Hi Jorge, You would see a 12x and 16x peak in your spectrum when displayed in orders, and with the shaft speed set/measured correctly to reflect actual shaft speed. The software is doing the calculating for you. Each peak will probably have some rotational sidebands at 1x, another way to check if spectral speed matches the actual shaft speed. Most software has the ability to display in orders which is a way we normalize speed to look at it in multiples of shaft speed. After all, the vast majority of faults and normal behavior encountered in routine condition monitoring activities is either an integer or non-integer multiple of shaft speed. rgds
Jorge, it is likely the Nash vacuum pump is a dual rotor scroll design; one drive rotor with 12 vanes and the other driven rotor with 16 vanes; the scroll vanes mesh. If that is the case, there will be only one vane mesh frequency at 12xDriveRotorRPM = 16xDrivenRotorRPM. See illustration nash dual rotor vacuum pump, parts diagram - Search Images (bing.com). Somewhat high vibration at mesh frequency and harmonics of mesh frequency are common on these machines. Vibration at each of the rotor RPM may also be evident. Gene.
Thanks Eugene, a reminder that I've predominantly worked in an industry where Nash vac pumps have a single shaft. I did try to think how one end of a shaft might have 16 vanes, and another part 12 vanes. So I agree the design is likely to have 2 shaft and the vane pass frequency in (Hz) would be the same. And on each point, when order normalized to respective shaft speeds, 16x and 12x. I would always set up some points at each bearing with point speeds set to the respective shaft speeds. rgds
Greater design detail from Jorge would be good. rgds
Good morning, attached is a diagram of the Vacuum Pump, which has a single shaft and on said shaft there are two rotors, one rotor (Pos. 3.1) has 16 blades and the other rotor (Pos. 3.2) has 12 blades. Greetings.
So you would see a 12x and a 16x and probably rotational sidebands. Expect a peak for the motor speed as well if my assumption of it being driven through a pulley reduction. No calculation required is the shaft speeds are set up correctly. I use CSI so would always measure shaft speeds with a speedvue laser. For the pump, I would use an Fmax of at least 120x, maybe even 150x. Minimum 1600 lines for the 120x and would step up to 3200 lines for the 150x Fmax. Think of it as the number of lines per order being enough to resolve the lowest frequency of interest, cage frequency in this case. Of the SRBs installed. It would be nice to have the bearing numbers. 222** dimension series at a guess. Which vibration software/hardware system do you use? Is the pump direct-driven or pulley reduction? Fixed speed? Line frequency in your country? rgds