Bristol Jupiter VIII F., VIII F.P., XI F., XI F.P.
Part 3: Lubrication and Induction Systems
Compiled by Kimble D. McCutcheon
Published 3 Apr 2025

 

Induction System

Carburettor

An oil-jacketed Bristol triplex pump-type carburettor supplied the mixture to an induction pipe that was bolted to the lowest part of the induction chamber cover exterior. This carburettor had a variable jet consisting of a fluted valve working in a throat, the mixture strength controlled by raising or lowering the valve. Two means were provided for operating the valve of which one can be operated in flight for purposes of mixture control, while the other took the form of a permanent setting only to be changed under conditions that approximated jet changes in a normal carburettor. The slow running jet formed a separate unit from the main jet, having its own calibrated air supply and a separate passage that broke into the throttle housing level with the throttle. The accelerating pump device momentarily enriched the mixture when the throttle was opened, thereby improving acceleration and making it possible to open the throttle rapidly. At the same time, normal fuel consumption was maintained when the throttle was stationary as the pump only came into play with the opening movement.

The Triplex carburettor consisted of three separate carburettors contained in one unit, thereby saving size and weight. It divided itself into three main assemblies. The upper one was the oil-jacketed choke (venturi) tube housings with the throttles mounted at their upper ends. The horizontal extension from the choke casting base formed the choke chambers top and provided a mounting into which were screwed the diffusers and slow running jets that extended through it into the float chamber beneath. The next casting was the float chamber, which consisted of a rectangular tank partitioned into three compartments, each fitted with a drain plug. The whole was bolted to the underside of the extension from the choke, which formed the float chamber top. A vertical extension at the casting starboard end housed the pump device barrel. The third casting was an air intake elbow the mouth of which was flanged for air intake attachment. A common duralumin feed pipe ran the length of the float chamber base casting, was attached under each needle valve seating and supplied fuel to the three float chambers.

Choke Tubes. Three choke housings had flanges at the top, which were drilled with eight bolt holes and faced for attachment unit to the induction elbow. The choke tube throat was almost at the bottom and immediately above this a passage entered an annular chamber formed between the choke tube wall and the choke housing. This chamber communicated with the choke tube bore by two rings of small holes drilled around the tube, and by these the mixture was drawn off from the diffuser. Immediately below the throat another row of holes was drilled in the choke tube wall. These communicated with another chamber formed between the choke tube wall and its housings; this chamber was partitioned from the upper one by a collar formed on the choke tube outer surface. These holes communicated with another and slightly smaller passage that constituted the air inlet to the diffuser. A small duct leading out of this passage into the float chamber established a balance of pressure between the air at the base of the choke tube and that within the sealed float chamber. The mixture from the slow running jet traveled through a passage formed on the float chamber top, which continued up the choke housing side and broke into the choke bore immediately above the throttle closed position.

Throttles. Three streamlined butterfly throttles were mounted on a common spindle near the choke housing tops and a lever at the spindle left end connected to the cockpit control lever and operated the three throttles simultaneously. Serrations on the lever enable its position to be fixed during installation. A transfer passage ran transversely across the throttle and formed in its thickness of it, overcame the flat spot that tended to occur during throttle opening when transitioning between the slow-running jet and main diffuser.

Oil Jackets. The three choke tube housings were cast integrally within a rectangular oil jacket that surrounded them and was part the oil scavenger circuit between the oil sump and the scavenger oil pump. The oil jacket top, floor and the corners were integral with the main casting, but the sides and ends were closed by bolted-on cover plates. A horizontal longitudinal partition ran the jacket's length halfway down its depth and divided it into two compartments. The starboard end plate was fitted with two unions, one above the other, for the connection of inlet and outlet pipes; each union opened into one of the compartments. Communication between the compartments at the jackets' opposite end was provided by a recessed panel in the cover plate at that end, and the oil was thus circulated from one chamber end to other. The remaining cover plates all made a surface joint with the partition.

Float Chamber. Each float chamber compartment housed a horse-shoe shaped cork float that was carried on a stainless steel lever riveted to the float middle. Narrow brass plates captured the float and gave additional support to the lever, which was soldered to the top plate. Thin copper rivets passed through the float and both plates. The needle valve mechanism was housed in a vertical chamber formed by a float chamber extension. The fulcrum bolt on which the float operated was mounted in bosses in the needle valve chamber walls. The boss by which it entered was threaded to receive a threaded bolt portion immediately below the head, and the opposite boss was bored with a plain hole to receive the bolt's plain end; a fiber washer was fitted beneath the bolt head. The needle valve was made of square-sectioned hardened stainless steel, the corners of which were rounded. A groove cut at its upper end received the forked float lever end. Below this the needle's stem was machined to circular section to a point towards the lower end where the section was again left square. After this the lower end was machined circular for a short distance and finally terminated in the usual conical end that engaged the seat. This construction resulted in the corners forming bearing surfaces in the long tubular guide's bore, which located the needle therein. Machined from solid steel bar, the guide extended below the float chamber floor and the needle valve seat was approximately level with the floor. The extension below the float chamber was used as the means for attaching the common feed pipe. The guide was formed with a collar resting on the float chamber floor and was drawn up against this by a tab-washered nut, screwed on from beneath. It therefore clamped the chamber floor between the nut and the collar. Flats in the feed pipe at points coincided with the needle valves, and holes were cut in these that cleared the nuts' hexagonal heads. A fiber washer inserted between the pipe surface and the float chamber floor made a fuel tight joint when a flanged cap fitted with a similar washer was screwed on to the extension lower end that extended across the feed pipe diameter and projected below. Four radially drilled holes in the extension portion within the feed pipe admitted fuel to the guide bore and four similar holes immediately above the needle valve seating passed it into the float chamber. The duralumin common fuel pipe had a square section with a circular bore. The pipe exterior was turned to circular section except for a narrow flange at each end and at the points beneath each needle valve seat, where the flat formed a seating for the pipe on the float chamber lower surface. A hexagon-headed brass blanking plug was fitted at one end of the pipe and a threaded union for the attachment of the fuel supply pipe at the other. Holes drilled in the blanking plug flats received locking wires that were threaded through them and through similar holes drilled in the narrow square flanges at each pipe end. The flanged caps that secured the pipe to the float chamber were also drilled with small holes for locking wires that passed through them and through similar holes drilled in the thickness of the squared pipe portion.

Diffuser. The diffuser was screwed into a boss on the float chamber top and extended vertically downward into a separate compartment within the float chamber, which was bolted to the chamber top and was known as the jet well. The diffuser lower end fitted into a hole at the jet well bottom where it was secured by a nut and tab washer. The mixture control valve fluted head was a working fit in a throat formed at the diffuser bore lower end. The valve head had three flutes of gradually increasing depth towards the bottom. A recess near the throat upper end communicated with the jet well interior by two rows of radially drilled holes, so that as the valve was raised or lowered the effective area of the flutes communicating with the recess was increased or decreased, permitting a larger or smaller quantity of fuel to enter the jet well, thereby controlling the mixture strength passing out of the diffuser. The valve stem extended upward through the diffuser bore and projected at the top where it was anchored to a nut machined with a four-start quick-acting thread that engaged a similar thread on a steel bush mounted at the diffuser body top. Rotating the nut raised the valve, which was returned to its lowest position by a spring captured between a shoulder on its stem and the steel bush body. The valve stem was threaded for a considerable distance from the top down to receive a flanged nut and its lock nut, which form the stop against which the quick-acting nut operated. The quick-acting nut top also included a flange upon which was mounted an index plate. A friction grip lever for operating the valve was mounted on the nut immediately below the flange. Fuel flow was adjusted by slackening the lever and holding it stationary while the nut and plate were turned through the various divisions on the plate. Since the quick-acting nut could only raise the valve return spring returned it to its downward position.

Mixture Control. The quick-acting nut on each valve was fitted with a short friction grip lever and the three levers projected toward the carburettor unit rear, where they were linked by a rod ensuring the three valves' simultaneous operation. The left lever had an extension coupled to one arm of a bell crank lever by a short ball-jointed link. The other bell crank arm was connected by a similar link to a common lever mounted on a sleeve forming the bearing for the throttle spindle. The common lever was formed with an extension to its boss upon which another lever was clamped, the latter providing for connection of the mixture control valve to a pilot's cockpit control. Interconnections between the throttle and mixture controls ensured that when the throttle closed the mixture control valves were automatically returned to the rich setting. The mixture control valve governed all fuel passing into the jet well and therefore into the choke tube (except the small quantity injected during acceleration by the pump device). The diffuser in which the control valve was housed consisted of a brass tube drilled with calibrated air holes that decreased in size and number from the lower end of the tube to about half way up its length. The diffuser tube upper end was of heavier construction and larger external diameter and was formed with a thread that screwed into a boss in the float chamber lid. Below the thread a recess was cut in the diffuser stem that communicated with the diffuser tube bore by two radially-drilled holes and which also communicated with the air passage from the choke base . Below the recess the boss bore contracted for a short distance to form a close fit with the diffuser, after which it opened out again to form a recess that communicated with the main passage by which the mixture was drawn from the diffuser into the choke; this recess opened into the jet well.

Slow Running System. The slow running jet tube was also mounted in the float chamber top and at its lower end dipped into the jet well. It was screwed into a duralumin adaptor fitted in the float chamber top. The slow running jet tube consisted of a brass tube conical at the lower end and then of constant external diameter to within a short distance of the top, where it was enlarged and threaded to enter a corresponding thread in its mounting. The tube lower end was drilled with an orifice that constituted the jet. A needle valve in the tube provided jet adjustment. At its lower end the needle was tapered to enter the mouth of the jet. A spiral of phosphor-bronze wire was soldered around the needle to centralize it in the tube. A knurled brass head at its upper end was drilled with holes for a locking wire. A small spring providing a friction grip was captured between the head and the adjacent boss at the tube top into which the head was screwed. A short distance piece was also fitted between the head and the boss, and limited the needle's entry depth into the jet. When the needle was screwed down to the distance piece the jet passed 100 cc per minute; when fully opened it passed 170 cc per minute. Thus, the needle did not close the jet completely. Four radially-drilled holes near the tube top opened into a recess formed partly in the duralumin adaptor and partly by the reduced tube diameter; this communicated from the tube to a passage running across the float chamber lid top. This passage joined the vertical passage running up the choke side and broke into the choke bore of the at a point coinciding with the throttle closed position.

Operating Principle. When the engine was stationary the carburettor fuel level roses to approximately halfway up the jet well height. When the engine was started and was drawing on the slow running jet the suction was shut off from the diffuser tube and was concentrated on the throttle edges. The slow-running jet tube lower end was submerged below the petrol level; the tube orifice was at this end. Practically undiluted fuel was therefore drawn up the slow-running jet tube into the recess surrounding the holes at the tube top. This rich mixture left the recess at the same strength and passed on its way through the slow-running passage. Before reaching the vertical passage on the choke side a calibrated diffuser air orifice entered the passage and partly relieved the suction therein, thereby reducing the mixture strength; the calibrated air nozzle was screwed into the float chamber top within the space enclosed by the jet well. The mixture, now partly diluted, passed up the vertical passage on the choke side. The transfer passage in the throttle assisted in overcoming the flat spot that occurred in the throttle range at the point where the fuel supply passed from the slow running jet to the main diffuser. The transfer passage enabled a large slow-running jet to be fitted, which obviated the flat spot; a jet would otherwise be so large as to cause liquid fuel accumulation in the induction system at the slow running throttle position. When the throttle was in this position, i.e. nearly touching the throttle chamber wall, a strong airflow occurred at both its upper and lower edges. Without the transfer passage the mixture would be withdrawn from the slow running jet passage at the lower edge only, which was adjacent to that passage. With a jet of sufficient size to overcome the flat spot (which was caused by the rapid suction decrease at the slow running jet passage that occurred when the throttle was opened), the air column passing over the passage with the throttle nearly closed would be insufficient to atomize the fuel, resulting in a "wet" mixture. The throttle transfer passage communicated suction at the throttle upper edge to the slow running jet passage, and the mixture strength passing up the transfer passage could be reduced the required extent by drilling diffuser air holes through the throttle underside and into the passage. There were two such holes in the throttle, a large one at the center and a smaller one between this one and the lower edge. The holes not only effected a mixture weakening, but also assisted in atomizing it. A small hole drilled through the throttle upper side into the transfer passage supplemented the air supply that flowed past the throttle when the throttle was in the slow-running position and provides the necessary correction to prevent an excessively rich slow-running mixture, irrespective of the degree to which it was found to be necessary to close the throttle on the slow running setting. When the throttle was opened sufficiently to start drawing from the main diffuser, a suction was established in the delivery passage from the diffuser that led to an air inrush through the air passages to the diffuser top. One of the two passages opened into the choke tube above the choke throat and was subject to suction while the other was below the throttle, and the air entering there tends to have a positive pressure. The entering air passed down the air inlet passage that communicated with the recess surrounding the large holes near the diffuser top and entered the diffuser tube by those holes. It pressed on the tube's fuel column , forcing its way through the small holes, and passing upward through the jet well under the delivery passage suction influence and passed out of the jet chamber top and into the choke tube. This occurred during engine acceleration and the reserve fuel in the jet well and in the diffuser tube formed a rich mixture that provided good acceleration. With the pump type carburettor, at this juncture the mixture was still further enriched. When the throttle was approaching the fully-opened position the reserve was exhausted and was unable to build up again while the throttle was in this position, as the fuel flow entering the well was restricted by the control valve, which, if correctly set, passed the appropriate quantity of fuel for the volume of air entering the choke tube, to form the correct mixture. A straight-through fuel flow was therefore established, the mixture being emulsified by the air supply passing down the diffuser tube, which broke up the fuel stream and diluted the mixture. The small holes drilled throughout the diffuser tube length varied size; those at the top were smaller than those at the bottom. By this arrangement the quantity of air admitted through each hole when the mixture was able to build up in the jet well was such that a constant mixture was obtained. Moreover, as the level sunk, more holes were uncovered and more air was therefore admitted; these two factors combined to provide the compensation that kept the mixture constant when the throttle was fully opened. An index plate on the carburettor body and a pointer on the throttle spindle end indicated the gate position when a gate throttle was fitted.

Accelerating Pump. The pump device rendered the mixture richer when the throttle opened from the closed position to about mid-way in its range, thereby effecting greatly improved acceleration and obviating any possibility of choking during this operation. The device comprised a pump, the barrel of which was formed integrally with the starboard-side float chamber. Fuel was fed into the pump barrel base from the float chamber by two passages in the intervening wall. The pump plunger, which was spring loaded to assist its downward movement, was fitted with a ball-jointed connecting rod that projected through the barrel cover cap and was linked up by a bellcrank lever and a link to a short lever on the throttle spindle end in such a manner that when the throttle was opened the plunger was depressed, and was raised when the throttle was closed. On its downward stroke the plunger delivered the fuel charge in the pump through the outlet at the barrel base, into a small chamber fitted with a delivery non-return valve at the barrel side. After passing through the non-return valve the fuel was forced through an external pipe to three small auxiliary jets situated centrally at the bases of the three choke tubes. The jets were mounted in a rectangular flange that conformed to the choke tube casting base shape to which it was secured by two screws and by the studs upon which the air intake was mounted; the flange was therefore clamped between the choke tube casting and the air intake. Passages in the flange conducted the fuel to the jets. The plunger, which was comparatively long for its diameter, was waisted at the middle, thus virtually constituting two working surfaces, one at each end, which were joined by the waisted center. The upper one served as a steady and the lower constituted the actual plunger. The actual plunger was drilled with diagonal ducts that led to an intake non-return valve fitted in the plunger bottom. Upon plunger upward movement, the ducts and valve passed fuel that flowed from the float chamber into the space formed by the waisted plunger portion to the barrel base. As the throttle was opened the plunger's downward movement delivered this fuel measure into the auxiliary jets. The arrangement of links between the throttle spindle and pump plunger virtually constituted a toggle action that effected a rapid pump plunger movement during the early and critical part of the throttle opening movement when the maximum mixture richening was required, with a progressive retardation towards the stroke end, until when the plunger was at the bottom the toggles were approaching their "dead center" position and scarcely any throttle spindle movement was imparted to the plunger. In this lowest plunger position, another passage in the barrel wall was uncovered that short-circuited the pump barrel base non-return valve and permitted fuel to be drawn through the power jet (when this was operative) by the suction exerted on the auxiliary jets in the choke tubes. This provided the additional fuel required for improved full throttle performance.

Component Details. The barrel bore was fitted with a gunmetal liner that extended over the whole length and projected about 1.25" above the top to provide for the plunger upward stroke completion. The lower liner end lay flush with the casting surface at the barrel lower end, which was closed by a bolted-on cover plate. The delivery non-return valve and dummy power jet were accommodated in a small chamber cast on the barrel side. The valve, its housing and seating were assembled as a complete unit that screwed into a threaded counterbore formed about half-way up the chamber bore. The upper bore end was fitted with a union for connecting an external pipe leading to another union on the flange that carried the auxiliary jets in the choke tubes. The power jet was housed in a horizontal passage immediately above the valve. The passage, which was bored radially with respect to the pump bore, was also tangential to the valve chamber bore and broke into it, thereby providing a fuel passage from the pump barrel to the auxiliary jets without passing through the valve. When fitted, the power jet consisted of a waisted brass screw plug with a square head, the waisted portion coinciding with the opening from the passage to the valve chamber. The jet orifice, which was drilled from the waist to the inner plug end, was calibrated and controlled the fuel quantity that passed to the auxiliary jets when the throttle was approximately nine-tenths open. At all other positions the passage from the pump barrel to the jet was closed by the pump plunger and was uncovered when the plunger reached its stroke bottom, when the waisted plunger portion coincided with the port. A hole was drilled through the jet head for a locking wire. In engines where the power jet was not employed a blanking plug was fitted instead of the jet.

A common cover cap that closed the pump barrel and valve chamber bases had a channel connecting the pump barrel and valve chamber bases, which provided a fuel passage from the pump to the valve chamber and then to the auxiliary jets in the choke tubes. The cover was fitted with a jointing washer to render it fuel tight. During acceleration the fuel was forced by the pump plunger from the pump barrel base to the valve chamber. The fuel lifted the delivery non-return valve in the chamber and passed direct to the auxiliary jets in the choke tubes. There were two passages in the intervening wall between the float chamber and the pump barrel. The lower one was primarily for the fuel supply, while the upper one was an air passage that lay above the fuel level in the float chamber and was provided to relieve the slight suction created in the pump barrel upper part due to the airscrew slipstream. Without the upper passage the suction would cause fuel to be drawn out with the air, but the provision of this passage above the level of the fuel in the float chamber relieved the suction by air drawn from the float chamber upper part. The plunger was of duralumin. The lower or plunger portion was fitted with a pin-located phosphor bronze piston ring. The plunger, which was hollow ended, accommodated in its bore the inlet non-return valve whose housing and seating were assembled as a complete unit that screwed into the bore. A flange at the valve housing base featured four holes for engagement of a pin spanner; the housing was secured in position by a small grub screw (set screw) entered through one of the holes. The four oblique holes in the plunger step surface, where the reduced diameter for the waist occurred, led to the valve and passed the fuel from the space formed by the waist, through the valve, into the pump base. Although the spring loading on the valve was heavier than would yield to the small weight of fuel above it, the valve was opened by the suction created beneath it by the upward plunger movement, the outlet from the base being sealed by the delivery non-return valve. The plunger upper end was also hollow and housed a socket for the ball that was attached to the connecting rod lower end. The ball socket upper portion was formed by a brass cap that was screwed into the plunger upper end with a pin spanner and was locked with a grub screw. The connecting rod screwed into a shank on the ball; the shank was formed with a hexagon for application of a spanner when entering the rod. A brass lock nut was fitted on the rod, and in addition the ball was secured against rotation by a taper pin that passed through the shank and rod; the nut was further locked by a tab washer. A cover plate with a central hole for the connecting rod was attached by three screws and was fitted on the barrel open end. The plunger spring was captured between the plate and the plunger. The connecting rod upper end was pivoted to one arm of the bell crank lever whose fulcrum was fixed on the throttle housing oil jacket end cover. The lever other arm was connected by a short knuckle-jointed link rod to the short lever on the throttle spindle end. The flange that carried the auxiliary jets was of aluminium. It was had a passage throughout its length on one side that served as a common feed pipe for the three hollow arms that carried the jets. All three auxiliary jets were calibrated to pass 320 cc, thereby providing equal fuel delivery to each choke tube. When the power jet was employed the measure of fuel passed by this was considerably less than the requirements of the auxiliary jets and these therefore acted as diffusers. Their comparatively large capacity was provided to permit fuel discharge from the pump under conditions of the most rapid throttle opening. The jets were made with squared flanges at their bases to receive a spanner and were drilled to take a locking wire.

Induction System

The induction elbow was exhaust- heated and consisted of three annular chambers that surround a steel pipe through which some of the exhaust gases passed. The three annular chambers were formed in a one piece aluminium casting and they were divided from each other by annular partitions. A central core ran through the whole and was reamed out to receive the steel pipe, which was shrunk into it. The elbow ends were formed to receive steel extension pipes that were carried outside the fuselage where they joined the main exhaust pipes. The junction between the extension pipe and the manifold was by a spherical joint that allowed sufficient movement to render the extension pipe self-aligning. An aluminium guard pipe surrounded the pipe as a protection from heat, and this was located axially by collars on the flanges that were riveted at the extension pipe ends and between which the aluminum pipe was held. Three short branches led from the induction elbow to three apertures in the circular induction chamber cover to which they were attached by four studs at each aperture.

The mixture supply from each carburettor was isolated from the remaining two by a three-start spiral housed within the induction chamber. The spiral carried the mixture in each of its three channels to three equally spaced cylinders. This arrangement not only ensured an equal mixture distribution to all cylinders, but also resulted in smoother running if one carburettor failed. The spiral also tended to produce a more homogeneous mixture. The induction elbow branches were appropriately marked with the cylinder numbers each carburettor served. Facing the engine rear, the port unit supplied cylinders 2, 8, 5, the center 3, 9 and 6, and the starboard unit 1, 4, 7. Upon entering the induction chamber the mixture was deflected in one direction around the spiral by the provision of six baffles so disposed around the spiral as to divide the induction passages formed by the spiral into three complete and separate passages, each of which led to the three cylinders served by the most direct route from the carburettors. The baffles were shaped to fit the spiral cross section except for a 0.004" clearance that was left between the baffle and the induction chamber cover.

The induction pipes were of light gauge aluminium tube and were held between the inlet branch pipe at the cylinder head and the spigot at the crankcase. The attachment at each pipe end consisted of a loose flange that was recessed to receive a rubber composition gland that encircled the pipe. When the flange was tightened by its four nuts the rubber was compressed against the pipe and formed an air-tight joint, at the same time allowing for the slight movement that occurred when the cylinder became hot and expanded. A small steel clip on one stud at each induction pipe end established an electrical earth connection. The inlet branch at the pipe's outer end was formed with two branches, each of which served one cylinder inlet port; two studs secured each branch to the cylinder port.

The joints between the carburettor unit and the induction elbow, and between the elbow and the induction chamber were made with thin sheet copper to facilitate heat conduction. Paper washers dressed with jointing compound were used for the joints between the induction branches and the cylinders. The joints between the induction chamber cover and the crankcase were also made with a paper washer of specific thickness, and liquid jointing compound.

Air Intakes. Three air intake types were used: the closed common, the open common (or Wapiti), and the Hinaidi. The closed common air intake consisted of a tube-shaped aluminium casting whose ends were formed with external hexagonal flanges for attachment of loose flanges on the extension pipes' inner ends of; the flanges were each secured by six bolts and spring-washered nuts. A facing on the casting top was formed with three apertures that corresponded with the carburettor choke tube housing facing bases. Eight studs projecting from the air intake facing attached it to the carburettor and also carried the  pump jets' auxiliary jet flange, which was clamped between the two. The studs were secured with nuts, spring and plain washers. A union for a drain pipe attachment was at the intake bottom. An aperture in the air intake forward face was fitted with a hinged aluminium shutter that admitted heated air from the lower cylinders. The shutter, which was not adjustable in flight, was set to suit the prevailing conditions. The aperture was fitted with a protective coarse-mesh wire gauze. The loose flanges were for attachment of either the usual straight extension pipe that ran transversely to the fuselage exterior, or for the upturned type for desert or sea use, where it was necessary that the pipe mouth was high and out the way, precluding sand or water entry.

The open common air intake consisted of an open forward-facing trough with a faced surface that attached to the carburettor. The intake mouth was protected with a coarse mesh gauze. The Hinaidi air intake was similar to the closed common type, but instead of the tubular shape being straight it was swept forward from the middle towards each end. A facing on the intake top provided for carburettor attachment and no hot air aperture was provided.

Priming System. Three priming nozzles were used to prime the induction system and were located in the induction chamber top; each nozzle entered one of the three spiral starts. The center nozzle had a union for a feed pipe connection and was interconnected with the other two by small pipes. Each nozzle's stem was bored to within a short distance of the inner end, where the bore diameter was reduced to a small orifice to form a spraying jet. A loose atomizer was housed in the bore to assist in breaking up the fuel so that it left the jet as a fine spray. The atomizer was a small plug formed with helical grooves on its outer surface that caused it to spin and break up the flow as fuel passed around it. The plug's rear end was not grooved and was of reduced diameter, acting as a stop to limit the its axial movement. The fuel entered by a radial hole in the stem coincident with the annular recess in the union and, entering the space between the reduced plug portion and the stem bore, passed through the grooves and out through the nozzle.

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