Silencers

Silencers are delivered in many different designs and types, dependent on the application and required sound reduction. Alara-Lukagro delivers, among other things: We dispose of advanced calculation programmes, laboratory measurements and measurements in practise which will help us select the optimal silencer for you. During this process, the attenuation spectrum, capacity, aerodynamic resistance, streaming sound, temperature, pressure, medium, pollution, type of material and obviously the price/quality ratio should be taken into account.

Absorption silencers

Absorption silencers Absorption splitter silencers can be delivered in both rectangular and cylindrical shapes. The rectangular silencers are provided with sound absorbing splitters. The cylindrical silencers are designed with or without edge absorption, with or without sound absorbing cores or with splitters. They are filled with glass wool, heat-resistant basalt wool and/or metal- or propylene wool. In order to protect the absorption material, perforated plate, glass coating/film, wire netting or synthetic foil is applied, all depending on your particular wishes. To reduce the pressure loss, the splitters can be provided with aerodynamically shaped leading- and trailing edges.

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Cylindrical silencers type AL-C

Cylindrical silencers type CD For application in, for instance round air ducts, chimneys and pipes, Alara-Lukagro offers you a complete series of cylindrical silencers and sound absorbing cores. Dependent on the required attenuation, flow rate, available length and the acceptable loss of pressure, a silencer with or without sound absorbing core (K) can be selected. For mounting in existing ducts, separate absorbing cores are available.

Standard lengths of the silencers and cores are: 500 mm, 1,000 mm and 1,500 mm. The cores are provided with mounting clips and can be applied directly onto the existing duct. The silencers can be delivered with a connection as desired:

The nozzle attachment is a rapid, simple connection by means of which the silencer is slid directly onto the duct. Flanges are mostly applied if a more solid connection is required. In that case, a selection can be made from different standard flanges. When crosscut attachments are used, the silencer is provided with a flat surface on both ends in which nuts have been applied according to a specific pattern. This way of attachment guarantees a solid construction and only requires a minor depth to build it in.

As a standard, the silencers are manufactured from sendzimir galvanized iron with ribs in the outer cover for additional firmness. The high-quality absorption material is not inflammable (Fire Class A1 in conformity with EN 13501-1), not hygroscopic, provided with a glass coating and covered with a sendzimir galvanized perforated plate. Upon demand, we are able to manufacture the silencers from other materials as well, for instance several qualities of stainless steel and aluminium. Optionally, we can provide the outer cover with a wet paint coating or powder coating in a standard RAL-colour, as desired.

In addition to silencers with standard dimensions, we are also able to deliver silencers according to your specification. Please contact our office in Groot-Ammers for possibilities and prices.

Pressure loss
Every type of silencer will cause flow resistance, which in turn causes pressure loss. The cylindrical silencers without core will cause a negligible pressure loss, namely an identical pressure loss as a duct with the same length and diameter.

A sound absorbing core will limit the free drain of a duct, as a result of which a larger loss of pressure will take place. The loss of pressure is, among other things, dependent on the air flow but is influenced by turbulence as well. For an optimal air conductivity, all Alara-Lukagro cores have been provided with aerodynamically streamlined head.

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Splitter silencers type AL-G

Splitter silencersThe range of rectangular splitter silencers has been developed after years of testing in labs and practical research based on application criteria. Alara-Lukagro disposes of calculation programmes with which the optimal silencer can be selected based on: Applications: A survey of the range of silencers, including specifications and test results, is available. Please use the application form on our contact page.

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Blow-off and start-up silencers (venting silencers)

Blow-off and start-up silencersThe blow-off and start-up silencers have been developed to reduce noise during the venting of steam and gases. The principle is based on a combination of controlled expansion and sound absorption. In the expansion part, the venting pressure is reduced to practically atmospheric conditions. During this process, a natural transformation takes place from a low frequency to a high frequency sound. Subsequently, the remaining high-frequency sound is reduced to the required level in the absorption part. The pressurized parts are designed, calculated and manufactured in accordance with the regulations of, for example the Steam Vessel Inspectorate, ASME, TÜV and British Standard.
Alara disposes of calculating programmes with which the optimal silencer can be selected based on: Types: The silencers can be manufactured from many different materials, for instance: Applications behind: Use our contact page to receive the required information in a simple way.

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1/4 wavelength vibration silencers

vibration silencersThe 1/4 wavelength vibration silencers are developed for gas flows in which more than 50 mg/m3 is transported. The splitters consist of chambers with a depth, corresponding with 1/4 of the wavelength of the main interfering frequency, as a result of which the sound in this frequency is 'extinguished'. By varying the depth of these chambers, the reduction can be attuned to the disturbing frequencies in the sound spectre. To 'broaden' the attenuating spectrum, a number of combinations is possible. Due to the vibration principle, the splitters possess a seemingly self-cleaning effect and pollution is limited to a minimum this way.
Alara-Lukagro selects the optimal silencer based on: Applications: Please use our contact page to receive the required information in a simple way.

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Hydraulic pulsation dampener type HPD

Hydraulic pulsation dampener type HPD Small variations in the streaming flow rate are always present immediately behind an hydraulic pump, caused by geometrical variations in the displacement volume of the pump and compression effects in the hydraulic liquid. These pulsations are transformed into pressure variations in the pressure pipe of the pump and cause pressure waves in your hydraulic system. These pressure variations could result in a strong sound radiation. Obviously, sound-proofing measures can be taken but the most effective solution is to solve the cause of the problem: the application of hydraulic pulsation dampeners.

The HPD pulsation dampeners are based on the expansion chamber principle, provided with a single or double chamber dependent on which type of dampener is selected. The type with a single chamber is provided with a so-called 'tuning pipe' that resists resonance by means of stationary waves. The type with the double chambers is located in a pipe in between both chambers. Both the single- and the double chamber version provide you with a very high attenuation level, during which the pressure level has a relatively small effect on the amplitude behind the dampener.


dimensions hydraulic pulsation dampener type HPD

pressure flow dimensions [mm] weight conn.
[bar] [l/min] A B C D E F G H I J [kg] [-]
160 40 502 215 160 450 340 55 72 65 70 - 10 G ½"
250 60 1.030 215 915 - - - - 67 75 - 16 G ¾"
250 140 828 320 - 710 560 - 134 48 75 114 24 G 1"
250 200 1.130 320 - 990 - - 165 48 75 114 35 G 1¼"
250 300 1.132 320 - 990 - - 165 48 75 114 36 G 1½"
350 60 1.030 215 915 - - - - 48 89 114 32 G ¾"
350 140 822 320 - 710 560 - 165 48 89 114 41 G 1"
350 200 1.130 320 - 990 - - 165 48 89 114 60 G 1¼"


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Transformation silencers

Silencer for venting off steam and gases
A transformation silencer has been developed to allow large quantities of gas to be vented over brief periods of time causing minimal sound production. The principle of this silencer is based on the 'transformation principle'. The gas is vented through large numbers of tiny holes. Venting causes a high frequency sound, but most of this is located in the ultrasonic frequency range and is therefore inaudible to the human ear. Dependent on a possible hearing problem caused by damage or age, people are sensitive to frequencies up to between 10,000 and 16,000 Hz. During venting with transformation silencers, the peek frequency is located at approx. 40,000 Hz. In reality, the noise is not silenced, it is only the spectrum of the venting sound that is transformed to higher frequencies. As the human ear is not sensitive to those frequencies, that part of the sound energy is not only inaudible but harmless as well.

Transformation silencer This type of silencer is successfully applied during venting off steam, pressurized air, CO2 and other clean gases. Only in case a polluted medium is used, attention has to be paid that the minute holes in the silencers are not obstructed.

In general
High noise levels are caused during venting off steam or gases, usually for brief periods of time. Since industrial venting takes place during both day and night, and in populated areas as well, specific requirements exist for the maximum allowable sound level during venting. As the required attenuation has to be combined with a relatively brief venting time, this always requires large and expensive constructions. If a transformation silencer can be applied, the same result will be achieved at much lower costs. With transformation silencers, an insertion loss (i.e. the difference in sound level with and without silencer, measured on the same place and under the same circumstances) from 20 up to 40 dB(A) can be realized. If, in addition, an absorbing outer cover is added, the maximum transmission loss could increase to more than 60 dB(A). The largest silencer built so far, based on the transformation principle, has a capacity of 300 t/h with an attenuation of 55 dB(A).

Construction
The transformation silencer consists of a pipe that is sealed at one end, usually with a diameter equal to the venting pipe. The inner side of the tube is provided with a large number of tiny holes with precise diameters. The pattern, number and diameter of the holes are determined by the required insertion loss and possibly the venting time. Therefore, practically each silencer is calculated separately.

With most common silencers, the gas is smothered first and the noise that is caused during this process is reduced by sound absorption. With a transformation silencer, the same attenuation can be achieved with much smaller dimensions. This results into a lower weight and the silencer can be manufactured at relatively low costs. The transformation principle also makes it possible to design a silencer with virtually no pressure loss. In principal, this silencer can be designed in such a way that the pressure loss of the silencer is negligible. This is particularly important when the silencer is mounted behind a safety valve. The very limited dimensions and, as a consequence, the low weight, enable the silencer to be applied immediately onto the venting pipe without a supporting construction. As a standard, the silencer is made of stainless steel. Due to the simple construction, without the application of porous sound absorption materials, matters like weathering and pollution are practically excluded. As a result, the silencer is extremely durable and suitable for hygienic applications.

Possible varieties
The diameter of the silencer can be adapted to that of the venting pipe. Due to the construction, this silencer is suitable for pipe diameters up to 125 mm.

The connection can be performed with a threaded nipple or with a flange, dependent on the customer specification. Next to stainless steel, the silencer can also be manufactured from other high-quality steel alloys, such as Monel, Hastelloy, etc.

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