Stack Vibration Dampers
Vortex Shedding

Frequently Asked Questions

Will the water freeze?
Is the Damper shipped full of fluid?
How will I know if the Damper is leaking fluid?
Will the fluid cause corrosion?
Is this device patented?
Is the damper shipped from France?
What if the damper does not work?
Does Meca's software handle dampers?
What damping ratio should I expect with a damper?
What if I have a hot stack?
Can a damper be used on a Flare?
Why use a damper instead of strakes?
Can a damper decrease my along wind loads?
How is the Multitech damper different than other dampers?
What is the cost of a damper?
What do Stack Software and Dampers have in common?
Will the water evaporate?

 

 

 

Will the water freeze?
A mixture of water combined with antifreeze is recommended with each design. Combining water with antifreeze with water will allow the damper to work well in very low ambient temperatures.

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Is the Damper shipped full of fluid?
Typically the damper is shipped empty. The customer is then responsible for filling the damper with the recommended mixture of water and antifreeze.

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How will I know if the Damper is leaking fluid?

During fabrication a pressure test is performed to ensure that the damper will hold product under atmospheric conditions. In addition, the damper is designed with at least two (2) chambers so that even if one fails the other chamber(s) will provide adequate damping. If the owner sees signs of a leaking damper, at the next opportunity it is recommended that a closer inspection of the damper be performed. It is worth noting, that Multitech's Engineers have been involved with over 200 installations of this design and have not yet experienced a damper leaking fluid.

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Will the fluid cause corrosion?
Some corrosion will be experienced, as is expected with all carbon steel. However, only modest corrosion rates have been witnessed on damper installations. The only required maintenance on a damper is to check fluid level every 3 to 5 years.

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Is this device patented?
Yes there is an international patent on this damper design.

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What if the damper does not work?
In over 200 installations, there has not been an instance where the damper did not work. The most critical aspect of designing the damper is to collect good information about the stack and surrounding structures from the client. We have the responsibility of communicating with the clients and ensuring that accurate information is obtained. To aid in this effort we have created a data sheet which clients can complete to ensure all applicable data is communicated.

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Does the software handle dampers?
There is a template within Stackdes, which enables our Clients to simulate the effects of a damper on their stack. Simply follow these steps: a) Model the stack within Stackdes. b) If vibration is expected email the Stackdes file to Meca for a free evaluation c) We will size the damper d) The size, weight, and new critical damping ratio will be communicated back to the client. e) With this information, the Engineer can quickly see the impact that the damper has on the structure. f) At No Charge, we will help you optimize your design by the use of a damper.

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What damping ratio should I expect with a damper?
Damping ratios up to 0.035 and up can be achieved, with the average being about 0.02. If needed, the damper can be designed to provide much greater damping. The damper size and effective additional damping are custom designed each time to provide the most economical solution.

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What if I have a hot stack?
In the case where the stack shell is hot, > 180 Deg. F, some special precautions must be taken. The damper will be designed so that there is a gap between the shell and the damper, to essentially break the thermal bridge. We do not want the damper to exceed the boiling point of water, which would cause the damper to experience internal pressure. By breaking the thermal bridges we ensure that the temperature will stay below the boiling point.

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Can a damper be used on a Flare?
Flares can generate high temperatures on the steel due to radiant heat. Since it is undesirable to have the fluid exceed the boiling point of the water, we must protect the damper from this radiant heat. This is done by putting "radiation shields" on the damper. These radiant shields act as sacrificial elements which do not allow the flame to have a direct line of sight to the damper.

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Why use a damper instead of strakes?

Strakes increase the shape coefficient on the upper 1/3 of the stack from 0.7 to 1.4. This doubles the loads on the upper portion of the stack, which can cause the entire stack and foundation to become significantly more expensive. A damper adds some dead load and wind load, but it is usually not a significant impact to the stack. There are some instances (Scruton Number < 8), where strakes are not a recommended solution. In this instance, only a damper will be sufficient. In addition, strakes should not be used when interfering stacks exist. In nearly all cases, Our Dampers will be much more economical than Strakes. If you would like to find out which option is best on your stack, we will do a free comparison.

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Can a damper decrease my along wind loads?

Yes. The damper increases the damping in the structure, which is represented in many codes by the structural damping coefficient (Bs). Some Codes, such as ASME STS-1-2000, take Bs into account when calculating wind loads. If Bs increases, the wind forces will decrease. Often the decrease in wind loads can be significant enough to offset the cost of the damper.

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How is the Multitech damper different than other dampers?
Our design uses fluid, where other designs typically use a moving mass with springs. Multitechs design allows the damper to double as a platform, or as a gangway (for multiple stacks). In addition, the design is less expensive because the damping medium (Water+Antifreeze) is far less expensive than a damping medium of steel.

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What is the cost of a damper?
The costs vary greatly, depending upon the complexity of the design. However, we guarantee you that our damper will be the least expensive damper that you can buy. If you contact us, we can provide you with a free evaluation and quote. If a damper is not the best solution for your problem, then we will tell you. Our goal is to give you all of the information that you need to make an informed decision.

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What do Stack Software and Dampers have in common?
So you may be asking, how is a company that provides stack software in the damper business? For starters, We have the largest user base for stack design software of any company in the world. Our users have provided us with a lot of valuable feedback concerning the issues they face in stack design. Two of the biggest problems Stack designers face are 1) How do you analyze cross wind vibration? 2) What to do when you encounter a vibration problem? We have devoted significant time and effort towards solving the first problem. With our Stackdes software, we have provided an easy and reliable method to analyze stacks for cross wind vibration. But once you realize you have a vibration problem what do you do? All too often, the solution has been to either redesign the stack (to be heavier) or add strakes. Both of these options often come at a significant cost. We have found that in contrast we can often add a damper for little or no cost, because of the offset savings from the benefits of the design (i.e. reduced wind loads, platforms, etc..) Since our Stackdes users have already taken the time and effort to model the structure, we do not have to take the time to re-invent the wheel. The Engineer simply emails us their input file, and we can hit the ground running. This streamlined system allows us to provide evaluations and quotes quickly to our customers.

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Will the water evaporate?
The damper chamber is completely sealed, so no evaporation occur. There is a threaded fill cap that enables fluid to be added if necessary.

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