By Rick Kushinski, Service Manager
Probably one of the most overlooked preventive maintenance tasks is to change the stuffing box packing annually.
As the packing ages, it becomes hard and brittle. In this state, it loses its ability to provide an adequate seal against the outer diameter of the shaft, as well as the inner diameter of the stuffing box. This can lead to increased air leakage through the stuffing box at higher vacuum levels or excessive seal water leakage along the shaft at lower vacuum levels. The latter can also contribute to a premature bearing failure if the leak is severe enough to allow water to enter the bearing housing. When this situation occurs, we commonly find that the packing gland has been tightened to the point of creating too much friction against the shaft, which in turn causes the metalizing on the shaft to overheat and possibly crack - making the situation much worse. At this point, the pump needs to be removed for repair.
Changing the packing annually will make the task much easier to accomplish, as the packing will still be pliable. It is also very important to remove all of the packing, and replace it with new parts. Many times, when pumps come in for repair, we find that the shaft packing rings that are easily accessible, the first two or three, have been changed out but the remaining rings were left in. This will lead to the same problems mentioned earlier.
While this task is being performed, make sure that the drip tray between the stuffing box and the bearing housing is not full of debris and that the drain is clear. A clogged drain will allow water to build up in the drip tray and possibly enter the bearing housing and contribute to a premature bearing failure.
When repacking make sure the slits in the packing are staggered. The goal is to stop an excessive leak at start-up or after repacking, not to prevent the water from getting to the outer rings.
The packing drip is decided by the two outer rings. Adjusting the gland in only these rings will compress the packing and make it tighter on the shaft. The last ring opening or slit should be at the bottom of the shaft, and the gland should be started or registered in the stuffing box. You do not want it to drop on the shaft.
To start the gland in the stuffing box, cut ¼ inch from the new ring and flatten it a bit. This will allow it to go into the stuffing box more easily. Do not force the gland into the packing box, as it will put too much pressure on the shaft and packing. Most of the packing is graphite impregnated Teflon and can wear into a shaft and groove it if you are not careful.
Install the first three rings into the stuffing box and use the gland to make sure they are seated correctly. Then install the fourth ring, start the pump and adjust the packing. If you can get the last ring in go ahead and install it – but make sure there is a drip, or that the packing is running at a temperature where you can leave your hand on it.
Packing that is too hot, or does not peak and then drops to a normal operating temperature is a cause for concern and may lead to packing or bearing failure. Check to make sure there is a slow drip, as no drip and high packing temperature may indicate that the packing is too tight and should be adjusted.
When starting a new pump, or a pump with new packing, the following tips that will help extend the life and performance of your pump packing: