Single point ‘Closed Loop’ system

Advanced single point mixer-ring closed loop system (2nd generation)

Suitable for carburetor, mechanical injection and some electronic fuel injection vehicles

There are a lot more parts to this system than in the picture!

Single point mixer-ring closed loop systems, known as second generation systems,  are much more advanced versions of the first generation open loop systems. By monitoring the exhaust gasses, these systems use computer control to continuously adjust the air / fuel mixture, keeping this correct to ensure emissions are kept down whilst performance and economy are kept at optimum levels. This also ensures that catalytic convertors, if fitted, are not damaged by an incorrect air/fuel mixture and on the more modern electronic fuel injection vehicles (of those that we advise), that engine warning lights and ‘limp home modes’ are not activated by the vehicles petrol ECU.


Suitable for carburetor, mechanical injection, and in some cases electronic fuel injection systems (single or multipoint), with or without a catalytic convertor.


The main system parts comprise of the LPG tank, fill point, vaporiser (reducer), the mixer-ring, ECU unit (computer), in some cases a petrol injector emulator unit, and various valves / solenoids, piping and wiring. A 2 position rocker switch with incorporated LPG fuel gauge is mounted on the vehicle dashboard. The LPG fuel gauge is a row of LED lights, the more LEDs that are lit the fuller the tank.


The switch positions are: run on petrol, run on LPG


Tech-stuff… How does it work?

The mixer-ring is placed on top of the carburetor or onto the air intake just before the throttle valve. It is precision engineered to allow a linear rate of LPG to be sucked into the engine along with air as with a conventional carburetor. The mixer-ring is connected via a hose to the vaporiser. The hose has an inline computer controlled stepper motor valve. The computer receives information about how the engine is performing from the vehicle’s lambda sensor in the exhaust and regulates the inline stepper motor valve to continuously adjust the air/fuel mixture, keeping the mixture correct. The vaporiser supplies fuel at near atmospheric pressure, so the LPG is literally sucked out of it by the vacuum supplied to it by the mixer-ring (adjusted by the inline stepper motor valve). Mixer-rings must be matched to each individual model of vehicle — they come in a large range of sizes and also have a range of venturi sizes that can be fitted inside. Getting any aspect of a mixer-ring system wrong can be the equivalent of putting the wrong carburetor on a vehicle and it would not run properly, even with the computer control of these second generation systems. After installation, the system is set-up and calibrated using a computer which ’talks’ to the computer we have installed on the vehicle. 


As with all aftermarket LPG systems, it is usual practice that drivers start on petrol and drive a minute or so before switching to LPG. This is because the vaporiser requires heat from the engine to convert the high pressure liquid LPG in the tank to a lower pressure gas so it can be used as a fuel for the engine. If the vaporiser were to get too cold, it may not be able to supply enough LPG for the engine if the driver were to suddenly apply heavy use of the accelerator pedal. If you have ever burst a full aerosol or butane lighter you will know what we mean by the above:- a lot of gas escapes at first until the evaporation cools the contents, then the gas escapes much more slowly. If the temperature were kept at the same level (as it is in the vaporiser connected to a warm engine) then the gas would continue to escape at the same rate.




Picture are of a mixer-ring and single point closed loop system ECU. There are a lot more parts involved in this system than those shown!

Text Box: Conversion Prices From £995 all inclusive
D.I.Y Kits From £ 665
Text Box: To contact us call: 
Simon on 01977 651025 
                  07816 237240

Saving motorists around 50% on petrol

  Site Updated January 2012