Sealing methods

Question 1

Function of seals

Answer 1

ensure that components are enclosed in a clean environment
ensure that lubricants cannot leak from components and casings
ensure that adequate pressure can be stored or harnessed

Question 2

Types of sealing systems

Answer 2

Poppet valves
Lip seals
Rubber 'O' rings
Gaskets
Gaitors and boots
Non-contact seals
Adhesive sealants

Question 3

Poppet valves(and uses)

Answer 3

The seal and the face of component are joined at different angles reducing the area of contact

Question 4

Advantages and disadvantages of poppets valves

Answer 4

effective at controlling air flow
easily opened and closed

restricted by the speed of operation
larger valve means greater weight therefore slower speeds are used in operation

Question 5

Mechanical seals

Answer 5

control airflow
no maintenance required
reliability of the seal depends on the material used

Question 6

Stainless steel

Answer 6

slow but long lasting

Question 7

Carbon and glass fibres

Answer 7

fast-acting but prone to failure at high vibrations by becoming more brittle therefore more maintenance required

Question 8

Uses of mechanical seals

Answer 8

compression rings(steel or iron)
oil scraper rings(steel)
reed valves(carbon fiber, steel, fiberglass)
poppet valves(steel or aluminium)

Question 9

Advantages and disadvantages of non-contact seals

Answer 9

no abrasion therefore no wear
high speed operations
no mechanical losses
no contamination
effective

expensive

Question 10

O rings

Answer 10

used in step-up rotation applications
hardness of the O rings is very important
material selection is very important to reduce contamination

Question 11

Advantages of O rings

Answer 11

cheap
really effective
they cope with high levels of vibration, chemical attacks

Question 12

Uses of O rings

Answer 12

shaft sealing
covers
high pressure applications(hydraulic rams)
sealing electronic components and control units
components subjected to vibrations
applications where components experience large variations in temperature change

Question 13

Types of gaskets

Answer 13

paper
synthetic rubber(viton)
metal(single or multi layer)
felt
neoprene
nitrile rubber
plastic polymer

Question 14

Advantages of gaskets

Answer 14

cheap

easy to manufacture in batches

Question 15

Considerations when using gaskets

Answer 15

the surface finish of the component is important

however, achieving a good surface finish is not cheap

Question 16

Uses of gaskets

Answer 16

sump sealing
sealing flanges(exhaust, water pumps)
sealing from dust contamination(external)
sealing from water entry
head gaskets(compression seal between the engine block & cylinder head)

Question 17

Considerations when using lip seals

Answer 17

lane marks are important

maintenance of tip seals depends on application

Question 18

Advantages and disadvantages of lip seals

Answer 18

cheap
seal high pressure

cannot cope with outside pressure

Question 19

Uses of lip seals

Answer 19

automotive wheel hubs
engine seals(crankshaft, canshaft, oil pumps)
air conditioning compression
transmission system

Question 20

Uses of gaitors and boots

Answer 20

to protect components from the external environment
to keep grease and oils around a component
prevent lubrication loss from driveshaft joints
protect steering racks and drive shafts from external contamination

Question 21

Advantages of gaitors and boots

Answer 21

cheap

surface finish not important

Question 22

Considerations when using adhesive sealants

Answer 22

hardness is important

using adhesive sealants inconjuction with gaskets is a bad idea

Question 23

Advantage of adhesive sealants

Answer 23

effective(permanent joints)

Question 24

Silicone adhesive sealants

Answer 24

RTV-various tensile strength from 2.2-25MPa
TSE - less tensile strength but sets harder
FRV-fuel and solvent resistant
C853 - electrically conductive