API 610 Cooling Water- Pedestals 2

[longeron]

I spent a good bit of time over the weekend looking for information on bearing housing, stuffing box jacket, and pedestal cooling. Does anyone have links or more information documenting the current philosophy on piping cooling water to these parts of a pump? I'm fairly certain that Heinz Block has published something recently on this topic.

 

[JJPellin]

You are correct. In Heinz Bloch's book "Pump User's Handbook" (Fairmont Press, Inc., 2004), he has an appendix (2) that lists a summary of reliability improvement options. The first two items on the list are "Do not allow pedestal cooling..." and "Do not allow jacketed cooling water applications on bearing housings..." His fifth point on this list is "...stuffing box cooling is generally ineffective..." I agree on all points. Pedestal cooling is unnecessary and detrimental. Jacketed cooling on a bearing housing can actually increase bearing temperature and shorten bearing life. I would only use a cooling jacket around a seal chamber for a dead ended application. I have used this effectively on a hydraulic recovery turbine that could not use any other API piping plan. But it is very rare that this would be the best option.

Johnny Pellin

 

[longeron]

Thanks Johnny.

 

[trashcanman]

JJPellin,

Please explain: Jacketed cooling on a bearing housing can actually increase bearing temperature and shorten bearing life.

I'm not a pump expert, and am curious as to why this happens. Thanks.

 

[JJPellin]

The old design for jacketed bearing housings had a cast in jacket that completely surrounded the bearing. The heat is being generated by the bearing. So, the bearing attempts to grow. The outer housing is cooled and attempts to shrink. Since a standard ball bearing has very little internal clearance, it doesn't take much to greatly increase the ball loading. And a heavily loaded ball generates more heat. Heinz Block first documented this phenomenon. They did testing on real pumps in a refinery installation and proved that the bearings ran cooler after the cooling water was eliminated. Please keep in mind that this only refers to jackets that completely surround the bearing. Newer pump may have cavities in the bottom of the housing that are cooling the oil. Others may have cooling coils or removable cast coolers in the bottom of the housing that cool the oil. If the oil is being cooled, this problem does not occur and the cooling can be beneficial.

Another problem with jacketed cooling can be condensation. In very wet environments, the top of the housing on a pump that is not running may cool down below the dew point of the surrounding air and condense moisture in the oil. This would be most likely in someplace with high humidity.


Johnny Pellin

 

[bk19702]

As JJPellin mentioned, a jacketed stuffing box is only useful on a dead ended seal flush application (API Plan 02). This flush relies on heat removal from the seal area through natural conduction/convection, so the jacket can be helpful in this instance.

Jacketed bearing housings are not a good idea for the reasons mentioned as well as the potential for contamination on older pump designs if the jacket integrity is compromised. We have witnessed this happen at our site on several older Union pump designs that at one time utilized jacketed bearing housings.