FAQ

Working principle of fm-500 flow meter for SANKI fuel dispenser

Currently, all flow meters of fuel dispensers fulfill metering by reciprocating motion of its piston. As shown in Fig. 7.3.2.1, under the action of high-pressure fuel, the piston travels a distance L from position 1 to position 2, and discharge a certain volume of fuel. On the assumption that the cylinder bore of flow meter is D, volume of the metered fuel may be "   ".

                                                    
                                             Fig. 7.3.2.1 Functional diagram of flow meter FM-500
We may analyze the above-mentioned equation, and find out that cylinder bore D of flow meter is a fixed value that may not vary during operation; major factors that may influence the metering accuracy and repeatability accuracy of flow meter are travel stroke L of the piston and the sealability of flow meter.
Two (2) types of motion mechanism are available for flow meters, i.e. crank arm type and cam type. The 2 types have their own merits and demerits, and there are no essential differences between them. To facilitate the analysis, crank mechanism will be taken as an example in the following. Both crank mechanism and cam mechanism may convert translational motion of piston into rotary motion of output shaft, and the two have their own dead center positions as well. In order to ensure the whole flow meter to run normally and pass through the dead positions successfully, multiple pistons (4 pistons in most cases) are usually adopted to drive the output shaft jointly.
Since flow meters are equipped with multiple pistons to work jointly, the flow meter needs a control command center to control the motion of the pistons such that the motions of the pistons may be coordinated properly. The control command center is exactly a distribution valve. A functional diagram of common flow meter is shown in Fig. 7.3.2.2.

                                                
                                                  Fig. 7.3.2.2 Schematic diagram of flow meter
When high pressure fuel is distributed by the distributing valve, via fuel pipes, it respectively enters into cavities A and B, while cavities C and D are connected to the outlet of the flow meter via fuel pipes and the distributing valve. Under the action of high-pressure fuel, piston group AC traves from A-end to C-end, and piston group BD travels from B-end to D-end. In the mean time, the two piston sets jointly push the crank to rotate clockwise, and the distributing valve rotates clockwise as well.

 

                                                    

                                                Fig. 7.3.2.3 Functional diagram of flow meter FM-500
When the flow meter moves to the position shown in Figure 7.3.2.4, the distributing valve closes all the inlet and outlet fuel circuits of piston set AC, so piston set AC is at the dead position. Then, piston set BD continues to move from end B to end D, and pushes the crank to continue to rotate.
Pushed by piston set BD, the distributing valve reopens the inlet and outlet fuel circuits of piston set AC, it is just that the inlet and outlet fuel circuits are switched, which enables piston set AC to cross the dead position, its moving direction is changed to moving from end C to end A, i.e. piston set AC realizes direction switching, as shown in Figure 7.3.2.4.

                                                     
                                                                Fig. 7.3.2.4 Functional diagram of flow meter FM-500

 

And so forth, under the effect of high pressure fuel, and controlled by the distributing valve, the flow meter works in a coordinated way. This is the whole working principle of the flow meter.