Mechanical Seals, Compression Packing and Valves

Question 1

Why are mechanical seals not to be used in fires safety?

Answer 1

when a mechanical seal fails it fails completely

Question 2

What are the 4 basic types of components mechanical seals are made up of?

Answer 2

a set of primary sealing faces (rings), a mechanism for holding the seal faces together (ex: springs), a set of secondary seals, metal components

Question 3

Where is the primary sealing point on a mechanical seal?

Answer 3

between the stationary face and the rotating face

Question 4

What are the factors that govern the amount of friction between the sealing faces in a mechanical seal?

Answer 4

seal ring material, smoothness and flatness of the seal faces, the amount of closing force

Question 5

What feature does a unidirectional gas seal have that keeps the mating faces from coming into contact while running? What is the typical gap produced in these seals?

Answer 5

One of the faces has gas grooves only a few microns deep machined into it. The typical gap would be 0.0001” to 0.0002”

Question 6

In an emergency, what can the seal faces in a mechanical seal be hand-lapped and polished to?

Answer 6

three light bands

Question 7

What are the different types of secondary seals that can be used on a mechanical seal?

Answer 7

O-rings, PTFE wedges, V-rings, U-cups

Question 8

What secondary seal can only take pressure in one direction, and is not tolerant of any misalignment and axial movement.

Answer 8

PTFE wedges

Question 9

What secondary seals are normally used in sets of 3 or more?

Answer 9

V-rings (chevron seals)

Question 10

What is used with a U-cup seal to keep it loaded?

Answer 10

an energizer/spreader ring

Question 11

What type of seal has a secondary seal that is pushed back and forth axially to maintain constant contact at the seal faces?

Answer 11

pusher seal

Question 12

What is the major disadvantage of a multiple spring closing mechanism?

Answer 12

tendency to clog at the spring pockets

Question 13

What type of seal has a static secondary seal, and is inherently hydraulically balanced?

Answer 13

non-pusher (bellows) type seal

Question 14

What are the 3 materials commonly used for the bellows in non-pushers seals?

Answer 14

rubber (elastomer), PTFE, welded metal

Question 15

What type of pumped medium would a friction drive not be used with?

Answer 15

any lubricating medium (ex: oil)

Question 16

What system has a fluid that is introduced at a higher pressure than that of the pumped medium?

Answer 16

barrier system

Question 17

Where would quenching fluids be introduced?

Answer 17

to the low-pressure side of the double seals

Question 18

What is normally recommended when steam is used for quenching?

Answer 18

throttle bushing

Question 19

What type of contamination control is used when there is a constant introduction of particles into the system?

Answer 19

cyclone seperator

Question 20

What is the maximum seal chamber pressure for an unbalanced seal?

Answer 20

300 psi

Question 21

What seals would be used when shaft speeds exceed 4500 ft/min?

Answer 21

stationary seals

Question 22

What seal setup is recommended when the stuffing box is too small, and/or the product is very corrosive?

Answer 22

Outside mounted single seal

Question 23

What pressures can an unbalanced single outside mechanical seal handle? A balanced?

Answer 23

15-75 psi, 400 psi

Question 24

What would a double mechanical seal arrangement be used for?

Answer 24

non-lubricated products, carcinogenic products, toxic products, hazardous fluids

Question 25

What are the two types of double mechanical seal arrangements?

Answer 25

face-to-face, back-to-back

Question 26

At what pressure is barrier fluid recommended to be at in relation the fluid pressure on the inner seal?

Answer 26

approx. 10% higher (min. 25 psi difference)

Question 27

When is a face-to-face arrangement used, and when does it act the same as a tandem seal?

Answer 27

When the stuffing box is too small to accommodate a back-to-back seal, acts the same as a tandem seal when the fluid pressure in the seal chamber is lower (buffer fluid) than that of the product as opposed to higher (barrier fluid)

Question 28

What are tandem seals also known as?

Answer 28

environmental seals

Question 29

What is one light band equal to?

Answer 29

11.6 millionths of an inch

Question 30

What tools would you use to check a seal face for flatness?

Answer 30

optical flat, monochromatic light

Question 31

What are some important points to remember when handling mechanical seals?

Answer 31

do not lube faces, keep hands clean when handling seals

Question 32

What would a wide track pattern on a seal face indicate? What about a narrow track pattern?

Answer 32

pump misalignment, overpressurizing

Question 33

What are the two types of closing mechanisms found on pusher seal?

Answer 33

single springs, multiple springs

Question 34

What are 4 reasons for providing flushing fluid?

Answer 34

lubrication, cooling, heating, cleansing

Question 35

How many light bands would seals be lapped to from the manufacturer?

Answer 35

1-3

Question 36

How many drops per minute must leak from compression packing?

Answer 36

40-60

Question 37

What type of fluid would a tandem seal use?

Answer 37

buffer fluid

Question 38

What type of non-pusher seal (bellows) would be good for high pressures?

Answer 38

the welded metallic type

Question 39

What is the purpose of compression packing?

Answer 39

to control leakage along moving parts

Question 40

In what application would compression packing be set to allow no leakage?

Answer 40

on a valve stem, also acts as a bearing in this case

Question 41

What are 3 types of motion compression packing may have to seal against?

Answer 41

rotary, reciprocating, helical

Question 42

What are the 3 types of automatic packing? What material are they normally made of?

Answer 42

cup packing, u-cup packing, v-cup packing, normally some kind of elastomeric

Question 43

Why is it important not to over-tighten jam packing?

Answer 43

The increase in friction between moving parts will act as a brake.

Question 44

Which way is automatic packing orientated in relation to the pressure its sealing against?

Answer 44

the lips face the pressure

Question 45

What jam packing type is the best for high pressures?

Answer 45

interlocking braid

Question 46

What packing component is installed in the stuffing box to aid in lubricating, sealing, flushing, and cooling?

Answer 46

a lantern ring

Question 47

Where does a lantern ring need to be located when used for cooling and sealing?

Answer 47

under the seal water connection

Question 48

When should carbon yarn not be used as packing material?

Answer 48

in the presence of strong oxidizers

Question 49

What type of packing material is used extensively in the food industry, but is limited in temperature and shaft speed?

Answer 49

PTFE fibre

Question 50

What are some causes of premature packing failure?

Answer 50

wrong type or size of packing used, improper installation, exposed to excessive heat

Question 51

Where does most of the wear on a pump shaft occur within the stuffing box?

Answer 51

On the outermost part of the shaft in contact with the packing.

Question 52

What are 3 metals commonly used in metallic compression packing?

Answer 52

Babbitt, aluminium, annealed soft copper

Question 53

What does the "S" preceded by a number indicate on a valve?

Answer 53

the steam rating of the valve

Question 54

What does WOG indicate on a valve?

Answer 54

water, oil, and gas rating

Question 55

What are gate valves not used for and why?

Answer 55

Throttling, because wire drawing (erosion) can occur on the gate and the gate seats.

Question 56

Why is an accurate alignment important during installation of a butterfly valve?

Answer 56

to prevent binding of the pivoting disc

Question 57

What valve is used for precise fluid flow control?

Answer 57

needle valve

Question 58

What does a globe valve work well for?

Answer 58

throttling or regulating flow

Question 59

What valve operates the same as a standard globe valve but has reduce turbulence, flow restriction and pressure drop? When is it used?

Answer 59

angle valve, used when a 90 deg change is needed in a pipeline

Question 60

What type of valve would be used for throttling when handling corrosive and toxic fluids?

Answer 60

diaphragm valve

Question 61

What is the function of a pressure relief valve?

Answer 61

to prevent equipment damage

Question 62

What is the difference between the cracking pressure and pressure required to fully open a pressure relief valve called?

Answer 62

pressure override

Question 63

Name the different categories of valve actuators:

Answer 63

manual, power, pneumatic, hydraulic, electric, variable position

Question 64

When would you not apply oil or grease to a valve?

Answer 64

when the valve is in oxygen service

Question 65

What can be installed and adjusted to greatly reduce the mechanical stresses on a valve?

Answer 65

pipe hangers

Question 66

What are the hazards you may encounter when working on valves?

Answer 66

high pressures, high temperatures, reactive agents, flammable liquids or gases, poisonous substances

Question 67

What should be done to the splits on new packing when installing?

Answer 67

they should be staggered

Question 68

What is the purpose of a balance valve?

Answer 68

smaller actuators may be used to operate the valve because less force is required