In the last issue, we discuss about mechanical seals and how the various components work together to seal the liquid from escaping at the pump shaft area.
In this issue, we will focus on a much simpler way of sealing a rotating shaft of a pump. It's by using gland packing. This method of sealing has been in use for a very long time, and is still being used today.
There are advantages and disadvantages in using them.
Perhaps the first and foremost reason for replacing them with mechanical seals is because of the fact that gland packing needs a small amount of leak for cooling purposes.
A person who installs a gland packing must ensure that the latter does not grip the shaft too tightly. A little dripping must be allowed for. Pumps that contain hazardous liquids should not use them at all.
Pumps that contain gland packing will usually be constructed with a small well and piping at the gland to lead the leak water away from the pump so as to ensure that the water will not damage the bearings, housing or foundation. This can really mess up the pump area if there is a choke at the drain piping that prevents the leaked water from flowing away.
The pump gland nuts may need to be tightened every now and then due to slight loosening after some time of operation. This is because the nut cannot be tightened hard against the soft packing.
Because the packing gland rubs against the shaft, it will tend to wear down the shaft. For this reason, and especially for larger pumps using packing glands, there will usually be a shaft sleeve that can be slipped over the shaft. The wear down will then occur only on the shaft sleeve. This can be replaced instead of the more expensive shaft.
Another disadvantage of using packing glands is the fact that there is a certain amount of skill needed for cutting and installing the gland in order for it to work properly. It's more difficult to get consistent results.
Although there are disadvantages in using gland packing, there are also good reasons for using them.
They are less expensive to use compared to mechanical seals. If chosen and installed correctly, they can last for a very long time.
When changing packing glands, the pump housing need not be opened up.
This can be an advantage when skilled labor is in short supply.
Keeping stock of spares is not a problem because they can be used for all pump brands as long as they have the same gland sizes. Pump packing materials are more robust compared to the fragile and delicate mechanical seals.
For more information on gland packing and pump troubleshooting, download the free software from http://www.free-marine.com/diagnoppad.htm "Uncover Remarkable Secrets of Youth!"
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