Which Silencer Is Right for You?

Today’s article is a guest article submitted to us by Ron Burg of Mahan’s Thermal Products, experts and specialists in heat exchanger and silencer technology. It is a very good general overview of the choices in silencers, and we encourage you to visit their website. We hope you find it interesting:


No matter what industry it is or which application is being used, utilizing heat exchangers and other types of thermal products in your facility can make noise control an issue. Fortunately, there are many ways for you to cut down on sound attenuation in order to create a better work environment.


There are many different types and models of silencers. If you need assistance selecting a silencer, reach out to trusted professionals such as Mahan’s to help guide you through the process. Six main types of silencers are included below.

Absorptive Silencer: With its classic dissipative design, the absorptive silencer absorbs noise energy through its many types of fibrous packing materials. When sound waves travel through the areas between the fitted fibers, the noise is dissipated from the viscous friction. Absorptive silencers work well on high noise frequencies between 500 and 800 Hertz. Anything above or below this amount, and the silencer will not be as effective.

Blower Silencer: These types of silencers are frequently used in wastewater treatment facilities and industrial processing facilities. Blower installations are typically noisy, making blower silencers essential. When choosing a blower silencer, consider the size and proper type for the application. These two aspects are critical for effectively reducing noise. The size of the blower should be based on gas volume alone, while the design of the silencer must be chosen with the blower size and operating speed in mind.

Engine Exhaust Silencer: Exhaust silencers come in a variety of styles and configurations, and have different attenuation grades. While you can create custom engine silencers, there are also standard styles that you can choose from. Puck-style silencers and low-profile silencers are great for places with minimal vertical space. Puck-style silencers are shaped like a hockey puck. Low-profile silencers are shaped in a rectangular fashion and are best for engines with dual exhaust turbos spaced far apart. Because of their rounded side panels, low-profile silencers are excellent for acoustic performance. Puck and low-profile silencers can come in residential, critical, and hospital attenuation grades.

Industrial Fan Silencer: Many process plants and industries require air fans, force draft fans, and induced draft fans, and they usually need some sort of acoustical treatment to fit into OSHA requirements. There are silencers for all fan types, and many are cost-effective, thanks to computer-enhanced technology. The advantages of each type of fan silencer depends largely on the application, pressure drop, and how much space is available.

Vacuum Pump Silencer: These types of silencers are used to eliminate liquid from gas flow vacuum systems by using liquid ring vacuum pumps or rotary positive blowers. Vacuum pumps are usually loud and require a high-performance silencer.

Vent Silencer: Vent silencers are frequently seen in oil and gas facilities and also in chemical processing heat recovery systems. These systems usually require a pressure relief valve (PRV) and need a vent silencer to effectively silence high-velocity air, steam, and gas vents. Vent silencers can be easily customized to fit any system.



Since 1969, Mahan’s Thermal Products has strived to provide quality production and sale of heat transfer equipment. Mahan’s is dedicated to taking care of its customers at all times and values the long-term relationships it has established with dedicated clients. Whether you need cleaning, repair, or building services or are looking to purchase a superior product at a competitive price, Mahan’s can assist you with your thermal product needs.


Pyrometers and Exhaust Gas Temperature



Exhaust gas temperature (EGT) is probably one of the most important leading indicators of engine failure. A pyrometer is a device that can indicate the temperature of gasses at different points along the engine’s exhaust system. Therefore, in order to get the best diagnostic information from pyrometers, they must be positioned or mounted at the proper locations along the exhaust system, since temperatures will vary along different points.

Pyrometers can help diagnose the following conditions, prior to severe engine damage:

  • Cooling system problems
  • Combustion problems (air / fuel mix)
  • Fuel system problems

Note that by “problems”, we mean catastrophic, replace the engine problems.

A good example of this temperature variance is with the turbocharger. Exhaust gas temperature can indicate problems with the turbocharger, so a pyrometer placed before and after the turbocharger will give an indication of potential for failure. Between intake and out, the temperature differential can be 300 degrees C or more.

However, MarineDiesel uses Variable Geometry Turbochargers (VGT) with its’engines. As the inlet varies in size, the temperatures will normally fluctuate as the aperture of the turbocharger changes shape. Therefore, how is change in temperature a leading indicator? Simple. What you are looking for is temperature anomalies, outliers, or changes over time. Your engine manual gives an indication of the proper temperatures and the levels that should be present. Actually, this becomes an issue more with experienced engineers. They have the knowledge of one or more engines, but every engine manufacturer designs their engines differently, and the ratings are different, meaning temperatures will be different between manufacturers make and model. Hence, the standard “refer to the manual” line, cliche though it may be. With most engines, the exhaust gas temperature should range, normally, from 500 to 700 degrees C. Again, this will vary.

Also important to note: Engines are tested and rated in factory test cells, where conditions are constant. In the real world, vessels operate in a wide variety of conditions, climates, and use. Heavy loads typically mean higher exhaust gas temperatures. These all have an impact on exhaust gas temperature, and adjustments to what is “normal” are required under differing conditions.

Another indication provided by pyrometers is that of emissions. Exhaust gas temperature can help diagnose incomplete combustion and non-compliance of emissions.




What is Marinization?



What is marinization?

A diesel is a diesel, right? It should work just fine whether you use it in a boat or a car.

This question occasionally comes up in inquiries to our parts department.

In theory, at least, any diesel engine should operate on any vehicle, land or sea. However, in the years we have been in the marine business, we have never seen one of these independent project come to a successful fruition. The normal scenario is that someone is either given, or has picked up very cheap, an old diesel automobile or truck engine, and they come to us when they cannot get it working.

Marinization is the engineering and manufacturing of engines specifically for marine use.

What are the differences between marine and land engines? There are many. However, the following systems are nearly always different: Cooling, exhaust, and gearbox.

Marine engines need to be liquid cooled. That means that they use a heat exchanger instead of a radiator. As has been written many times before on this blog, heat is an engine’s worst enemy, and the heat produced by combustion must be dispersed effectively in some manner.

As to exhaust, engines used on land typically use a dry exhaust system. Try this on the water and you will have a very noisy engine, indeed. A big issue with wet exhaust systems is that they typically require modified cylinder heads in order to function properly. That old school bus engine most certainly would require new cylinder heads.

Transmissions, or gearboxes, are another issue. We refer back to the old school bus engine. Though you might save a little on the engine, you will need a marine gearbox with proper ratio in order to use that engine on the water. Gear ratios for marine engines are substantially different than on land.

Electronics and electrical systems are also substantially different on marine engines. Something often overlooked is the need for a new control panel, since all of the gauges will be different. Wiring suitable to the marine environment is also necessary. Add in the fact that if the engine to be marinized is electronic, the ECU programming will be completely different. This problem can become extremely expensive to correct, and normally cannot be done by the average person or mechanic.

This brings us to the environment, in general. Marinized engines use components that are manufactured from non-corrosive metals and alloys. Engines used on land are not.

When all of the above is added up in the decision making process, that bargain engine most likely will not turn out to be as big of a bargain as it may seem. In our experience, nearly every one of these projects has resulted in very expensive failures.

Marinediesel has spent the money in properly engineering the marinization of our engines. We have already made the mistakes. We have engineered a bonafide marine engine, suitable for use on boats.

That is the definition of marinization and a very brief explanation about the steps necessary to accomplish the goal of diesel use on water.




Maintenance Tip of the Week – Exhaust Temperatures 11/03/2014


Maintenance Tip of the Week

Pay close attention to exhaust temperatures. Never ignore system alarms or faults. Exhaust temperature is a primary indicator of cooling or combustion problems and incorrect temperatures indicate that immediate attention is required.






Engine noise is often one of the most critical criteria demanded by MarineDiesel customers. With military or government users, reduced noise is often essential to the successful completion of missions. On commercial or recreational projects, noise has an enormous impact on passenger or crew comfort, and is often regulated in some areas. Few things can be as irritating as being stuck on a boat with a noisy engine.

All engines produce noise to some degree. It is the level of noise that is critical.

Silencing equipment, vibration, engine mount type and quality, insulation, combustion, and the length and type of exhaust all impact noise levels. Vessel speed and sea state have an impact. Indeed, even the material of vessel construction has an effect, since metallic hulls produce more noise than resin or grp hulls.

Controlling noise starts with the engine. Reducing vibration will always result in lower noise levels. Using the proper engine mounts goes a long way towards controlling noise. At MarineDiesel, we have the facilities that allow us to test and control noise by duplicating real-world conditions. We often will test multiple silencers, engine mounts, or exhaust layouts exactly as they will be constructed on-site. This allows us to make changes to not only the type of equipment, but to the engine itself that can mitigate excessive noise.

This engineering goes beyond simply using one brand of silencer over another. In fact, we can let the customer know exactly how the noise can be controlled.

We have designed engines and exhaust systems that produce under 50 dB of noise at 2 meters. This is impressive by any standard.

This service and capability is one thing that sets MarineDiesel apart from our competition.

This engineering and quiet operation is one of the first things that our customers tell us when they sea trial. MarineDiesel manufactures one of the quietest engines in the market.


Maintenance Tip of the Week – Exhaust 09/01/2014

Maintenance Tip of the Week 09/01/2014

The entire exhaust system must be checked for dents, holes, restrictions, and air flow. If there is power loss, then most likely there is an increase in vacuum back pressure causing the power loss. The silencer may have been mismatched, and that could also restrict the air flow.


Maintenance Tip of the Week – Exhaust 05/26/2014


Maintenance Tip of the Week


Always check the exhaust system for dents and blockages. Restricted air flow in the exhaust system can trigger fault codes or seriously hamper performance.

Ask Professor Diesel 04/28/2014 – Engine Noise


This week’s question comes from Ibrahim in Indonesia about engine noise

Dear Professor Diesel:

We installed your MD170 engines two years ago, and they have been working great. However, recently, they seem to be very noisy. Is this normal? Are there ways to correct the problem?


Engines can get noisier over time, especially with heavy use. The reasons why can come from a variety of sources:

  1. Vibration over time loosens bolts, fasteners, and belts
  2. Fuel and oil filters have not been changed according to the schedule listed in your manual, or you have been operating with dirty fuel
  3. The engines are using the wrong fuel
  4. Oil has not been changed
  5. The engine timing is off
  6. The injectors are dirty

With the limited information you provided, it sounds as if your engine is ready for overhaul. How long has it been since this was done? If the engine was recently overhauled and mechanical causes can be eliminated, a variety of noise reducing methods are available, such as:

  1. Insulating the exhaust.
  2. Adding silencers.
  3. Changing the exhaust configuration.


If you have a question you would like to ask Professor Diesel, simply fill in the form below:


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