Troubleshooting Mechanical Seals At Equipment Disassembly

Leakage can occur at any time throughout the life of the mechanical seal

. To troubleshoot leaking seals effectively it is helpful to know just when the leakage starts. This is the advantage of being able to troubleshoot a running pump, or one that is still hooked up to its piping.

By noting the type of leakage and when the leakage occurs, we can do a more thorough job of analyzing any seal failure. In addition to leakage we'll also be looking for other symptoms that are visible to the trained troubleshooter.

We'll start with the different types of leakage. Please look at the following diagram of a stationary seal design in an API gland and installed on a jacketed pump

The leakage can be detected visually, by odor, or by instrumentation. A strobe light can sometimes be used to determine its location. As you can see in the above diagram, there are several leak paths possible. The seal can leak :

At the lapped faces. Since they are a wearable surface the leak will probably get either better or worse. It should never remain constant. The leak started because:

The outside springs in a dual cartridge seal were painted during routine maintenance. The spring load has been reduced because of thermal growth, axial thrust, or impeller adjustment.

The seal was set-screwed to a hardened shaft and the set screwa have vibrated loose. One or both of the seal faces is not flat. Solid tungsten carbide and silicon carbide faces are often lapped flat on only one side. Check to see if the face has been installed backwards.

The dynamic elastomer has swollen up and seized the spring loaded face; preventing it from remaining in contact with the stationary face.

The product has prevented the lapped seal faces from remaining in contact.

Dirt has gotten into the sliding components. The product has crystallized. The product solidified or became very viscous. The product is vaporizing across the seal faces, expanding and blowing them open.

At the static and dynamic elastomer locations.

This type of leak tends to remain constant and will often stop when the small opening clogs up with solids. The leak can be caused by a damaged rubber part, or damage on the surface where the elastomer seals. In some instances the elastomer is not seated properly. It twisted because of either poor installation, excessive shaft movement, or high pressure extrusion.

At the gland gasket.

This is the easiest leak to detect because it's very visible and does not change with shaft rotation. Between the shaft sleeve and the shaft.

This is a common problem with double ended pumps, where the sleeve is used to position the impeller and there is no method of sealing the sleeve against the impeller.Between the seal face and its metal holder.

The leakage frequently increases, as the product mechanical seal temperature increases,because the metal face holder has an expansion rate three times that of the carbon face.

by: Bowman

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