Quality of packing
FOR PUMP AND AGITATORS
1. Remove all old packing from teh stuffing box. It is quite a business to pull out packing from the depth of stuffing box. The use of packing hook produces an easier work as illustrated below.
Clean the box and shaft throughly and examine them for wear or scoring (replace or repair them if wear or scoring is excessive). If clearance of neck bush at the depth of stuffing box should be great, insert hard bush jor replace neck bush. In case or rotary shaft, if displacement is greater than 0.07mm, set the shaft to the right position.
2. Use the right size coil packing. To determine the correct coil packing size, measure the diameter of the shaft (to get the I.D. of packing) and inside diameter of the stuffing box (to get O.D. of packing). Subtract the I.D. from O.D. and devide by two. The result is the required size of coil packing. It is best to employ the next size larger.
3. Cut coil packing into ring. Never wind a coil packing into a stuffing box. Rings can be cut either with butt joint or diagonal joint (skive joint). The best way to cut packing rings is to cut them on a mandrel of the same diameter as the shaft in the stuffing box area. Hold the coil packing tightly and firmly on the mandrel but do not stretch excessively. After cut, try mit in the stuffing box to make sure that it fills the packing space with no gap in the joint at the O.D. of the ring.
|To cut rings from a coil packing that is unusually soft or that has a tendency to fray excessively, it is advisable to apply a small piece of tape at the point where the cut is to be made, then cut through the tape.
4. Install one ring at a time. Make sure that it is clean and has not picked up any dirt in handling. If clean oil is available, lubricate the shaft and the inside of the stuffing box. Joints of successive rings should be staggered and kept at 90° apart. Recommendable stagger is 90° apart for 4 rings, 120° apart for 3 rings and 180° apart for 2 rings. Each individual ring should be firmly seated with a tampering tool.
5. After the last ring is installed, take up bolts finger tight or very slightly snugged up. Do not jam the packing ring into place by excessive gland loading. Start pump, and take up bolts until leakage is decreased to a tolerable minimum. Make sure that gland bolts are taken up evenly. Stopping leakage entirely at this point will cause the packing ring to burn up.
6. Allow packing ring to leak freely when starting up a newly packed 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 seals until leakage is reduced to a tolerable level. Never try to stop leakage entirely.
7. If all possible, provide through a lantern ring means of lubricating the shaft and packing ring by supplying grease, oil, water, or the liquid handled in the pump. Fittings for these purpose are standard on most pumps.
8. If the stuffing box has a lantern ring, make sure the lantern ring, as installed, is slightly behind the lubricant inlet so it will move under the inlet as follower pressure applied.
9. Replace the packing when leakage cannot be controlled by further take-up on the follower.
FOR VALVES AND EXPANSION JOINTS
1. Follow all the steps 1, 2, 3 and 4 as described for pumps and agitators. Rings used on valves and expansion joints are generally cut with diagonal joints. In preparing diagonal cut rings, make certain that the first ring carefully cut and then tested on the shaft. It can then be used as a master for cutting other rings on a flat surface to insure that the additional rings are cut precisely at the right angle.
2. Bring the follower down on the packing to the point where heavy resistance to wrenching is felt. During this time, turn valve stem back and forth to determine ease of turning. Do not wrench down to the point where the stem will not turn.
3. After the valve has been on the line a day or so, even if no leakage exists, the follower should be tightened slightly. Obviously if leakage is occurring the follower must be tightened.