Evaporator pressure regulators
Evaporator pressure regulators
Evaporator Pressure Regulators valves (EPRs) are designed to provide an economical means of exactly maintaining evaporator pressure and temperature under fluctuating evaporator loads. The key role of an EPR is to prevent the evaporator pressure from dropping below a prearranged value or setting. A consistent vanishing temperature is maintained at the valve setting as evaporator loads decrease. When the evaporator load increases, the valve opens on a Growth of Inlet pressure above its setting. Controlling evaporator temperature, by maintaining the overload pressure of the refrigerant in the evaporator, provides more consistent evaporator temperature than a predictable thermostat or suction pressure cut-out control.
These methods of EPR control allow the evaporator pressure to reduction as the load drops off; dropping the evaporator temperature and decreasing evaporator performance, while increasing evaporator frost form up. Manik offers three types of evaporator pressure regulating valves, covering applications from small spot coolers to large multiplex supermarket systems. The ORIT-6 and ORIT-10 EPRs are direct acting and offered with standard modification ranges and fitting options. The (S)ORIT and (S)ORIT-PI pilot operated EPRs provide more capacity at minor pressure drops, and provide extra features including solenoid shut off for defrost applications. These applications are divided as single evaporator or multiple evaporator systems.
- Single Evaporator Compressor System – There are many single evaporator systems which operate EPRs for precise evaporator temperature control. However, there are some factors to consider. Suitable valve selection is hard. Since pressure drop in the draw line is lost efficiency, EPRs are commonly huge to reduce suction line pressure drop. Single evaporator systems can agree as little as 2 psi drop across direct acting EPRs drop across SORIT and 1.0 psi drop across SORIT-PI pilot operated EPRs,) and still preserve suitable control. Severely oversized valves can source pressure hunting and negatively affect temperature control. In calculation, special consideration must be given to single compressor systems. In these applications the suction pressure can drop to an unpleasantly low level as the EPR throttles to keep the evaporator pressure. In these cases, a discharge bypass valve must be used to keep acceptable compressor suction pressure. These valves are typically piped with the valve exit feeding the suction line downstream of the EPR. Special considerations must be taken to defend the compressor from overheating when using a discharge bypass valve.
- Multiple Evaporator Systems – Most of the supermarket applications use many evaporators piped to a common suction header. These evaporators can be worked at different temperatures for the various products being refrigerated. This is the most commonly useful application for pilot operated EPRs. Any group of evaporators where the preferred saturation temperature is higher than the saturation temperature corresponding to the common suction pressure will need an EPR. If a normally closed solenoid valve is used, energizing the coil will avoid the EPR and allow the case to pull down to the common suction pressure. De-energizing the coil will return controller to the EPR. Pilot Operated EPRs are extensive open in the little temperature operating mode and can be electrically switched to control at the valve set point