The differences between an

Aquamist PWM -V system (Pulse Width Modulated - Valve)
and
PPS system (Progressive Pump Speed).





Delivery method:
- PPS system: controls flow by changing pump speed.
- PWM-V system: controls flow by pulsing an inline valve (same principle as the OE fuel injection system)



Atomisation:
- PPS system: low flow = low pressure = poor atomisation (video)
- PWM-V system: constant pressure at any flow = constant good atomisation. (video)
Consequences:
Poor atomisation results in large droplets resulting in uneven fluid entering each cylinder.
Modern manifolds are not designed for transporting fluid loaded air.



Response time:
- PPS system: slow response due to rotational inertia of the pump. typically between 0.1 to 0.5 second.
- PWM-V system: Fast response time. typically within 0.003 second.
Consequences:
In consistency in Air-fuel ratio under transient load due to the pump's inability to change speed.
A rotating mass has ample inertia resulting in after-spray dribble. (video)



Dynamic range:
- PPS system: only produce 2x between 50-200 psi. (A typical PPS system operating pressure range)
- PWM-V system: comfortably manages x10 minimum flow range between 0-100% duty cycle
Consequences:
Without the dynamic range, PPS system can only operate in a narrow power range of 2x. Not really ideal for Daily Driver.



Linearity:
- PPS system: A linear "pressure" increase does not produce a linear "flow" through an atomisation nozzle. Error can be as much as 120%+.
- PWM-V system: Flow linearity is in the region of 5%, can be improved by a custom designed valve on request.
Consequences:
Wacky AFR under different load and engine speed is common - nightmare to tune.



Cost considerations:
- PPS system: It is basically a motor speed controller, design cost is low. Regardless of how many gizmos are included.
- PWM-V system: Each PWM valve individually calibrated by technicians to ensure flow consistency under harsh engine bay environments. Cost is high.
Consequences:
PWM-V system production cost is high. PPS systems are normally 30% lower to produce. But overall performance is 5x poorer.