A Different Kind of Engine

Diagram of the simple pump

Fig. 1

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How about an internal combustion engine that has no flywheel, no cooling jacket, no moving parts except a few mushroom valves, practically no lubrication, is light weight and has a high thermal efficiency?

This sounds like a tall order, but Herbert A. Humphrey of England invented a machine that had these qualities. His invention is commonly called the Humphrey Gas Pump and it was used to pump water and compress air. Its outward appearance has no resemblance to an internal combustion engine; it is only in operation that the two are similar.

For heads up to 50 feet, the gas pump is very simple. A piece of pipe with a stand-pipe at one end and a combustion chamber at the other, the latter being surrounded by a few simple fittings. Figure 1 is a diagram of the simple pump. It consists of a conical explosion chamber C, fitted at the top with inlet valve I, the exhaust valve E, and a scavenging-valve not shown. A simple interlocking gear is arranged between these valves by means of which, when valve I has opened and closed, it is locked in the closed position and valve E is released. When valve E has opened and closed, it is locked and valve I is released.

Imagine a charge of gas and air compressed in the top of chamber C and fired by a spark plug which projects through the top of the casing. All the valves are shut when the explosion occurs, and the increase in pressure drives the water downward in the pump and sets the whole column of water in the discharge pipe in motion. The column of water attains kinetic energy while work is being done on it by the expanding gases, so that when these gases reach atmospheric pressure the column of water may be moving at say, six feet per second. The motion of this column of water continues until the pressure behind it falls far enough below the atmosphere to open the exhaust-valve E and the water valves V. Water rushes in through these water-valves and follows the moving column in pipe D, and at the same time it rises in chamber C in an effort to reach the level in the suction tank.

When the kinetic energy of the moving column has been expended in forcing water into the high level tank, it comes to rest and, there being nothing to prevent a return flow, the column starts to move backward toward the combustion chamber and continues with increasing velocity until the water reaches the level of the exhaust valve, which it shuts by impact. A certain part of the burned gas is trapped in the cushion space beneath the inlet valve, and the energy of the moving body of water is expended in compressing this burned, gas to a greater pressure than that due to the static head of water in the tank T. A second outward movement of the column now begins and when the water reaches the level of valve E, the pressure in the compression space is again atmospheric and further movement of the water opens valve I, which has been released by the interlocking device, thus drawing in a fresh charge of gas and air. Once more the column of water returns under the pressure of the elevated tank and compresses the charge of gas and air, which is then ignited to start a new cycle of operations.

Ignition is timed by an apparatus resembling a pressure switch, which closes the electric ignition circuit at the point of maximum compression, and an ordinary battery, coil and spark plug.

In starting the pump for the first time, compressed air is allowed to flow into the combustion chamber until the volume of the air thus introduced is slightly larger than the usual charge. The exhaust valve is then suddenly opened by means of a hand lever, and the escape of the compressed air permits a movement of the water column, which gives the cushion and suction strokes, and so draws in a fresh combustible charge, which, on ignition, starts the engine (pump) working regularly. If the pump is stopped when working regularly, it will always stop with a fresh charge in the combustion chamber, under pressure, so that the only operation necessary for starting is to close the switch on the ignition circuit. The pump can therefore be started and stopped from a switchboard.

The Humphrey Pump described above works on the four-cycle principle, requiring four strokes for completion of one cycle. The time required for the completion of a cycle is governed in design by the length of the 'play pipe' D. Typical rate might be on the order of 12.5 cycles per minute. Other variations of design used double cylinders to draw water twice each cycle and in effect operate as a two cycle pump. If the column of water oscillating in the play pipe of a Humphrey Pump is used as a water piston and caused to rise and fall in an air vessel fitted with suitable valves for the inlet and outlet of air, the combination constitutes an air compressor of high efficiency.

I do not have information on the number of Humphrey Pumps built or years they were built, but it appears that units which could pump against a head of 300 feet were built, and units in excess of 35 horsepower were built by 1923.

Information for this article has come from the 1923 McGraw Hill Book Company, Inc.'s book, Internal Combustion Engines.