Publisher Summary This chapter presents an overview of pump flush system. Pump flush systems use the same fluid phase as the process to meet their objectives. They utilize a liquid, as in the case of gas seal systems which utilize the compressor process gas or external source of gas. As pump flush systems utilize a liquid, they tend to be simpler than liquid seal systems in compressor applications. The function of a pump flush system is to continuously provide cool clean flush fluid to the specified points at the correct pressure, temperature, and flow rate. The inner seal chamber consisting of the single mechanical seal and the throat bushing, actually comprise a double seal with respect to the flush liquid. This is because the flush liquid has two paths that are through the seal and through the throat bushing. Conceptually, this seal configuration is exactly the same as that of a mechanical contact seal in a compressor application. The mechanical contact seal represents the inboard seal, and the throat bushing represents the outboard seal. The internal components of the flush system depend on the particular seal configuration.