The two main variations in a seals setup
Beyond the most common design types, mechanical seals are typically categorised into two main setup types; pusher and non-pusher.
What are pusher and non-pusher mechanical seals?
In a nutshell, pusher seals have a dynamic secondary seal which moves axially with the major seal face, whereas non-pusher seals have a static secondary seal which stays stationary against the shaft or sleeve. Below we explain the two types in more detail.
Pusher Mechanical Seals:
The main purpose of a pusher seal is to make sure that the sealing fluid is spread across the face of the seal and that it does not leak out into the atmosphere.
A pusher seal is most commonly used in low-temperature settings and in services that have light ends such as ethylene, methane and propane.
A pusher-type mechanical seal has a primary sealing ring which is put together using springs and a specially designed O-ring. This dynamic secondary seal moves axially with the major seal face. See O-Ring Mounted seals type for more information.
Non-pusher Mechanical Seals:
On the other hand, a non-pusher seal is made up of a bellows assembly and can be used in high temperatures as “grafoil” secondary seals help non-pusher seal better handle the rise in temperatures, unlike the pusher type.
The bellow is the only thing that is needed in this type of seal to prevent any sort of leakage into the atmosphere. There is no use of the dynamic O-ring as the secondary sealing element is the bellow itself.
A bellow is a component of the seal that has two main functions; one, it performs the task of a load element, and secondly, it also works as a sealing element. See Rubber Bellows seals type for more information.
Quick guide to pusher and non-pusher seals:
- Closing force supplied by springs
- Used in low temp. services
- ‘O’ ring secondary seals
- Used in light end services
- Closing force supplied by bellows (no dynamic ’O’ ring)
- Can be used in high temp services (metal bellows)
- Metal bellows use ‘grafoil’ secondary seals to handle high temperature
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