opr valve operation in rack system

[coldkeeper1]

There are so many different arrangements of piping in today´s rack systems that it seems to me that I would never finish learning about them.
In this particular rack, I´ve identified four different regulators: DDPR (differential defrost pressure regulator, located in the compressors´discharge manifold), IPR (inlet pressure regulator located between the condenser outlet and liquid receiver), OLDR (located in the main liquid line downstream from the receiver outlet), and OPR (outlet pressure regulator, located between the discharge manifold and the top of the liquid receiver). The rack manual indicates that this is a floating head, receiver gas defrost system.
My question is: in this case, does the OPR keeps always a constant pressure in the liquid receiver regardless of the fluctuations in the condenser pressure, or does it keeps only a minimum pressure, allowing the receiver pressure to float, just as the condenser pressure does ?

[Silhouette]

If the system is floating then it will keep a minimum pressure in the receiver to maintain the TXV minimum operating differential. The condensing pressure should not try to float below this pressure!

[Silhouette]

Just read your explanation again and noted the Saturated gas defrost.
If the DDPR has a solenoid coil on it, the OPR may just be a pressure back up for the defrost to maintain Sat gas pressure when there is a system on defrost.