4. Calculating the noise emission

4. Calculating the noise emission

4.1. Sound development with control valves

The high sound emission from control valves which sometimes occurs with certain operating conditions results from the internal flow procedures which generate the fluid sound in the form of pressure and velocity pulses in the flowing medium (Flow conditions with control valves). These propagate themselves in the pipelines with the medium sonic velocity and induce mechanical vibration.

Fluid sound --> internal sound power

Solid-borne sound --> external sound power

Closed pipeline system

External < internal sound power

Air sound from external sound power

Open pipeline system (output into open air with gases)

External = internal sound power

Air sound from internal sound power

The sound radiation thus mainly comes from the pipelines and to a lesser extent from the valve body. An important sound measurement is therefore the internal valve sound power emitted into the pipelines. It is caused by subsequent flow procedures (throttling) inside the control valves.

With compressible flow media (gases and vapors)

Turbulence due to jet (turbulent flow) leaving the throttle cross-section ("vena contracta") at a higher speed leads to turbulence and relieves with wide-band noises.

When the sonic velocity is reached and the downstream pressure (relief above critical) further decreases, substantial sound level increases with a tonal character due to periodically varying compression thrusts in the ultrasonic range behind the throttling point (flow above critical section).

Superimposed noises occur due to flow speeds which are too high in the valve outlet cross-section (> 0.3 times sonic velocity) in particular due to relieves and compression thrusts in the diffusor-type extensions often used behind the valve (flow velocity in the return pipeline).

With non-compressible flow media (liquids)

Due to a pressure reduction to the vapor pressure of the liquid in the throttling point area vapor bubbles are formed which subsequently implode due to the pressure recovery (cavitation and flashing) which becomes noticeable as a sudden drumming noise when cavitation starts.

Medium-independent

Vortices (which periodically float away) form in the jet mixing area at high frequencies due to smaller differential pressures or flow volumes in the lower control range, amplified by resonance and feedback effects inside the valve (seal vibration) and in conjunction with the complete system; result: unpleasant whistling which is not acceptable in heating systems, for example.
These noises cannot be calculated in advance unlike those previously mentioned.

The internal valve parts can vibrate mechanically due to the excitation from the flow. This must be avoided because of the risk of destruction, for example due to double plug guidance with the vibration-prone parabolic plug or better due to a V-port plug with an additional guide in the seat and defined directive force radial to the plug axle which are almost always used with SAMSON linear control valves for valves > 10.

4.2. Important influencing variables on the height of the noise emission

The VDMA method 24422, 1979 version (old VDMA standard) will provide a clear overview and quick order of magnitude estimate for the noise emission.

Compressible media (gases and vapors), VDMA 24422 (1979)

Valve inlet pressure [bar abs.]

Valve inlet temperature [K]

Standard density , standard conditions

Pressure ratio or differential pressure ratio

Valve correction element (type), standard valves with special noise reducing measures = 0 dB

Pipeline correction element, , for nominal pressure 40 = 0 dB

Noise pressure level in [dB(A)] at 1m from the pipeline behind the valve

You can see that the sound pressure level rises with an increasing inlet pressure , increasing temperature at the inlet, with a larger differential pressure ratio x and increasing (mass flow). The noise level falls with higher standard density. The following picture shows typically measured sound level characteristics for linear control valves over the differential pressure ratio x., pressure and temperature are constant. The two level curves are for a standard valve with V-port plug and the same valve with the same value setting with a flow divider III as a noise reducing primary measure. When x=0.5, you can read off a noise reduction of .

This diagram also shows, however, that the effect of noise reducing measures in the valve can diminish substantially when there is a diffusor-type pipe extension behind the valve (outlet velocity) and Mach numbers in the valve outlet cross-section > 0.3. The noise reduction of elements such as flow dividers with increasing differential pressure ratio x normally increases so values of -30 dB can easily be reached. The valve sizing program takes these effects into consideration in the SAMSON standard noise calculation method.

Non-compressible media (liquids), VDMA 24422 (1979)

Valve inlet pressure [bar abs.]

Vapor pressure [bar abs.] (temperature-dependent)

Density at inlet [kg/m3]

Pressure difference ratio

value [m3/h]

Valve correction element (type), standard valves with special noise reducing measures = 0 dB

Valve parameter: z value (load-dependent)

Pipeline correction element, , for nominal pressure 40 = 0 dB

Noise pressure level in [dB(A)] at 1m from the pipeline behind the valve

cavitation-free

Cavitation

You can see that the sound pressure level rises with increasing difference between the inlet pressure and the vapor pressure as well as a larger differential pressure ratio and increasing value (mass flow). The noise level falls with higher density. The z value in the range 0 to 1 should be as high as possible.

The following diagram shows a typical sound level characteristic over the differential pressure ratio . value, pressure and vapor pressure are constant

Calculation and measuring results are shown.

Cavitation begins when the differential pressure ratio exceeds the valve parameter z value. There is a drumming noise which very quickly increases by 20 to 30 dB(A) compared with the sound level without cavitation. The sound level decreases again due to the decreasing bubble implosion pressure differential with increasing and due to the high medium compressibility due to increased internal vapor formation. It almost reaches the sound level which would result if you extrapolated the sound level curve in the turbulent area in front of the cavitation up to (flashing, constant vaporization on the downstream pressure side).

The diagram above shows that VDMA 24422 (1979) calculates a sound level which is too high in this area. Extensive measurements on the SAMSON test bench led to the following correction via .

When the downstream pressure falls below the vapor pressure , there is a further increase with asymptotic approach to a limit value due to the increasing velocities on the downstream pressure side with almost constant mass flow. SAMSON measurements led to the following equation:

The z value should not be confused with the American value above which vapor bubble formation starts in the core "vena contracta" jet and the quadratic flow characteristic no longer applies. This value is thus greatly linked to the FL value for pressure recovery (). When cavitation starts - defined by the z value to be determined acoustically - shearing layers with turbulence occur in the areas close to the jet edge. The vapor pressure is reached in the centers of these shearing layers. The vapor bubbles forming at the edge of the jet and not in the jet core are swept away to the downstream pressure side where they implode (see Cavitation and flashing). This condition does not yet conceal a risk of material destruction, this is only to be expected for but only for sufficiently high pressure differences 25 bar.

The following diagram shows that a considerable amount of incorrect information can be obtained when the value is used in the noise calculation equations instead of the correct z value.

Linear control valves have a relatively narrow or value range whereas the z value is more dependent on the throttle trim design. Standard valves without special noise reducing measures in the nominal size range have z values under z=0.35 at 75 % load. The z value can be increased substantially with linear control valves in particular by arranging the throttle geometry in a special way (e.g. in the form of the hydraulic diameter ).

4.3. Overview of noise calculation standards

The calculation methods used today apply to sound development from turbulence, compression thrusts and cavitation. A perfect model is not known.

In the VDMA guideline 24422 (1979) (section 4.2), a group of leading German control valve manufacturers and users from the chemical industry developed a simple, except for with limit ranges (relief into a vacuum or the open air, very small differential pressures) proven calculation method on an empirical basis for predicting the noise emission of control valves without particular sound reducing measures in the form of the sound pressure level to be indicated at 1 m away from the valve. Sound levels of low-noise versions calculated according to this can be corrected using the terms for gases and vapors and for liquids.

Planners of complex systems, however, frequently require the spectral distribution of the sound power converted in the valve and the connected system. As a result of this a completely revised version of the VDMA guideline was published in 1989 which starts with the internal sound power induced in the valve. The calculation of the frequency-dependent pipe transmission loss for the sound power emitted from the pipeline was taken from the VDI guideline 3733 (noises with pipelines).

This method was integrated for liquid flows in part 8-4 of DIN IEC 534. In 1994 an American method also based on the internal sound power like part 8-3 was implemented for gas and vapor flows.

All of these methods have their weakness at certain points, however the VDMA guideline 24422 (1989) in conjunction with the VDMA sound measuring guideline 24423 (1993) (measurement of the internal sound output) is best. This has been carried out by SAMSON AG due to extensive sound measurements (internal and external measurements with water, air and water vapor) over the last years.

The following sound calculation standards are thus available in the valve sizing program. The SAMSON standard method is always used first here. The necessary characteristic value suggestions in the program procedure are oriented with free entry, they are otherwise linked to the respective type when the SAMSON database is used. The SAMSON standard calculation method is virtually the VDMA guideline 24422 (1989) with inlet characteristic values adapted to measurements and additional modifications to the original equations which plainly deviate from reality (e.g. differential pressure-dependent, frequency distribution above all with liquids).

Compressible flow media (gases and vapors)

VDMA 24422 (1979)

VDMA 24422 (1989)

DIN IEC 534 Part 8-3

SAMSON modified on the basis of VDMA 24422 (1989) and VDMA 24423 (1993)

Non-compressible flow media (liquids)

VDMA 24422 (1979) variable over z, LF

VDMA 24422 (1989) identical to DIN IEC 534 Part 8-4

SAMSON modified on the basis of VDMA 24422 (1989) and VDMA 24423 (1993)

4.3.1. Internal sound power, throttle power and acoustic degree of conversion

The sound development path from the valve throttling point to the air sound via the pipeline system was described in the section on sound development.

The internal sound power is the sound power emitted into the pipelines from the flowing medium which can be measured, for example, across the pipeline interior cross-sectional area.

All new sound calculation standards such as VDMA 24422 (1989) and DIN IEC 534 now have one thing in common, i.e. that the internal sound power is proportional to the hydraulic throttle power is proportional. In accordance with Lighthill's theory an acoustic degree of conversion or efficiency has been introduced which should of course be as "fast" as possible in contrast to other technical applications.

This is ensured, however, by physics alone as acoustic degrees of conversion naturally have very low values approx. .

Due to the wide and unwieldy number range the logarithmic representation is usually chosen in the form of
so the upper value range is transformed to the value range -80 to -30 dB (logarithmic marking).

The acoustic degree of conversion depends on the valve style, various characteristic values as well as the differential pressure ratio.

The following two pictures show examples of SAMSON linear control valves for gaseous and liquid media (here for VDMA 24422 (1989) at 75% load.

The sound internal power can be calculated from the throttle power and the acoustic degree of conversion by changing the above equation around. The audibility threshold power 10-12 Watt is also used however with the power as reference sound power due to the low number values.

With critical gas flow, these internal noise power levels can be 140 dB and higher. This corresponds with a throttle power of 10000 Watt with a degree of conversion of -30 dB (critical flow).

The VDMA guideline and DIN IEC 534 differ in the calculation of the throttle power and the acoustic degree of conversion.

The throttle power is proportional to the product of . The differences will be clearer in the sections for the individual standards.

4.3.2. Frequency spectrum of the internal sound power

The calculation of the internal sound power from the throttle power and conversion degree refers of course to a particular frequency range (e.g. 500 to 8000 Hz with VDMA 24422 (1989)). The frequency spectrum is in some circumstances also required for the system planning.

The frequency distribution function F(f) is thus a quotient of the sound internal power proportion to the total sound internal power assigned to a frequency band with the average value f (e.g. octave). When logarithmic notation is used, the following results:

In accordance with Lighthill's theory the frequency distribution F(f) has a characteristic maximum in a range which changes with the differential pressure ratio x or the velocity of the jet leaving the throttling point (vena contracta) and its diameter Lighthill used the Strouhal number St common in flow acoustics for this.

He established that with sub-critical flow the maximum sound power is always in the range 0.2 to 0.3. The form of the frequency distribution function was always similar enabling it to be combined in a function F(St).

This means

the frequency of the maximum noise power proportion rises as the jet velocity increases or jet diameter decreases

when the jet velocity level is high (gases/vapors, left-hand branch of the frequency distribution function), the sound power proportion for a constant frequency with increasing or decreasing jet velocity

when the jet velocity level is low (liquids, right-hand branch the frequency distribution function), the sound power proportion for a constant frequency rises with increasing jet velocity or with decreasing jet diameter

Now the throttling point of a control valve is not a "circular hole" so you will also need a valve style correction factor which depends on the geometric shape of the plug and of the valve and of the valve body and on the valve position.

DIN IEC 534 Part 8-3 (gases and vapors) has simplified things here and uses the valve form factor which is also required for the valve Reynold number.

The Strouhal number for the sound power maximum changes for flow above critical with the differential pressure ratio. A peak frequency is always calculated from this parameter. The sound power and also the acoustic degree of conversion are assigned this frequency.

Measurements from SAMSON show that the correction factor can only be determined using measurements and cannot be simply calculated from geometry. It is also not necessarily the same as with flow calculation.

The velocities with gas and vapor flow are usually always so high that the maximum Strouhal number (depending on the frequency) in the frequency range concerned is smaller than 0.3 so the left-hand branch of the upper frequency distribution curve is decisive. Frequencies in the most sensitive frequency range of the human ear between 2000 and 4000 Hz are the main part of the sound power there as high frequencies do not reach the outside due to the pipe transmission loss.

VDMA 24422 (1989) uses a 3dB increase per octave mid frequency independent of the differential pressure ratio.

Due to the lower velocities in the vena contracta with liquids in the turbulent range the right-hand branch of the frequency distribution function is more important so VDMA 24422 (1989) calculates a 3dB fall per octave mid frequency here which is also transmitted to the cavitation range.

Extensive measurements from SAMSON AG show that this assumption is incorrect and that the frequency distribution depends considerably more on the differential pressure ratio as turbulence and cavitation implosion mechanisms overlap here. By introducing a modified Strouhal number for the cavitation range and separation of the two proportions you obtain similar characteristics for the frequency distribution function as Lighthill with pure turbulent flow.

This is looked at in more detail in the sections for the description of the individual sound calculation standards. The frequency dependent parts with and are also looked at there.

4.3.3. External sound power, external sound pressure level and pipe transmission loss

A control valve is connected to a pipeline system in most cases so the external sound power dependent on the internal sound power is converted into air sound.

The external sound power is smaller because the pipeline mass contributes to sound insulation which greatly depends on the frequency however.

The pipe transmission loss is thus defined as the relationship of the internal sound power to the external sound power. The sound pressure deviations (internal sound pressure level) of the flowing medium have an effect on the inside wall of the pipeline.

The sound internal power level is known to be related to the pipe inside cross-section. The internal sound pressure level is constant in the pipe internal volume on the condition that there is reflection freedom. The sound internal power related to the pipe inside coating is thus obtained using the surface ratio.

In logarithmic notation the pipe transmission loss in dB is obtained as

the difference between internal sound and external sound power level.

The pipe transmission loss is frequency-dependent with a pass-range which depends on the elasticity (pipeline material sonic velocity, with steel 5100 m/s) and on the diameter of the pipeline in the form of the ring expansion frequency.

The most important influence factors of pipe transmission loss are:

: Pipe material sonic velocity

Steel 5100 m/s

Plastic 2620 m/s

: Inside pipe diameter

: Pipe wall thickness

: Pipe material density

Steel 7800 kg/m3

Plastic 1200 kg/m3

Product of important}

Steel / plastic: 12.65

: 10 log(12.65) = 11 dB

The equations for pipe noise insulation from the individual guidelines or standards differ.

Once the frequency proportion of the external sound power has been determined, the total external sound power is calculated according to the following equation:

Individual frequencies are not used as a rule, but frequency bands in the form of octave mid frequencies (VDMA 24422(1989)).

The term stands for the so-called A-evaluation which takes the sensitivity of the human ear into consideration. This is identified by a and dB (A) for the total sound power. The human ear senses frequencies around 4000 Hz with objectively the same (measured) sound power, louder than at 1000 Hz.

On condition that there is reflection freedom in the space around the pipeline, the sound pressure level in [dB(A)] can be calculated from the external sound power .

The sound pressure level is measured as a rule 1 m () away from the pipeline. A pipe length of is taken into consideration with VDMA 24422 (1989) for gases/vapors, for example. A level for the sound pressure around 11 dB lower in comparison with the external sound power is obtained for a pipe nominal value mm.

With gas and vapor flow, the sound power is mainly transmitted from the pipe line behind the control valve as the higher flow speed in the pipeline at the point favors sound relaying.

With liquids, the sound is relayed almost equally in both directions except if there is extensive cavitation when the sound emission will be greater in the inlet pipeline.

4.3.4. VDMA 24422 (1979) for gases and vapors, equations

Valve inlet pressure [bar abs.]

Valve inlet temperature [K]

Standard density , standard conditions

Pressure ratio or differential pressure ratio

Valve correction element (type), standard valves with special
noise reducing measures = 0 dB, adaptable to measurements

Pipeline correction element, , for nominal pressure PN 40 = 0 dB

Noise pressure level in [dB(A)] at 1m from the pipeline behind the valve

Characteristics:

well suited for quick estimates for standard valves ()

no frequency information

no information on internal sound and thus for expulsion
into the open air (no pipeline)

Valve outlet mach number

4.3.5. VDMA 24422 (1989) for gases and vapors, equations

Jet power (throttle power)

Velocity in the throttling point (vena contracta), mach number , sonic velocity

critical differential pressure ratio xcr depending on xT value
(Source DIN IEC 534 Part 2-2 basics (flow capacity, paper by De Fillipis))

acoustic degree of conversion for sound emission in the frequency range
of fi = 500, 1000, 2000, 4000 and 8000 Hz

: Level constants : Gradient constants

Standard linear control valves:

Butterfly valves:

Adapting these valves using VDMA 24423 (1993, measuring standard)

internal sound power level in frequency range of = 500, 1000, 2000, 4000 and 8000 Hz

Internal frequency distribution = 500, 1000, 2000, 4000 and 8000 Hz

Pipe transmission loss ( = internal diameter from the maximum of the
internal diameter of and (pipe extension)

: Pipe material sonic velocity

Steel 5100 m/s

Plastic 2620 m/s

: inside pipe diameter, minimum of DN and D2

: Pipe wall thickness

: Pipe material density

Steel 7800 kg/m3

Plastic 1200 kg/m3

: Medium sonic velocity, outlet

: Medium density, outlet

: Valve outlet mach number

, however, in principle any length behind the valve

Characteristics:

detailed look at the physics

better detection of the limit ranges (e.g. relief into vacuum)

however, only applicable up to outlet mach numbers as old VDMA standard also

frequency dependence in 5 octaves

Internal sound power important for system planners
(e.g. sound absorber sizing, release into the open air)

Standard values correct for standard linear control valves with and 75 % load

4.3.6. VDMA 24422 (1979) for liquids, equations

Valve inlet pressure [bar abs.]

Vapor pressure [bar abs.] (temperature-dependent)

Density at inlet

Differential pressure ratio

Valve correction element (type), standard valves without special noise reducing measures = 0 dB, adaptable to measurements

Valve parameter: z value (load-dependent), from measurements

Pipeline correction element, , for nominal pressure 40 = 0 dB

Noise pressure level in [dB(A)] at 1m from the pipeline behind the valve

without cavitation

with cavitation

Characteristics:

well suited for quick estimates for standard valves
()

no frequency information

no information on internal sound and thus for
expulsion into the open air (no pipeline)

for : calculation of sound level which is too high, thus there is the following correction using LF in the valve sizing program

no information on flashing the following calculation in the valve sizing program:

4.3.7. VDMA 24422 (1989) or DIN IEC 534 Part 8-4 for liquids, equations

Jet power (throttle power)

Velocity in the throttling point (vena contracta)

acoustic degree of conversion for sound emission in the frequency range
of = 500, 1000, 2000, 4000 and 8000 Hz

without cavitation for

Level constants : Gradient constants

Standard linear control valves:

Adapting these valves using VDMA 24423 (1993, measuring standard)

with cavitation

Standard linear control valves: ,

Adapting these valves using VDMA 24423 (1993, measuring standard)

Internal sound power level in frequency range of = 500, 1000, 2000, 4000 and 8000 Hz

Internal frequency distribution = 500, 1000, 2000, 4000 and 8000 Hz

Pipe transmission loss ( = internal diameter from the maximum
of the internal diameter of , and (pipe extension))

: Pipe material sonic velocity

Steel 5100 m/s

Plastic 2620 m/s

: Inside pipe diameter, minimum of DN and D2

: Pipe wall thickness

: Pipe material density

Steel 7800

Plastic 1200

: Medium sonic velocity, outlet

: Medium density, outlet

, however, in principle any length behind the valve

Characteristics:

detailed look at physics

better detection of the limit ranges (), however, with higher vapor pressures level too high as VDMA 24422 (1979)

Frequency dependence in 5 octaves, not correct however (see SAMSON standard method)

Internal sound power information

Standard values , sound values clearly too low in some ranges

4.3.8. DIN IEC 534 Part 8-3 for gases and vapors, equations

Jet power (throttle power)

Velocity in the throttling point (vena contracta), actually contradicts DIN IEC 534 Part 2-2 (De Fillipis basic paper)

Mach number , sonic velocity

critical differential pressure ratio depending on value

further critical differential pressure ratios for classification in 5 regimes

with and

further mach number behind narrowest throttling point (ultrasound there)

acoustic degree of conversion for infinitely large frequency range and "internal valve", transmission to fluid in the pipeline under the assumption that 1/4 of the internal sound power is emitted there.

thus exhaust around 6 dB (see sound internal power below)

A: level constants B: Gradient constants

cannot be adapted to measurement, dependent on value

internal sound power level in complete frequency range

no frequency distribution instead only peak frequency
(Frequency where frequency distribution is maximum, see section on frequency distribution)

Regime | Condition | Level exp. A | Inclination exp. B | Mach number Ma | Stpeak
I |  |  |  |  |
II |  |  |  |  |
III |  |  |  |  |
IV |  |  |  |  |
V |  |  |  |  |

Pipe transmission loss ( = internal diameter from the maximum of the internal diameter of and (pipe extension))

Characteristics:

as with VDMA 24422 (1989) internal sound and external sound

acoustic degree of conversion , but not related to the pipeline,
to "valve inside" instead

Dependent on valve style via !!!

Calculated in 5 regimes (dependent on x)

Total efficiency for all frequencies

Conversion into pipeline on the assumption that 1/4 of the sound power is emitted into the pipeline

Degree of conversion, however, clearly too low

Frequency dependence only in the form of peak frequency

Strouhal number St

Valve form factor

Not all necessary information for system planners

Weakpoint: no information on internal sound measuring methods,
Correction only (external sound as VDMA 24422 (1979)),
pure theoretical methods

Pipe transmission loss similar to VDMA 24422, equations diiferent however

Valves with flow dividers I, except for III, cannot be calculated

4.3.9. SAMSON standard method with gases/vapors (based on VDMA 24422 (1989))

Equations as VDMA 24422 (1989) in principle however with modifications based on approx. 500 air sound measurements (internal and external sound)

constants for describing the degree of conversion

adapted to measured degree of conversion in the range

variable with differential pressure ratio x above all for x<0.2 as otherwise sound levels which are too high are detected, old VDMA standard gives result which is too loud here!

Taking the influence of higher mach numbers into account with pipe extensions behind the valve on the acoustic degree of conversion due to overlapping of a second sound source (diffusor) based on numerous measurements

exact determination of the frequency distribution, furthermore calculation of the octaves 31.5, 63, 125, 250 and 16000 Hz, a list of the equations would take up too much space here.

Pipe transmission loss equations modified because the standard VDMA guideline calculates pipe transmission loss which is too small.

4.3.10. SAMSON standard method with liquids (based on VDMA 24422 (1989))

Equations as VDMA 24422 (1989) in principle, however, with modifications based on approx. 1500 water sound measurements (internal and external sound)

Adapting to measurements

Adapting to measurements

more exact frequency information on frequency distribution functions with valve shape factors specially adapted to measurements
(see frequency spectrum)

Detecting influences with for higher vapor pressures

Detecting flashing

4.3.11. Basic acoustics

What is sound ?

In air, fluid or solid body:

Pressure variations

Velocity variations

Sound power in measuring surface

In the case of continuous operation (e.g. no expulsion valve) with very high Mach numbers in the valve outlet and pipe extensions behind the valve in some circumstances use of fixed restrictors in the diffusor to raise the pressure, the large pipeline having to be large enough for the Mach number there to be less than 0.3.
The fixed restrictor steps should be calculated as flow divider I (Type 250) () if they have the same hole pattern (hole diameter 3 mm, hole spacing 5 mm), otherwise as standard valve with )

As in the science of electricity, the individual particles experience resistance here in the form of pressure variations when they vibrate at the velocity . The impedance is used as a measurement for this.

If there is reflection freedom in the sound space (space filled with air, pipeline filled with water) this impedance depends on the density and the sonic velocity of the medium,. i.e.:

This product is a measurement for the elasticity of the medium. A high sonic velocity (e.g. non-compressible liquids such as water 1200 m/s) means a low elasticity or a high sound resistance (impedance).

The sound power with reflection freedom is:

All sound calculations with control valves have this condition as a basis because as a rule the reflection conditions in the space and in the pipeline are unknown. Depending on the reflection conditions and depending on the frequency range, the calculated sound power can now be smaller or larger.

Due to the wide number range of the value the logarithmic notation will be used with different reference sizes.

Sound power level 1 Watt = 120 dB

Sound pressure level 1 mbar = 140 dB

Connection between

4.4 Recommandations for sound problems

4.4.1. Frequently asked questions

Are several valves connected in parallel or in series ?

n sound sources supply respective sound power level

externally:

Total sound power

Example: 2 equal sound power levels with ,

Result approx. 10 log(2) = 3 dB increased sound power

If the sound level is required at a greater distance, will the sound pressure level at 1m distance be at all relevant ?

(e.g. expulsion into the open air and residential area at distance S=500 m)

at a greater distance S valve as globe spotlight or normal spotlight:

Example: , how large is at 1 km distance?

Is there thermal insulation ?

maximum noise reduction 5 to 8 dB

Is acoustic insulation perhaps planned ?

acoustic insulation up to 25 dB sound level reduction

pipe sheathing S 100 mm here

4.4.2. Primary sound measures in valves with gas and vapor flows

Sound essentially influenced by velocity in throttle cross-section or by pressure difference.

One possibility: multi-stage pressure decrease

several control valves in series

multi-stage plug inside housing (SAMSON type 256)

fixed restrictors (however only optimally effective with maximum amount)

however, normally not the desired effect with compressible medias very high velocities occur even before the critical flow in a stage is reached

Better additional elements such as flow dividers I or III with linear control valves

Jet distribution and flow stabilization principle

Jet distribution leads to small valve shape factors Fd or small jet diameters so the frequency maximum is shifted to higher frequencies (interference principle) and the definitive frequency range 500 to 8000 Hz has a smaller part of the same sound power (see frequency spectrum).

4.4.3. Primary sound measures in valves with liquid flows

Sound essentially influenced by cavitation

Highest possible z value

One possibility: multi-stage pressure decrease

Several control valves in series

Multi-stage plug inside housing (SAMSON type 256), however only small nominal sizes, e.g. 5-stage:

Fixed restrictors (however, only optimally effective with maximum amount)

Special plug with specially sized geometry in view of cavitation freedom on request

No measures possible with flash operation () fixed restrictors behind valve can lead to cavitation operation (!)

Cavitation has not only risk of sound, but also possibly material destruction

in continuous operation with and
(with linear control valves > 0.73)

otherwise no special measures if no sound requirements

advantageous:

reduced seat bore

no gray cast housing

with : stellited plug

with : hardened plug and seat (1.4112)

with starting condition (boiler drinking water valve)

Angle-type valve without/with fixed restrictors, flow in closing direction (actuator quantity!) and complete opening during start when the greatest pressure difference should be expected

Possible parallel operation of valves (stepping) each with open or closed valve in front and behind