Dynamic seals Flashcards
1
Q
Dynamic seals are grouped into what two main categories? (2)
A
- Contact
- clearance
2
Q
Dynamic seals can only be non positive, true or false?
A
false, can be positive and non positive
3
Q
____ used as a non positive seal controls leakage between stationary and moving parts
A
packing
4
Q
When sealing with packing, what are the four types of motion you can seal? (4)
A
- reciprocating
- rotary
- helical
- swinging rotary
5
Q
Packing can be used as a positive seal to:
A
Prevent any leakage between stationary and moving parts
6
Q
What are the three categories of packing? (3)
A
- Compression
- Automatic
- Floating
7
Q
Packing installed in the moving unit is called:
A
Inside packed
Ex: Cylinder pistons, valve air spools
8
Q
Packing installed in the stationary unit is called:
A
Outside packed
Ex: stuffing box
9
Q
Packing must withstand: (4)
A
- Temperature
- Pressure
- various fluids
- shaft misalignment and movement
10
Q
Hard packing withstands ____ better than soft packing
A
extrusion
Note: Hard packing also creates more friction
11
Q
With compression packing, the amount of sealing or leakage is controlled by the ammount:
A
the packing is compressed
12
Q
Compression packing is made of these 3 classes of material: (3)
A
- fabric
- Metallic
- plastic
13
Q
____ compression packing material is made of strong, pliable materials such as braided asbestos, metal, graphite, cotton, flax, wool, aramid, carbon or PTFE
A
Fabric packing
14
Q
____ compression packing material is made from materials such as lead, copper, or aluminum. Machined or pressed into rings.
A
Metallic packing
15
Q
____ compression packing material is moulded to fit specific needs
A
Plastic
16
Q
Compression packing cross sections may be: (3)
A
- Round
- Square
- Rectangular
Type used depends on stuffing box design, temperature, pressure, fluid type
17
Q
Some packing is impregnated with lubricant, such as graphite or teflon. This makes the packing:
A
self lubricating at start up
18
Q
Lantern rings are often used with compression packing. It is a channeled ring with a H cross section, and holes cut radially. The purpose of a lantern ring is to:
A
distribute sealing liquid under pressure to the packing
19
Q
Sealing liquid is used to prevent air infiltration as well as provide: (3)
A
- Lubrication
- Cooling
- Cleaning
20
Q
When sealing water is provided from the high pressure side of the pump, it is called:
A
internally supplied
21
Q
Compression packing is removed periodically because:
A
it deteriorates from wear and dries out
22
Q
Remove old packing using:
A
packing puller
23
Q
A stuffing box code of 2-L-3-G means:
A
2 rings of packing, lantern ring, 3 rings of packing, gland
24
Q
You can determine the correct amount of packing by:
A
measuring stuffing box depth, subtracting width of lantern ring, dividing remainder by the width of packing
25
You can determine the correct size of packing to use by:
Subtracting the shaft OD from the bore ID
26
Cutting packing is best done:
On a wooden mandrel
27
Packing can be cut as a square end cut or:
Skived cut
28
For rigid packing, use a _____ to place it over the shaft
s twist
29
If packing is slightly bulged, you can flatten it with a:
roller
30
Ensure packing joints are staggered at least ___° from each other
90°
31
After the last packing ring is installed, allow the gland to enter the stuffing box by ___" to ___"
1/8" to 3/16"
32
If packing is too tight, it can cause excessive heat build up and can:
burn the packing and damage the shaft
33
Which packing ring compresses the most?
the ring closest to the gland
34
____ packing uses system pressure to improve its sealing action
automatic packing
35
V ring and U ring packing and O rings are considered balanced packing because:
they seal on both the ID and OD. Pressure is balanced at both diameters.
36
Cup packing is considered unbalanced because:
It seals on one diameter only
37
V ring packing has a V shaped cross section and is used in sets of:
3 or more rings
Note: depending on the working pressure
38
V ring packing can be used as in inside or outside packed seal. V ring packing must be used with:
shaped internal and external adapter rings
39
With V ring packing, which adapter ring, internal or external, is closest to the gland?
Internal
40
The external adapter ring merely shapes the V ring and is not subject to wear, but the internal ring must be soft enough to compress slightly but hard enough to:
Prevent extrusion
41
V ring packing should, where possible, be installed as :
endless rings
42
At initial installation, V rings are tightened just enough to:
prevent leakage
43
Some V rings use ______ to maintain constant pressure
spring loaded external adapter rings
Note: leaves no chance of overloading the packing. Can be multiple springs or one large spring
44
V ring packing sets used on double acting pistons should
Face away from each other
Note: Internal adapter ring should be supported by a solid backing
45
The adapter ring can be made of a non metallic material and can act as a:
bearing
46
V ring sets can be made of the same or dissimilar materials. Dissimilar materials consist of hard and soft materials, the soft materials sealing and the hard materials act as:
spacers and bearing rings
47
U ring (U-cup) packing is a circular, one piece moulded ring with a U cross section, made from one of the:
Synthetic elastomers
48
U ring packing is designed to be used in set of ____ per seat
1
49
U ring packing can be inside or outside packed. Due to its low friction, U ring packing is generally used in systems under 1500 PSI. Above that, a ____ is required
support ring aka anti extrusion washer
50
Two U rings should not be placed:
against each other
51
At low pressures, cup packing may seal at the lip, but it doesn't normally seal until:
The heel diameter has been expanded to the cylinder wall
52
Compared to cup packing, U ring packing:
requires less maintenance time
53
Cup packing with double acting pistons require a rigid ____ between the two cups
separator
Note: In some cases, the separator acts as a guide as well
54
Cup packing material can be: (5)
- leather
- synthetic
- rubber
- elastomer
- impregnated fabric
55
O rings are used as ____ on slow turning shafts or reciprocating parts
dynamic seals
56
The groove that sits an O ring usually has a width 135% to ___% of the O rings cross section
150%
57
The squeeze on an O ring required to produce a seal is at least ___ %
10%
Can be 10-30% or 10-40% for static seals
58
O rings are rated up to 1500 PSI with properly designed grooves, or up to ___ PSI with a backup washer or anti extrusion ring
3000 PSI
59
Backup washers are often made of: (3)
- Leather
- Teflon
- Moulded nylon
60
____ are used with O rings to eliminate extrusion, permit wider clearance, form a seal across a clearance gap, and act as a dirt wiper
back up washers
61
Back up washers require a:
wider groove
62
___ an O ring into its seat. Stretch it only as much as needed.
roll
Lubricate the O ring. Protect the O ring from cuts and from nicks from sharp metal corners
63
____ is a seal that is retained in a groove, but not held in a static position.
Floating packing
64
Automotive or steam piston rings are often used when rapid travel and frequent cycling are needed. Material in the rings can be cast iron or steel (plain finish or chrome plated). Piston rings are, or are not a positive seal?
Are not. They leak slightly
65
What are some advantages of floating packing? (3)
- Less friction
- High pressure applications
- Less affected by temp.
66
What are two disadvantages of floating packing? (2)
- Conforms to mating surfaces less
| - Longer run in period
67
Lip seals are used in pressures of 2-__PSI
2-10PSI
68
Lip seals are primarily used on rotating shafts that are partially or totally immersed in lubricant. A _____ is formed at the point of contact
hydrodynamic film
Note: film is about 0.001" thick
69
To maintain the hydrodynamic film on a lip seal, the shaft surface must be controlled. For speeds up to ___m/s, the shaft should have a ground finish. For speeds above that, the shaft should be hardened and ground.
8m/s
70
Materials used for lip seals are: (3)
- Felt
- Leather
- Synthetic rubber
71
A lip seal has a lightweight, pressed ____ housing
metal
72
Lip seals rely on the elasticity of the material or a garter spring to maintain:
contact with the shaft surface
73
A lip seal positioned to keep lube in is called:
inclusion seal
74
A lip seal positioned to keep contaminants out is called:
exclusion seal
75
Double lip seals can be mounted in 2 ways: (2)
- Back to back
| - same direction, tandem
76
If possible, use a _____ to install a seal in a housing
pressing device
When installing, lubricate the shaft, housing and sealing edges.
77
When installing a lip seal into a bore, ensure the bore is free of:
Sharp edges
78
When installing a lip seal on a shaft, ensure any sharp edges on the shaft are:
Covered, with plastic, shim stock, or even paper
79
Use a leader (mounting sleeve) or a light gauge shim stock to install a seal over a shaft, unless the shaft has a:
chamfer with a long taper
80
What are 4 emergency repairs you can make when dealing with a worn lip seal surfaces? (4)
- Change the seal to a wider seal (move lip contact)
- Reverse the seal (move lip contact)
- Install a spacer behind a replacement seal (move lip contact)
- Install a thin sleeve over the worn spot of the shaft
81
A ring seal is a non positive seal mounted in a groove of the housing. They can be made of: (4)
- Cork
- Felt
- Leather
- Synthetic rubber
82
Cork, felt and leather ring seals are _____ washers with a sealing edge broader than that of the lip seals. Over an extended period, they tent to polish the shaft
precision cut
83
____ ring seal material is used in slow speed, light duty applications up to 65°C
Cork
84
___ and ____ ring seal materials are used in slow, light duty applications up to 105°C
felt and leather
Note: these seals absorb some lubricant and redistribute it as a film between it and the shaft
85
____ ring seal materials are used in high speed applications and can withstand temperatures up to 250°C
synthetic
Note: this seal retains lube without absorbing it, and resists acids and alkalis
86
A ____ is a non-positive seal mounted on the stationary housing. It flexes against axially moving parts. Expel debris away from seals, packing, bearings
wiper/scraper
Note: the lip allows lubricant to remain on the rod or guide, but restricts entry from the atmospheric side
87
a synthetic rubber or plastic wiper protects against:
dust, fine materials
88
A metallic wiper protects against:
solid abrasive materials
89
____ are positive seals which have one end secured to the housing, and the other to the moving part.
Boots and bellows
90
A boot is used for:
short movements
91
A bellow is used for:
large movements
92
A ____ seal is a positive seal which has a flexible membrane which spans between the stationary and moving parts.
diaphragm seal
93
A _____ diaphragm seal is designed for a small amount of movement
flat diaphragm
94
A ____ diaphragm seal is a moulded membrane and rolls on the two mating surfaces as it moves
rolling diaphragm
95
A mechanical seal must always run in fluid. _____ feed fluid into the product side of the seal
flushing ports
96
If a mechanical seal has its flushing water supplied by the product discharge, it may need to go through a:
cyclone strainer
Note: May also go through a heat exchanger to remove heat
97
Quenching is done through _____ on the atmospheric side of the seal
quenching ports
Note: comes from an external source
98
A ____ seal is a non-positive seal which is mounted in the stationary housing. The minimal clearance between it and the rotating shaft restricts the amount of leakage from the high to low pressure sides. Considered the simplest of seals.
Bushing seal
99
A ____ seal is a non positive seal with a series of concentric or helical grooves in the housing bore. A drain hole is places at the bottom of the seal to make the seal effective. Concentric grooves fill with lubricant to prevent entry, helical grooves return the oil to the bearings.
Annulus seal
100
A _____ seal is a non positive seal which has a cupped washer-like flange mounted to the rotating shaft. It is placed just outside the seal housing to assist a ring seal in sealing. Relies on centrifugal force
Slinger (flinger) seal
101
A ____ seal is a non positive seal which has a tongue and groove design. A series of internal and external passages form a maze like path for debris. Can seal radially, axially, or a combination. Radial requires a split housing. Used in high speed applications. The passages can be lubricated to force out debris.
Labyrinth seal
