The idea of the rotary positive machine was not a new one. Many earlier examples are known, the most famous being the Pappenheim Engine, perhaps dating to the 17th century. The German engineer Franz Reuleaux described this engine as well as a number of other early examples in his Kinematics of Machinery. These devices all used a similar principle, that of two opposite rotating wheels geared together by teeth or lobes. They were used as pumps and ventilators among other purposes.
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Reuleaux also states that shortly before the Roots invention almost identical blowing devices were constructed in England. He cites one made by George Jones of Birmingham in and an earlier one of . it is not impossible that the Roots simply copied recent British work and secured an American patent for it. However, as far as it is known, there would have been no way for the Roots to know about the British work, and the examples cited by Reuleaux preceeded their work only by a year or two at any rate. Thus, although the idea was an old one, the Roots should be credited with perfecting the design and first putting it into operation on a large scale.
This is the conclusion of the London-published Engineer of reporting on the exhibit of the Roots company at the Paris exhibition: "Mr. Roots has the merit of having brought the machine independently to such a state of perfection as to render it superior in many respects to the ordinary fan, and to make it an aspiring competition with the blowing cylinder."
The first major use of the Roots blowers was in cupola furnaces. The first two experimental machines were tested in foundries and large numbers of blowers were manufactured for this purpose. A large blower for the West Cumberland Hematite Iron Works in Workington, England, was described in . At the Philadelphia Centennial, Roots blowers were praised by the Scientific American Supplement as efficient and economical devices for use in foundries:
In a force-blast blower there are two great benefits: economy of power and certainty of result. The blowers exhibited by the Messrs. P.H. and F.M. Roots, of Connersvi1le, Indiana, seem to come up to these requirements.
In reference to economy of power, they, operating by a regular displacement of air, which is forced forward in constant quantity at each revolution use all the power applied either in driving the machine or forcing the air forward. Friction is slight. The internal parts do not come in contact during running, simply approaching each other as close as possible without an actual contact; this renders the blower practically air-tight. The power applied is absorbed but slightly in running, and is therefore almost entirely applied to the work of forcing the air forward. Results are as far as possible certain with these blowers...In securing the best possible results, the proportional amounts of iron to be melted, fuel used, and of air supplied in a given time, should be fixed and unvarying. As these blowers measure and force forward a definite quantity of air at each revolution, constancy of melting conditions are secured."
In industrial Management magazine reported that rotary blowers were still largely used for cupola work. It also stated that they were most economical for pressures between 1/2 pound per square foot and 8 or 9 pounds per square foot.
Another major use of the blowers was in mine ventilation. This was a relatively new field and Roots blowers constituted some of the largest installations in the 19th century. Already by several Roots blowers were in use in mines of the Comstock lode. Two of the largest Roots blowers ever made were installed at the Chilton Colliery near Ferryhill, Enqland in . The impellers each had a diameter of 25 feet and were 13 feet wide. The maximum capacity of the two machines was 200,000 cubic feet per minute. The ventilator was housed in an engine house with a perforated roof. The Engineer of London, reporting on the results of tests run on various ventilators, concluded that the Roots machines were the most efficient that had been installed in mines. The other ventilators compared were those of Cooke, Waddles, Rammell, Leeds, and Guibal.
Of the many uses to which the blowers were put, certainly the most spectacular was in the underground subway constructed by Alfred Beach in under Broadway in New York City. This "aeolar" had an iron shell 21 1/2 feet high and impellers 16 feet long. At 60 revolutions per minute it produced 100,000 cubic feet of air a minute. Costing $20,000, the machine was transported on five large platform cars. The "Western Tornado", as it was called, was pictured in a contemporary pamphlet with the figure of a man inside to show the huge scale. The "aeolar" provided the power for a 22 seat passenger car which ran on tracks from Murray to Warren streets. The car was literally blown to one end and then sucked back by the action of the machine. Other uses were in pneumatic tubes, aeration and agitation, supercharging and scavenging on diesel engines, and in vacuum processes.
Most of the patents which the Roots brothers took out after were modifications of their first scheme. In almost every case these alterations were intended to allow a closer fit, less friction in operation and cheaper means of construction.
The case was modified In a series of patents. Originally sheet metal bent to the proper shape was used. In the Roots patented a shell made of two pieces of cast iron joined together by metal plates. In they further modified the design by placing packing strips in the case which formed the contact surface for the impellers. This was done to cut down on friction and to allow the cast iron case to be made rough since the impellers were no longer in contact with it. This reduced the costs of boring and polishing. Later in the same year a patent was obtained specifying soft metal or plaster of Paris for this purpose.
The shape of the impellers was also modified several times. In , the Roots patented a design for impellers which were constructed of a metal core adjusted to the desired shape by wood strips. This was more economically constructed than solid iron impellers and allowed them to be renewed without entirely reconstructing the entire impeller. In the same year, the Roots also modified slightly the shape of the impellers creating the Figure-8 shape which became very common thereafter. The design of the impellers was subsequently modified in , , and .
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Our novelty casting of the 6-71 GMC blower is based on a mechanical &#;air mover&#; design with an interesting history. The Roots device is a positive displacement pump, used as an air pump or fluid pump. It moves air, but does not compress. The basic design was patented in by Philander Higley and Francis Marion Roots (hence the name) of Connersville, Indiana, as an air pump for mines, grain elevators, blast furnaces, and other industrial applications. As an air pump, it pulls air by trapping it with meshing lobes against the outer side of the blower case and pushes air from the intake side to the exhaust side. In an engine application, when pumped into a confined space such as an intake manifold, positive pressure is developed, along with an increase in temperature of the pressurized air (not a good thing). An intercooler can be used to help cool the charged air.
Roots blowers are typically used where the volume of air moved is large compared to the pressure differential. They also can be run in reverse to measure flow of gases or liquids, such as a gas meter. Since there must be operational clearance between the rotors, a single Roots blower can only pump across a limited pressure differential. Use of Teflon wiping strips in race car blowers increases efficiency, but only so far. If a Roots blower is operated out of normal parameters, the heat generated can expand the rotors to the point that they jam, with obvious results. Since Roots blowers can pump large volumes, but only at moderate compression, they are sometimes used in blower stages, frequently with intercoolers used between to cool the gas (air).
Use of Roots type blowers on internal combustion engines started around , including patenting by Gottlieb Daimler of a Roots supercharged engine design, making the Roots design the oldest of supercharger designs currently used. Also in Germany, Mercedes worked at making the Gottlieb Roots style blower work, and by released a production vehicle with a blower. They made several successful Roots blown models over the next several years.
In the mid Thirties, General Motors wanted to come up with a compact and powerful diesel design, as most of the diesel engines of the time that produced much power were large and cumbersome. In , they finalized development of a 2 stroke diesel engine with six cylinders of 71 cubic inches each (totaling 426 cubic inches, coincidentally). It was called a &#;6-71&#;. These 2 strokes did not have a separate intake stroke, so a forced induction system was required, and the Roots blower design was used for the purpose, resulting in the GMC 6-71 blower. In the application, the blowers did not provide significant air compression, just air movement, and the engines were considered naturally aspirated. Turbochargers are added when boost is required. There are numerous GMC engine models with a different number of cylinders and corresponding blower case length. Some of the models were built by joining two existing models together, i.e. two 6V-71 joined to make a 12V-71.
The earlier Roots blowers used on hotrods and race cars were usually taken off a GMC diesel and modified for such use. The blowers used currently in the top blown classes of racing are derivatives of these units, usually using the same nomenclature like 10-71, 12-71, 14-71, as different blower manufacturers added case and rotor length as air flow requirements increased.
There are also 53 and 92 series GMC engines with blowers, but for some reason they were not adapted for performance use.
Barney Navarro is usually credited with the first installation of a GMC blower on a race car/hot rod. This was a 3-71 unit brought to him by Kong Jackson (Roto-Faze ignitions), taken off a WWII landing craft. Barney was making his own patterns and having castings done for flat head Ford intake manifolds and heads at that time, so he modified an intake pattern to fit the blower, and had one cast. He bored the blower case a little to increase rotor clearance for the heat build up with the boost he was going to run. He used a V belt drive and four Stromberg carbs running alcohol through the blower to a destroked flathead V-8 in his roadster, which ran 147 mph. Barney ran the car at the dry lakes and dirt circle tracks, having to solve drive belt issues rather than mechanical issues with the blower. He also ran the roadster at the drags in Santa Ana in , one of the first to run a blower in a drag racing venue. Tom Beatty, who worked with Barney, built a belly tank lakester, using a Navarro blower setup, and set an open wheel top speed record with it. Beatty made manifolds and drive kits for the GMC blowers and expanded their use considerably.
An interesting side-note about the &#;Mini-Blower&#; casting and Barney Navarro. When Larry (who came up with the Mini Blower idea, and built the patterns) was a kid, he went with his dad all the time to the local auto parts store in Eagle Rock, California, where they lived at the time. Every so often they would see &#;Barney&#; at the parts store or on the street, and his dad would talk for a while. Larry never knew Barney&#;s last name, as he was just his dad&#;s friend &#;Barney&#;, who had a shop in Eagle Rock. Later, when Larry was in his twenties, he had a friend Frank, in Glendale, California, who worked on cars as well. Every once in a while, when over at his friend&#;s house, the neighbor lady&#;s son would show up to visit, and pop over to see what was going on, like stuffing a Racer Walsh cam into a Pinto. The visitor (Barney, again) was just the &#;guy with the interesting twin turbo Corvair, who built some sort of medical equipment&#;. As well as building cars and heads and manifolds, etc., Barney developed a heart and lung machine used by the Kaiser Hospital in Hollywood for 13 years. It wasn&#;t until years later when Hot Rod magazine did an article on Barney Navarro that this all came together. Larry saw the article, with some early pictures of Barney, and thought he was familiar. He showed the article to his dad, who said &#;Hey! That&#;s Barney!&#;. Later, in a conversation with Frank, the friend from Glendale, Larry mentioned the article and showing it to his dad, and that it was Barney Navarro, he used to see as a kid. Frank said &#;what do you mean used to see him when you were a kid? He was the guy who used to see what we were up to when he came by to visit his mom next door to my parent's house&#;. Small world. Ask about Larry&#;s dad and Kent Enderle (Enderle Fuel Injection) for another story. Back to blowers.
While there may be small leakage at low rpm, since the Roots design is positive displacement, it can&#;t flow backward, as a centrifugal blower can, keeping low RPM efficiency near its high RPM efficiency. This results in decent low RPM boost, and therefore, good low and midrange power. There is no lag. As Roots blowers are a simple design, with self-contained lubrication, they are very reliable and reasonably priced.
Eaton Corp. began a development program in to bring an updated Roots type blower to the OEM level for power enhancement on luxury and performance cars. The new Eaton TVS units use high helix rotors with three or four lobe rotors, and an axial air intake at the front or rear. These more efficient units were first used on the Thunderbird Super Coupe, and numerous variants on other OEMS since, including the LS9 Corvette, which uses a thin heat exchanger (intercooler) between the blower and heads. The Eaton blower for the new Mustang GT500 has four lobe rotors.
So, 100-plus years later, the Roots style blower is still in use on race cars and at the OEM level, and still inspires awe when seen sitting on top of an engine. There are centrifugal blowers, screw-type blowers, and turbochargers, which all have their place in history, past and present, but there is nothing like the whine of a Roots.
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