Screw Compressors can have multiple stages. Most are Single Stage twin screw compressors, but some compressors can be dual stage or multiple stages. Identify how many stages the compressor has, because this can change how many bearing points to install on the machine.
Twin Screw and Lobe Compressors Install Locations
Single Stage Twin Screw Compressors and Lobe Compressors typically have 2 shafts. One shaft is driven by the motor, and the second shaft gets rotation from a gear set on the Driven End or Non-Driven End of the pump, or sometimes can be driven by the blades of the compressor.
Try to identify where the gear set is that is translating rotation, and where the bearings are that support the shaft. Install on the metal piece that is holding the bearings, and try to avoid installing over the gear set, which might not show all of the vibration from the bearings.
Dual Stage Screw Compressor
Dual Stage Compressors can have multiple stages on the same shaft, or they can have a bull gear that drives two primary shafts. Each of those primary shafts might have a timing gear to drive the secondary shafts.
In the event it is the bull gear design, the bull gear shaft should have 1 or 2 bearings to install. Then each stage could have up to an additional 4 bearings each.
Single Screw Compressors Install Locations
These Single Screw Compressors have 3 shafts. The main rotor shaft that is driven by the motor has the compression screw. The other two shafts spin perpendicular to the screw shaft and have rotating starwheels which are driven by the compression screw. The main shaft has 2 bearings. The starwheel shafts have 2 bearings each.
In the below drawing, the Main Rotor accelerometer points show 2 points for each bearing because they are showing where to install for a singe axis accelerometer. For the Main Rotor Roller Bearing and Angular Ball Bearing locations, you only need to install one sensor at each bearing because our sensors are triaxial vibration sensors.
Source: https://media.copeland.com/d9ea9f82-83b1-4c13-8de6-b16b010cfe09/vss-vsr-vsm-vsh-vssh-bare-shaft-compressor-ios-manual.pdf (page C-1)
Source: https://armstrongcompressors.com.ph/rotary-compressors/screw-compressors/oil-free-screw-compressors/