Giovanni Battista Venturi was born in 1746 in Bibbiano, a small village in the Province of Reggio Emilia, Italy. At the age of 23, he was ordained as a Catholic priest and, in the same year, was appointed as a teacher of logic at the University of Reggio Emilia. In 1774, he moved to the University of Modena as a professor of geometry and philosophy. Over the next years, Venturi would also have success as a university-level mathematics instructor, a civil engineer, a politician, a statesman, a confidant of Napoleon I Bonaparte, and, in later years, as a renowned historian.
But perhaps his greatest achievement was made in 1797, with the publication of Experimental Inquiries Concerning the Principle of the Lateral Communication of a Motion in Fluids. Venturi discovered that fluids moving through a gradually narrowing pipe gain speed. Scientifically explained, it can be said that since the number of fluid molecules going in and coming out of the pipe is constant, they have to gather momentum in order to move through the constriction.
Venturi further noticed that at the same time when the fluid flowing through the constriction speeded up, the pressure the fluid exerted on the pipe walls dropped. In fact, the pressure is the lowest where the speed and constriction are the greatest, creating a partial vacuum. Known as the Venturi effect, this phenomenon is used to this day to move, push or drag one fluid by using nothing else than the motion of another – the “lateral communication of motion in fluids,” as Venturi described it.
The same phenomenon is observed in airflow. The Venturi effect predicts that a narrow air passage or opening that acts as a constriction will force the flow of air from a high-pressure area through a low-pressure area (or constriction), hence creating a natural flow of air.
In 1909, nearly a hundred years after Venturi first published his findings, the Rumely Company launched its first tractor in La Porte, Indiana (USA).
Meinrad Rumely, who along with his brother Jacob founded the M. & J. Rumely Company in 1853, was a blacksmith turned agricultural equipment manufacturer. The company’s corn shellers and horse-drawn threshers were successful enough so M. & J. Rumely Co. shortly afterward expanded its agricultural product lines and sales regions. In 1895, Rumely started building steam-powered traction engines and, by 1908, was experimenting with internal combustion tractors.
“Kerosene Annie” was Rumely’s first prototype tractor built in 1909 and led the company to become the first American tractor manufacturer to use kerosene, a cheap petroleum-based fuel. However, Rumely tractors had many other unique features aside from the use of kerosene. For one, the Rumely “Oil Pull” used oil instead of water as a cooling medium to keep the engine at a steady temperature.
During the period of 1910–1930, four models of “Oil Pull” tractors were manufactured by Rumely. Around the same time, the tractor history in South Africa took off. Not that tractors had not already been used in South Africa, but the popularity of tractors increased especially during the 1920s with tractor manufacturers from all over the world, including Rumely, exporting their models to South Africa. The history collection of the National Museum possesses an example of one such Rumely “Oil Pull” tractor, a 20-30 model ‘W’. The smallest of the super powered Rumely tractors, the 20-30 Rumely, first came into production in 1928. When production ended in 1930, 3 952 models had been manufactured. With its heavy duty, two cylinder engine it was claimed that the ‘W’ could put out 20 horsepower (hp) on the drawbar and 30hp on the belt, which was mostly used to power threshing machines and other agricultural equipment. Unfortunately, not much more is known about the ‘W’ in the collection other than that it was donated to the National Museum by the then Vrystaatse Boerderymuseum.
The Rumely “Oil Pull’s” oil-cooling system, the most unique feature about Rumely’s tractors, works largely the same way as a water-based cooling system, pumping the oil from the engine through the radiator before circulating the cool oil from the radiator back through the engine. The reason behind using oil instead of water is that kerosene engines tend to produce a lot more heat under load compared to petrol engines and oil has a much higher boiling temperature than water and does not freeze in the winter.
One may wonder what keeps the oil from overheating during the long hours when the engine is running as there is no fan in the radiator as with modern water-cooling systems. The answer is simple: the Venturi effect.
The shaft in which the Rumely “Oil Pull”‘s radiator is built narrows towards the top, almost like a chimney. Therefore, taking advantage of the fact that air expands, becomes lighter and rises above cool air when heated, together with the constriction in the shaft, a low-pressure vacuum is created, causing fresh cool air to be sucked into the shaft and to push the hot air out through the constriction. Thus, the presence of the Venturi tube facilitates the constant circulation of air through the radiator, cooling the oil without the need for a fan. And now you also know why a chimney is shaped like a pyramid.
Giovanni Battista Venturi (1746 – 1822)
The Venturi effect
Rumely “Oil Pull” tractor with its chimney-shaped radiator
source: Elmar du Plessis