There is a seemingly endless variety of mechanical seals. In fact, even after all these years in the seal repair business, we still have seals sent into the shop for repair that we’ve never seen before! Luckily, all mechanical seals function on the same principles.
All types of pumps require a seal, and a mechanical seal is just one way to seal a pump. The purpose of any seal is to prevent whatever the pump is pumping from leaking out between the part of the pump that is stationary and the part of the pump that turns.
Before the widespread adoption of mechanical seals in industrial manufacturing, it was typical to use graphite packing to plug leaks in a pump. It is actually still used today in a lot of pumps. However, packing can’t handle friction as well as a mechanical seal. Water must be constantly flushed over the packing to keep it from overheating, and even then, it has to be replaced frequently since it wears down so quickly. Engineers realized that a more efficient solution was needed to prevent their pumps from leaking.
Enter the mechanical seal.
So how does a mechanical seal work? What makes it better than traditional packing?
There are 4 basic elements present in pretty much any mechanical seal: there will be a rotating seal face, a stationary seal face, a closing force, and the secondary seals.
The rotating and stationary seal faces are two extremely flat surfaces that are pressed together. The rotating seal face will be attached to the part of the pump that rotates while the stationary seal face will be attached the pump housing which is stationary.
The closing force is the part of a seal that squishes the two seal faces together. Usually this force is created by springs, but elastomers and magnets can also be used.
The most crucial part of the seal is where the rotating face and stationary face come together. The two faces must be SUPER flat; the evenness of these surfaces cannot fluctuate more than 2 millionths of an inch, which is about 100 times smaller than the width of a human hair! To achieve this extreme level of flatness we use a lapping machine. What this machine does is similar to when you use sand paper to smooth a wooden surface except, instead of sandpaper, a lapping machine uses diamond encrusted plates. Through the lapping process, these two surfaces will become so ultra-flat that they create a vacuum when they meet, which then makes it very difficult for fluid to fit between them and leak out.
Finally, we have our secondary seal, which helps stick the pieces of the mechanical seal to the pump and seal any gaps at these junctions. Normally, there will be one secondary seal for the stationary part of the seal and another secondary seal for the rotating part. These seals function similarly to the rubber on the inside of a pickle jar lid when you screw it closed.
So that’s the basic run-down on how a mechanical seal does its job. Seal repair experts like the team here at SAF can help keep your seals in tip-top condition. When a seal is working properly, it helps save companies money by improving a pump’s efficiency, and they also help protect workers and the environment by keeping harmful chemicals safely contained inside the pumping system. That makes seals a pretty worthy investment!