SUBJECT : Troubleshooting mechanical seals at the pump site 4-2

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 occurs while the pump is both running and stopped.

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:

At the static and dynamic elastomer locations.

At the gland gasket.

Between the shaft sleeve and the shaft.

Between the seal face and its metal holder.

Through fretting damage

The seal leaks only when the pump is running.

The seal leaks only when the pump is not running.

The leak occurs only at start up and then stops after a short time.

The seal leaks intermittently, or after the pump has run for a fixed period of time

Look for reoccurring events that initiate the leakage. They can include:


The leak rate is changing, It gets better or worse.

The faces spit liquid.

Fire hose type leakage. The leak is following shaft rotation.

Intermittent leakage.

The seal area is damp. There is no visible leakage.

Constant dripping. It never changes. This cannot be a damaged seal face leak because seal faces are a wearable surface and the leak rate would have to change.


Heat is being generated at the seal faces. Unbalanced seals generate more heat than hydraulically balanced seals.

A seal component is rubbing the inside diameter of the stuffing box, or against a solid that has attached its self to the inside of the stuffing box.

The sleeve, shaft or rotating seal is hitting a stationary component.

A foreign object is loose in the stuffing box.

A suction recirculation line was used to lower stuffing box pressure. The high velocity recirculation is heating up the return line.



The convection tank

Flow meter not indicating.

No flow through the quench and drain connections.

Loss of jacket cooling. The incoming and outgoing lines are at the same temperature.


For information about my CD with over 600 Seal & Pump Subjects explained, click here  

 Link to Mc Nally home page