Discharge-Bypass Valves Application
DBVs provide a cost-effective method of compressor capacity control instead of cylinder unloaders or handling requirements following the last step handling cylinders.
The air-conditioning systems, minimum allowable temperature of boiling, that will allow to avoid coil depends on the icing of the evaporator design. The amount of air passing through the coil also defines the permissible minimum temperature of the evaporator. The refrigerant temperature can be below 32F (0C). However, coil icing, as a rule, does not arise, the air velocity, since the external surface temperature of the pipe to be above 32F (0C). For most systems, air-conditioning, a minimum temperature of boiling should be 26 to 28F (3.3 2.2C). DBVs installed at the factory. They start to open the evaporating pressure equivalent to 32F (0C) saturation temperature. Thus, the evaporating temperature from 26F (3.3C) of its nominal capacity. However, because they are regulated, these valves can be installed for opening above the boiling point.
On refrigeration systems, discharge bypass valves are used to prevent suction pressure will be lower than the minimum limit recommended by the compressor manufacturer.
A typical application will lower the temperature, the compressor is designed for operation at the minimum temperature of the Refrigerant boiling point on 22 40F (40C). Required boiling point at normal load conditions 30F (34C). Discharge-bypass valve will be selected to start to open at a pressure equivalent to 34F (36C) and work around enough hot gas 40F (40C)to prevent further reduction of the suction pressure. Valve settings on manufacturerР‚'s recommendations.
Discharge-bypass valve is used in a branch line from the discharge line as close as possible to the compressor as possible. Behind the couple can enter the low side in one of the following locations:
At evaporator inlet distributor
At evaporator inlet without distributor
To the suction line
Figure 11 to 38 shows the bypassing input in the evaporator distributor. The main advantage of this method is that the system thermostatic expansion valve will respond to the increased steam superheat at the evaporator outlet and will provide liquids required for desuper heating. Evaporator, and also serves as an excellent mixing chamber for bypassed hot gas and liquid-vapor mixture from the expansion valve. This ensures that dry steam reaches the compressor suction. Oil return from the evaporator is also improved, because the speed of the evaporator is held high and hot gas.