The SU carburettor was a constant-depression carburettor made by a British manufacturer of that name or its licensees in various designs spanning most of the twentieth century.
34-457: The S.U. Carburetter Company Limited also manufactured dual-choke updraft carburettors for aero-engines such as the Rolls-Royce Merlin and Rolls-Royce Griffon . Herbert Skinner (1872–1931), pioneer motorist and an active participant in the development of the petrol engine, invented his Union carburettor in 1904. His much younger brother, Carl (Thomas Carlisle) Skinner (1882–1958), also
68-421: A cold engine. By restricting the flow of air into the throat of the carburetor, the choke valve reduces the pressure inside the throat, which causes a proportionally greater amount of fuel to be pushed from the main jet into the combustion chamber during cold-running operation. Once the engine is warm (from combustion ), opening the choke valve restores the carburetor to normal operation, supplying fuel and air in
102-443: A lean condition (which can cause engine damage). For this reason Japanese motorcycle manufacturers ceased to fit slide carburettors and substituted constant-depression carburettors, which are essentially miniature SUs. It is also possible - indeed, easy - to retrofit an SU carburettor to a bike that was originally manufactured with a slide carburettor, and obtain improved fuel economy and more tractable low-speed behaviour. One of
136-546: A motoring enthusiast, had joined the Farman Automobile Co in London in 1899. He helped Herbert to develop the carburettor. Herbert's son could remember his mother sewing the first leather bellows. It would be given on loan to The Science Museum , South Kensington in 1934. In 1905, Herbert applied for a patent, which was granted in early 1906. Later, Carl sold his interest in footwear business Lilley & Skinner and became
170-519: A partner in G Wailes & Co of Euston Road , London, manufacturers of their carburettor. Herbert continued to develop and patent improvements through to the 1920s, including the replacement of the leather bellows by a brass piston, even though he was a full-time director and divisional manager of Lilley & Skinner. S. U. Company Limited — Skinner-Union — was incorporated in August 1910 to acquire Herbert's carburettor inventions, and it began manufacture of
204-446: A richer fuel mixture when starting the engine. Most choke valves in engines are butterfly valves mounted upstream of the carburetor jet to produce a higher partial vacuum, which increases the fuel draw. In heavy industrial or fluid engineering contexts, including oil and gas production, a choke valve or choke is a particular design of valve with a solid cylinder placed inside another slotted or perforated cylinder. A choke valve
238-419: A similarity to that of the slide carburettor, which was previously used on many motorcycles . The slide carburettor has the same piston and main needle as an SU carburettor, however the piston/needle position is directly actuated by a physical connection to the throttle cable rather than indirectly by venturi airflow as with an SU carburettor. This piston actuation difference is the significant distinction between
272-445: A slide and an SU carburettor. The piston in a slide carburettor is controlled by the operator's demands rather than the demands of the engine. This means that the metering of the fuel can be inaccurate unless the vehicle is travelling at a constant speed at a constant throttle setting - conditions rarely encountered except on motorways. This inaccuracy results in fuel waste, particularly as the carburettor must be set slightly rich to avoid
306-399: Is approximately constant. Under steady state conditions the upwards and downwards forces on the piston are equal and opposite, and the piston does not move. If the airflow into the engine is increased - by opening the throttle plate (also known as the "butterfly"), or by allowing the engine revs to rise with the throttle plate at a constant setting - the pressure drop in the venturi increases,
340-420: Is asymmetrical: it heavily resists upwards movement of the piston. This serves as the equivalent of an "accelerator pump" on traditional carburettors by temporarily increasing the speed of air through the venturi when the throttle is suddenly opened, thus increasing the richness of the mixture. SU carburettors do not have a conventional choke flap, which in a fixed-jet carburettor enriches the mixture for starting
374-409: Is communicated to the upper side of the piston via an air passage. The underside of the piston is open to atmospheric pressure. The difference in pressure between the two sides lifts the piston. Opposing this are the weight of the piston and the force of a spring that is compressed by the piston rising. Because the spring is operating over a very small part of its possible range of extension, its force
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#1732880918564408-536: Is made by letter prefix which indicates the float type: The Imperial sizes include 1-1/8", 1-1/4", 1-1/2", 1-3/4", 1-7/8", and 2", although not every type (H, HD, HS, HIF) was offered in every size. There were also H models made in 2-1/4" and 2-1/2", now obsolete. Special purpose-built carburettors (Norman) were made as large as 3". To determine the throat size from the type number: If the final number (after one, two or three letters, beginning with H) has 1 digit, multiply this number by 1/8", then add 1". For example, if
442-546: Is sometimes installed in the carburetor of internal combustion engines. Its purpose is to restrict the flow of air , thereby enriching the fuel-air mixture while starting the engine. Depending on engine design and application, the valve can be activated manually by the operator of the engine (via a lever or pull handle) or automatically by a temperature -sensitive mechanism called an automatic choke. Choke valves are important for naturally-aspirated gasoline engines because small droplets of gasoline do not evaporate well within
476-515: The GNU Free Documentation License which was imported into Misplaced Pages before November 2008 and is therefore validly licensed for use on Misplaced Pages. All relevant terms must be followed. The original article was at "PowerPedia:Carburetor" . Updraft carburettor An updraft carburetor is a type of carburetor in which the air flows upward within the device. Other types are downdraft and sidedraft. An updraft carburetor
510-504: The extraction of petroleum (and other heavy-duty fluid handling contexts), a choke valve (or "choke") is an adjustable flow limiter that is designed to operate at a large pressure drop , at a large flow rate , for a long time. A choke is often a part of the " Christmas tree " at the wellhead . The most familiar choke design is a solid cylinder (called a "plug" or "stem") that closely fits inside another cylinder that has multiple small holes through it (the "cage"). Gradually withdrawing
544-467: The business. Carl Skinner (T. C. Skinner) became a director of Morris's privately held empire, and remained managing director of S.U. until he retired in 1948 aged 65. Production was moved to the W. R. Morris-owned Wolseley factory at Adderley Park , Birmingham . In 1936, W. R. Morris sold many of his privately held businesses, including S. U., to his listed company, Morris Motors . Manufacture continued, then by The S. U. Carburetter Company Limited, which
578-425: The carburettor. Since the needle is tapered, as it rises and falls it opens and closes the opening in the jet, regulating the passage of fuel , so the movement of the piston controls the amount of fuel delivered, depending on engine demand. The exact dimensions of the taper are tailored during engine development. The flow of air through the venturi creates a reduced static pressure in the venturi. This pressure drop
612-494: The carburettors in a factory at Prince of Wales Road, Kentish Town , in North London. Sales were slow. Following the outbreak of war in 1914, carburettor production nearly stopped, with the factory making machine gun parts and some aircraft carburettors. With peace in 1918, production resumed, but sales remained slow and the company was not profitable, so Carl Skinner approached his customer, W. R. Morris , and managed to sell him
646-715: The correct stoichiometric ratio for clean, efficient combustion. The term "choke" is applied to the carburetor's enrichment device even when it works by a totally different method. Commonly, SU carburettors have "chokes" that work by lowering the fuel jet to a narrower part of the needle. Some others work by introducing an additional fuel route to the constant depression chamber. Chokes were nearly universal in automobiles until fuel injection began to supplant carburetors. Choke valves are still common in other internal-combustion engines, including most small portable engines, motorcycles , small propeller-driven airplanes , riding lawn mowers , and normally-aspirated marine engines. In
680-469: The downsides of the constant depression carburettor is in high performance applications. Since it relies on restricting air flow in order to produce enrichment during acceleration, the throttle response lacks punch. By contrast, the fixed choke design adds extra fuel under these conditions using its accelerator pump. SU carburettors were supplied in several throat sizes in both Imperial (inch) and metric (millimetre) measurement. The carburettor identification
714-411: The engine from cold by restricting the air supply upstream of the venturi. Instead a mechanism lowers the jet assembly, which has the same effect as the needle rising in normal operation - increasing the supply of fuel so that the carburettor will deliver an enriched mixture at all engine speeds and throttle positions. The 'choke' mechanism on an SU carburettor usually also incorporates a system for holding
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#1732880918564748-404: The fuel under all operating conditions. This self-adjusting nature makes the selection of the maximum venturi diameter (colloquially, but inaccurately, referred to as " choke size") much less critical than with a fixed-venturi carburettor. To prevent erratic and sudden movements of the piston it is damped by light oil (20W Grade) in a dashpot , which requires periodic replenishment. The damping
782-415: The name The S.U. Carburetter Company Limited, which continues to manufacture carburettors, pumps and components, mainly for the classic car market. Relocating SU carburettors feature a variable venturi controlled by a piston . This piston has a tapered, conical metering rod (usually referred to as a "needle") that fits inside an orifice ("jet") which admits fuel into the airstream passing through
816-401: The piston rises and falls according to the rate of air delivery. Since the position of the piston controls the position of the needle in the jet and thus the open area of the jet, while the depression in the venturi sucking fuel out of the jet remains constant, the rate of fuel delivery is always a definite function of the rate of air delivery. The precise nature of the function is determined by
850-420: The plug uncovers more and more holes, progressively reducing the resistance to flow. If the holes are regularly placed, then the relationship between the position of the valve and the flow coefficient (C v ) (the flow rate per unit pressure) is roughly linear. Another design places a closely fitted cylindrical "sleeve" around the outside of the cage rather than a plug inside the cage. A choke may also include
884-448: The pressure above the piston falls, and the piston is pushed upwards, increasing the size of the venturi, until the pressure drop in the venturi returns to its nominal level. Similarly if the airflow into the engine is reduced, the piston will fall. The result is that the pressure drop in the venturi remains the same regardless of the speed of the airflow - hence the name "constant depression" for carburettors operating on this principle - but
918-465: The profile of the needle. With appropriate selection of the needle, the fuel delivery can be matched much more closely to the demands of the engine than is possible with the more common fixed-venturi carburettor, an inherently inaccurate device whose design must incorporate many complex fudges to obtain usable accuracy of fuelling. The well-controlled conditions under which the jet is operating also make it possible to obtain good and consistent atomisation of
952-452: The same, only their needles are interchangeable. In 1929 SU introduced the Petrolift electric fuel pump, which could be fitted as a substitute for the vacuum type pumps common at the time. This was superseded in 1932 by the L type fuel pump, which used a solenoid to operate a diaphragm pump. As of this edit , this article uses content from PESWiki , a source licensed under the terms of
986-737: The stock Linkert, Bendix or Keihin carbs with SU's until the Keihin Constant Velocity carb became stock in 1990. S.U. carburettors remained on production cars through to 1994 in the Mini and the Maestro , by which time the company had become part of the Rover Group . Hitachi also built carburettors based on the SU design which were used on the Datsun 240Z , Datsun 260Z and other Datsun Cars. While these appear
1020-415: The throttle plate slightly open to raise the engine's idling speed and prevent stalling at low speeds due to a rich mixture. The beauty of the SU lies in its simplicity and lack of multiple jets and ease of adjustment. Adjustment is accomplished by altering the starting position of the jet relative to the needle on a fine screw (26TPI for most pre-HIF versions). At first sight, the principle appears to bear
1054-490: The twentieth century. S.U. also produced carburettors for aircraft engines including the early versions of the Rolls-Royce Merlin , but these were of the conventional fixed-jet updraught type rather than the firm's patented constant-depression design. Standard S.U. carburettors were also a popular upfit for Harley-Davidson motorcycles, given their space saving "side draft" design and superior ability to self-compensate for changes in air density/altitude. Many owners replaced
SU carburettor - Misplaced Pages Continue
1088-524: The type number is HS6, the final number is 6: 6/8 = 3/4", add 1, total is 1-3/4", etc. If the final number has 2 digits, it is the throat size in mm. For example, if the type number is HIF38, the final number is 38, size is 38 mm etc. S.U. carburettors were widely used not only in Morris's Morris and MG products but such British makes as Rolls-Royce , Bentley , Rover , Riley , Turner , Austin , Jaguar , and Triumph , and Swedish Volvo , for much of
1122-620: Was incorporated 15 September 1936, as part of the Morris Organisation, later known as the Nuffield Organisation . The companybecame a subsidiary of British Leyland , and traded under the name SU Carburetters. The S. U. Carburetter Company Limited of 1936 was voluntarily liquidated in December 1994. In 1996, the name and rights were acquired by Burlen Fuel Systems Limited of Salisbury , which incorporated an entirely new company with
1156-443: Was the first type in common use. In it air flows upward into the venturi to mix with the fuel. An updraft carburetor may need a drip collector. Choke valve In internal combustion engines with carburetors , a choke valve or choke modifies the air pressure in the intake manifold , thereby altering the air–fuel ratio entering the engine. Choke valves are generally used in naturally aspirated engines to supply
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