correct size of packing is important, as square braided packings are made in such a way that distortion to another dimension distorts the sealing faces and creates the need for excessive gland pressure to prevent leaks, causing overheating, with it's attendant problems.
|Slight pressure with a 'rolling pin' action is permissible, to facilitate some packing installation.|
Packing rings should be cut square around a shaft of the same diameter as the pump being re-packed. A square cut avoids unravelling. Wrapping the packing around the shaft two or three times, then cutting longitudinally along the shaft, will ensure rings of the correct length with neatly fitting ends.
|If rings are cut while the packing is stretched out straight, the ends will meet at an angle when the ring is placed around the shaft and a gap is created. The rings on either side will then squeeze into this gap, preventing the ring from closing - a common cause of leaks.|
||When placing rings over the shaft, it is preferable to open a ring sideways and not with a spreading action.|
|Rings are installed individually, with staggered joints. Each ring should be pushed home with a tamping tool or a dummy gland spacer, to ensure seating of the whole set. This is particularly necessary with installation of metallic rings.|
|Never rely on seating the rings
with gland pressure alone, as the rings nearest the gland will be
overloaded, whilst those at the bottom of the stuffing box may be quite
loose and provide no sealing effect whatsoever.
It has been proved that 70% of packing wear, and consequent shaft wear, takes place with the last two rings at the gland end, hence the need to spread the packing load as evenly as possible throughout the stuffing box.
|Where a lantern ring is used, be sure to line it up carefully with the flushing or lubricant connection, remembering that, as the packing is compressed through adjustment, the lantern ring will move along the stuffing box and should not be allowed to loose it's contact with the opening.|
Once the turns of packing are installed, tighten the gland firmly, to ensure final seating of the packing, then free-off the adjusting nuts and re-adjust, to just over finger-tight. The gland should enter the stuffing box to the depth of one turn of packing.
Packing does not stop leakage, it only controls leakage.
This adjustment procedure can take several hours. It is
unfortunate that such care is rarely taken in practice.