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The piston concept working principle

The piston technology working principle is based on the equilibrium of the forces between the spring and the pressure acting against the piston.

In normal working condition the CNG flows through the nozzle section where the pressure falls from the tank value (i.e. maximum 220 bar) down to the outlet pressure (i.e. 9 bar). The pressure force (Fp - green arrows in the picture) in the low pressure volume (green area) acts by pushing the piston up for reducing the nozzle section, thus limiting the flow. The pressure force acts against the spring force (Fs – red arrows in the picture) that pushes the piston down, consequently enlarging the nozzle section. The whole system is in equilibrium  when the pressure force acting on the piston is the same as the one given by the spring.

Functioning of the regulator during the vehicle drive

  • When the driver pushes the accelerator pedal to increase the vehicle speed, a higher flow rate is required. The pressure on the low pressure volume decreases thus reducing the pressure force acting on the piston. The spring force becomes higher than the pressure one and pushes the piston downward, consequently creating a higher nozzle section allowing a higher flow rate. The output pressure returns to a higher value that balances the one of the spring again.
  • When the driver slightly releases the accelerator pedal for decreasing the vehicle speed, a lower flow rate is required. The pressure on the low pressure volume raises, hence increasing the pressure force acting on the piston. The pressure force becomes higher than the piston one and pushes the piston upward. As a consequence, the nozzle section and the flow rate are reduced. The output pressure returns to a lower value balancing the one of the spring again.
  • When the driver completely releases the accelerator pedal the flow rate becomes null (i.e. during deceleration fuel shut off), the pressure force becomes higher than the one given by the spring and the piston moves upward until its top reaches the nozzle and shuts it completely. Under this condition the CNG stream is completely stopped until some flow rate is required again. An elastic sealing element is fitted on the top of the piston in order to render  it more effective under this peculiar condition.