Stirling Liquid Piston Pump

The idea is credited to a Scottish inventor called Robert Stirling in 1816. The idea is that a fixed quantity of air is pushed between two chambers one hot and one cold. The resulting changes in air temperature and pressure can then be used to perform work.

I have seen this little pump in many forms In the late sixty's I saw one on a television science program one made entirely of glass with ball bearings for the valves and heat from a from a spotlight to power the device. Another I have seen was made from metal piping and heat supplied from a lit gas jet to power the device.

The one in the illustration can be made from cheap plastic irrigation water piping fittings and values from a cheap plastic hand liquid pump.

The one thing common to all models is that all joints be air tight. The items you will need

as in illustration or to make it a little easier you could use small irrigation or garden water fittings that come with threaded ends.

It is then just a case of screwing them together. The flat valves could be pieces out of the liquid pump

Two three or two litre empty plastic coke bottles with their tops .These will be the air chambers one for hot one for cold


The alignment is of as in the illustration. The illustration is pretty clear I believe and just to add to it, the following information may be of assistance to you

Remove the tops from the coke bottles and drill a quarter inch hole in center of each top

Cement with plastic putty or whatever you have available the tops in one side of a T Piece make sure that it cannot move and is air tight . You will need two of these , and when the unit is finished the plastic bottle will be screw into the glued plastic tops.

Connect other pieces as in diagram. You may use what ever you can for valves but they should be light round and flat or even

a glass marble fitted into a rounded drill hole in flat piece of plastic inserted or glued into a irrigation connection piece and

most important they must only allow water to flow in one direction and block it from flowing backwards

The other type of valve could be the same drilled hole but with a piece of flat rounded plastic resting on top of it placed on such a way that it cannot move sideways but can move freely upwards and downward.

Priming the pump

Place suction inlet into source of water and pour water into top of unit until level with second level piece under the plastic bottle tops. Water should now be flowing out of the outlet pipe when correct level is reached

Place plastic bottles in position ,one bottle should be exposed to sunlight and the other kept as cool as possible.

Improvements that could be worth trying are

Put some black paint inside a plastic bottle and roll around until the inside surface is covered with the black paint. This will be the bottle exposed to the solar heat.

The other could have a large tin can collar with a small hole in bottom of the can to allow the thread of plastic bottle to exit and be joined to rest of connections. This should have a water tight seal to prevent leakage. When properly sealed, add water to collar and natural evaportion will keep thre plastic bootle cooled.

Or alternately use more connections so that the bottles could be stood right way up and the cooling bottle put into can from the top.

How it works:

The invention alternatively pulls up water through the bottom value and then pushes it through the top valve.

When the air heats up in the hot air bottle pressure expands thus forcing the water in tube out . When the air is cooled down it contracts creating a vaccum that pulls water up through the bottom and so on.

The unit should keep working until heat source is removed. You may need to experiment to make this unit work more efficiently.

Possible use

Although this is only a demo unit a bigger one could be built and used in a hydroponic garden for water cycling

This an article sent to me by an internet contact which explains the Stirling pump in more detail. (Geoff)

Stirling -cycle Liquid Piston engine with no moving parts.

Pollution-free and totally silent, fueled by waste heator sunshine, it can Pump water at no Cost whatever

By David Scott

Brrr! It's midwinter and there's a Power blackout. The furnace is still Producing all that lovelv warmth, but the electric water pump isn't working, so there's no way to circulate the heat throughout the house. And vou're cold. If you only had a pump that didn't rely on electricity, one that could be Powered by the waste heat going up the chimney.

l saw such a Pump at Harwell,Britain's. atomic-energy. research laboratory.

It's an ingeniously simple machine: It has no mechanical moving parts except a couple of ball valves. It needs no seals, no lubrication, no attention.

And it can run on free fuel-like waste heat or concentrated sunshine.

Robert Stirling came up with the hot-air external-combustion engine that bears his name In any Stirling-cycle engine, a fixed quantitv of gas is pumped back and forth between hot and cold chambers bv varying the chamber volumes. ;the resulting changes in gas temperature cause cyclic pressure variations that can perform mechanical work, Harwell's variation on the Stirling cycle engine runs along in eerie silence. Water, sioshing back and forth, does the work.

Runs on air

If the idea of a liquid acting as the pistons in an engine sounds familiar, vou mav be thinking of John Roesel's engine that is part of his on-site energy package. The two engines are similar: Both are based on the Stirling cycle, and both use liquid Pistons. But although Roesel's engine is simple, the engine at Harwell (the boffins there call it the Fluidyne) is even simpler. To begin with, the Fluidyne uses the simplest of elements: Air is its gas and water its liquid. Roesel's engine needs an inert gas (argon or helium) and a special liquid formulated to neither. freeze nor boil over a wide temperature range. And Roesel's engine depends on a number of mechanical elements: spray,. injectors, timed pumps. and a hydraulic motor and flywheel to provide output.

The Fluidynneeds none.

Its simplicity would make the Fluidyne an ideal engine for technologicallv primitive locales. It could provide foolproof irrigation in a developing country, or circulate water in a solar-heating unit.- The original Fluidyne pump looks like an experiment you might have done in chemistry lab: a bunch of glass tubes clamped to an Erectorset structure. "Now watch what happens," said Dr. Colin West, one of the Harwell research scientists, as he carefully aimed an infrared lamp at one end of a U-shaped tube. In a few moments the model began rocking slowly and a crooked tube lashed to one end scooped water out of a bowl with each dip.

It was uncanny The first diagram below and explanation below this page tell how this all happens. The Fluidyne meets the basic requirements of a Stirling cycle engine:

Energy feedback is supplied by the output tube, which not only does the work, but also keeps the displacer tube moving. And there are cyclic variations in the volumes of the hot and cold chambers. The phasing of these volume variations is critical. For maximum output, the change in the gas volume in the cold chamber should lag about 90 deg. behind the hot. This means that, for example, the volume of the cold chamber will reach its maximum one-quarter of the way through the cycle after the hot chamber maximum-volume point. This phase difference is provided by carefully fixing the natural resonant frequencies (the rate at which the water would normally slosh back and forth) of the displacer tube and the output tube. The resonant frequency of one is somewhat lower than the other. Thus, though they have to rock back and forth together, the surges of liquid can be 90 deg out of phase.

Second generation

This kind of fine tuning is essential to the little engine, so the physics involved gets a bit tricky, though the design is indeed simple. "Let's make it simpler yet," thought the Harwell scientists. So they put together a second-generation Fluidyne, one that does awav with the rocking. The advantage: The pivot and spring, subject to wear and fatigue, are eliminated. In the stationary Fluidyne, the two cold chambers are combined as one, which is connected to the hot chamber by the displacer tube. The longer output tube then leads from the bottom of the hot chamber to a vertical tube with ball valves below and above the T-junction. This is the pump, with inlet and outlet valves, and that's all there is to it. To find out what happens in Fluidyne II, see the second diagram. As you can see, the stationary Fluidyne follows the same principles as its ancestor, but in place of mechanical motion, it uses the principle of the water-jet pump to give energy feedback. With each stroke, the oscillating water drags or pushes some of the displacer liquid with it. This hydraulic interaction provides the energy feedback needed by any Stirling-cvcle engine, and the pump keeps going as long as there's heat.

Engine in a bottle

With this exciting nonmechanical concept proven, the Harwell scientists went one step further. Their third-generation Fluidyne works like the second, but it's more compact and easier to construct. The lab model is based on a -lass dis-tillin,- flask with three necks (see bottom diagram). What you have is an engine in a bottle. I saw all these machines running. "But what kind of a job can they do?" I asked Colin West. He showed me a larger experimental unit made from ordinary copper pipe and brass fittings, and with a bit more attention to thermal efficiency. The hot chamber is heated by a close fitting electric element. wrapped in fiberglass insulation, and the cold one chilled by a water jacket. With an input of 250 watts it can lift a gallon of water a minute through a head of three feet,It's still a crude design" he stressed. "For a start, the high thermal conductivity and capacity of the metal displacer tube mean a large heat leakage between the hot and cold ends, which plastic or ceramic could prevent. But remember," he went on,these pumps are intended for situations where heat -natural or waste-is more readily available than electricity. Then the power or fuel consumption is not so important." Heat requirements are modest:

You have to keep the system's water below the boiling point to avoid steam, which would condense in the cold chamber and cause trouble. 175 deg. F is about the optimum. The Fluidvne will need plenty of development. But could be that Harwell has come up with a something-for-nothing device of real promise for an energy-starved and noise-Polluted world.

Fluidyne 1: seesaw pump

Heat, applied to one end of a water-fiiled U-shaped dispiacer tube, expands the trapped air in a connecting air Pipe. As pressure builds. it thrusts equally against ail water surfaces. But only one mass of water is free to move: that in output tube. which is open at other end. As water is pushed a little way through out. Put tube. the rig overbalances and tilts to the left on its pivot point. compressing a spring (top).

The water, rising in hot chamber of displacer tube, pushes hot air toward cold chamber where there is now more space. Air temperature drops and volume contracts. sucking water back through output tube.

This over balancess machine in other direction, and it rocks back to right, extending spring (bottom). This Motion Pushes cold air back to heated space. and cycle repeats.

Frequency is about one cycle per second.

Fluidyne II: stationary pump

Pump alternately sucks up water through the bottom ball valve and expels it in spurts through the top valve as the gas in interconnected air spaces above the hot and cold chambers aternately expands and contracts.

The air goes through its cyclical change in volume as it is forced from hot to cold chamber and back again by sloshing of water in the displacer tube. As water in displacer tube sloshes to the right, it rises in the hot chamber, fails in the cold.

Air is shunted into the cold chamber where temperature fails and volume contracts. This sucks water up through the bottom ball valve. Eventually. gravity begins to restore the balance in a pendulum-like effect. Water sloshes back to the cold chamber.

This forces the air to the hot side where it is heated and expands. forcing water out of the top ball valve. Gravity again pulls the water back toward the hot side: the cycle resumes.

Fiuidyne Ill: pump in a bottle

Smaller and more rugged third generation Fluidyne works like number 2. Dimensions of all water-filled components are critical. and entire unit must be finely tuned to sustain oscillation.