Bearing Protectors - Inpro/Seal ® & Oil Seals
A bearing protector is any device that protects the bearings from loss of lubrication or contamination. For ANSI pumps, this device is either an oil seal (lip seal), or a labyrinth bearing isolator (Inpro Seal). These devices are necessary to keep the oil in the bearing housing, while keeping the contaminants (water, process fluid, other) out. Even one drop of water inside the bearing housing can reduce bearing life by up to 48%.
For decades, oil seals, also called lip seals or radial shaft seals, were the normal devices used to protect bearings from contamination and loss of lubrication. However, as more attention was focused on overall operating and maintenance costs, the use of bearing isolators became more commonplace. Today, the Inpro seal is standard equipment on most new ANSI pumps sold, including the Goulds 3196 process pump.
Oil seals come in many forms and materials, but they essentially work the same way. The oil seal has a lip, or a flap, that makes constant, uniform contact with the rotating shaft to prevent contaminants from entering the bearing housing. Due to the contact the elastomer lip makes with the rotating shaft, there will be friction and wear. This guarantees the lip seal will fail at some point.
Tests from the oil seal community quantify the life of an oil seal under normal conditions to be just about one month. Given that bearings have an intended life of 50,000 hours, it doesn't make sense to protect it with something whose life is measured in days.
The most common oil seals are quite cheap - for this reason alone, it's not a bad idea to have a few around just in case. Below is a chart of SKF oil seals (CRW1 type) that will fit the STX and MTX power end (bearing housing).
|Type||Shaft (in)||Bore Diameter(in)||SKF Oil Seal (CRW1)|
|STX Line||1.375||2.835||SKF 13920|
|STX Thrust||0.875||1.25||SKF 8624|
|MTX Line||1.75||2.875||SKF 17653|
|MTX Thrust||1.125||2.00||SKF 11340|
Inpro Bearing Isolator
The Inpro bearing isolator is a device invented by Inpro/Seal company, and they continue to be the market leader and industry standard. According to their description, the device is a "non-contact, non-wearing, permanent bearing protection device." It uses a labyrinth system to keep the contaminants out and the oil in. Sometimes it is referred to as a labyrinth seal, an Inpro seal, or a bearing isolator. All of these names refer to the same device.
Inpro bearing isolators were the first integrated two-part bearing protection devices. They consist of a rotor and a stator. The rotor turns with the shaft by means of an O-ring on the inside diameter of the rotor. The stator is pressed into the bearing housing itself or to the adapter mounted to the bearing housing.
This rotor acts as a slinger. If a mechanical seal or packing leaks or there is external cleanup or if a pump is outdoors in the weather, the rotor slings the liquid away preventing it from entering the bearings and contaminating the lubrication. Even liquid under pressure slows down to zero velocity because it has to turn a series of right-hand bends to get past the rotor. Any liquid that makes it that far collects between the rotor and the stator, gravity feeds to the bottom of the rotor and exits the device through a hole or a gap.
The stator is a labyrinth. Oil being slung inside the bearing housing tries to escape past the bearings. The lips of the labyrinth have just a few thousandths of an inch clearance on a side. The oil gets slung into the lips of the labyrinth. The oil gravity feeds to the bottom of the device where a trough allows the captured oil to return to the sump.
In addition, the Inpro is unitized. This means that the two pieces cannot walk away from each other during service. An additional benefit of this device is that the bearing-bronze components do not touch. This makes them reusable. Also, this device can act as a disaster bushing. In the case of a catastrophic bearing failure they can act as a sacrificial bushing and save the running gear (impeller, casing, rear cover) from serious damage. They can be used in motors, fans, gear reducers and other mechanical devices. They have become a de facto standard in the ANSI pump market.