Dynamic seals Flashcards by Brandon Hatt

Dynamic seals are grouped into what two main categories? (2)

Contact

- clearance

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Dynamic seals can only be non positive, true or false?

false, can be positive and non positive

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____ used as a non positive seal controls leakage between stationary and moving parts

packing

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When sealing with packing, what are the four types of motion you can seal? (4)

reciprocating
rotary
helical
swinging rotary

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Packing can be used as a positive seal to:

Prevent any leakage between stationary and moving parts

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What are the three categories of packing? (3)

Compression
Automatic
Floating

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Packing installed in the moving unit is called:

Inside packed

Ex: Cylinder pistons, valve air spools

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Packing installed in the stationary unit is called:

Outside packed

Ex: stuffing box

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Packing must withstand: (4)

Temperature
Pressure
various fluids
shaft misalignment and movement

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Hard packing withstands ____ better than soft packing

extrusion

Note: Hard packing also creates more friction

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With compression packing, the amount of sealing or leakage is controlled by the ammount:

the packing is compressed

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Compression packing is made of these 3 classes of material: (3)

fabric
Metallic
plastic

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____ compression packing material is made of strong, pliable materials such as braided asbestos, metal, graphite, cotton, flax, wool, aramid, carbon or PTFE

Fabric packing

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____ compression packing material is made from materials such as lead, copper, or aluminum. Machined or pressed into rings.

Metallic packing

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____ compression packing material is moulded to fit specific needs

Plastic

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Compression packing cross sections may be: (3)

Round
Square
Rectangular

Type used depends on stuffing box design, temperature, pressure, fluid type

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Some packing is impregnated with lubricant, such as graphite or teflon. This makes the packing:

self lubricating at start up

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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:

distribute sealing liquid under pressure to the packing

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Sealing liquid is used to prevent air infiltration as well as provide: (3)

Lubrication
Cooling
Cleaning

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When sealing water is provided from the high pressure side of the pump, it is called:

internally supplied

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Compression packing is removed periodically because:

it deteriorates from wear and dries out

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Remove old packing using:

packing puller

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A stuffing box code of 2-L-3-G means:

2 rings of packing, lantern ring, 3 rings of packing, gland

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You can determine the correct amount of packing by:

measuring stuffing box depth, subtracting width of lantern ring, dividing remainder by the width of packing

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You can determine the correct size of packing to use by:

Subtracting the shaft OD from the bore ID

Cutting packing is best done:

On a wooden mandrel

Packing can be cut as a square end cut or:

Skived cut

For rigid packing, use a _____ to place it over the shaft

s twist

If packing is slightly bulged, you can flatten it with a:

roller

Ensure packing joints are staggered at least ___° from each other

90°

After the last packing ring is installed, allow the gland to enter the stuffing box by ___" to ___"

1/8" to 3/16"

If packing is too tight, it can cause excessive heat build up and can:

burn the packing and damage the shaft

Which packing ring compresses the most?

the ring closest to the gland

____ packing uses system pressure to improve its sealing action

automatic packing

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.

Cup packing is considered unbalanced because:

It seals on one diameter only

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

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

With V ring packing, which adapter ring, internal or external, is closest to the gland?

Internal

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

V ring packing should, where possible, be installed as :

endless rings

At initial installation, V rings are tightened just enough to:

prevent leakage

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

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

The adapter ring can be made of a non metallic material and can act as a:

bearing

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

U ring (U-cup) packing is a circular, one piece moulded ring with a U cross section, made from one of the:

Synthetic elastomers

U ring packing is designed to be used in set of ____ per seat

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

Two U rings should not be placed:

against each other

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

Compared to cup packing, U ring packing:

requires less maintenance time

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

Cup packing material can be: (5)

- leather - synthetic - rubber - elastomer - impregnated fabric

O rings are used as ____ on slow turning shafts or reciprocating parts

dynamic seals

The groove that sits an O ring usually has a width 135% to ___% of the O rings cross section

150%

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

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

Backup washers are often made of: (3)

- Leather - Teflon - Moulded nylon

____ 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

Back up washers require a:

wider groove

___ 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

____ is a seal that is retained in a groove, but not held in a static position.

Floating packing

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

What are some advantages of floating packing? (3)

- Less friction - High pressure applications - Less affected by temp.

What are two disadvantages of floating packing? (2)

- Conforms to mating surfaces less | - Longer run in period

Lip seals are used in pressures of 2-__PSI

2-10PSI

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

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

Materials used for lip seals are: (3)

- Felt - Leather - Synthetic rubber

A lip seal has a lightweight, pressed ____ housing

metal

Lip seals rely on the elasticity of the material or a garter spring to maintain:

contact with the shaft surface

A lip seal positioned to keep lube in is called:

inclusion seal

A lip seal positioned to keep contaminants out is called:

exclusion seal

Double lip seals can be mounted in 2 ways: (2)

- Back to back | - same direction, tandem

If possible, use a _____ to install a seal in a housing

pressing device When installing, lubricate the shaft, housing and sealing edges.

When installing a lip seal into a bore, ensure the bore is free of:

Sharp edges

When installing a lip seal on a shaft, ensure any sharp edges on the shaft are:

Covered, with plastic, shim stock, or even paper

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

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

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

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

____ ring seal material is used in slow speed, light duty applications up to 65°C

Cork

___ 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

____ 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

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

a synthetic rubber or plastic wiper protects against:

dust, fine materials

A metallic wiper protects against:

solid abrasive materials

____ are positive seals which have one end secured to the housing, and the other to the moving part.

Boots and bellows

A boot is used for:

short movements

A bellow is used for:

large movements

A ____ seal is a positive seal which has a flexible membrane which spans between the stationary and moving parts.

diaphragm seal

A _____ diaphragm seal is designed for a small amount of movement

flat diaphragm

A ____ diaphragm seal is a moulded membrane and rolls on the two mating surfaces as it moves

rolling diaphragm

A mechanical seal must always run in fluid. _____ feed fluid into the product side of the seal

flushing ports

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

Quenching is done through _____ on the atmospheric side of the seal

quenching ports Note: comes from an external source

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

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

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

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

Dynamic seals Flashcards

(101 cards)