Pressure differential valve selecting

How do you select pressure differential valve?
For example it's Danfoss NRD, Sporlan ORD...
Danfoss don't say the calculation of determine quantity of NRD.
Sporlan gives:

Quote:

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In those cases where the ORI-10 is applied on systems with more capacity than the ORD-4
or when more than one head pressure control valve is
used, it is necessary to use two or more ORD-4 valves in parallel.

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Could anybody explane how do you determine quantity of pressure differential valve in system with pressure regulating?

Danfoss pressure regulator KVR may install on liquid pipe after condencer or on discharge pipe before condencer. Sporlan pressure regulator ORI may install only after condencer...
Therefore I think there is two variants of calculating how much pressure differential valves are need...
Does anybody know calculating method when two, three or more pressure differentials need in system? Or may be are there any ideas about it?

I've never fitted any, so don't know :o

Jon

From the little that I have read, Sporlan, you size the valve(s) on the duty duty and set the pressure at your required condensing temperature.

I have come across large chiller systems 200Kw plus and the balance line is 1/2 " and an ord vav. Larger ammonia systems, no ord just a balance line from discharge straight onto receiver, below condenser of course.

I'm very surprised that you don't use it...
http://www.danfoss.com/BusinessAreas...f6e172329.html