Screw compressor resonance/vibration in discharge

Long time reader, first time caller

My company did a DX plant upgrade (A/C) and have installed a 134a bitzer screw (around 300kw capacity) which was sized and designed by a separate engineer. The discharge pipework has a very loud internal resonance coming from 2 spots (*): brief pipe rundown

Rises from compressor then horizontal 2m
*a straight that drops and climbs with two 45 degree bends with 1m in between elbows
5m then right bend then 15m
*a left hand bend, runs 1m drops vertical 0.5m then straightens horizontal (loudest)
Then outside to condenser

The unit is still slightly undercharged going off vessel on pump down (DX so unsure of full), the discharge pipe work is 2" 1/8, no mufflers/eliminators

Addition of gas towards 'full' has helped and reduced pulsations a little
All fixings are tight but not really relevant given the nature of the noise
Pressures run around 780-800kpa (pressure controlled) and 210 kpa

Neither myself or my supervisor have had much experience with this issue, can anyone provide insight into what's causing the noise? And/or a solution?

better post a picture of the pipe work of discharge line

is it when the compressor stops or during running?

Pulsing within the discharge line can be a result of the system being undercharged particularly when you have no liquid seal within the receiver.
Check the temp of the liquid line?

Screws also have a natural resonance at certain running conditions.
Sadly you may have to call in someone if you feel its a issue.
Sorry to be vague.
Grizzly

Thanks for the quick responses guys.

I'll get a picture when I go back next, maybe even a video of the noise.

During normal running

I'm assuming the receiver would have a pickup at the bottom on the outlet but looking at it makes me think it's just on the side, but sight glass is always full now, it was a little short on liquid before, receiver has 3 sight glasses and all were empty but bottom one stays full now after addition of gas. Haven't got a number for the liquid line only feel which was deemed okay.

Were going to talk to the guy who designed it because ultimately if he designs them he should have come across this before

Quote:

---

Originally Posted by Rexy

Long time reader, first time caller

My company did a DX plant upgrade (A/C) and have installed a 134a bitzer screw (around 300kw capacity) which was sized and designed by a separate engineer. The discharge pipework has a very loud internal resonance coming from 2 spots (*): brief pipe rundown

Rises from compressor then horizontal 2m
*a straight that drops and climbs with two 45 degree bends with 1m in between elbows
5m then right bend then 15m
*a left hand bend, runs 1m drops vertical 0.5m then straightens horizontal (loudest)
Then outside to condenser

The unit is still slightly undercharged going off vessel on pump down (DX so unsure of full), the discharge pipe work is 2" 1/8, no mufflers/eliminators

Addition of gas towards 'full' has helped and reduced pulsations a little
All fixings are tight but not really relevant given the nature of the noise
Pressures run around 780-800kpa (pressure controlled) and 210 kpa

Neither myself or my supervisor have had much experience with this issue, can anyone provide insight into what's causing the noise? And/or a solution?

---

There has to be an oil seperator in there somewhere as well!

Nope no seperator, it's a drop in compressor unit so I guess whoever designed it decided it dosent need it.

Attachment 11794Attachment 11795Attachment 11796

Pictures go from outside back to plantroom

We're going with a discharge muffler either on the rise out of the compressor or on the first horizontal
The systems designer couldn't confirm if it'll fix it or not but we don't have many options

Would you have a picture of the package / compressor?

Attachment 11797
Old and bad angle but all I have for the moment

And the discharge muffler has fixed it

Thanks, always good to know the outcome - cheers!