A small vessel frequently installed beneath the low-pressure receiver and other larger vessels is an oil pot whose purpose is to accumulate oil to facilitate periodic draining. Figure 10.17 shows oil pots with their typical connections, including the line from the bottom of the low-pressure receiver, the drain line, and the equalizer line, which is connected to the vapor section in the upper portion of the low-pressure receiver. Without the equalizer line it may be difficult to achieve drainage into the oil pot because of the vapor pressure that could build up. In addition, since the oil pot is usually classified as a vessel, it must be protected by relief valves.
If both the inlet line and the equalizer line are flush with the top of the oil pot, as shown in Fig. 10.17a, it will be possible to completely fill the vessel with liquid, which could be dangerous should all the valves in the connecting lines be inadvertently closed. To avoid the possibility of complete liquid filling of the vessel, the equalizer line can be extended into the oil pot a short distance. When the level of oil (and refrigerant) rises in the oil pot to the bottom of the equalizer line, liquid is forced up the equalizer line but the vapor space at the top of the vessel is preserved.