Loud noisy in start up screw compressor

[chichi]

Dear All,

I work on a screw compressor that at 1th second of start up it has loud noisy and then its sound is normal.i want to know causes of this problem

thanks for your advise

[HallsEngineer]

Hello,

I would imagine the noise is caused by lack of oil on start up which is normal if the compressor has no oil pump. If it has a continous running oil pump it should come in slightly before the machine

[NoNickName]

PWS start or wye/delta start. The noise is different at startup.

[chichi]

Hello ,

this compressor has a external oil pump that it works about 1 second befor of start compressor and "oil diff press" get to 3bar (oil press-disch press).
one time the pump worked about 10s befor of start compressor for move capacity slide to minimum and then compressor ran but the loud nois heared

[chichi]

PWS start or wye/delta start. The noise is different at startup.

Hi,
the drive compressor work with a star/delta circuit
and this noise is heared at begining time of start up hence compressor is in star condition

[HallsEngineer]

What sort of noise is it banging screaming scraping? also single screw or twin screw?

[chichi]

What sort of noise is it banging screaming scraping? also single screw or twin screw?

yes.it looks like high grinding sound and this compressor has a male screw and a female screw

[chichi]

I read some times this problem apear when oil or liquid refrigerant has been inside of compressor.
Is this true?

[HallsEngineer]

Is it male or female drive that effects the noise.

[GHAZ]

Hi chichi screws can hydrulic with excess oil and liquid refrigerant ,what happens is the screws hit or grind against face plate, if you have an external oil supply,make sure the solnoid valves on oil line are not passing when compressor is not running,if you got oil line sight glass check for minute bubbles in it,if there are bubbles in it then change it

[chichi]

Is it male or female drive that effects the noise.

Hi,

this compressor works with male drive but i don't know close point of the noise

[RUSTY]

Hi, could be slide valve touching rotors tips, or maybe your getting a hit of liguid on start up? .Vibration analysis may tell you more.

[chichi]

Hi, could be slide valve touching rotors tips, or maybe your getting a hit of liguid on start up? .Vibration analysis may tell you more.

Hi,this problem occur just in 1th second of start up of compressor sometimes and after that the compressor works normally and without vibration and abnormal sound,
also distance of compressor to liquid separator is 2.5m and sometimes we have Hi level alarm of liquid separator.can it cause by liquid entering compressor?

[RUSTY]

Hi, what are the run hrs & when was the last overhaul, is the compressor on a single or two stage system, what make of compressor & is the motor controlled by a VSD. vibration analysis is some thing i do once a year same with a oil analysis.

[RUSTY]

sorry should of added ,it is possiable to get a slug of liquid after youve high level your vessel .what kind of level control do you have?

[chichi]

sorry should of added ,it is possiable to get a slug of liquid after youve high level your vessel .what kind of level control do you have?

Hi,we are in first initiation of this compressor(it's a new compressor)&it is a single stage system,motor&compressor are controlled by PLC also the alignment of compressor is acceptable and compressor works with no vibration.liquid level is controlled by AKS38 liquid level float switch

[Ambrish_bajpai]

Liquid slug creates lot of sound and as you have said that you have checked all other possibilities therfore there are high chances of liquid slugs. Liquid Separator seems to be very close to compressor . check the sizing of Liquid seperator . it may solve the problem.

[RANGER1]

chichi ,
From your description it sounds like oil compression on start up .
If suction liquid seperator level is ok before , during and after start up as well as suction line of compressor comes off top of main suction line it may be eliminated .
Depending on type/brand of compessor , an oil injection solonoid can be installed to prevent excess oil entering rotors on start up . Solonoid would be off until machine up to speed .
If there is a regulating valve in this line you could close it to test operation during start up . If noise disappears could be cause .
Does it happen if you do a few starts close together ?

[Ambrish_bajpai]

chichi,
In case the problem is not solved than there are chances of oil flooding into the system , may be due to faulty valves, due to excessive supply. We ahve faced such problem in one of the project and oil flodding into casing was one of the problems for nioise at start up.

[chichi]

chichi ,
From your description it sounds like oil compression on start up .
If suction liquid seperator level is ok before , during and after start up as well as suction line of compressor comes off top of main suction line it may be eliminated .
Depending on type/brand of compessor , an oil injection solonoid can be installed to prevent excess oil entering rotors on start up . Solonoid would be off until machine up to speed .
If there is a regulating valve in this line you could close it to test operation during start up . If noise disappears could be cause .
Does it happen if you do a few starts close together ?

Hi,
ther is no solenoid valves in oil injection line just there is 4 solenoid for capacity control and injection of oil through by oil pump after start up.
this sound is heared in 1th start after few days and if it is stopped and again is started this problem don't occur.

[chichi]

chichi,
In case the problem is not solved than there are chances of oil flooding into the system , may be due to faulty valves, due to excessive supply. We ahve faced such problem in one of the project and oil flodding into casing was one of the problems for nioise at start up.

Hi,
level of oil in compressor is above of sight glass and i don't khnow exact volume of oil in compressor and oil separator.
Is extra volume of oil a cause for this?

[RANGER1]

chichi ,doesn't sound good as oil could end up filling rotor's and housing in idle period .
Iguess you will drain to correct level and see how it goes .
Level in ( vertical ) seperator should not be above bottom of rotor casing to keep rotors free of oil in idle period .
Suction check valve should also be in good order so oil does'nt migrate into machine also .

[NH3LVR]

One cause of a loud noise on startup is oil flooding the compressor. (As RANGER1 suggested)
If the suction check is not closing the oil will move back through the compressor up the suction line. It makes a terrible screeching sound when the compressor starts.
If you have a bypass valve around the suction check that is open too far the same thing can happen.

[Magoo]

Sounds like oil migration into screw case over extended shut down. Check suction and discharge check valves, and oil temperature is at design, too cold oil injected at start-up can also create nasty noises at cold start up. I would have thought that oil supply / delivery line should have solenoid valve to stop oil equalization at shut-down to stop oil migration from separator.
My thoughts..., Magoo

[chichi]

thanks for yoyr advise

I think this problem happend for liqued entry to compressor also oil temperature of ambient was low.
I adjusted level of oil according by factory advise (decrease of oil in oil seperator)
Now compressor starts normally and problem is removed.
again i have appreciation of all