api steam turbines

To inerease the amount of steam flow: —_______ the pressure difference or == increase; increase, or enlarge the nozzle opening while keeping the pressure differ- ence constant, The pur

STEAM TURBINES

Unit 1 Principles

PILOT 8—PUMP AND COMPRESSOR DRIVERS

UNIT 2—STEAM TURBINES

page Unit 1

Prineiples " ama 2

Single- and Multi-Stage ‘Turbines 7 -.ssv 6 Stationary Buekets , es l6 ga 8

Reaction Turbine š ¿v2 10 Condensing and Non-Condensing Turbines , 11 Extraction and Induction , eaves bá t3 8S FTE Me eq on 12

Governors "—._

sua ĐỔI Direct-Acting Flyball Governor — ố:

Effects of Uneven Betigs and Cooling , đĩ Shaft Bow, an 2H :giangrE§

Packing Box Bi iat

Visual Inspections Before Startup

Review and Summary,

Steam turbines may differ from one another in size, appear- ance, and construction, but all steam turbines are similar in operation and work on similar principles

Tn Unit, 1 of this program, you will learn how impulse and

reaction turbines convert thermal energy to mechanical energy You will learn how condensing and non-condensing turbines work, how turbine speed is controlled, and how the overspeed trip protects the turbine against failure of other

speed controls,

In Unit 2 you will learn the construction of the turbine: rotor and casing, diaphragms, seals, and packing boxes, including labyrinth and carbon-ring paeking You will learn the con- struction of the bearings and bearing combinations used in

turbines, of single- and mulli-evalve governors, aml of the ail-

tion; of uneven heating and cooling; lenkuge of steam, vibra-

tion; lubrication and lubrication problems; speed adjustment, instrumentation, and visual inspections to be conducted before

startup,

Through this understanding of turbine principles, eanstrne- tion, and contrel, you will be better able to assure the efficiency and safety of turbine operations

HERE ARE SOME SAMPLE ITEMS TO GIVE YOU

PRACTICE WITH "PROGRAMED LEARNING",

First, we say something, like this:

“A program may look very much like a test, or examl-

nation, but it is nog a test,"

Next, we ask you for an interpretation, or we say more about

what we have just said but leave somethings out for you to fill

in, like this:

“A program is not a

Next, you fill in the blank, and then move down the mask at

the right to see if your answer is correct,

4f your answer is wrong, review until you can see why it is

wrong, and then go on to the next item, If your answer is right,

&o on at once Instead of a blank to fill in, we may give you

a choice of two answers Circle or underline the right one

“No one grades you on the answers you give in studying

a program However, filling in all the answers is important

for your own learning and remembering,

“It (is/is not) important to fill in all the answers as you

study a program,”

Here is one more example:

"A program permits you to study at your own rate of

speed ‘Take time to read each item carefully, because skim-

ming and guessing make for poor learning

“In studying a program, it is (helpful/wasteful) to give

each item close attention."

Notice that the left-hand pages from here on are printed upside

down, The program is designed so that you wilt go through all

the right-hand pages first, and then turn the book upside down

and go through the other pages

Now, go on to Page 2 and begin,

[1]

Before beginning, coyer this

column with the mask,

test

helpful

Now pull the exhibits out of the center of the book

Asteam turbine changes thermal energy to

Heat is the flow of thermal energy Thermal

can be changed to mechanical energy

energy,

When water boils and turns to steam, the steam has

more energy than the water had

Heating water in a closed container (increases/de-

creases) the pressure of its vapor

Steam pressure in the container becomes (higher/

lower) than the pressure of the atmosphere

The higher pressure forces steam Lo expand through

thê ————

Steam is forced out of the nozzle at (high/low) speed

or velocity,

A jet of steam strikes the bucket, and the bucket moves

Mechanical energy is produced as the high-velocity

strikes the bucket and causes it to move

When steam expands through the nozzle, its pressure

(increases/decreases)

As the pressure of the steam flowing through the noz-

zle is reduced, the velocity of the steam increases

The nozzle changes steam pressure to steam

turns

High-velocity steam striking the _

the retor and produces mechanical work

Increasing the pressure difference (increases /

decreases) the amount of flowing steam

As steam leaves the nozzle, its pressure and tempera-

ture (inerease/deerease)

Us velocity _ =

Heat (thermal energy) produces steam pressure, and

the steam pressure is converted to steam velocity by

the nozzle

After steam strikes the buekets, steam velocity

(inereases/ decreases)

The rotor turns and produces mechanical work, The

steam has (gained/lost) energy

More steam produces more work than less steam when

both are at the same temperature and pressure

If more nozzles are added, or if the nozzle is enlarged,

(more/less) steam strikes the buckets

More nozzles or a larger nozzle produces more

decreases

lost

more

mechanical

To inerease the amount of steam flow:

— _ the pressure difference or == increase; increase, or enlarge the nozzle opening while keeping the pressure differ-

ence constant,

The purpose of the nozzle is;

to steam at the buckets and to convert direct

gteam_. —_— tosteam —_., pressure, velocity

The rotor in this turbine differs from the rotor in the

The buckets are mounted on a — tither than wheel

directly on the shaft

The three basic parts are still a rotor, a nozzle, and a

source of . _ steam

- The nozzle or nozzles are located in the wall of the

SgHf—-_.-———› chest

The flow of steam into the steam chest is controlled by

By controlling the amount of steam flowing into the

steam chest, the governor valve controls the output of

energy mechanical , The rotor is mounted inside a metal aes casing

Wor the steam to flow into the casing through the noz-

ale, the steam pressure in the casing must be — lower, or less

than the steam pressure in the steam chest

Without a pressure difference, the steam cannot flow

andno _ — can be produced mechanical work, or energy

[41

31 The high-velocity steam directed toward the buekets

is an impelling foree (impulse) which causes the rotor

to turn

Because the turbine uses the impulse of steam on the

buckets to turn the rotor, the turbine is ealled an

—————— turbhine impulse

32 Look at the drawing,

SHAFT CASING xã

GOVERNOR

VALVE STEAM OUT

STEAM IN

A B

33, Because there is less load on turbine A, turbine A

needs (more/less) energy than turbine B to do its job less

34 The most convenient way to increase the power output

of the turbine is to allow steam into the more

steam chest

35 When more energy is needed, the governor valve is

_to let more steam into the steam chest opened

36 If the load on the shaft increases (but the steam flow

is not increased), the speed of the rotor (inereases/

37 Opening the governor valve the speed of increases the rotor

38 The speed of the rotor also increases as the load

on the shaft is decreased,

39 If the rotor Lurns too fast, it may be damaged Speed

is controlled by the valve governor

40 Shaft speed depends on:

the amount of _ on the shaft and the amount load

of flowing, into the steam chest steam

[5]

Single- and Multi-Stage Turbines

41, The area into which steam expands is a stare,

Steam pressure is (inereased/decreased) in a stage

42 When pressure is reduced in one stage only, a turbine

is called single-stage

If steam pressure is reduced in more than one stage

the turbine is called multi- — —

43, Look at the drawing

This turbine has (one/more than one) wheel

4d, Pressure is reduced in_ stage,

45, This is a_ -stage turbine

46 Look at the drawing

Ist STAGE 2nd STAGE 3rd STAGE

47 Pressure is reduced in — —_— stages

48 This is a _-stage turbine

49 <All of the stages are located in _ — 0aging

50, Steam leaves the turbine through the

single

three three

multi one

exhaust

51 Look at the drawing

CASING NOZZLE BUCKET

HEAT: SOURCE Ist STAGE LAST STAGE

All the wheels are mounted on shaft

52, Each stage is isolated by as whieh holds

the nozzles

58 All the previous drawings have shown — _ main

nozzle per stare

54, Instead of one large nozzle, a row of smaller nozzles

ean he used

HIGHER PRESSURE

STATIONARY DIAPHRAGM

There is row of nozzles per stage

55 A turbine designed for a high inlet pressure and low

exhaust pressure generally has its pressure reduced

in several stages ‡

Turbines having large pressure drops between inlet

and exhiuust are usually (single-/multi-) stage turbines

multi-56 Look at the drawing

an

(Rotor A/Rotor B) is single-stage A

(Rotor"A/Rotor B) is multi-stage, B

(Rotor A/Rotor B) reduces pressure in steps B

(Rotor -A/Rotor B) is probably in the larger turbine B

57 Steam expanding from stage to stage increases in

volume To provide for the larger yolume in the later

stages, the buckets are longer _

Tn Rotor B, the buckets on the last wheel are longer

than the buckets on the first wheel

Stationary Buckets

58 One kind of stage uses two rows of buckets instead

of one,

But since there is only one pressure reduetion, there

59, The row of nozzles directs steam at the first row of

buckets,

DIRECTION

OF MOVING BUCKETS

277

BUCKETS

As the steam leaves the buckets, it is moving in the

(same direction as/opposite direction from) the mov- opposite direction from

ing buckets,

[8]

GU, In order to move a second row of buckets in the same

direction as the first, the — _ must be redirected steam

61 Look at the drawing

62, These stationary buckets the steam jets redirect

into another row of moving buckets

63, Since the stationary buckets do no change the pressure

of the steam jets to any great extent, they (are“are not) are not like a row of nozzles

64 The stationary buckets are mounted on the casing and

STATIONARY BUCKET

Although the picture shows more than one wheel in a

stage, most stages have just wheel one

[91

Reaction Turbine

66 In an impulse tarbine, all the steam expansion oeeurs

through a stationary nozzle

All turbines deseribed so far are _ turbines impulse

67 A reaction turbine has a large portion of the expansion

ovcurring in the buckets or blading of the wheel

A turbine having a large amount of expansion oceur-

ring in the wheel blading is a (reaction/impulse) reaction

turbine,

68 Look at the drawing

“HIGH”

VELOCITY STEAM

PRESSURE STEAM

HEAT SOURCE

These reaction turbines have no stationary nozzles

All the = drop occurs in the wheel or rotor, pressure

69 The turbine blading acts like moving nozzles

70 In the impulse turbine, expansion of steam (pressure

drop) oecurs across the stationary nozzles

in the reaction turbine, some or all expansion occurs

in the ———— mounted on the rotor, buckets, or nozzles

71 In the reaction turbine, the steam expands as it flows

through the buckets

In the impulse turbine, sleam (expands/does not ex-

pand) to a great extent in the buckets does not expand

72, Normally, reaction turbines, like impulse turbines, have

stationary nozzles, but in the reaction turbine, (part,/

none) of the expansion ovcurs in the buckets part

78 Reaction turbines, although sometimes more efficient

than impulse turbines, require more stages than im-

pulse turbines They are seldom used as pump or

compressor drivers :

Plants usually use (reaction/impulse) turbines impulse

[10]

Condensing and Non-Condensing Turbines

Therefore, steam exhausts from the turbine at a

(owershigher) pressure than steam ent ng the lower

turbine

Sleam flows from the boiler at a higher pressure and

leaves the turbine through the ata lower exhaust

pressure

Low-pressure steam can still be used to run a turbine,

Low-pressure steam ean expand into an area of still

Look at the drawing

STEAM CHEST INLETS

Turbine B hasa ————— — installed at the exhaust, condenser

A condenser removes heat and thus lowers pressure

The condenser cools the steam leaving the turbine and

changes it into water

(Turbine A’Turbine GB) is a non-condensing turbine Turbine A

The exhaust pressure of turbine A is Chigher/lower) higher

than the exhaust pressure of turbine B

When the steam is condensed, the water may be re

turned to the boiler for =— ‘ reheating

The non-condensing turbine (utilizes/does not utilize) does not utilize

all of the available thermal energy present in the steam

[11]

83

84

From the same amount of steam (at the same inlet

pressure), the (condensing/non-condensing) turbine

produces more mechanical work

Since large pressure drops are common in condensing

turbines, the steam pressure is usually reduced in steps

Condensing turbines are usually — —— -_ -stage

Lovk at the drawing

Ist STAGE INTERMEDIATE FINAL

Some steam may be removed from or added to a stage

before it reaches the —

Steam removed from a siage can be used for processes

that need steam at pressures and temperatures (above,

below) the pressure and Lemperature of the exhaust

Removing steam at an intermediate stage is extraction

Steam from the turbine can be used

for other processes

Steam may also be fed or “induced” into the turbine

Sometimes excess steam is available in the plant, at

the pressure of a turbine’s intermediate stage

The governor valve regulates the amount of steam

allowed into the Lurbine and the amount of —

work produced

When a heavier load is placed on the turbine, (more/

less) power is needed than when the turbine is only

partially louded

The speed of the driven equipment must be controlled

to perform its operating function,

The _ valve is used to control turbine

The governor is a mechanism which opens and closes

the governor valve

The speed of the turbine is controlled by the

If the turbine starts to speed up or slow down, its

speed must be brought back to normal,

The governor corrects for changes in

The drawing shows a flyball governor

FLYBALL

SPRING

AT REST HIGH SPEED

The fiyballs are held together by the force of a

As the governor turns, the spinning (centrifugal) foree

moves the flyballs ({arther apart/closer together)

At (low/high) speed, the force of the spring keeps the

flyballs together

At speeds, the fyballs move farther apart

The — the governor turns, the farther apart

the flyballs move

Direct-Acting Flyball Governor

Look at Exhibit 1 When the turbine is not operating,

the spring holds the flyballs close to the shaft

Before the turbine is started, the governor valve is

(wide open/closed tight)

As the shaft starts to turn, the force of the “

prevents the flyballs from moving apart

As the shaft approaches operating speed, spring ten-

sion is overcome by the force of spinning (centrifugal

foree), and the balls move (toward/away from) each

other,

As the flyballs separate, the governor valve is (opened /

closed)

When the turbine reaches operating speed, the governor

valve allows (more/less) steam in than at startup, and

the turbine stops accelerating,

When an inereased load on the turbine slows the tur-

bine down, the flyballs are pulled in toward each other

The governor valve is — so that the turhine

(speeds up/slows down)

higher faster

If the load is suddenly removed, the turbine —_ up

If the inlet steam pressure is suddenly reduced, turbine

speed (inereases/deereases)

‘The governor valve must

Tf the exhaust pressure rises, the turbine speed (inereases/

decreases)

As the load is removed from a fully-loaded turbine, speed

If a governor could compensate completely for this change

in speed, the speed at zero load (would/would not) be

the same as the speed at full load

With no difference between the speeds at full and no load,

regulation would be zero

But if the governor design permits some increase in speed

as the turbine load is decreased, the turbine regulation

(is/is not) zero,

A narrow governor tends to keep changes in speed as

small as possible,

A governor with zero regulation is an extremely —

governor

Most narrow governors do not maintain zero regulation,

but keep the drift in speed as low as 4%

A governor with 4% regulation is still a

governor,

To find the speed drift, multiply the rated speed by the

percentage of regulation,

To find the speed at no load, (add/subtract) the speed

drift to the rated speed

(4% of 3000 is 120.) If a turbine's rated speed at full

load is 3000 RPM and its governor has 4% regulation, its

speed at no load is RPM

A direct-acting flyball governor that is narrow keeps

turbine speed changes (lurge/small),

Friction in the governor mechanism tends to resist move-

ment of the governor itself

The governor must overcome the resistance of this

The governor must also overcome unbalanced forces of

steam pressure and steam flow in the —_

valve,

[14]

speeds

decreases open

On turbines equipped with a narrow flyball governor,

if there is a slight change in turbine speed, the gover-

nor must first overcome friction and any unbalanced

before it can move the governor valve

The flyballs cannot control the speed within a small range,

because the forces opposing the governor cause the valve

to overtrayel,

Correcting for load change, the governor moves the valve

OO ca a

Overshooting constantly, the governor never precisely

finds the operating speed,

The turbine is continually speeding up or _

down a little

This alternate speeding and slowing is “hunting”; that

is, the governor hunts for the correct setting,

A narrow flyball governor correcting small changes in

turbine speed is more likely to than a

broad governor,

A broad governor does not move the yalve as far to cor-

rect a small change in speed as a narrow governor does

Only a (large/small) speed change causes the broad gov-

ernor to move the valye from the opened to the closed

position,

For a given speed change, the broad governor moves its

valve 4 shorter distance than the narrow governor, and

thus does not, overshoot the correct valve setting,

The broad governor (tends/does not tend) to hunt,

A broad governor usually has a range of operaling speed

as broad as 10%

As the load is decreased from full load to no load, turbine

speed (increases/decreases) by 10‘4 of full-load speed

If a turbine’s rated speed at full load is 3500 RPM, with

10% regulation, its speed at no load is

RPM

Hydraulic Governor

125

126

Look at Exhibit 2, which shows a hydraulic yovernor,

To regulate turbine speed, the hydraulic governor uses an

EXHIBIT 1

SPEED CHANGER

GOVERNOR SPRING t

|

| ~— GOVERNOR LINKAGE

PIVOT STARTUP

SPRING

FLYBALL

GOVERNOR SPRING

RETURN LINE TO RESERVOIR

LEAK- OFF

OIL PRESSURE

PISTON

STEAM TO

ont EXHIBIT 5 L_ sưng

¬- CYLINDER RESTRICTION

ORIFICE

STEAM TO

STEAM CHEST | TRIP VALVE

RETURN LINE TO RESERVOIR

@ BOILER

sTEAM To_ |ÌÌ STEAM CHEST

When the turbine is not running, the oi] pump puts no

pressure into the hydraulie piping,

With no pressure on the governor valye, the valve remains

(closed /open)

As the shaft turns, oil is pumped into the piping to the

valve,

Most of the oil passes out of the leak-off and returns to

the reservoir to provide a constant supply of

fo und from the oi] pump,

‘The governor valve is connected to a flexible diaphragm

Changes in oil adjust the valve

When the turbine speeds up, more oil is pumped

The oil pressure goes (up/down)

The increased pressure acts on the diaphragm to (open/

close) the valve

If more load is placed on the turbine, the turbine and the

oil pump slow down

Oil pressure goes (up/down), and the valve — _

If oil pressure in the hydraulic system is lost, the gover-

nor valve moyes to a fully-open position

Thus if the hydraulic system fails while the turbine is

running, the turbine“ _,

‘Temperature affects the viscosity (thickness) of the oil

A change in oil temperature may affect the governor

—

Temperature must be carefully controlled Too much hot

thin oil passes through the oil leak-off so that sufficient

oil pressure does not build up in the system and the tur-

bine operates at (too high,/too low) a speed

Jold thick oil pumps very well and not enough of it passes

through the leak-off Pressure in the hydraulie system

becomes too great and tends to (open/close) the gover-

nor valve

A change in temperature changes.the governor valve set-

ling and the turbine — setting

Hydraulic governors are well suited to high-speed use

A high-speed turbine works best with a (hydraulie/

flyball) governor,

Since temperature changes can affect the adjustment of

the hydraulic governor, hydraulic governors are usually

The oil-relay governor combines the features of the

hydraulic and the governors

Oil pressure operates a

The spring keeps the piston in place until a change in

öjl ——————“^ aets on the piston

Flyballs position the pilot valve that controls the oil

flowing through the oil inlet and the oil sof

the oi] relay

At normal operating speed, both the oil inlet and outlet

are partially open

Bul when the governor valve must open to compensate

for an increased load, the flybualls reduce the outlet

opening and increase the _ opening

To close the governor valve, the flyballs reduce the

opening and increase the opening

Unless the inlet is fully open or fully closed, oil con-

stantly circulates through the relay system, regardless

of the setting

Oil from the outlet connection is returned to an oil

to be pumped into the hydraulic system

again

Tf oil pressure is suddenly lost (through failure of the

oil pump, for example), the spring forces the piston to

close the valve,

With the oil-velay governor, loss of oil pressure does

not cause the turbine to — as with the

hydraulic governor

The oil-relay governor uses hydraulic foree to move the

valve so that it has (more/less) power than a fiyhall

governor by itself

It easily maintains narrow control by overcoming [ric-

tion and the unbalanced forces of steam The oil-rclay

governor can be a narrow governor and (tends,‘does

not tend) to hunt

Of the available governors, the (direct-acting flyball/

hydraulic/oil-relay) governor is superior in maintain-

ing a narrow range of speed

Since the flyballs adjust the speed setting, a change in

vil temperature (affects/does not affect) the turbine

speed setting

[17]

ftlyball piston

151 In some turbines, the oil relay is not operated by a set

Changes in eleetric current adjust the pilot valye, which

opens and closes the“ _ — and _ openings

Overspeed Trip

153 ‘The governor regulates the turbine under normal con-

ditions, but sometimes abnormal conditions occur

If all load is suddenly removed from a fully-loaded tur-

bine, the turbine may — a

154 Sometimes the governor reacts too slowly or fails to

respond at all

if the steam is not shut off promptly, the turbine

¬ until it Hies apart

155 A trip pin in the turbine shaft is used to shut off the

flow in an emergency

156, ‘The drawing shows a trip pin in the shaft

At normal speeds the trip pin remains inside the

157 ‘The pin consists of an unbalanced weight held in the

shaft by a —— :

158 TỶ the turbine overspecds, the pin is ejected from the

by centrifugal force (force of rotation)

The trigger releases a latch holding the trip lever,

which is then pulled down by a

The force of the spring the trip valve

The trip valve closes and cuts off the steam flow to the

steam

‘The turbine

Unlike governors (which are self-correcting), the

overspeed-trip mechanism must be ———— after the

turbine stops

Look at Exhibit 6

Large trip valves use oil under pressure to open them

and hold them open,

The spring-loaded valve is held open by the pressure

of the

When the turbine overspeeds and the trip pin is ejected,

the pin triggers a latch, as in Exhibit 4

The latch opens the oil _ valve

The force of the ejects the oil from the

cylinder, and the trip valve slams shut

As with the direct-acting trip, the mechanism must

be after the turbine has slowed down

Overspeed-trip pins are set to act at speeds 10 to 15%

over Lhe maximum turbine speed

If the turbine overspeeds 8% over the maximum, the

pin (is/is not) ejected from the shaft

Other overspeed safety devices are used on turbines

On one type of small turbine, the rotor is equipped with

a brake rim that is activated when the turbine

The brake acts like the brake of a car When the rotor

overspeeds, centrifugal force stretches or expands it

until its rim rubs on the wall of the and

slows down the rotor,

lf the brake-rim rotor does overspeed, some damage

may occur to the wheel

The rotor might have to be — after over-

speeding

[19]

lateh

spring closes

REVIEW AND SUMMARY

173 The purpose of the nozzle is to:

a) allow steam to flow from the steam

b) direct the steam jet at the

¢) convert steam —_

174, Foy the turbine to operate, there must be a pressure

betaveen the steam chest and the exhaust

houses the rotor

- Iyball governor

#FOV€@f'HoT valve

» Steam chest nozzle

easing:

single-

casing

Mechanical energy is transferred to the driven equip-

ment by coupling the pump or compressor shaft to the

————— of the turbine

The output of mechanical energy and the speed of the

rotor are regulated by the =

Steam can be induced or extracted from a turbine at

A governor that cannot find the correct operating speed

and is continually increasing and decreasing turbine

speed is said to be —

A (narrow/broad) flyball governor is more likely to

hunt

The oil-relay governor is (more/less) likely to hunt

than a mechanical flyball governor in a narrow range

because it has the power to overcome the unbalanced

forces resisting the governor

In case the governor does tot correct overspeeding, Lhe

_ is used as a safety đevice

Unit 2 Parts and Equipment

PARTS AND EQUIPMENT

The Rotor

1 The rotor eonsists of wheels, buekets, and a _

2 The buckets are usually made separately and then

mounted on the =——

3 On some rotors, a hot wheel is placed on the shaft and

allowed to cool Cooling causes the wheel to shrink and

fit tightly on the shaft

On other rotors, the shaft and wheel are forged as one

4 The (built-up/solid) rotor is first made in two parts,

then shrunk together as one unit

5 Because of ils single-unit construction, the (built-up,

solid) rotor is the strongest,

6, Howeyer, the — — rotor is less costly to make

The Casing

ue

10

The turbine operates because there is a difference in

pressure between steam in the steam ehest and steam in

the casing

Steam pressure is (higher/lower) in the steam chest

than in the casing,

Without this pressure difference, steam (would flaw/

would not flow) through the nozzle

Tf the exhaust becomes blocked, pressure builds up in

the easing ‹

As pressure builds up in the casing, the —_

difference is lost

Because the turbine is designed for greater pressure

in the sleam chest than in the casing, the (easing /

steam ehest) is made stronger,

Tl pressure in Lhe casing were allowed to go up ag high

as the inlet pressure, the casing would be — ¬

For this reason turbines must never be started with

the (inlet/exhaust) valve closed,

Some turbines have a safety valve installed on the ex-

haust line to relieve excessive pressure,

The valve prevents excessive pressure from —

the casing

[28]

shaft wheel

unit, or piece built-up

solid built-up

14,

16

On some turbines, a sentinel valve whistles if pressure

in the casing rises too high

This valve warns of high in the easing

However, the valve does not adequately

relieve the pressure,

Under correct startup and vperating conditions, the

sentinel valve should never open to sound a warning

Tf the sentinel yalve ever starts to open, the operator

must take immediate action to _ _ the pressure

Diaphragms and Labyrinth Seals

17,

18

21

22

In a multi-stage turbine there is a_ - _——

in pressure between stages

Look at the drawing

The is the stationary part mounted to

the casing It separates tao stages and holds the

nozzles

Leakage of steam occurs where the extends

through the diaphragm

Steam passing through the nozzles and striking the

buekets does useful work

Steam leaking along the shaft, bypassing the nozzles

in the diaphragm, (does,’does net do) useful work in

that stage

Usable is lost

The diaphragm could be made to surround the shaft

closely, but if the shaft rubs on the diaphragm and

damages it, (part of the/the whole) diaphragm has

23

2A

Since the diaphragm is made of hard metal, the shatt

a if the diaphragm rubs against it damaged

Look at the drawing

NOZZLES

~t—— DIAPHRAGM

<j—— LABYRINTH SEAL

A labyrinth seal is inserted in the space where the

passes through the diaphragm shatt

The labyrinth seal reduces the — hetween the space

diaphragm and the shaft

The seal is made of soft metal (like, brass), so that if

it rubs on the shaft it does not ——— the shaft damage

to any extent

The seal becomes damaged if the turning shaft rubs

apainst it

The seal is removable from the diaphragm so that if

it is damaged it can be without replacingr repliced the whole diaphragm,

The labyrinth consists of metal rings ar ridges that

fit close to Lhe shaft

The ridges (tonch/do not touch) the shaft do not touch

A small spree between the shaft and the labyrinth

[#51

30 As s(oum enters the seal, it forms eddies (whirlpools)

Steam pressure (increases/decreases) as it passes

through the compartments

31, The decrease in pressure as steam passes through the

seal permits a (large/small) amount of steam to pass

between the shaft and the seal

The pressure at lhe exhaust of a non-condensing tur-

bine is (greater/less) than the air pressure around it

33 Steam lends to leak from the packing boxes where the

. _ extends through the casing

34 The greater the amount of leakage from the packing

box at the inlet side, the greater the loss of usable

— _ to the atmosphere steam With leakage of steam from this packing box, (more/

less) steam must flow through the steam chest nozzles, more

35, The bearings are close to the packing boxes,

Condensate from escaping steam can get into the

and damage them hearings

36 The exhaust steam from

usually usec

non-condensing turbine is

in for process or heating requirements

A leak at the exhaust end of the shaft loses _ steam

which could be used for other purposes

37 Packing boxes reduce or minimize steam leakage where

the shaft extends through the soa sy casing:

88 The packing boxes on some equipment are packed with

rings of soft material

‘This soft material prevents from leaking steam through the casing

39 1n turbines, the soft packing wears out quickly and

{is’is not) a food sealing: material is not

410, This is a packing box fitted with a labyrinth seal

LEAK-OFF FOR LOW

PRESSURE STEAM —+ CASING

LEAK-OFF TO DRAIN OR GLAND EJECTOR

Like the interstage-diaphragm Tnbyrinths, this seal

minimizes leakage of steam along the —, shaft

[27]

41, The ridges of the packing rings form small compart-

ments which resist the flow of ——

42 Toward the outer end of the packing box, two or more

remove steam, to be used again in a lower pressure system or disposed of in a drain or ejector

43, Look at the drawing

TRỢ TH STEAM

STEAM FROM ~ | LEAK-OFF

CONNECTION

EJECTOR

High-velociiy steam flowing through the

draws steam leakage out of the leal:-of,

44 These seals and leak-offs allow (a great deal of /very

little) steam to leave the casing

đã In the condensing turbine, the exhaust-steam pressure

is less than the outside air pressure

Leakage along the shaft at the exhaust end of the tur-

bine allows (steam to escape/air to enter) the exhaust

If air is allowed to enter the exhaust and is not

removed by an ejector, the exhaust pressure (increases,’

decreases) increases

The packing box at the high-pressure steam inlet end

resists the flow of steam leaving the casing along the

——- shaft,

‘The packing box at the low-pressure end of the von-

densing turbine prevents from entering the air

TO DRAIN OR GLAND EJECTOR

In this packing box, steam is (added/removed) be- added tween sections of the labyrinths,

Sealing steam injected into the packing box flows in

two directions along the _ shaft Air attempts to enter the exhaust through {he packing

box bul the flow of sealing: prevents it, team The portion of the sealing steam flowing toward the

easing passes into the exhaust and is condensed by the

Since this steam is condensed, it (does¿does nel) Ín- does nob crease exhaust pressure,

[29]