5.10 VALVE NOISE

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5.10.1 Sources of Valve Noise

Valves and regulators used with steam and gas lines can be a significant

source of noise. There are two primary sources of noise generated by valves:

(a) mechanical noise generation and (b) fluid noise generation, either

hydraulic for liquids or aerodynamic for gases (Faulkner, 1976).

Mechanical vibration of the valve components results from flowinduced

random pressure fluctuations in the fluid within the valve and

from impingement of the fluid against flexible parts of the valve. In conventional

valves, the main source of noise from mechanical vibrations arises

from the sidewise motion of the valve plug within its guiding surfaces. This

noise source usually produces sound at frequencies below 1500 Hz and is

often classified as a metallic ‘‘rattling’’ sound. The noise emitted from this

source is usually of less concern to the designer than the damage of the valve

plug and guide surfaces resulting from the vibration. In fact, noise from

valve vibration could be considered beneficial, because the noise warns of

186 Chapter 5

TABLE 5-13 Median Sound Power Levels for Various

Types of Equipment and Home Appliances

Appliance LW, dB Equipment LW, dB

Air conditioner 70 Backhoe 120

Clothes dryer 70 Concrete mixer 115

Clothes washer 70 Crane (movable) 115

Dishwasher 75 Front loader 115

Food blender 85 Jackhammer 125

Food disposal 90 Pneumatic wrench 120

Hair dryer 70 Rock drill 125

Refrigerator 50 Scraper/grader 120

Vacuum cleaner 80 Tractor 120

Source: Environmental Protection Agency (1971a).

Copyright © 2003 Marcel Dekker, Inc.

conditions in the valve (wear, excessive clearance, etc.) that could result in

valve failure.

Some control valves used valve plugs that were fitted with skirts that

guided the valve body ports. Flow openings were cast or machined into the

skirts. Mechanical vibration of this type of valve was a serious problem,

because there was a large clearance between the skirt and the body guides.

The vibrations of the valve plug could be reduced by using guide posts on

each end of the valve plug. One commonly used design technique for control

valve noise reduction is to rigidly attach the cage member containing the

flow openings to the valve body. The movable valve plug is closely guided

within the inside diameter of the cage. By proper attention to the valve

internal design, noise generated from mechancial vibrations can be reduced

to negligible levels, compared with other sources.

Another source of mechanical vibration noise arises from valve components

resonating at their natural frequencies. Resonant vibration of valve

components produces a pure-tone component, usually in the frequency

range between 3 kHz and 7 kHz. This vibration can cause high stresses in

the component that may lead to fatigue failure. Flexible members, such as

the metal seal ring of a ball valve, are subject to mechanical vibrations of

this type.

The hydrodynamic flow noise from a valve handling liquids arises

from several sources, including (a) turbulent velocity fluctuations in the

liquid stream, (b) cavitation when bubbles of vapor collapse after being

momentarily formed in the fluid within the valve, and (c) flashing

(vaporization) of the liquid when the pressure within the valve falls below

the vapor pressure of the liquid.

Turbulent velocity fluctuations in a liquid flow generally result in

relatively low noise levels. The high turbulence levels in valves is produced

by the rapid deceleration of the fluid as the velocity profile changes shape

beyond the valve outlet.

Cavitation of the fluid is the major cause of hydrodynamic noise in

valves. As the liquid is accelerated within the valve through valve ports,

static pressure head is converted to kinetic energy, and the pressure of the

liquid decreases. When the static pressure of the liquid falls below the vapor

pressure of the liquid, vapor bubbles are formed within the liquid stream. As

these bubbles move downstream into a region of higher pressure (greater

than the vapor pressure), the bubbles collapse or implode and cavitation

occurs. Noise generated by cavitation has a broad frequency range, and

often has a sound similar to that produced by solid particles within the

liquid stream.

Flashing of the liquid occurs when the pressure of the liquid drops

below the vapor pressure of the liquid at the inlet temperature to the

Noise Sources 187

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valve. The resulting flow from the valve is two-phase flow, a mixture of

liquid and vapor. The deceleration and expansion of the two-phase flow

stream produce the noise generated in a valve handling a flashing liquid.

The aerodynamic flow noise from a valve handling gases arises from

turbulent fluid interactions within the flowing stream due to deceleration,

expansion or impingement of the fluid (Lighthill, 1952).

5.10.2 Noise Prediction for Gas Flows

The Fisher Controls Company has developed one technique for prediction

of valve noise (Stiles, 1974). The correlation was developed from A-weighted

sound level measurements at a location 1.219m (48 in) downstream of the

valve outlet and 0.737m (29 in) from the surface of the pipe connected to the

valve. This location corresponds to a distance ro ј 1:424m (56.1 in) from

the surface of the valve. For valves located outdoors, the A-weighted sound

level may be estimated from the following correlation:

LA ј LAрroЮ _ 20 log10рr=roЮ (5-42)

The following correlation may be used for valves located indoors, where R is

the room constant for the room in which the valve is located:

LA ј LAрroЮ ю 10 log10

4 ю рR=4_r2Ю

4 ю рR=4_r2

oЮ

" #

(5-43)

For valves handling a gas, the Fisher Controls equation for the Aweighted

noise generated by the flow through the valve may be estimated

from the following:

LAрroЮ ј17:4 log10р_P=_PoЮ ю 22:5 log10рCgЮ

_ 32:4 log10р_pt=_stsЮ ю LрCЮ _ 24:4

(5-44)

The quantities in Eq. (5-44) are defined as follows:

_P ј pressure drop across the valve

_Po ј 6:895 kPa ј 1:00 psi

Cg ј valve-sizing coefficient for gas flow

_p ј density of the pipe material

_s ј density of steel ј 7800 kg=m3 ј 0:282 lbm=in3

t ј thickness of the pipe wall

ts ј thickness of the same nominal diameter SCH 40 pipe

The factor L(C) is a function of the pressure drop across the valve _P

and the inlet pressure to the valve P1. This factor is given in the following

expressions for some commonly used valve types:

188 Chapter 5

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(a) Cage-style globe valve, standard trim

LрCЮ ј

0 [for р_P=P1Ю _ 0:151_ 17:4log10р_P=P1Юю14:3 [for р_P=P1Ю > 0:151_

_

(5-45)

(b) Cage-style globe valve, whisper-trim

LрCЮ ј _7:5 [for р_P=P1Ю _ 0:563_ 87:0log10р_P=P1Юю14:2 [for р_P=P1Ю > 0:563_

_

(5-46)

(c) Guided-plug globe valve

LрCЮ ј

0 [for р_P=P1Ю _ 0:216_ 16:1log10р_P=P1Юю10:7 [for р_P=P1Ю > 0:216_

_

(5-47)

(d) Standard ball valve, swaged body

LрCЮ ј

0 [for р_P=P1Ю _ 0:093_ 9:4log10р_P=P1Юю9:7 [for р_P=P1Ю > 0:093_

_

(5-48)

The valve-sizing coefficient Cg for gas or steam flow is a dimensional

parameter. For gases other than steam, Cg is defined by the following

dimensional relationship:

QgрscfhЮ ј CgP1рpsiaЮЅрMa=MЮрTo=T1Ю_1=2 sin_ (5-49)

where:

scfh ј standard cubic feet per hour, or ft3=hr at To and Po

To ј 519:78R ј 288:7K and Po ј 14:696psia ј 101:325 kPa

T1 ј absolute temperature of the gas at the inlet of the valve

P1 ј absolute pressure of the gas at the inlet of the valve

Ma ј molecular weight of air ј 28:95g=mol

_рradiansЮ ј р59:64=C1Юр_P=P1Ю1=2

C1 ј Cg=CV

CV ј valve-sizing coefficient for liquids (dimensional)

Some representative values for the parameter C1 are given in Table 5-14.

The valve manufacturer should be contacted for data for a specific valve.

For mass flow of steam, the valve-sizing coefficient Cg is defined by the

following relationship:

mрlbm=hrЮ ј

0:0022CgP1 sin _

Ѕ1 ю р_sat=_Ю_1=2 (5-50)

The quantity _sat is the density of saturated steam at the upstream pressure

P1, and _ is the density of the steam at the upstream pressure P1 and

temperature T1.

Noise Sources 189

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5.10.3 Noise Prediction for Liquid Flows

The Fisher Controls correlation for the A-weighted sound level generated by

flow of a liquid through a valve is the following expression:

LAрroЮ ј10KL log10р_P=PoЮ ю 20 log10рCVЮ

_ 32:4 log10р_pt=_stsЮ ю Lр           Ю ю 9

(5-51)

The quantities in Eq. (5-51) are defined as follows:

KL ј

1 [for 0 _          _ 0:167_ 0:50 ю 3      [for      > 0:167_

_

(5-52)

where:

             ј

_P

P1 _ Pv

P1 ј upstream pressure

Pv ј vapor pressure of the liquid at the upstream pressure

The factor Lр   Ю is a function of the valve type and the pressure ratio            .

This factor is given by the following expressions for some commonly used

valve types:

(a) Globe valve, standard cage trim

Lр        Ю ј

0 [for 0 _          _ 0:34_ 48      р1 _ 1:86         Ю [for 0:34 <  _ 1:00_

_

(5-53)

190 Chapter 5

TABLE 5-14 Flow Coefficients for Various Valves

Valve type Description Body design C1

ј Cg=CV CV=ЅDрinЮ_2a

Globe Single port A 35.0 12.90

Globe Single port BF 32.0 9.67

Globe Single port GS 35.0 14.90

Globe Any valve plug D 30.0 10.32

Globe Single port DBQ 33.0 12.90

Angle Single port DBAQ 34.5 10.32

Angle Single port 461 18.0 12.90

Ball Hi-Ball V25 20.0 11.60

Butterfly Swing-through vane 758 open 30.0 28.3

aD is the inside diameter of the pipe in inches.

Copyright © 2003 Marcel Dekker, Inc.

(b) Ball valve

Lр        Ю ј

0 [for 0 _          _ 0:50_ 100    р0:70_ Ю [for 0:50 <  _ 1:00_

_

(5-54)

(c) Butterfly valve

Lр        Ю ј

10 [for 0 _        _ 0:24_ 95:6   р1_1:25           Ю [for 0:24 <  _ 1:00_

_

(5-55)

The valve-sizing coefficient CV for liquid flow with no flashing is

defined by the following dimensional equation:

QLрgpmЮ ј CVЅ_PрpsiЮ_w=_L_1=2 (5-56)

where:

_w ј density of water at the fluid temperature

_L ј density of the liquid

Some representative values of the sizing coefficient are given in Table 5-14.

The valve manufacturer should be contacted for data for a specific valve.

There are several other correlations that have been developed for prediction

of the noise from valves. Nakano (1968) obtained the following

relationship for the sound power level for a valve handling a gas flow:

LW ј A ю Blog10рmTFЮ (5-57)

where:

m ј mass flow rate of the gas, kg/s

T ј absolute temperature of the gas at the inlet of the valve, K

F ј 1 _ Ѕ1 _ р_P=P1Ю_р__1Ю=_

_ ј specific heat ratio for the gas

The constants A and B depend on the valve type. For a globe valve, A ј 90

and B ј 10:0; for a gate valve, A ј 83 and B ј 15:6; for a ball valve, A ј 97

and B ј 12:8; and for an angle valve, A ј 82 and B ј 13:1:

The A-weighted sound level generated by valves manufactured by the

Masoneilan Corporation has been correlated by an expression based on the

internal conversion of fluid kinetic energy into acoustic energy (Baumann,

1970). This method has been extended to other valves also (Baumann, 1987).

Example 5-6. Natural gas (molecular weight, 20.3 g/mol; specific heat

ratio, 1.252) flows through a GS globe valve with standard trim at a flow

rate of 14 _ 106 scfh (14MM scfh or 110.1 std m3/s). The natural gas enters

the valve at 300K (808F) and 4.250MPa (616.4 psia). The pressure drop

Noise Sources 191

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across the valve is 2.40MPa (348 psi). The gas flows through an 8-in SCH80

steel pipe, for which the outer diameter is 8.625 in (219.1mm) and the pipe

wall thickness is 0.500 in (12.7mm). The wall thickness of a standard 8-in

SCH40 pipe is 0.322 in (8.2 mm). Determine the A-weighted sound level at a

distance of 15m (49.2 ft) from the valve, if the valve is located outdoors.

For the GS globe valve, the parameter C1 ј 35, as given in Table 5-14.

The factor _ is needed in Eq. (5-49) is as follows:

_ ј

59:64

C1

_P

P1

_ _1=2

ј р59:64Ю

р35:0Ю

2:400

5:250

_ _1=2

ј 1:2805 rad

The valve-sizing coefficient for gas flow through the valve may be calculated

from Eq. (5-49):

Cg ј р14_106Ю

р616:4Ю sinр1:2805Ю

р20:3Юр300Ю

р28:95Юр288:9Ю

_ _1=2

ј 20,230

The pressure ratio term is as follows:

_P=P1 ј р2:400Ю=р4:250Ю ј 0:5647 > 0:154

The factor L(C) is given by Eq. (5-45) for a globe valve with standard trim:

LрCЮ ј 17:4 log10р0:5647Юю14:3 ј 10:0 dB

The A-weighted sound level at the reference distance ro is found from

Eq. (5-44):

LAрroЮ ј17:4log10р2400=6:895Юю22:5log10р20,230Ю

_32:4 log10р0:500=0:322Юю10:0_24:4

LAрroЮ ј 44:2ю96:9_6:2ю10:0_24:4 ј 120:5dBA

The A-weighted sound level at a distance of 15m from the valve may be

found from Eq. (5-42):

LA ј 120:5_20log10р15=1:424Ю ј 120:5_20:5 ј 100:0dBA

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