seals level 2 Flashcards
Seals
7Static seal
No relative motion
Dynamic
Seal between moving and stationary parts (eg packing
Two types of flange blind
Pancake and spectical
Purging
Displace potential hazzerd substance with substance that is non hazzerdith
Fully confined
4 sides trapped tounge and groove.
unconfined
2 sides squeezed allows gasket two move freely towards or away
Partial confined
3 sides prevents blow out confined on 2 flat sides and edge
Two finishes on a flange
Smooth or serated
What is harder flange or gasket on a metallic gasket
Flange the gasket has to be able to form.
Witch flange face is for higher pressure
1/4” pressure above 900
What holds tounge and Grove gasket in place
The flange (fully confined 4 sides)
5 requirements of gasket
1.Bolt load
2.Pressure and temp extremes
3.fluid compatability
4.compattabilty of flange and joint design
5.with stand ware
Replace gasket with
Same gasket could test fit to see if this essay stays correct or need to use thicker one .
Aerobic vs anerobic
Aerobic become hard in presence of air.
Anaerobic absence of air.
Mechanical leak is how much and called what
5 drops /hour
Called lubrication.
Can a mechanical seal be adjusted to stop a leak.
No when it fails it fails completely. This is why they cannot be used for fire safty.
Items used as primary seal faces of mechanical seal
Ceramics and carbon are main ones for water
Secondary seal on mechanical seal
Square/gasket packing
V-packing
U-cups
Delta rings
O-rings
Orientation of mechanical seal faces to shaft center line
Always perpendicular
When used with shaft sleeve how many sealing points
5
Why do gas seal have grooves
To separate matting surface and reduce ware
Disadvantages of ptfe wedge as secondary seal
Requires heavy seal force that can cause overheating
Suction =
Change in atmospheric pressure
Advantage of v-ring as secondary seal
Can be turned around to seal in vacuum situations
Non pusher reqiures
A push to keep seal faces together no pusher =static
Pusher seal =
Dynamic
Flushing vs quench
Flushing is rinsed
Queched is cleaned
Single mechanical seal can be installed
Either inside or outside mounted they have one primary sealing point.
Double mechanical seal
Two seals with two rotating seals that face in opposite direction
Purpose of barrier liquid in back to back seal arrangement
Lubricate
Form a barrier to isolate pumping medium from seals and atmosphere.
Seals face what way in tandem seal arrangement
Seal face away from product
External seal is
Seal on bearing housing (pillow block)
Intregal seal
Seal attached to bearing has to be prelubricated (also called a shild)
A rubbing seal is required too
Contact to shaft also
Capable of retaining oil
Positive seal against moisture and fine contaminants.
Positive seal
Seal that prevents any fluid from leaking from one side to another
What shaft imperfections contribute too lip seal leaks
Burrs and deposits grit.
Lip seal direction
Inclusion seal in
Exclusion keep dirt out
What must be done to felt ring before installing
Must be soaked in oil
Operation of spiral groove seal
Overcome disadvantage of non contact seal by acting as a flinger to keep containment away from important parts
Labyrinth defined as
A torturous path
If lantern ring is used to keep harmful abrasives and chemicals out it is located.
6 o’clock or at bottom
Standard o ring psi _
And with anti extrusion rings _ psi
1500- 3000
O ring fully confined psi eg b fitting
10,000 psi
O ring Grove width
120-150 percent
O ring squeeze static and dynamic
Static 20 percent
Dynamic 10 percent
Less because it’s moving want less ware
O ring depth of Groove dictates…
The o ring squeeze
Secondary seal in machanical seal is
Static
Primary seal in mechanical seal is
Dynamic
What psi must lantern ring receive to keep pumping medium away from packing
10-15 psi
Positive seals used when it is vital that no atmospheric containment reach working parts
Boots and bellows
Lip seal psi
2-10 psi
Gasket to be careful of for special applications like steam turbine
Asbestos
all static seals are
Positive
Seals that control amount of leak
Non positive
Positive seals
Prevent leak
Seals between stationary parts
Static
Seals between moving and stationary part
Dynamic
