Bullgear compressors

The bullgear design uses a direct-driven helical gear to transmit power from the primary driver to a series of pinion-gear-driven impellers that are located around the circumference of the bullgear. Figure 36.4 illustrates a typical bullgear compressor layout. 

The pinion shafts are typically a cantilever-type design that has an enclosed impeller on one end and a tilting-pad bearing on the other. The pinion gear is between these two components. The number of impeller-pinions (i.e. stages) varies with the application and the original equipment vendor. However, all bullgear compressors contain multiple pinions that operate in series. 

Because of their cantilever design and pinion rotating speeds, bullgear compressors are extremely sensitive to variations in demand or down-stream pressure changes. Because of this sensitivity, their use should be limited to base load applications. 

Because a bullgear compressor incorporates a large helical gear, the shaft displays moderate to high axial... 

The actual dynamics of centrifugal compressors are determined by their design. Common designs are overhung or cantilever, centerline, and bullgear. 

In addition, the large helical gear used for the bullgear creates an axial oscillation or thmsting that contributes to instability within the compressor. This axial movement is transmitted throughout the machine-train. 

The mode of operation of a specific application should be the first consideration. The inherent design of each type of compressor defines the acceptable operating envelope or mode of operation that it can perform with reasonable reliability and life cycle costs. For example, a bullgear-type centrifugal compressor is not suitable for load-following applications but will prove exceptional service in constant-load and volume applications. 

There are two types of commonly used centrifugal compressors (1) in-line and (2) bullgear. 

The bullgear centrifugal compressor (Figure 44.7) is a multi-stage unit that utilizes a large helical gear mounted on the compressor s driven shaft and two or more pinion gears, which drive the impellers. These impellers act... 

Centrifugal There are two major types of centrifugal compressors used in industrial applications in-line and bullgear. 

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