Performance of butterfly valves as a flow controller

,

PERFORMANCE OF BUTTERFLY VALVES AS A FLOW CONTROLLER

by

Kenny Eom

' l

PERFORMANCE OF BUTTERFLY VALVES AS A FLOW CONTROLLER

Submitted August, 1986

November 1986

by

Kenny Eom

UTIAS Report No. 318

Acknowl edgement

Grateful acknowledgement is made to N. Mi11igan who assisted in the preparation of experimental set-up, and to Prof. B. Etkin, who suggested and supervised this research.

Abstract

Butterfl y val yes have been used tor shut-off and throttl i ng-control application. It is found that the information available on loss coefficients of butterfly valves for good throttling control is limited at present. This report investigates the performance of two different configurations of butterfly valve: perforated blades and different diameter of solid b1ades that allow partia1 opening of the va1ve at c10sed position. The experimenta1 resul ts support the suitabil ity of a butterfly valve for good flow cont ro 1 •

Acknowledgement • Abstract • • • • Contents

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Notation

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1.0 INTRODUCTION

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2.0 TEST CONFIGURATION AND METHOOS

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3.0 LOSS COEFFICIENTS

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4.0 RESULTS ANO DISCUSSION

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5.0 CONCLUSIONS REFERENCES TABLES FIGURES

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i i i i i v 1 1 2 2 3 4

o

C_Q 9 6H K 6P R U 69 9 diameter of pipe flow eoeffieient gravity

tota 1 head loss loss eoeffieient total pressure loss

Notation

bloekage ratio (= area of disk/area of pipe or duet) mean vel oe ity

eontrollable blade angle [= 9(0.95 ~ax) - 9(0.05 ~ax)]

1.0 INTRODUCTION

Butterfly valves are advantageous over gate, globe, plug, and ball valves in a variety of installations, particularly in the larger sizes. The most obvi ous advantages are savi ngs i n wei ght, space and cost. They are suitable for shut-off and throttling-control applications; they are especially suited for handling large flows of liquids or gases at relatively low pressures and for handling slurries or liquids with large amounts of suspended sol ids [1]. Operation of a butterfly val ve is quick and easy because a 90-degree rotation of the spindle moves the flow control element from the fully closed to the fully opened position.

Butterfly val yes are one of the oldest known types of control val ves. When a valve is required for control purposes, a predetermined partial opening of the valve will be required in order to have good control characteristics. Furthermore, in order to afford good stable control , a smooth control curve with no hysteresis is required and the valve should not be over1y sensitive in any region.

The first attempt at collecting and collating pub1ished data was made by Cohn [2] in 1951. Based on a flow formu1 a adopted by Cohn, a study of butterly val ve flow cha racteri st i cs was conducted by McPherson, Strausser and Williams [3]. But the information availab1e on 10ss coefficients of butterfly valves for goodthrottling control is limited at present.

The object i ve of thi s work is to measure and to present the results obtai ned by usi ng perforated bl ades and different di ameters of sol id b1 ade that allow partia1 opening of the va1ve at the c10sed position (b10ckage

ratio, R

=

area of disk/area of pipe or duct). 2.0 TEST CONFIGURATION AND METHODS

The test configuration consists of a butterfly valve, orifice, blower, Helipot industria1 servo system, piezoresistive pressure transducers, instrumentation amplifer, analog filter (4th order Chebyschev), Keithly data acquisition system, and an IBM-PC (see Fig. 1). The total pressure loss, AP_{1 ,} across the valve is measured as shown in Fig. 2, and a constant diameter, D

=

4", is maintained between station 1 and station 2. In order for hydraulic grade lines to be unaffected by the valve, a distance of 20 upstream and 4D downstream is allowed for the measurements of APl (see Fi g. 2). Two pressure transducers are used to measure pressure loss across the orifice and butterfly valve. Data from these units are conditioned by an ENDEVCO· Model 4423 signal conditioner. Signal filtering is provided by 4th order Chebyschev fi lters. Data is fed vi a an AID converter i nto an IBM personal computer for analys is. In order to study the effects of closing angle, and partial opening of the valve at closed position, two different types of valve configuration are used in this work: (I) perforated disk (screen type), and (2) sol id disk (see Fig. 2). Each disk (blade) allows partial opening of the valve at closed position

(%

opening of valve) and its solidity is listed in Table 1.

3.0 LOSS COEFFICIENTS

In order to study particular aspects of internal flow, there are considerable advantages in adopting one performance parameter, the system loss coeffi ci ents, for all system components.

A loss coefficient is defined as the nondimensional difference in total pressure between the extreme ends of two long pipes or passages. In non-dimensionalizing the pressure loss, the convention is to use the component's inlet velocity pressure, except when the component is an inlet from a large space when the pipe or passage velocity pressure is used. The long pipe or passage before the component ensures a developed flow at inlet, and the long pipe or passage at outlet from the component ensures that losses caused by flow redevel opment af ter the component are debited to the component. The inlet and outlet developed friction gradients are projected to component and the difference between them estab1ished. The loss coefficient, K, is given by:

K~=~

U2 ~

2g 2

where 6H is the total head loss, m of fluid

~p is the total pressure 10ss, in N/m2 U is the mean velocity, m/sec

The corre1ation between 10ss coefficient, K, and flow coefficient,

Co,

adopted by Cohn [2] is found to be

4.0 RESULTS AND DISCUSSION

In order to test the performance of butterfly val yes intended to produce good throttl i ng cont rol, the percentage openi ng of the val ve at closed position is varied systematically. Based on mean pipe velocity head, the loss coefficients of solid disks at b10ckage ratio of 0.976, 0.950, 0.915, 0.900 and 0.800 were obtained at Reyno1ds number of 104 • From experimental data, the 10ss coefficient is p10tted against c10sing ang1e for each disk and the effect of blockage ratio on 10ss coefficients are shown in Figs. 4 to 8. It is presumed that the very slight negative values of 10ss coefficients, K, in figs. 5 to 8 result from a change in ca1ibration of the pressure transducer due to sensitivity of the temperature. In addition, the peak values of K occurring in the vicinity of the 90° blade ang1e instead of at the 90° b1ade ang1e are due to the ca1ibration inaccuracy of the potent i ometer • Accord i ng to results obtai ned from predetermi ned percentage opening of the va1ves, the curves are smooth and have reasonab1y good slopes for good thrott1ing control when the solid disk allows 0.950,0.915 blockage

- - -- - - -- - - -- -- - - -- - -

-ratio, and no hysteresis was found. Reyno1ds numbers of 3.8x104 and 2.4x104 were tested for 5% and 10% opening of the va1ve, respective1y. Within this 1imited range of Reyno1ds number, the 10ss coefficient appears to be virtua11y independent of Reyno1ds number. With a view to investigating the effect of a screen type of b1ade on 10ss coefficients, both perforted disk and solid disk at b10ckage ratio of 0.915 were tested and the results are given in Fig. 7. As an i11ustration, Fig. 9 shows flow separation, fo110wed by intense mi xi ng and flow re-attachment, generated by system components used in this work. As shown in Fig 6, the maximum 10ss coefficient of a solid disk is a 1itt1e 1arger than th at of a perforated disk when the va1ve approaches the c10sed position. However, the difference between va1ues of 10ss coefficients of the solid disk and of the perforated .oisk is not large. As shown ' in Fig. 10, good corre1ation was obtained between' cotrollab1e b1ade ang1e, 69, and percentage opening of the va1ve (b1ockage ratio). On the other hand, b10ckage ratio is p10tted against maximum 10ss coefficient of va1ve, K max' in Fig. 11. In an industria1 app1ication, when the controllab1e ~ 1S determined from the specification of air flow system,

the

controllab~e

b1ade ang1e, depending upon the accuracy of thrott1ing

control, can be chosen. Then, the corresponding b10ckage ratio can be found in Fig. 10 and the resu1ting Kv xis a1so determined from Fig. 11. Furthermore, venturi-type butterfly vWfve insta11ation, as shown in Fig. 12, can be emp10yed to get amp1 ified or attenuated K by simp1y exploiti ng the fact that Kl = K₂ x (U₂/U_I)2.

5.0 CONCLUSIONS

The systematic investigation of the performance of the butterfly va1ve by varying the b10ckage ratio allows to perceive the capability of a butterfly va1ve for thrott1ing control purposes. As the position of the va1ve changes, fair1y good corre1ation is obtainedfor each va1ve given the fixed b10ckage ratio in the va1ues of 10ss coefficients.

REFERENCES

1. Schwei tzer, P. A. " IIHandbook of Val vesll

, Industri al Press Inc., 1972.

2. Cohn, S.O., IIPerformance Analysis of Butterfly Valvesll

, Instruments,

Vol. 24, Aug. 1951.

3. McPherson, M.D., Strausser, H. S., and Williams, J. C., IIButterfly Valve Flow Characteristicsll

, J. Hydraulic Division, ASCE, Vol. 83, No.

HYl, 1951.

4. Miller, D. S., IIInternal Flow System", BH RA Fluid Engineering Series, Vol. 5, 1978.

Tab1e 1

% Opening of Va1ve Used by Different Types of Va1ves

Type of Va1ve 810ekage Ratio, R

, . Perforated Disk 0.915

Sol id Di sk 0.976, 0.950, 0.900, 0.800

R

=

area of disk area of pipe or duet

Analog Fi Iter Instrumentation Amplifier

l<G <2000

Pressure Transducer Potent

i

ometer i 1 Helipot Industrial Servo System Butterfly Valve

Keithly DAS

(AID

Converter 8 Channels, 14 bits Resolution )

IBM

PCIXT

Pressure Transducer Data Analysis

I

- ... ~ Flow Orifice

Figure 2

2

t\

P

---1~ ..

Flow Across Butterfly Valve.

t----d---.t

_1"

32

Thick

\

,/

Rod

I~

dia

Section A-A

a) Solid Disk

890

I I I I I I I I

790

I-

-••

•

•

690

r- ~ ~

•

> ~ ~590 r-

-I-

_•

Z

La.J

₄₉₀

~

--

•

U

-LL LL

₃₉₀

~

•

-La.J

0

_•

u

₂₉₀

_~ -Cl)

•

Cl)

•

9

190

~

-•

•

•

90

r-

•

-•

,

.

.-.efI'1

0

..

I I I I

0

10

20 30 40 50 60 70 80

90

BLADE ANGLE

_[8J

Fi gure 4 Loss Coefficients of Butterfly Valve vs. Blade Angle

295~~--~--~~--~--~~---245

... 195

z

w

-U

La..

145

La..

w

o

u

en

95

en

9

45

Re at fu lIy open posi tion

o

3.8

x

10

4

• 24

x

10

4

•

o o

•

o

•

o

•

o

•

o

•

i

o

o~~~~~~~~~~

o

10 20 30 40 50 60 70 80 90

BLADE ANGLE

[8]

75

,....----, > ~ L--....I

t-z

₅₅

LLJ

u

-

_IJ..

IJ..

LLJ

o

35

u

Cl) Cl)

9

15

.0

...

•

•

•

•

• 0 o

•

00

•

Solid

Disk

Perforated

Disk

-5~~

__

~

__

~

__

~

__

~~

__

~

__

~~

o

10 20 30 40 50 60 70 80 90

BLADE ANGLE

[8]

Fi gure 6 Loss Coefficients of Butterfly Valve vs. Blade Angle

85

75

Re ot fully open position

_o

_3.8

_xl0

4

• 2.4

x 10

4

65

~ 0 >

ia!

~ ~

55

0

...

Q

Z

i

w

45

0

-

•

U

Q

-LL

_•

0

LL

₃₅

_~

w

0

~

u

C>

en

25

C>

i

en

_~

0

..J

15

.0

5

-5~~~~~

__

~~

__

~~

__

~~

o

20 30 40 50 60 70 80 90

BLADE ANGLE

[8]

- - - ---~-- ---

25r---r-1~,r-~1---'1---'1---'1--~1---1--

20--t-

15

f-z

W

-U

LL

10

~ LL

W

o

U

Cf) Cf)

o

...J

_•

-..

....

...

,

•

•

•

•

•

•

••

••

•

••

..

••

-.,..

...

o

_{',I_ ••}

~

_-~

___

j',

_••

-~~-

_.--~-

--5 ______

1 __

~1 __ ~1 __ ~1~ __ 1~ __ ~1 __ ~1 __ ~1 __ ~

0102030405060708090

BLADE ANGLE

[8]

Fi gure 8 Loss Coefficients of Butterfly Valve vs. Blade Angle

a) Orifice Plate

b) Screen

c) Butterfly Valve

a:::

...

0

-~

a::

w

<.!) <{ ~

u

g

CD

1.00

_ - - - , , . . . - - - r - - - - r - - - - . , . . . . - - - - r - - - ,

0.95

0.90

0.85

0.80

0.75

' - - _ - - - - I ' - - _ - - - J . _ _ ---'-_ _ --'-_ _ --J....----I

o

10

20

30

40

.

CONTROLLABLE BLADE ANGLE

J

68

50

[degrees]

Figure 10 Blockage ratio, R, versus controllable blade angle, 69.

IOOO~---~---~

...

w

3

~

100

lL..

o

I-Z

W

-u

-lL.. lL..

W

o

u

Cf)

10

Cf)

9

~

::>

~

x

<t

~

I~---~---~

0.6

0.8

1.0

BLOCKAGE RATIO, R

Butterfly Valve

~-.

UI

U2

. ,

_ _ _ _ _ _

- ' / Section 2

~'-

_ _ _ _ _ _

_

Section 1

IITIAS Report No. 318

University of Toronto, Institute for Aerospace Studies (IITIAS) 4925 Dufferi n St reet, Oownsvi ew, Ootari 0, Canada, ~3H 5T6

PERFOR~ANCE OF BUTTERFLY VALVES AS A FLOII CONTROLLER

fom, Kenny

1. Butterfly valve

I. IJTIAS Report No. 318 Il. Eom, Kenny 2. Flow control

~

Butterfly valves have been used for shut-off and throttling-control appl1cation. It is found

that the information avallable on loss coefficients of butterfly valves for good throttling control is limited at present. This report investigates the performance of two different configurations of butterfly valve: perforated blades and different diameter of solid blades that allow part1al opening of the valve at c10sed position. The experimental results support the

suitability of a butterfly valve for good flow control.

IITIAS Report No. 318

IIniversity of Toronto, Institute for Aerospace Studies (IITIAS) 4925 Oufferin Street, Oownsview, Ontario, Canada, I13H 5T6 PERFORt'ANCE OF RUTTERFLY VALVES AS A FLO\/ CONTROLLER Eom, Kenny

1. Butterfly valve

1. IITIAS Report No. 318 Il. Eom, Kenny 2. Flow control

~

Butterfly valves have been used for shut-off and throttling-control application. It is found

that the i nformati on ava 11 abl e on loss coeffi ei ents of butterfly val ves for good throttl1 ng

control is l1 .. ited at present. This report investigates the performance of two different

confi gurat i ons of butterfly val ve: perforated bI ades and different di ameter of soli d blades that allow partial opening of the valve at closed position. The experl ... ental results support the

suitabllity of a butterfly valve for good flow control.

Available copies of I:his report: are limil:ed. Rel:urn I:his card 1:0 UTIAS, if you require a copy. Available copies of I:his reporl: are limil:ed. Rel:urn I:his card 1:0 UTIAS, if you require a copy.

tlTIAS Report NO. '318

University of Toronto, Institute for Aerospace Studies (UTIAS) 4925 Dufferln Street, Oownsview, Ontario, Canada, 113H 5T6

PERFORMANCE OF RIITTERFLY VALVES AS A FLOW CONTROLLER

Eom, Kenny

1. Butterfly valve

I. UTIAS Report No. 318

2. Flow control

Il. EOf'l, Kenny

~

Butterfly valves have heen used for shut-off and throttling-control application. It is found

that the information avall ab 1 e on loss coeffi ei ents of butterfly val ves for good thrott li ng control is limited at present. This report investigates the performance of two different configurations of butterfly valve: perforated blades and different diameter of sol1d blades that allow partial opening of the valve at closed position. The experimental results support the

suitabllity of a butterfly valve for good flow control.

UTIAS Report No. 318

University of Toronto, Institute for Aerospace Studies (UTIAS) 4925 Oufferin Street, Oownsview, Ootario, Canada, I13H 5T6

PERFORMANr.E OF RIITTERFLY VALVES AS A FLOW CONTROLLER

Eom. Kenny

1. Rutterfly valve

I. IITIAS Report No. 318 Il. Eo .. , Kenny 2. Flow control

~

Rutterfly valves have been used for shut-off and throttling-control application. It is found that the i nformat i on avall abl e on loss coefti ei ents of butterfly val ves for good thrott li ng control is limited at present. Thi s report i nvest igates the performance of two di fferent configurations of butterfly valve: perforated blades and different diameter of solid blades that allow partial opening of the valve at closed position. The experimental results support the