Vibration of a recip. air compressor 2

[GregLocock]

OK you've got some instrumentation. The plots aren't very helpful are they? You need to look at the vibration each side of each isolator, and look at the transmissibility across the mount.

Then you need to start building a system model, at least in your mind if not on paper. As Tmoose implies, a modal approach is the most straightforward way. You can use forced response (ODS) data instead but it will lead to puzzling results like softer mounts giving more vibration.





Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[jeyaselvan]

Often, while I have isolation related vibration problem I always start with the measurement of ODS. This will throw you information on whether the system is deflecting in the shape as expected. While you have a rigid body resonant response, you would rather see the deflection shape corresponding to the mode shapes.
I have attached a sample ODS to illustrate the understanding. In this partiular case, the expected deflection shape (you would know this from your designs) is a second order vertical, while I measured an ODS corresponding to the rolling deflection shape, which is nothing but the rigid body roll mode shape coinciding with the second order excitations.

Jeyaselvan

 

[mdossaji]

If my forcing vibration is more in the horizontal direction and I want to calculate the radial deflection then what kind of load do I have to incorporate into my equation? Would the load due to compression be considered or would it be strictly the centrifugal force of the counterweights?

 

[Tmoose]

I think Compression is an internal "force" acting on the tops of the pistons, and opposed by an equal and opposite force thru the crankcase etc.
The sum of unbalanced inertial forces of (+) crank (and any other) counterweights, (-) whatever the equivalent "piston" inertia is, wiht offsets and ???.

Crank counterweights have to be substantial to cancel 1/2 of the reciprocating hardware.

http://www.motorcycle-superstore.com/ProductImages/OG/2008_Hot_Rods_Crankshaft_Assembly.jpg

And 1/2 is close to the compromise chosen for many 1 and 2 cylinder engines,as anything else starts to favor vertical at the expense of horizontal, or vice versa.

Is the motor face mounted to the compressor? Or, is the frame required to resist the (pulsing) torque required to spin the compressor?

I'm still interested and concerned about the actual floor mounting vs test rig.

Dan T