The advantage of a mechanical
seal is the very low leakage (some leakage is necessary for lubrication and
cooling). The leakage is so small that they are therefore also called
leak-free. If media are pumped, which do not evaporate quickly, you can clearly
see that a mechanical seal is not leak-proof. With oil, for example, the space
around the seal will become completely greasy.
A mechanical seal (mechanical seal) consists of a number of
parts that together ensure a good seal:
● The rotating ring
● The stationary ring in the pump
cover, the counter ring
● One or more springs pressing the
rotating ring axially against the stationary ring.
● An O-ring that seals the rotating
ring on the shaft.
● An O-ring that seals the stationary
ring in the pump cover.
● often there is also an adjusting
ring present to give the desired
● Bias to the spring or springs.
● locking pin (s)
● The actual seal is the narrow gap
between the stationary and rotating ring.
Things To Be Aware Of the Mechanical
Seal
A disadvantage of the
mechanical seal is that in case of repair / replacement, the pump must be
partially dismantled in order to repair / replace the seal. In addition,
skilled personnel is required to replace a mechanical seal, especially with
more complicated versions. There are variants that are easier to replace
(cartridge seal), but these are a lot more expensive.
Rinse (flushing)
The wear of a mechanical
seal increases as more frictional heat is generated on the sliding
surfaces. The cooling in the seal chamber and the lubrication between the
sealing surfaces are therefore very important. The temperature in the seal gap
must be as low as possible, so that no evaporation of the leaked liquid, which
functions here as lubricant, can occur here. Therefore measures are taken to
remove the frictional heat between sealing surfaces. The cooling of the sealing
surfaces with liquid is called flushing. There are two methods: internal
flushing and external flushing. If no rinsing is used, one speaks of a
"dead end seal".
Materials, types and versions,
standard seal
In order to obtain good running properties of the rings with
respect to each other, they are made of different materials. Good heat
conduction is important here. Often they must also be resistant to attack by
chemical or heavily abrasive liquids. Often a compromise must be sought between
these requirements. Mechanical seals are available in many versions. For
example, there are only seals and double seals. In the letter, a distinction is
made between double in "back to back" setup and double in
"tandem" setup. There are also so-called "cartridge seals".
Here all parts, which together form the seal, are pre-assembled on an axle
sleeve to form one seal pattern.
