Check valve selection

[Aik]

There is interesting problem of check valve selection in parallel working compressors. I select check valve for liquid line (condenser/receiver) for total compressors capacity, but when some compressors not work there are low opening degree and there is a risk of instabillity of working, because the flow of refrigerant is to small to open this valve. Velosity in thise pipe must be no more then 0.5 m/s, if I select more smaller valve then it will open on minimum compressors capasity but on maximum capasity velosity of liquid will be 1.4 m/s. Could you tell me how can I solve this problem?

[Sandro Baptista]

Many check valves start opens at 0,1 bar or less. So in this particular case if you have a column of 1 m » 2 m of liquid (depending of the refrigerant density) between condenser outlet and receiver it will no problem.

[Aik]

Many check valves start opens at 0,1 bar or less. So in this particular case if you have a column of 1 m » 2 m of liquid (depending of the refrigerant density) between condenser outlet and receiver it will no problem.
Good. What will you do when in the same situation check valve will situate on discharge pipe?

[Sandro Baptista]

Do you mean on the discharge pipe of each compressor?

[Aik]

Do you mean on the discharge pipe of each compressor?
No, one for all compressors, for example after general oil separator.

[Sandro Baptista]

In that case is more complicated...but depending the number of compressors and/or its capacity stage may have an unique valve that accept as minimum capacity 15-20% without generate high pressure drop ate 100%.

If there is only one rack with one general oil separator I don't see the necessity of install check valve albeit many plants have it.

[Aik]

If there is only one rack with one general oil separator I don't see the necessity of install check valve albeit many plants have it.

Check valve on discharge pipe protect from condensation refregirant in oil separator when unit not work in case with air condenser when ambient temperature is high then temperature in the compressor's room.

[Sandro Baptista]

The refrigerant can be evaporated by electric heat around the oil tank; or shut off by electric valve the oil return to the oil thank and heating the oil separator or give a time to open the EVR to oil tank after the compressor working about 10 min.

[Aik]

The refrigerant can be evaporated by electric heat around the oil tank;

You are right, but not all oil separators have electric heat.

[Sandro Baptista]

You can buy it separate from the oil separator. It is an electric strap that is put around the oil separator. It is sold on PECOMARK, DISCOLIS, or other suppliers.

Or use a timer as I explain above

[RANGER1]

Have you looked at Danfoss check valves as I know your predicament for selection can be difficult to avoid fluttering.
On industrial we use duo check valves which handle your circumstances but of course you may not want flanges .

[GBRD]

How sensible it is to have one check valve in the discharge line for parellel compressor operation? Won't it hamper the compressor capacity?

regards

[desA]

I'd suggest using one check-valve per compressor - correctly sized to suit compressor delivery.