Noisy check valves (NRV Danfoss)

[MarcoL]

Hi. I've a big problem with some noisy (chattering) check valves.
The refrigerating circuit of the chiller has:
- 3 Frascold semi-hermetic compressors (R407C, 60HP)
- antivibrating/flexible piping
- NRV Danfoss check valve (42mm)
So there are 3 compressors in parallel operation in the same circuit.
Last week we tested some different valves (Italian Brand), with Kv=35 and they were noisy.
Now we installed NRV check valve (Kv=29) but they are still very noisy.
When the 1st compressor starts up, there are no problems.
Then 2 or 3 compressors are working simultaneously, all the valves are noisy.
The diameters of the lines are: 42mm for each compressor and then the discharge pipe/collector is 64mm.
Possible solutions:
- we are trying to install a bigger discharge pipe, 88.9mm, to reduce the speed inside the discharge pipe, after the check valves
- another idea is to use NRVH valves instead of NRV, with strong spring (please, consider that we've already installed NRV valves after semi-hermetic compressors in a huge number of chillers, without problems)
- someone suggest me to install the check valve near the compressor, before the flexible pipes
What do you think about the problem ? Do you have any advice ? Thanks

[passandscore]

I would install the NRVH models after the antivibrating/flexible piping just before the header.

NRVH is supplied with a spring to ∆p = 0.3 bar. Used in refrigeration plants with compressors connected in parallel.

See attached link.
http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/DKRCCPDFE0E102.pdf

[PaulZ]

Hi Marcol
If the check valves are chattering it could be that they are too big. If the discharge line is 42 mm it may pay to go down a size on the valve that way the valve will stay open even under low gas flows.
Regards
Paul

[Sandro Baptista]

I also agree with PaulZ. When are working more than one compressors maybe the last compressor is working at part load and so the massic flow / pressure loss it is not enough to maintain the valve almost or fully open and so the internal vorticity makes the valve chattering. When you have the 3rd compressor working the 2nd one is at 100% capacity and its own check valve is chattering?