Revmaster has been manufacturing the RevFlow series injector carburetor since 1981. The major components of the RevFlow are precision die cast, not machined from bar stock. The die casting process allows for many intricate features to be cast in, thus reducing manufacturing costs. The injector unit incorporates a once-patented variable jet for fuel metering and a guillotine slide which controls the air flow. The two parts work in unison, thus providing the engine with the proper fuel/air mixture.
The fuel metering needle is ground with a flat tapered side which gives it an asymmetrical shape. The needle is attached to the slide and is allowed to float so it is self-aligning when inserted into the fuel nozzle. The head of the needle is configured so it cannot rotate while in service and is spring-loaded so the fuel mixture can be fine-tuned during the initial installation via a slotted adjusting screw. Several throat sizes and needle configurations are available.
The guillotine slide is actuated by a wheel and leaf spring that opens and closes to the throat opening when the wheel is rotated via the control arm. The slide has four flutes that guide it very precisely on several surfaces so the transition from idle to full power is without hesitation.
When the slide is in wide-open position, there are no other obstructions in the way of the air flow except for the needle, thus allowing for much greater air flow than with throttle bodies which have typical butterfly valves. The flat side of the needle is oriented towards the engine and produces a low-pressure on the back side which in turn causes fuel to flow in relation to the air flow.
This characteristic has altitude compensation benefits due to the variance in air density at higher altitudes. In order to manually control the mixture, the injector unit is equipped with a manual mixture control and idle cutoff. Besides controlling the mixture, this system will allow the fuel to be cut off at the nozzle, thus eliminating fuel leakage from the fuel line. Then, on restart, the fuel is at the nozzle for priming and starting.
The unit is equipped with two control arms; one for throttle and one for mixture cutoff. They require vernier type controls with at least 3.5″ travel with solid wire ends. Cable housings are connected to the injector body via cable housing attach points. This eliminates any movement in the cable housing which can cause erratic control problems. The wire ends of the controls are secured at the control arms with barrel clamps.
The fuel inlet fitting is a flared AN-4. The unit is mounted to the intake system by a hose and two clamps. The hose I.D. on most units is 1.5″. Flanged adapters can be provided on request.
In the event multiple units are required, such as for in-line engine applications, up to four units can be ganged on a single throttle shaft.
RevFlow injector sizes range from 28, 30, 32, 34, 36, 38, 40, 42, and 44mm. An alternate air source assembly is recommended for most single unit installations. This unit consists of an air filter, open on both ends, mounted onto the air horn of the injector and held on with a clamp. The ram air tube is clamped onto the opposite end.
The tube incorporates a valve that controls the ram air. When in the closed position the ram air is cut off and the engine is digesting warm filtered cowled air.
The RevFlow injector is a 1 to 2 psi low pressure injector. It will function well on gravity feed, although some applications require a fuel pump. When a fuel pump is installed, the fuel pressure should be maintained at a nominal 1.5 psi. This is best accomplished with a fuel return line to the source. The return line can be restricted to achieve the 1.5 psi.
For VW engine applications, Revmaster manufactures a special oil pump/fuel pump/oil filter assembly. This allows for an engine-driven fuel pump to be incorporated into certain requirements.
The RevFlow injector unit is floatless; therefore, it lends itself to many installation configurations; horizontal, vertical, etc. The RevFlow injectors have been installed in many various types of experimental aircraft over the years, with excellent service history. The unit is not type certificated and no such claims have been made, intentionally or otherwise.
Under certain moist atmospheric conditions with air temps ranging anywhere from 20 to 90 degrees F it is possible for ice to form in the induction system. The rapid cooling in an induction system using a float type carburetor is caused by the absorption of heat from the air during vaporization of fuel and, also due in part to the high air velocity, causing a low pressure area through the carburetor venturi. As a result of the latter two influences, the temperature in the mixing chamber may drop as much as 79 degrees F below the temp of incoming air. If this air contains a large amount of moisture, the cooling process can cause precipitation in the form of ice, generally in the vicinity of the butterfly which may build up to such an extent as to cause engine stoppage. In a float type carb, the fuel jet is ahead of, or just below, the venturi and throttle butterfly which means that the fuel is being impinged directly in the worst possible place for icing…the carb venturi. Since the RevFlow injector carburetor does not contain a venturi, nor a butterfly valve, the fuel and air is mixed further downstream, beyond the float type venturi refrigeration chamber. The absence of these parts accounts for the decreased likelihood for ice in this type of system.
If ice were to form, it would most likely collect in the intake manifold T area, however, tightly cowled engines with internal exhaust systems would retard or preent this from happening. The alternate air source/ram air cut off valve also assists in this matter. When the ram air is cut off, the engine will digest warm air through the alternate air filter. The exhaust system we usually have in the KR air frame is a four into one, whereas the #4 exhaust pipe runs parallel to the intake manifold. This exhaust heat keeps the intake system above freezing.
The higher the pressure drop in the intake tract, the more likely the system could ice. At higher power settings the pressure drop is lower and less prone to icing. At lower power settings, the pressure drop is much higher and more prone to icing. Auto fuel vaporizes more completely in the same time as 100LL. Thus, a lower air temp will result. This will create a lower threshold for icing. This should be considered when switching over to auto fuel.