PDA

View Full Version : Check valve for discharge pipe







GENERALCOOL
27-07-2017, 07:09 PM
Dear All,

I heard that when air-cooled condenser is above of compressor, We must use check valve at discharge pipe of compressor.
Why we should check valve ? for prevent returning liquid on top of valve plate of compressor ? Or it has other reason ?
If we use "Inverted P trap" at inlet of condenser, It is not enough for prevent liquid migration ?

Thanks if you help me in this topic.

With best regards.

FaultCode
27-07-2017, 07:42 PM
Yes a check valve or inverted trap should be fitted at the condenser inlet.

This McQuay design guide might be of help to you, see page 15. http://bit.ly/2w4dsHI

GENERALCOOL
28-07-2017, 08:58 AM
Yes a check valve or inverted trap should be fitted at the condenser inlet.

This McQuay design guide might be of help to you, see page 15. http://bit.ly/2w4dsHI


Thanks a lot

chemi-cool
28-07-2017, 09:20 AM
Refrigerant migrates to the cold place and to the lower place.
Check valve before the condenser will stop the liquid in the condenser from migrating to the compressor discharge chamber and rist the discharge valves from braking at start up.

A.Mortezania
02-08-2017, 05:48 AM
Dear All,

I heard that when air-cooled condenser is above of compressor, We must use check valve at discharge pipe of compressor.
Why we should check valve ? for prevent returning liquid on top of valve plate of compressor ? Or it has other reason ?
If we use "Inverted P trap" at inlet of condenser, It is not enough for prevent liquid migration ?

Thanks if you help me in this topic.

With best regards.



This photo is your answer
14935

Matjecito
30-01-2018, 09:30 PM
Hi all,
Recently we discovered some issues with check valves mounted in the discharge line of a multiple R507 compressor system (6 VSD controlled DMW piston). After an issue in the oil separator we found some inner parts of the valves back in the bottom of the separator and it showed several failed.
How your dealing normal with preventive maintenance on these types, as it's a bit difficult when they are soldered in the discharge lines :)

Thanks your thoughts guys

15084
15085

Glenn Moore
30-01-2018, 11:57 PM
There is no preventative maintenance for these non return valves apart from selecting the correct valves for the system design.
Check valves for use with variable speed drives are difficult to select as the gas volume can vary by a large amount.
When selecting NRV's it is selected against the volume flow that will keep the valve fully open. If the valve is not kept fully open because the volume flow is too low then the piston starts to chatter and bang open and closed causing it to break.
The NRVH has a heavier return spring and will cause the piston to bang up and down until destruction occurs.
A better solution would be the NRV with the lighter spring as it needs less flow to lkeep it open. With discharge gas flows frequencies and harmonics can be a disastrous situation .
With piston compressors if the nrv is not sized correctly the nrv piston will oscillate at the same rate as every piston pulsation say an 8 cylinder compressor running at 1500 rpm running for 1 hour will lead to the nrv piston oscillating 720,000 times an hour . At that rate it won't last for very long, also the Ptfe seat will be smashed to pieces,preventing it from closing tight.
An Nrv should be a smaller size than its surrounding pipe work so that it creates a small pressure drop helping to keep it in the fully open position and allowing the NRV to safely to its job

Grizzly
31-01-2018, 07:42 AM
Excellent advice Glenn.
Thanks Grizzly

Josip
01-02-2018, 06:52 PM
This photo is your answer
14935

I know this photo is from AC_Guide_McQuay, but for me a very bad example of refrigerant piping .... in this case discharge line from compressor/s to condenser/s ...

Discharge pipe should run straight vertical above condenser (without horizontal runs - if possible) and then down to condenser inlet (in this case - two elbows less) and without inverted trap. Just at highest point of discharge pipe (this should be above condenser) we can install NRV-check valve and after that pipe must run with slope to condenser inlet.

Best regards, Josip