Seals Flashcards
What is the function of packing?
It restricts leakage between a moving part and a stationary part.
Name two functions of a seal.
Keep lubricant in
Keep contaminants out
Name three types of seals.
Lip seals Shaft seal Double lip seals Labyrinth seals Mechanical seals
Name three types of compression packing.
Braided
Plastic
Metal foil
What kind of seal face material would you choose for water? For gasoline? For oil? For acids?
Water – Nickel, ceramic, stellite, bronze
Gasoline – Nickel, ceramic, stellite, cast iron
Oil – Nickle, ceramic, stellite, cast iron
Acid – Ceramic, stellite, Hard faced stainless, Carpenter 20 stainless
Name three materials used for packing binders.
Grease Wax Elastomers Teflon Other Resins
What is the function of a positive drive on a seal?
It allows the seal to rotate along with the shaft.
Name five types of positive drive designs in seals.
Dent drive Key drive
Pins Dowels
Snap rings Slot and ear drive
Set screws Roll pins
Drive through the elastomer Press fit or shrink drive
Springs
What are some special characteristics of fluids that must be considered when choosing a seal?
See if it is (TRUE FACE)
Toxic/noxious Flammable
Radioactive Abrasive
Unstable Corrosive
Explosive Expensive
What special operating environment conditions can affect seal choice?
Very low temperatures
Very high temperatures
High pressure
Vacuum; exclusion of water and particle contamination from ingression
What are the ten most important things to find out before specifying a seal?
Dimensions Fluids handled
Temperature range Pressure range
Motion Speed
Material in contact with seal Cycle
Mechanical condition Special requirements
Give some performance advantages of different elastomeric packing materials.
Natural rubber – wide temperatures
Chloroprene ( Neoprene ) – oil resistant
BUNA N - Inexpensive and available
BUNA S – oil resistant
Thiokol – resists aromatic hydrocarbons
Polyisobutylene ( Butyl) - resists solvents
Polyacrylate – phosphate ester resistant
Fluorinated ( Viton, Teflon ) - high temperature, resistant to synthetics
Silicones – high temperature
What elastomeric seal material is most resistant to degradation by petroleum fluids?
Fluorocarbon such as Viton or Teflon
Name three seal materials that can be used with synthetic lubricants.
Teflon
Viton
Buna N
What are three types of seals used with journal bearings?
Contact ( felt, cork )
Face (lip, radial, axial)
Mechanical ( the Best )
What type of face loading on a seal eliminates the need for springs?
Magnetic
What is one of the most important functions of a felt packing seal?
Seal out dust
A seal that keeps oil in is called a ____________ seal.
Retention
If both retention and exclusion are required, then a _______ seal is required.
Double lip or mechanical
In many applications labyrinth seals are effective at both exclusion and retention
Which way should a lip seal face to retain lubricant?
Inward
What are the advantages of mechanical seals compared to lip seals?
Suitable for higher speeds
Lower leakage
If “zero leakage” were required in an application, what kind of seal would you use?
Double mechanical seal with seal oil between them.
Where is the most common area of wear in a pump packing assembly that can allow leakage?
On the pump sleeve between the packing and shaft
To slow excessive leaking of a packing seal, it is necessary to tighten the ______.
Packing gland nuts
