This is an idea for pumping a liquid from low pressure to high pressure, using that liquid as the working fluid for a Rankine cycle heat engine, which in turn pumps the liquid.
As the liquid enters the system, it must be subcooled. That is, it's temperature needs to be below it's boiling point, for
that pressure. Generally, this is not an onerous requirement.
The liquid passes through a manifold which splits it into two streams.
One stream passes through a check valve, then flows through a liquid powered ejector pump, then out of the system.
The other stream passes through a combining manifold, where it joins with additional liquid.
The mixed liquid then enters a device generally known as a steam injector [link]. This is a technology which has been in common use for over half a century, in steam engines. In normal use, it uses steam from a boiler to move feedwater into that same boiler. In our system, the vapor might not be steam, and the liquid might not be water, but the principle is the same. The most important thing to keep in mind is that steam injectors are thermodynamically efficient.
A small portion of the liquid that entered the injector will come out, through an opening called the "overflow." This overflow liquid will be warmer than it started, but still at low pressure. We cool it back down, and recirculate it back to the mixing manifold.
The high pressure liquid coming out of the injector passes through a check valve, and into the lowest part of our boiler.
The boiler is of a slightly unusual design... but not particularly bizarre. There's a middle, heated, region, where boiling happens, a large upper unheated region, in which there will be some liquid and some vapor, and a large lower unheated region.
At the bottom of the boiler, right next to the check valve admitting liquid, is a quick acting pressure actuated valve, probably a butterfly valve. This valve switches from fully closed to fully open when the boiler pressure rises above a threshold, and from fully open to fully closed when the pressure falls below that threshold. The liquid from this valve passes through the ejector pump, and out of the pump system. If it's desirable to cool off the liquid coming out of the pump system, the best place to do it is probably between the boiler and ejector.
At the topmost point of boiler are two valves in series (or possibly one valve with a more complicated actuator). The first valve is activated by a float. When the float moves above a certain upper threshold, the valve closes. When the float moves below a certain lower threshold, the valve closes. The second valve in the series is pressure activated; like the liquid releasing valve at the bottom of the boiler, it quickly opens and closes as the pressure rises and descends below a threshold.
Lastly, we have a temperature/pressure control system. Since the vapor in the boiler is saturated, all we really have to worry about is overpressure. A tube is attached to the boiler at the very bottom, leading to a hydraulic actuator. This actuator presses against a spring, and against a thermal control mechanism, reducing heat to the boiler when the boiler's pressure gets to high. This might be done by turning off a burner, or diverting heat flow around (instead of through) the boiler.
By using as high a boiler pressure as we can, we achieve high thermal efficiency, which in turn results in less fuel consumption. By using an ejector pump between the boiler and the output, we can have the boiler's pressure higher than the output pressure, with losing power due to throttling. Another effect of the ejector pump is that (if we haven't bothered to cool the liquid coming out of the boiler) it reduces the output temperature by diluting the warm liquid with cool liquid straight from the intake.
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There are several possibly good uses for this pump, some of which I'll list.
First, as a fuel pump for the burner of a furnace, water heater, or other process heat. By using fuel at a high pressure, it can be sprayed into very fine droplets. This in turn results in quick evaporation, complete combustion, and minimal particulate formation. Also, the high powered spray helps move air through the burner, which reduces the amount of work needed by the system's fans.
Second, as a hydraulic fluid pump. For this task, the boiler would probably be directly fired. This pump is nearly silent, of course, and it effectively has a built in hydraulic reservoir. I think it would be especially cool if this device were used to power a vehicle -- wheels, power steering, etc..
Third, as a fuel pump for diesel and gas turbine engines, using the engine exhaust heat to heat the boiler.
It's slightly less suitable for pumping gasoline, because we generally want that fuel at as cool as possible, and it's almost inevitable that this pump will slightly heat the fuel. Also, gasoline has components which are quite volatile, which reduces the efficiency.
It's also not very suitable for pumping ground or surface water. It's not the dissolved oxygen that's the problem -- it's easy to make the device immune by using stainless steel. Dissolved minerals, however, would be an issue.