Seals Flashcards
What is a Static seal?
A seal used between two stationary parts.
What is a Dynamic seal?
A seal used between a moving and a stationary part.
What is the purpose of a seal?
To prevent leakage of fluid (liquid or gas) and to prevent contaminants from entering.
Are all Static seals a positive seal?
Yes.
What is a Positive seal?
A seal that prevents leakage between stationary and moving parts.
What is a Non-Positive seal?
A seal that controls leakage between stationary and moving parts.
What are the three functions of Gaskets?
- seal against a pressure load
- seal against leakage
- control position
The force exerted by the bolts (bolt load) on a gasket must be greater than what?
Internal pressure and hydrostatic end force.
What are the four gasket and flange arrangements?
- flat face
- raised face
- tongue and groove
- spigot and recess
When are non-metallic gaskets used?
Low pressure applications.
When are metallic gaskets used?
High pressure and high temperature.
How does a metallic gasket seal?
By the malleability of the gasket when compressed between two surfaces.
What are the two types of sealants?
Hardening and non-hardening.
What are the two types of hardening sealants?
Flexible and Rigid.
What are the two types of Dynamic seals?
Contact and Clearance.
What is a Contact seal?
Seals that make contact with the two surfaces to be sealed.
What is a Clearance seal?
In a Clearance seal the two parts do not touch each other but still maintain a seal.
Can a Dynamic seal be both Positive and Non-Positive?
Yes.
What is Inside packed?
Packing installed in the moving unit.
What is Outside packed?
Packing installed in the stationary unit?
What are the four things Packing must withstand?
- temperature
- pressure
- various fluids
- shaft misalignment
What does a Lantern Ring (Seal Cage) do?
It distributes fluid under pressure to the packing.
What is used to remove old packing?
Packing Puller.
Name two types of Balanced packing?
U-Ring and V-Ring.
Is Cup packing considered to be balanced?
No.
What percent of the O-Rings cross section determines the width of the groove it sits in?
135% - 150%.
Generally what is the “squeeze” placed on an O-Ring?
10% of the ring diameter.
What should be used with O-Rings if psi is above 1500?
Anti-Extrusion Rings or Backup Washers.
What type of packing is retained in a groove but not held in a static position?
Floating Packing.
Are piston rings considered a Positive Seal?
No because they leak slightly.
What are the two facings of a Lip Seal called?
Inclusion (inward) and Exclusion (outward).
What are Ring Seals?
A non-positive seal which is mounted in a groove in the housing.
What is a Wiper Seal?
A non-positive seal mounted on the stationary housing to expel foreign material.
What are Boots and Bellows?
They are a positive seal with one end attached to the housing and one end attached to the moving part. Boots are shorter than Bellows.
What is a Diaphragm seals?
A positive seal usually used in pumps. It is made from a flexible membrane that does not allow fluid transfer from one chamber to another.
What are the two types of Diaphragm seals?
Flat and Rolling.
What is a Mechanical seal?
An extremely efficient axial seal.
Does a Mechanical seal need to be constantly run in fluid?
Yes.
What are the four types of Clearance seals?
- bushings
- annulus
- slinger
- labyrinth
