The Humphrey pump is a large internal combustion gas-fueled liquid piston pump. The pump was invented by H. A. Humphrey and first presented in paper to the Institution of Mechanical Engineers on 19 November 1909. A pump capable of pumping 250,000 gallons per hour to a head of 35 feet was exhibited at the 1910 Brussels Exhibition, where it was awarded two Grands Prix, for both engines and pumps. A small number of pumps were built between 1906 and 1925 for use in large-scale water supply projects. Although only a few pumps were built, some continued in service into the 1960s.
Operation
Humphrey's pump consists of a large U-shaped tube, filled with water. One end is sealed by a heavy cast iron, or steel, 'combustion head'. The combustion head contains the inlet and exhaust valves, the ignition source and withstands the pressure of the combustion chamber. Water enters the pump through sprung inlet valves below the combustion chamber. A distinctive feature of the Humphrey pump, compared to others, is that the water only has to flow through this single set of valves: there are no non-return outlet valves, only the inertia of the delivered water within the outlet pipe is used to control its flow. As there are no delivery valves opening and closing suddenly, the water flow changes smoothly, avoiding water hammer and the usual problems for this type of pump. Combustible gas, mixed with air, is supplied into the combustion chamber and then fired by an electric spark. The force of the expanding gas drives water downwards from the combustion chamber and accelerates it along the delivery pipe. Once the chamber pressure drops to that of the inlet water, the delivered water is no longer being accelerated but the large mass of water in the long pipe continues to flow by its own inertia. This reduces the pressure in the chamber below atmospheric, which causes the inlet air and gas valves to open, drawing in fresh air as a scavenging effect. As the water begins to flow back down the U, this increases the chamber pressure and causes the exhaust valves to open.
Four-stroke and two-stroke cycles H A Humphrey patented both four-stroke and two-stroke versions of his engine. The four-stroke design required mechanical interlocks to the inlet valves, so that the exhaust and scavenge valves open once during the cycle to allow scavenging of the exhaust, but not during the compression cycle afterwards. A two-stroke cycle was also possible, if adequate scavenging could be achieved. The air trapped within the combustion chamber of a Humphrey pump has two roles: both for combustion and also as an air spring to maintain the oscillating water column. As this spring action involves a large volume of air, relative to the minimal air needed for combustion, the air cools easily to below the ignition temperature to pre-ignite the next charge. There would still be a risk of inefficient four-stroking though, unless the scavenging is effective enough to sweep out the previous exhaust gases. This was done by using a tall, thin combustion chamber so that the combustion air remained roughly isolated from the majority of the chamber's air and so was scavenged through the exhaust valves first. There was no separate scavenge air valve. A large amount of experimental work on the two-stroke version of the Humphrey engine was conducted by multiple companies in the hope of improving the type's efficiency and power density. In practice however it was impossible to prevent the incoming gas from mingling with the products from the previous combustion cycle resulting in the loss of gas through the exhaust valves. The only 2-stroke Humphrey pump to enter service was a single example designed by A.P Steckel and installed at the Sun shipyard in Pennsylvania in 1925. All other commercial installations were of the 4-stroke type.
Limitations and advantages The main limitation of the Humphrey pump is that it has no suction capacity, in fact it must be installed in a dry sump several meters below the supply level. Given the pump's physical size and the need to protect the equipment against flood events, this is no small engineering exercise, requiring (in the Cobdogla example) several thousand tons of concrete. Its advantages however are: with no moving parts except for the dozens of spring-loaded inlet valves, it has low maintenance and high reliability. The Humphrey pump's efficiency was also good by the standards of the time. The demonstration pump exhibited at the Brussels exhibition was tested by Prof W.C Unwin in 1909 and was found to require around 33% less fuel gas than would have been consumed had contemporary gas burning engines been used drive pumps moving the same amount of water to the same height.
Installed pumps
… excerpt ends here. Continue reading the full article.
