Question:
Pls let me know the vibration monitoring of reciprocating compressors. what are the allowable limits and which unit to be used. At what point the vibration pick up to be located. Can we find out any inaccuracy to the sleeve brgs. of compressor by vibration monitoring. Can we find out any piston/piston rings/cylinder bore related problems with the help of vibration monitoring.How effective is vibration monitoring of compressors in increasing the MTBF in case of compressors.

Regards,

Anurag

Choices:
do'nt really know

 

As per our knowledge by experience, it is really difficult to find any clear picture about the bearing condition from the data collecting by a general purpose accelerometer. The high level Piston pass frequency peaks will make the Analyst difficult to notice the comparitively low level defect frequencies from the bearings. Trending the levels may help to get an overall picture about the condition of the equipment. Sidebands around the piston frequencies may help to identify some of the bearing faults.Vibration data from a displacement probe installed on the bearings may be more reliable for a reciprocating compressor.

There are no written allowable limits for recips. API says nothing about where to place the sensor and which maximum vibration is allowed.
With a acceleration sensor at the crosshead slide and the continous measuring of the vibrations the whole drive train (piston-rod-crosshead-connection rod-main bearing) is monitored.
So you get to know if there´s a developing of clearances if the vibrations increase in the areas where the rodload changes from tensile forces to pressure forces and vice versa.

Leakages at rings can be caught by measuring the indicated pressure in the cylinder chambers.

Problems with broken rings can be detached with the crosshead sensor. (high vibrations in dead centers while pieces are slammed against the head for a few revolutions before they are blown through the discharge valves.
Additional informations of the rod can be caught with a rod position sensor which measures the vertical movement of the rod.
Statements to the conditions of the cylinder liner, and the allignment can be made.

To monitor a reciprocation compressor with the analyses for rotating machines is hard because they are two different machines. (reciprocating vs. rotating, low rpm - high rpm ....). In the FFT there´s no special change. I recommend to analyse the time signal per revolution.

@Peter: Looks like you know what you are talking about. Any hands on-experiences available ?

Anurag
The recommended locations for vibration measurement in alternative machine are: 1- the crankshaft line, and 2- the superior level of block, the top limit of pistons.

The vibration limits are unknow, because are sensitive to load and foundation assemblers.


Ricardo Góz, from Brazil