Figure 7.30 shows changes in pressure that develop in a condenser when the equalizer line connects the top of the receiver to the inlet to the condenser. As the condensing refrigerant flows down through the condenser, a pressure drop occurs, -Δp. The equalizer line forces the pressure in the receiver to be the same as that of the condenser inlet, so some means must be found to recover the drop in pressure that occurs in the condenser. The +Δp to cancel the -Δp derives from the static head of a column of liquid refrigerant. In Figure 7.30 the liquid column is adequate to provide this gain in pressure. If the difference in elevation from the bottom of the condenser to the liquid level in the receiver is inadequate, the system achieves the necessary column of liquid by backing liquid into the condenser. Liquid that is forced back into the condenser is the root of many low-capacity problems with condensers. Incidentally, the arrangement shown in Figure 7.30 is a satisfactory alternate to the configuration of Figure 7.29, but Figure 7.29 is preferred because it does not require as much length of liquid column and the equalizer line is shorter.