Skip to content

Why Do Sanitary Mechanical Pump Seals Fail?

December 5, 2014
Mechanical Pump Seals

Sanitary Pump Mechanical Pump Seals

We sell a lot of sanitary pumps and almost all of those pumps have some type of mechanical seal.  We’ve talked a lot about seals on this blog in 2014. The mechanical seal in a sanitary pumps separates the “clean” process from the “dirty” outside world. Failure of the mechanical shaft seal is the most common cause of pump downtime. The shaft seal is exposed to a wide variety of conditions and it can be quite difficult to identify why a seal failed. This post will take a look at the most common costs of seal failure and readdress how we reduce the frequency of seal failure.

Running Dry/Lubrication Failures

The first cause of failure we’d like to highlight in this post is what we call “lubrication failures”. Proper functioning mechanical seals use hard seal materials that depend on lubrication provided by the fluid being pumped. Obviously, if you don’t have any fluid in the pump, that’s not good and your seal will fail. But dry running is not the only time seals can be insufficiently lubricated. At high temperatures or near a fluids vapor pressure, the fluid does not always act as a good lubricant. Lack of lubrication again will lead to friction and heat generation and ultimately seal failure.

The easiest fix for lubrication challenges is to use a mechanical seal with a flush. By using a flush fluid that is compatible with the product, seal life will greatly increase in these challenging applications. Seals are essential for high temperature or vacuum applications.

Contamination/Product Ingress

Another common problem that leads to seal failure is buildup of product on the mechanical seal faces. Sanitary pumps are subject to large swings in temperature, pressure, and velocity. These constantly changing conditions increase the risk of sedimentation in or near the sealing gaps between seal faces. This is a common problem when pumping fluids that tend to solidify quickly and scale on seal faces. As the deposits accumulate on the seal faces, the sealing gap opens further. The result is a leaking seal. This leaking can start slowly at first and increase with time. Accumulation of abrasive particles can also lead to seal face damage, making a bad situation worse. To combat this, exceptionally hard seal faces are recommended for these abrasive applications.

Again, the fix here is to use a mechanical seal with a flush. The flush fluid helps not only to lubricate the seal faces, but also keep them “clean” and prevent product from getting into the seal gap.

Operator Error

There are two primary sources for operator error that results in seal failure. The first is damage during seal removal or cleaning. Carbon, a common material for mechanical seals, is very brittle. Mishandling can easily chip seal faces which quickly leads to a problem. When servicing a pump, care should always be taken to ensure the seals are handled carefully and the seal faces are adequately cleaned.

The second source of operator error is also from improper cleaning. When a pump is taken off line, if it is not properly cleaned, product can solidify on the seals and essentially “lock” the seal faces together. When the pump is brought back online, the high motor starting torque can damage the stuck seals. It is critical to ensure the pump is cleaned properly and product is not left in the product zone. This means CIPing your Universal 2’s and pulling the rotors out and cleaning your Universal 1’s.

Chemical and Physical Degradation

This is the most obvious source of seal failure. If you are pumping an abrasive product, make sure you select compatible seal materials. As a seal wears, the originally smooth seal face becomes worn and pitted, resulting in leaks. And while much emphasis is placed on seal face material selection, it’s also important to ensure that the elastomers used are compatible as well. Swelling and failure of the elastomers can also compromise the seal chamber ,leading to failure. For more information about seal face or elastomer compatibility, refer to our previous posts on the topic.

Vibration

The life span of a mechanical seal is directly affected by shaft movement.  Vibration can cause carbon face chipping and seal face opening.  Seal face opening can result in contaminants to penetrate between the seal faces causing premature wear.  There are a host of causes for excessive vibration including, bent or warped shafts, pump and drive misalignment, worn or loose bearings and unbalanced rotating components.

To conclude, mechanical seal failure is often a combination of a variety of factors. The mechanical seal is a dynamic area of the pump that experiences both temperature and pressure swings. Running dry, operator error, and compatibility issues can all lead to premature seal failure. For help troubleshooting your pumps mechanical seal, contact a Holland Sales engineer today.  

No comments yet

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: