Guide to Vibration Isolation Of Fans

The general model used to define transmissibility is the amount of force transferred through the isolating medium—is based on a single degree of freedom (vertical motion), undamped system on a rigid supporting structure. These assumptions are overly simplistic, as rotating machinery typically has at least six degrees of freedom, vibration isolation media often provide some damping, and the supporting structure is rarely completely rigid.

Practical guidelines for isolation efficiency consider equipment horsepower and speed, suggesting appropriate isolation types. Effective vibration isolation is crucial for maintaining equipment performance and structural integrity.

Types of Support for Vibration Isolation

Vibration isolation equipment is essential for reducing the transfer of vibrations from machinery to the supporting structure. Depending on the equipment and the rigidity of the supporting structure, different methods are used to mount the equipment on isolation devices such as springs and pads. Here are the primary types:

1. Vibration Isolation Base
   • Used for equipment with insufficiently stiff frames or to mount both the equipment and its driver.
   • Constructed from structural members like channels, I-beams, or angles for rigidity.
   • Includes built-in slide rails or slide bases if the motor is not mounted on the fan.
   • Height-saving brackets are often included (see Figure 2).
2. Vibration Isolation Rails
   • Employed similarly to vibration isolation bases, usually for smaller fans (arrangements 9, 10, or 4).
   • Adds stiffness to the fan’s mounting platform.
   • May include height-saving brackets if necessary (see Figure 3).
3. Inertia Bases (Concrete-filled vibration isolation base)
   • Used in similar installations as vibration isolation bases but with added concrete for increased stiffness.
   • The concrete weight lowers the installation’s center of gravity, providing greater stability for larger equipment.
   • Preferred for fans directly coupled to motors to maintain coupling alignment.
   • Often built with structural members stiff enough to be shipped without concrete.
   • May include a bottom pouring pan for ease of installation (see Figure 4).
4. Isolation of Fans Mounted on Curbs
   • Custom-designed isolation equipment for mounting fans on curbs.
   • Typically variations of the isolation base, tailored to specific applications.

Important Considerations

• Flexible Connections: All equipment mounted on isolators must have flexible connections to inlet and outlet ductwork. Rigid connections can bypass the isolation and transmit vibrations directly through the ductwork.

These various support types ensure that vibration isolation systems are effective, preventing vibration transmission and protecting both equipment and structures from potential damage.