THE STEAM POWER CYCLE, a brief overview The feed phase is straightforward; water drawn from the condenser or storage tank is pumped under pressure into the boiler.  Larger powerplants have multi-stage centrifugal feed pumps but piston pumps are more practical in automotive sized power plants. An almost bewildering variety of piston pumps have been used over the years: Single and double acting. Simple and compound. Single and multiple cylinders, inline and radial layout. Powered by the driver or passenger pulling a lever, directly by the engine, with an electric motor, a built-in steam cylinder… Flow rate controlled by varying the stroke, deactivating valves, pressure relief devices And so on…. For all this diversity, the basic operating principles are nearly always the same; a reciprocating piston or ram causes the volume inside the pump body to fluctuate, alternately drawing and expelling a fluid while check  valves direct the flow accordingly. A common variety of high-pressure pump is found in pressure washers. To the left we see that the crankshaft and connecting rod reciprocate the ram in a closely fitting cylinder lubricated by oil from the crankcase while the upper portion of the ram reciprocates in a cavity without touching the sidewalls.  Check valves in the cylinder head, shown in close up at right, are discs held against their seats by springs and permit water to flow in one direction. The two seals separate the water in the upper pump end from the oil in the crankcase. Pressure washer pumps are readily available in a number of sizes and pressure ranges for a few hundred dollars, a simple and effective solution for an automotive feed pump. Note how the feed water and engine exhaust flow paths intertwine in the drawing at left, representing the action of the feed water heater.  As you recall, heat rejected to the environment by the condenser is lost from the system and reduces overall efficiency.  The feed water heater reduces these losses by transferring some heat energy directly from the exhaust steam to the feed water. Feed heaters also come in all manner of shapes and sizes, mostly in a “shell and tube” design wherein a shell encapsulates one or more tubes with fluid flowing in the tube interior(s).  A second fluid is pumped through the shell and is free to circulate around the tube interiors, with heat transferring from one fluid to the other by passing through the tube walls.  If this sounds familiar, it is how the Stanley fire tube boiler functions with hot gasses being the fluid passing through the tubes. Such a heat exchanger is shown at right, the shell being made in two halves bolted together on a central flange while the tube is a helical nest wound from the center outwards. As in boilers, the fluids flow in opposite directions to promote best heat transfer.  The steam enters at the outer edge of the shell and works past the tubes before entering out the center bottom.  The steam enters the tube from the center and spirals outwards, departing at the rim. One would assume finned tube construction due to the lower steam density and conductivity, but this is rarely the case.  The amount of heat transferred by the feed heater is not relatively great and the space and weight savings finned tube could provide are not that significant. One potential difficulty arises if the water temperature in the condenser is too high, the pressure drop at the pump suction can partially flash this boiler feed water into steam, the resulting vapor lock preventing feed water from reaching the boiler, a condition that can sometimes harm the pump not to mention overheat the boiler and cause serious damage or destruction.  Should vapor lock be a problem, a very mild booster pump with low suction and discharge pressure can be added,  the suction pressure is low enough to avoid vapor lock and the discharge pressure is high enough that the feed can no longer flash in the feed pump inlet.