There are many brands and styles of Evaporator Pressure Regulating valves (EPR), but none as common as the Parker / Sporlan SORIT and ORIT valves.
The diagram above clearly shows some of the common applications. An EPR or “hold back” valve maintains a set suction line pressure and therefore coil temperature. This is critical in situations where multiple evaporators of different design temperatures connect back to a shared suction header as is common in grocery store refrigeration.
The EPR valve “holds back” pressure in the evaporator to a set pressure so long as there is a pressure differential between the evaporator coil and the shared suction header. The suction header must have a LOWER pressure than the lowest design pressure of any evaporator connected to it.
A SORIT valve is an EPR valve or ORIT (Open on Rise of Inlet Pressure) valve that also includes a solenoid stop. The purpose of the solenoid stop is to
prevent the defrost gas from entering the suction line and overheating/overloading the compressors when the defrost solenoid opens and back feeds the evaporator to defrost.
For a full and detailed explanation of ORIT and SORIT valves, you can read BULLETIN 90-20 from Parker Sporlan.