Why No-Load Testing is important in Reciprocating compressors after complete overhaul ?
After complete overhaul (i.e. replacement of worn out bearings -main bearings,conn rod big end bearings,small end bearings,cross head shoe replacements,piston rings and rider rings ,stuffing box pair of rings,etc etc) following should be checked during idle run (no-load ) test for establishing soundness of assembly .
Prior to start up for idle run:
1.Check and ensure that CE (Crank end or BDC) and Cylinder Head End (TDC) clearances are measured correctly by lead wire and micrometer and values maintained as per OEM recommendation.
2.Check piston rod run out (vertical and horizontal) to ensure correctness of piston and cylinder assembly with respect to slide body or distance pieces wherever applicable.
3.Start auxiliary oil pump and observe that oil is going to all the bearing locations as well as cross head pin and crank shaft main bearings through oil passages .
4. keep barring the crank shaft while oil is flowing to all required locations. Lube oil pressure should not be less than 2.5 kg/cm2 (g).
5.Close all the doors of cross-head guide .
6.Ensure valve and valve covers from cylinders are removed prior to No load Testing.
Observations during No-load Testing
1.Run the compressor for 15 minutes and stop to measure/observe followings:
- Temperatures at crank shaft main bearings and intermediate bearings if provided.
- Temperatures at all conn rod big end bearings and small end bush bearings.
- Lube oil pressure and Temperature before and after oil cooler.
- Water temperature at in let and outlet of oil cooler.
-Temperatures at all cross heads shoes.
- Piston rod temperatures at stuffing box packing locations.
- Gear box bearing temperatures
-Any other abnormality if any.
2. If all the readings in step 1 above are within satisfactory range, run the compressor for next one hour and repeat all those readings mentioned in step 1 above.
3.If all the readings in step 2 above are satisfactory within acceptable range ,run the compressor for next two hours and repeat the readings mentioned in step 1 above..
4 If the readings in step 3 above are within acceptable range run the compressor for next one hour and repeat the readings mentioned in step 1 above.
5. If readings in step 3 and 4 are almost steady ,stop further running. This completes the satisfactory idle run test for minimum 4 hours.In case readings are not steady even after 4 hours of no load trial , repeating the running further is not advisable rather we should check for cause of increasing trend of temperature .It could be the misalignment or poor workmanship which needs attention to be addressed / fixed the problem. After correction , repeat the fresh no load trial as per step 1 to 5 above till the parameters are steady within 4 hours of cumulative running.
Many end users are not following above procedures .They directly start the compressor for load trial .There are two main disadvantages in this case :
1. It may result in catastrophic failure of compressor or bearing seizure because of possibility of poor
workmanship/practices which could have been noticed in first 15 minutes no load trial run.
2.Very fast wear rate of rider rings and piston rings resulting in their low MTBF. As most of the rider rings
are made of PTFE with graphite filler,during no load a layer of PTFE is formed on sliding surfaces of
cylinder liners which further reduces the coefficient of friction during load testing or load trial.
After complete overhaul (i.e. replacement of worn out bearings -main bearings,conn rod big end bearings,small end bearings,cross head shoe replacements,piston rings and rider rings ,stuffing box pair of rings,etc etc) following should be checked during idle run (no-load ) test for establishing soundness of assembly .
Prior to start up for idle run:
1.Check and ensure that CE (Crank end or BDC) and Cylinder Head End (TDC) clearances are measured correctly by lead wire and micrometer and values maintained as per OEM recommendation.
2.Check piston rod run out (vertical and horizontal) to ensure correctness of piston and cylinder assembly with respect to slide body or distance pieces wherever applicable.
3.Start auxiliary oil pump and observe that oil is going to all the bearing locations as well as cross head pin and crank shaft main bearings through oil passages .
4. keep barring the crank shaft while oil is flowing to all required locations. Lube oil pressure should not be less than 2.5 kg/cm2 (g).
5.Close all the doors of cross-head guide .
6.Ensure valve and valve covers from cylinders are removed prior to No load Testing.
Observations during No-load Testing
1.Run the compressor for 15 minutes and stop to measure/observe followings:
- Temperatures at crank shaft main bearings and intermediate bearings if provided.
- Temperatures at all conn rod big end bearings and small end bush bearings.
- Lube oil pressure and Temperature before and after oil cooler.
- Water temperature at in let and outlet of oil cooler.
-Temperatures at all cross heads shoes.
- Piston rod temperatures at stuffing box packing locations.
- Gear box bearing temperatures
-Any other abnormality if any.
2. If all the readings in step 1 above are within satisfactory range, run the compressor for next one hour and repeat all those readings mentioned in step 1 above.
3.If all the readings in step 2 above are satisfactory within acceptable range ,run the compressor for next two hours and repeat the readings mentioned in step 1 above..
4 If the readings in step 3 above are within acceptable range run the compressor for next one hour and repeat the readings mentioned in step 1 above.
5. If readings in step 3 and 4 are almost steady ,stop further running. This completes the satisfactory idle run test for minimum 4 hours.In case readings are not steady even after 4 hours of no load trial , repeating the running further is not advisable rather we should check for cause of increasing trend of temperature .It could be the misalignment or poor workmanship which needs attention to be addressed / fixed the problem. After correction , repeat the fresh no load trial as per step 1 to 5 above till the parameters are steady within 4 hours of cumulative running.
Many end users are not following above procedures .They directly start the compressor for load trial .There are two main disadvantages in this case :
1. It may result in catastrophic failure of compressor or bearing seizure because of possibility of poor
workmanship/practices which could have been noticed in first 15 minutes no load trial run.
2.Very fast wear rate of rider rings and piston rings resulting in their low MTBF. As most of the rider rings
are made of PTFE with graphite filler,during no load a layer of PTFE is formed on sliding surfaces of
cylinder liners which further reduces the coefficient of friction during load testing or load trial.
Roller bearings are similar to ball bearings in the way they are made, having the key difference that they contain cylindrical rollers instead of balls.
ReplyDeletewhite metal bearings
Hi there! glad to drop by your page and found these very interesting and informative stuff. Thanks for sharing, keep it up!
ReplyDelete- reliability centered maintenance
Thank u
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