Seals Flashcards
What are the two basic ways to seal a bearing?
Seal the bearing housing (external)
Attach the seal to the bearing (integral)
What are the main advantages of a rubbing seal?
1: capable of retaining oil and grease
2: provide positive seal against moisture and fine contaminates
What are some disadvantages of a rubbing seal?
Limit operating speed
What are the different types of rubbing seals?
Lip seals
V ring seals
Felt seals
Mechanical seal
Integral rubbing seal
What is a very inexpensive seal but limited to speed and temperatures?
Felt seal
This seal has a temperature range from -40 degrees to 200 degrees C but is limited to 4m/S or 13.12 ft/S?
Lip seal
Smooth surface is not critical, v-ring orientation depends on whether it can hold grease and oil, and surface speeds are 12 m/s. What seal am I?
V-ring seal
This seal is used in severe service conditions
Wet environments
Low peripheral speeds
Dirty environments with solids
Provides leak proof retention of fluids
?
Mechanical seal
These seals do not require mounting as they are part of the bearing
Only retains grease and keep out contamination
Capable of keeping out fine contamination including liquids and vapours
Better suited for low surface speeds
Integral rubbing seal
What are the different types of non rubbing seals?
Radial labyrinth seal
Axial labyrinth seal
Combination labyrinth seal
Sealing washer set
Flinger ring
Integral non rubbing seal
Smooth gap seal
This seal does not restrict the operating speed but cannot keep out fine contaminants such as liquids and vapours?
Integral non rubbing seal
The seal either flings contaminants away or flings oil back in?
Flinger seal
This seal is the cheapest non rubbing seal but only works in dry dust free environments and for grease only?
Smooth gap seal
This seal can only be used in a split housing and only can support very small amounts of axial and radial loading?
Radial labyrinth seal
This seal can be used in one piece housing and can support axial movement?
Axial labyrinth seal
This seal can handle both axial and radial movements?
Combination labyrinth seal
This seals sealing efficiency can be increased by adding more sets?
Sealing washers
What is the purpose of a gasket?
Seal against a pressure load
Seal against leakage
Control positions
When using gaskets to seal housings what piece of information is crucial and why?
The original gasket thickness must be known because using a different size can change the internal clearance.
What are the different types of gasket joints?
Flat(full) face
Raised face
Tongue and groove faced
Spigot and recess
Gasket material should?
Withstand bolt load without being crushed
Withstand the necessary temperature without being crushed
Be compatible with the product being contained
Upper temperature limit of paper gasket?
120 degrees C
This gasket can be impregnated with neoprene, seals good against water, oil and solvent. It’s usable temperature ranges from -30 to 150 degrees C?
Cork
This seal has excellent sealing properties against water and air and has an operating temperature limit of 121 degrees C?
Natural rubber
This gasket is very dangerous if not handled properly?
Asbestos
This gasket material does not perform well at low temps but have a very high upper temperature limit of 232 degrees C?
Acrylic PTFE
Like acrylic this seal performs up to temps of 250 degrees C but has a much better lower temperature range of -190 Degrees C?
Teflon
Metal gaskets will be more adequate for what?
High pressure high temperatures applications
What are two main types of gaskets?
Full face (covers around the bolts)
Ring gasket (inside bolts)
What tool is used to make the holes for new gaskets?
Gasket hole punch
What is the correct way to tight down new gasket?
Lubricate both sides and gradually tighten in star formation. In long covers tighten from the centre in a star working way out to the edge.
What two ways can o rings be used as _______ or _______?
Static (stationary)
Dynamic (moves)
Multi lobbed, square, or rectangular o rings are used in which application?
Usually hydraulic
What are the two main groups of dynamic seals?
Contact (make contact with two surfaces to be sealed)
Clearance (seals without touching each other.)
What are some examples of contact seals?
Packing
Lip
Diaphragm
Mechanical
What are some types of clearance seals?
Bushings
Annulus
Slinger
Labyrinth seals
What three categories are there for packing?
Compression
Automatic
Floating
Packing installed in a moving unit is called?
Inside packed
Packing installed in a stationary unit is called?
Outside packed
Why do they call it compression packing?
Because it relies on pressure to form a seal.
What are the three types of material used in compression packing?
Fabric (braided asbestos, graphite, cotton, flax, wool, aramid, carbon or PTFE)
Metallic (lead, copper, or aluminum)
Plastic (moulded to fit specific needs)
Compression packing comes in which shapes?
Round square or rectangular depending on stuffing box design, temperature, pressure and type of fluid
What is the lantern ring(seal cage) used for?
Distributes sealing liquids under pressure preventing air infiltration and provides lubrication.
When cutting new rings what tool do you use?
A wood mandrel same size as the shaft diameter.
What angle do you cut rings at?
Either straight or diagonal
Where do you place the joints in relation to each other?
Usually 90 degrees to each other
When setting the gland in the packing what is the procedure?
Place gland in stuffing box by 1/8 to 3/16”
Tighten the nuts to seat and form the packing to the stuffing box and shaft
Ensure gland is square in the box
Undo nuts and allow packing to expand
Finger tighten nuts and start pump
Gradually tighten nuts evenly (sixth of a turn or one flat) until leakage is reduced to the recommended lubrication level.
What happens when packing is tightened to much?
Leaking will stop causing to much friction. This will burn packing and damage shaft.
How does automatic packing work?
By using system pressure to improve its sealing action by forcing the flexible lips of the packing onto its contact surfaces.
What are considered balanced packing?
V-ring
U-ring
O-ring
They seal on both the ID and OF
What is unbalanced packing?
Cup packing
Only seals on one diameter
V-ring packing is also known as?
Chevron packing
V ring packing uses how many sets?
3 or more depending on working pressure
On initial instal of v rings are tightened just enough to prevent leakage. How is this done?
Either by operating the unit and tightening the gland until any leaks cease.
Or
If packing is frequently replaced a spacer can be made the thickness of the gap between the gland and housing
V ring packing sets used in double acting cylinders should face which way?
Away from each other
How come u-ring replaces cup packing?
Requires less maintenance time.
O rings are used in which way?
As dynamic seals on slow moving or reciprocating parts such as valve spools
What is the size of the groove in which the o ring sits?
135 to 150 percent of the o rings cross section.
Why is diametral squeeze important?
To maintain proper seal
How much squeeze on the O ring is ideal?
10 percent of ring diameter
What pressure are standard o rings good to?
1500 psi 3000 psi when back up washers are used
