Vibration problem in frick TDSH 355

[satish cool]

I have a screw compressor of model TDSH 355 (1400TR) frick make. Refrigerant is ammonia. I am facing problem that the vibration of vertical is 12 mm/s. the compressor is running smooth. and compressor is overhauled with new bearing and O rings. we are using a vertical separator. Compressor is lower than the separator in elevation. the distance between compressor and separator is about 14 M. line size is 8". One concentric reducer is used on the compressor discharge port. After that the line is vertical for 3M. Operational parameters are normal.
Can any body help me on this matter to reduce the vibration

[Josip]

Hi, satish cool

welcome to RE forums ...

I have a screw compressor of model TDSH 355 (1400TR) frick make. Refrigerant is ammonia. I am facing problem that the vibration of vertical is 12 mm/s. the compressor is running smooth. and compressor is overhauled with new bearing and O rings. we are using a vertical separator. Compressor is lower than the separator in elevation. the distance between compressor and separator is about 14 M. line size is 8". One concentric reducer is used on the compressor discharge port. After that the line is vertical for 3M. Operational parameters are normal.
Can any body help me on this matter to reduce the vibration

You have had the same problem before overhauling or after?

Vibrations are present within full capacity range or not?

What about horizontal and axial vibration?

Where is installed NRV on discharge pipe?

Vibration of electric motor (solo test run)?

Best regards, Josip

[satish cool]

Dear Josip,
I am facing the problem from initial commissioning stage, so that we go for overhauling. But the problem is same.
Vibration is present on full load but little less, mean it goes down for 1 mm/s
Horizontal vibration is maximum 6.5 mm/s, Axial maximum 8 mm/s. Vertical maximum 12 mm/s
We have provided GVD Valve after secondary oil separator and there is no NRV between compressor and primary oil separator.
Vibration of electrical motor on solo run is 2 mm/s. On coupled condition vibration is 2.5 mm/s

[Magoo]

Too much oil injection can cause this problem.

[Josip]

Hi, satish cool

Dear Josip,
I am facing the problem from initial commissioning stage, so that we go for overhauling. But the problem is same.
Vibration is present on full load but little less, mean it goes down for 1 mm/s
Horizontal vibration is maximum 6.5 mm/s, Axial maximum 8 mm/s. Vertical maximum 12 mm/s
We have provided GVD Valve after secondary oil separator and there is no NRV between compressor and primary oil separator.
Vibration of electrical motor on solo run is 2 mm/s. On coupled condition vibration is 2.5 mm/s

Seems, someone missed to follow start up procedure ....

Preparations before start up

1.Turn on the power voltage and the control voltage. Check the emergency stop button.
2.Check the oil level in the oil separa- tor. Oil level visible in the upper sight glass.
3.Check that all valves are positioned in accordance with Table 2 Position during operation, including secondary side of oil cooler.
4.Reset any alarm in accordance with the instructions for the control system.
5.Check on the control display that the compressor capacity control system
is in minimum slide pos. 0-4%.

Initial start-up procedure

The personnel who are going to start up the plant must be well-qualified and have a thorough knowledge of refrigeration technique.

During the initial start-up of the unit it is imperative that the hand expansion valve on the main oil injection line is fully open to ensure adequate oil flow.
There is still an orifice installed in the compressor to control maximum oil flow. At initial start-up of the compressor the hand expansion valve must be fully open. After initial start-up of the unit the hand expansion valve should be adjusted.

First method ... The best method to determine target discharge temperature is to run Cool-
Ware™/Comp 1. Run CoolWare™/Comp 1 or ScrewSelect with the operating conditions of
the compressor. The program will give you a theoretical discharge temperature of the compressor.

Second method ... If you do not have access to Cool- Ware™/Comp 1 or ScrewSelect, 82°C
[180°F] is a good target discharge temperature for a high stage ammonia compressor. Booster applications and compressors using HFC and HCFC refrigerants may run cooler. Compressors with high discharge pressure may run hotter.

The first method is used for compressors with external oil cooling (Refrigerant cooled (thermosyphon), water-cooled and glycol-cooled). Before the initial start-up of the compressor close the hand expansion valve completely. Open the valve back up and count the turns that it takes to fully open the valve. After the initial start-up close the valve to
achieve approximately 82°C [180°F] discharge temperature or the theoretical temperature from CoolWare. Do not fully close the valve at any time while the compressor is running.

The second method is used for compressors with liquid injection oil cooling. Because the discharge temperature is controlled by the liquid injection thermal expansion valve you will not be able adjust for the correct oil flow by using the discharge temperature.

Failure to properly adjust this valve can lead to excessive noise
and vibration of the compressor and unit, premature failure of the bearings, liquid loading of the rotors, liquid starvation of the rotors and catastrophic failure of the compressor.

Hope this is of some help to you...

Best regards, Josip

[satish cool]

Thanx Josip for this information,

We have followed the same steps. Our discharge temperature is 80 Deg C. I also think about the premature failure of bearing. but when we done the overhauling the bearing found ok. we assembled the compressor with new bearing. But the problem exist. we never observed that refrigerant liquid come to compressor. We have provided Knock out drum on suction line.
I want to share on more thing with you our compressor elevation is lower than separator and oil cooler. Our discharge line position can understand by the attached drawing. Can this may be a cause of the Vibration and abnormal sound. Our Motor is with axial float of 12mm. can this thrust load impact on compressor and produce vibration and sound

Regards, Satish123.jpg

[Josip]

Hi, Satish

Thanx Josip for this information,

We have followed the same steps. Our discharge temperature is 80 Deg C. I also think about the premature failure of bearing. but when we done the overhauling the bearing found ok. we assembled the compressor with new bearing. But the problem exist. we never observed that refrigerant liquid come to compressor. We have provided Knock out drum on suction line.
I want to share on more thing with you our compressor elevation is lower than separator and oil cooler. Our discharge line position can understand by the attached drawing. Can this may be a cause of the Vibration and abnormal sound. Our Motor is with axial float of 12mm. can this thrust load impact on compressor and produce vibration and sound

Regards, Satish123.jpg

Speaking about separator you mean oil separator at discharge line not a suction one-knock out drum ...

One question .... when compressor is stopped for a while (hour, two hours or a day) what is a sound coming from compressor in the moment of restart .... hard start for a couple of seconds ... and maybe give some sound like to have a stones in between screws ...

... if yes then maybe discharge pipe is flooded with oil (due to long discharge pipe and elevation difference) which flows back to compressor discharge port causing vibration ... especially at part load ... you said vibrations are 1 mm/s less at full load ...

... you can check this by draining oil from discharge line (with small external oil pump) and put all oil into oil separator (btw - what about oil level in oil separator - must be well bellow compressor's discharge pipe) ... with empty discharge pipe your compressor should run without vibration for a couple of minutes until, again, you refill discharge pipe with oil .... horizontal run is not that big problem, but in 3m of vertical 8" pipe you can store almost 100 lit of oil


Regarding motor ... it is with slide bearings and oil pump ... did you check axial magnetic center ... during motor solo run and install a coupling according it ...

Hope this will help you with some idea ...

Best regards, Josip

[satish cool]

hi josip,

Thank you very much for your valuable support.

During initial start-up compressor running smoothly for 10-15 sec. but after that abnormal sound is coming then we load the compressor 60 to 70 % capacity compressor sound reduce and compressor running smoothly but vibration increase compare to unload condition.

Our oil separator level is near about compressor suction port. Is there any alternative solution to solve this problem.

Motor is with manual axial float instead of magnetic float and as discussed with motor supplier when we run the motor the shaft reach position of full float i.e.12mm. as per their recommendation we adjusted the float on centre and coupled with compressor. Is it possible that when compressor is running motor shaft try to reach maximum float position and provide a thrust load on the male rotor which cause the vibration and abnormal sound.

[Josip]

Hi, satish cool

hi josip,

Thank you very much for your valuable support.

During initial start-up compressor running smoothly for 10-15 sec. but after that abnormal sound is coming then we load the compressor 60 to 70 % capacity compressor sound reduce and compressor running smoothly but vibration increase compare to unload condition.

Our oil separator level is near about compressor suction port. Is there any alternative solution to solve this problem.

Motor is with manual axial float instead of magnetic float and as discussed with motor supplier when we run the motor the shaft reach position of full float i.e.12mm. as per their recommendation we adjusted the float on centre and coupled with compressor. Is it possible that when compressor is running motor shaft try to reach maximum float position and provide a thrust load on the male rotor which cause the vibration and abnormal sound.

This sound coming 10-15 seconds after start is similar to sound when we have liquid on suction (I assume you knew that sound) or sound is close to sound of stone milling machine ...

Can you, please, explain bold text above .... sorry I do not follow that ...

But having noise and vibrations cause can be ....

Main oil injection valve closed to much .... check and open

Main oil injection valve open too much ... check and adjust

Slide valve/slide stop out of calibration ... over or under-compression ... calibrate

Coupling loose on shaft .... check

Liquid refrigerant overfeed ... adjust liquid injection

Refrigerant flood back .... check the system

Regarding motor ... we always use magnetic center ... just run the motor solo and mark the axial shaft position and then install coupling accordingly to avoid any additional axial load to compressor bearings ... maybe you can try this way ...

Best regards, Josip

[RANGER1]

Josip, very good advice.
It would also be nice to know conditions compressor is running at ie suction & discharge pressures also oil temperature. At the same time compression ratio.
Coupling alignment checking soft foot on motor & compressor.
Does it also have any other connections on compressor like economiser.
IS there anything else on skid that could influence vibration?
Is compressor fixed speed?