Genset AV-Mounts - Spring Based or Elastomeric Rubber Based?

We have many of our esteemed customers discussing the Best Anti-Vibration mounts for Diesel Generators. Here, we try to look at the options available and provide comprehensive study and results based on our experience with large OEM manufacturers.

Basically we have found that there are 2 types of vibration mounting systems for Diesel Generators:

★ Spring Based AV Mounts.

★ Elastomeric Rubber Based AV mounts.

Spring Mounts are basically AV Mounts which have metal enclosed body and a single spring or a collection of springs inside for vibration damping. Some Spring AV mounts would also have some damping fluids for achieving faster damping characteristics.  The Spring AV Mounts would have some rated deflection at rated static and dynamic loads.

The Elastomeric Rubber Based AV Mounts on the other hand are typically made from rubber elastomers. These AV Mounts will have metal plates at top and bottom. These metal plates will have the necessary bolting requirements for fixing these mounts onto the diesel engine frame and then mount the engine on top of this mount. 

Both the Spring and Elastomeric Rubber based AV Mounts can act as Generator AV Mounts. Do note that these mounts isolate the vibrations that are produced in the generator due to reciprocating motion of piston in the cylinder and unbalance, friction in the bearings and small misalignment in the genset coupling. Both these Spring Based and Elastomer Based isolators (AV Mounts) isolate these vibrations and prevent them to transmitting into the channel and generator frame.

So, how does these two types of AV Mounts actually differ in providing good vibration isolation:

★  The Spring Based AV Mounts typically provide 10-50mm of static deflection. This high static load deflection is useful for providing a very high vibration isolation efficiency of 90-98%. The Elastomeric Rubber Based AV Mounts on the other hand are typically providing 4-10mm of static load deflection and lower vibration isolation efficiency of 75-90%.

 ★ For spring AV mounts you will see that the vibration isolation efficiency above is better, the problem is that this vibration isolation efficiency is obtained while continuous machine operation. So, if you have a Diesel Generator that will be running continuously for say 12hours to 24 hours, then Spring mounts will provide better vibration isolation during those working hours. On the other hand, when you switch-on or switch-off a generator mounted on Spring AV Mounts, there will be vigorous jerky movement called 'Headbang'. While mounted on Rubber based AV mounts also, the generator engine moves but gradual movement is damped further by the elastomer.

★  The Spring Based AV Mounts are typically suitable for machine running below 1000 RPM like

HVAC Applications, FANS, High impact producing machine like Presses, Hammers,  etc.The Elastomeric Rubber Based AV Mounts on the other hand are more suitable for machines running above 1000 RPM as these produce higher frequency vibrations. For example closed systems like acoustic gensets, diesel generators, compact digi-sets, compressors, mobile mountings, combustion engines, marine engines etc will be more easily and robustly mounted on Elastomeric AV Mounts. 

 

275kVA Diesel Generator mounted on Elastomeric AV Mounts.

 

★  The Design of Spring Based AV Mounts are typically made to absorb high Vertical Vibration Forces. The lateral and centrifugal / torsional vibrations are not effectively isolated using Spring Based AV-Mounts. The design of the Elastomeric AV-Mounts on the other hand can be modified to incorporate damping of vertical, horizontal and centrifugal /torsional vibrations. 

 ★  Another point regarding the design of Spring mounts is their inherent vertical height. To achieve higher static load deflections, the design of spring mounts typically ranges from 50mm to as high as 500mm. This on one hand provides higher Vibration Isolation Efficiency and good mount design, it

also increases the risk of engine toppling and shaky movement due to higher heights. The Center of Gravity (CG) of the Generator system is also raised. An Elastomeric AV mount on the other hand can be as simple as a rubber pad not more than 10mm in height and good Elastomeric Anti-Vibration Mountings for Gensets can be anywhere between 30mm to 100mm. 

★ Now comes the most important aspect - economics of the AV Mounts. Typically, Spring Based AV Mounts will be atleast 50% costlier as compared to their counterparts in the elastomeric domain. 

The real advantage of Spring Based mounts is their ability to dampen vibrations to the maximum possible extent while still being economical for large manufacturers. The elastomeric mounts are compact, economical and can still perform and deliver very good vibration isolation. We do note that most of the automotive engines are mounted on elastomeric rubber based mountings due to the overall advantage and safety of the elastomeric mounts as described in the discussions above. 

Various Elastomeric AV Mounts from CYMAATICS.

We would be discussing about the various vibration measurement standards and their relative definitions for various machines like Gensets, Compressors, HVAC - Air Conditioning Units.