How to kill a mechanical seal

Welcome to my article about prolonging seal life…

That should have been the title of my article, but would it be as fun as one of my guilty pleasures of 2020 with the Coffin Dance Meme? Probably not. But there are a lot of parallels in the pump and seal business and the memes from 2020. Allow me to clarify what I mean by that…

The clip usually starts with someone who is not aware of certain dangers of a situation or is preoccupied with other things until fate intervenes and then well… let’s just say people try to make the best of the last moments here in this world. Fortunately most of the clips are montaged in a way to maximize the contrast effect for amusements sake.

For someone who is not active in the pump and seal industry I learned that handling a seal or a pump does not necessarily come naturally for everybody for many different reasons. Sometimes the causes can be many, such as assumptions, miscommunication or worse: a lack of interest or knowledge. The seal then fails where this could have been easily prevented and then the jokes start!

I say, let’s put these jokes in the coffin and say goodbye to them, starting by reading this article on how to prolong seal life!

So what does a seal need for a healthy life?

Seals fail because of 2 reasons:

1.     Seal faces open or

2.     Part(s) become(s) damaged

A mechanical seal needs to be kept cool and well lubricated with a clean fluid film between the faces that is stable! The seal is like a fuse in the system and should under normal circumstances last until the seal faces wear out. A fluid film makes sure there is a thin layer between the faces that is typically 1 micron (0,001 mm) thick. Its purpose is to minimize face contact while providing lubrication and to reduce heat generation. This can be done with a single seal or double seal, where the fluid film is generated by the product with the single seal, as the fluid films with double seals can be a circulating fluid of a liquid or a gas or a combination. Seal life is directly affected by temperature, pressure and speed. Seal faces also generate kilowatts of heat depending on the hydraulic pressure, speed of rotation and the type of face materials used. Other seal influences are the axial and radial movement and how it is fixed to the housing and fixed to the shaft.

So now that we understand a bit what is essential and important to keep a seal healthy, let’s look at some issues that damage a seal…

Dry running!

Make sure that there is fluid in the pump and never turn on a pump with no fluid. Not even for short periods. With no fluid film between the seal faces, a seal can get damaged in less than a couple of seconds. Seal faces that rub together will overheat and render these faces useless. The O-rings will overheat as well, harden and lose its sealing properties. All in all resulting in heavy seal leakage when fluids are introduced.

So here is a short list of most common reasons for having no flow in a pump:

1.     The delivery valve is closed

2.     The suction valve is closed

3.     There is a blockage in suction or delivery in the pipe work

4.     An auto valve is shut elsewhere in the system

5.     A blocked strainer or filter

6.     The pump is not primed

7.     The tank is empty

In my next article I will zoom in a bit more on causes such as cavitation & overheating.

Hope to welcome you back then...