What is a double mechanical seal ?
Double seal is designed to ensure maximum seal safety. It is consist of two seal are arranged to 1 whole set. Inboard and primary seal make seal contain in the pump housing, outboard and secondary seal prevent flush fluid from leaking outside. There are two seal arrangement for double seal- back to back, face to face.
5 reason to use double seal.
1，To avoid leakage of fluid
2，If one of seal failure, it should prevent process fluid from contamination
3，Preventing dangerous things from getting into atmosphere
4，By controlling the amount or type of fluid film on seal faces. Maximum life of seal.
5，When process fluid in not proper for lubrication. Barrier fluid will work.
How double seal work in pump(reactor,agitator) ?
A double seal have two primary seal which barrier and buffer fluid area. Each primary seal consist of softer and narrower stationary seal, and fit with harder and wider rotary seal. This arrangement make softer seal face keep integrity of harder seal. Pump reactor and agitator have almost same working principle.
How many types for double mechanical seal arrangement？
A double seal comes in rotary and stationary versions. There are two typical configuration. That is back to back, face to face.
Is there any difference between single and double mechanical seal ?
Back to Back seal arrangement
For this double seal arrangement, Both narrow seal face are mounted back to back. This is original concept of double seal-taking two component mechanical seal, and taking those into stuffing box, back to back. This arrangement used in most general application.
Face to face seal arrangement
When equipment is space constrained to accommodate back to back arrangement, face to face can be used. In this configuration, one portion of seal is mounted in pump housing. The rest portion is mounted outside of pump housing.
Something about double mechanical seal barrier fluid.
What is function of barrier fluid ? It is flush in one of hole of mechanical seal, then flush out the other one. When fluid pressure is not very high, we will choose oil seal as one of primary seal.
Barrier fluid is 1~2 bar higher than pumped fluid pressure.
When to use barrier fluid ?
1, Used when fluid is very dangerous and one of primary seal failure put worker and environment in danger.
2, Enable seal fluid move across inboard seal and lubricate seal faces.
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