High Vibration of reciprocating compressor

[sjpark]

I have a problem that reciprocating compressor has very high vibration, 23 mm/sec Peak value.

The period of cylinder is 547 rpm. The dominant freq is 5 x rpm, the amplitude is 22 mm/sec at that freq(2735cpm).

on shop test report, it just had 5 mm/sec around.
After installation in field, the compressor has very high vibration. So, We put a tension bar between structure and the compressor to reduce vibration. It affected reducing vibration for a while. 23mm/sec -> 14 mm/sec

2 month latter, now vibration is increasing.
In my thought, there is no reason for that.

Who has any information about this kind of problem.
Please let me know.

 

[pmover]

a couple of questions . . . and then opinions . . .

1) was a pulsation study accomplished before installation of the recip compressor? a design study that uses the selected recip compressor and proposed piping design, including inlet/outlet drums, bottles, etc. to determine the predicted levels of pulsations.

2) if item #1 was accomplished, then is installation of compressor and associated piping done in accordance with the design pulsation study?

based on information provided and as typical with these installations, the anchor bolts/nuts for various requipment (compressor, surge drums, piping tie-down clamps, etc.) need to be check periodically; especially after maintenance work and initial installation. increasing levels of vibration with operational time seem to indicate the "system" is getting loose. yes, there are reasons for increasing levels of vibration!

if item #1 was not accomplished and if funds are available, perhaps a pulsation study can be accomplished based on the existing design. if not, and you have the inclination yourself, then obtain the pulsation design criteria from API-618 and other reference documents and conduct the pulsation analysis/design yourself. of course, you do have existing operational data to help/guide you.

good luck!
-pmover

 

[sms]

Is the machine fully loaded, or are you running with either cylinder ends unloaded or pockets open? A double acting machine should be running even harmonics of run speed, 2, 4, 6, while a unloaded machine will make odd harmonics. Something is resonant to 5X. Your tension bar helped, is it still in good shape? Did it come loose or wear out? Is it still applying the same level of force to the system?

-The future's so bright I gotta wear shades!

 

[sjpark]

Thank you so much for your replys.

Actually, I'm user not desinger. So, I have no idea for pulsation study. The manufacturer said it was good in the shop and showed me the test report.

I suspect wrong installation. At this time, why vibration was incresing slightly after reinforce stiffness.
The force level is the same before, 2 month ago.

Anyway, your information is useful to me.Thanks

 

[zdas04]

sjpark,
I think we've reached the point that further answers without more data just become wild conjecture.

What size machine is it? Is is sitting on the ground or on a prepared foundation and grouted in? What are the materials of the foundation?

David

 

[sjpark]

thank you zdas04,

you mean size, the compressor is aroud 4 meter(lengh) x 2 meter(height). It is grouted with frame like H-beam(steel) on the ground.

 

[crjones]

Is the crankcase vented and if so are the vents open, sometimes these are plugged for shipping.

 

[1969grad]

What zdas04 means is what is the hp of the unit.

IMO, the first rule is to set the unit on a concrete foundation weighing 3X the unit weight if it is a balanced opposed unit. If you cannot afford the concrete then you cannot afford the machine.

Will a unit not vibrate if it is setting on the ground (compacted gravel)? Maybe especially if the skid is filled with concrete.

 

[zdas04]

Thanks 1969Grad, that is exactly what I meant.

I recently came across some new research that calls for 3X the unit weight plus 6X any unopposed force. The unopposed force is supposed to be in the job book, but I've never seen it. In the future I'm going to ask for it on new machines. The paper I read said that the unopposed forces can result in needing nearly as much concrete mass as the raw weight of the compressor calls for (i.e. the unopposed forces may be as much as half the weight).

David

 

[1969grad]

I have always heard 3X and 5X instead of 6X.

The above rule of thumb is far from being new research. Fact is that foundation engineers way older than I have used it with satisfactory results before I got out of school. To say it is a proven guideline would be an understatement.

 

[zdas04]

Like the CBS commercials a few summers ago said "If you haven't seen it, it is new to you".

The paper I saw was dated 2003, but it sounds like it was simply building on long-standing techniques.

David

 

[dcasto]

We set upto 2000HP engine driven opposed cylinder compressors on pack material all the time. The speeds range from 1000 to 1400 rpm.
A 5 times speed, pardon the pun, sounds more accoustical than mechanical for a reciprocating machine. Thry adding a tuning orifice between the flanges on the suction and discharge of the cylinders. If there are multiple clinders per stage, check for piping lenghts as they join together, make sure they are equal.