"It is a certainty that man makes mistakes. Nothing is perfect. Thus all man made innovations must be imperfect."


This kind of inaccurate reasoning leads to misleading statements or conclusions. When adopted as truth, they may become tough fallacies.

Engineering and innovation is hindered by fallacies, and it seems extremely difficult to reset our fallacies, even when we have seen the proof and know that we are wrong.

Thus, we conclude, the best way to cope with fallacies, is to know nothing...

Pump efficiency

Pump & motor efficiency fallacies

Towards realistic loss measurements

For many years we (as hydraulic community) are making mistakes when measuring and comparing the efficiency of pumps and motors.

Measurements that are based on ISO 4409 and ISO 4391:

  • Overestimate the overall losses of pumps and underestimate the overall losses of motors. The difference can be up to 14%.
  • Underestimate the hydro-mechanical losses of pumps and strongly overestimates the hydro-mechanical losses of motors. The mistake can be more than 50%.
  • Strongly overestimate volumetric losses of pumps and the volumetric losses of motors are underestimated. The difference can be up to a factor 2 or even more.

We concluded that ISO 4409 (and other related ISO standards) are no longer sufficient in producing accurate information and may present inconsistencies.


New definitions of efficiencies and power losses are needed.

Together with an international group of leading fluid power experts, Innas has derived a new set of equations for establishing and defining the losses and efficiencies of hydrostatic pumps and motors.


To facilitate pump improvement, an approach is proposed which focuses on segregating power losses, and equations are defined for the overall loss, hydro-mechanical loss and volumetric loss. The details are described in this paper and presentation.


We appreciate your questions and comments,  or your support for this new approach, per our e-mail.



The 2-stroke fallacy

The measurements

Two stroke engines have terrible emissions. The Chiron free piston engine, uses a two-stroke combustion process.

Thus: The Chiron must have terrible emissions.

The Chiron Free piston engine also uses a two stroke principle. The piston is not connected to a mechanical crankshaft mechanism, which dictates the piston movement. The relative low mass of the piston allows for extremely fast accelerations in the top dead centre, leaving too little time to produce NOx. Simultaniously the HCCI proces allows for low soot emissions, and a high efficiency.

large swash angle

small tilt angle - poor efficiency


In Bent axis pumps, increasing the tilt angle to 45o or more, is often considered as the design variable that offers the best possible power density, and resulting in the best efficiencies.

In Swash plate pumps, also increasing the swash angle to a maximum value of ~21o offers the best efficiencies.

The Floating Cup only has a 8o tilt angle, and will therefore suffer from a poor efficiency.

The Floating Cup design achieved total efficiencies over 97%, exceeding the older principles as the bent axis and swash plate designs.

The tilt angle is just one design variable that affects efficiency. Friction, leakage between interfaces, flow losses are of equal importance when designing a pump.


The zero emission fallacy

The measurements

Electric cars do not burn gas or diesel. They lack a combustion engine, and therefore they do not emit particles. Hence, electric vehicles have a positive effect on reducing particle emissions. This, on its turn has a positive effect on human health, related to Particle Matter (PM).

We analysed the recent literature on non-exhaust emissions of vehicles. We found a positive relationship between weight and non-exhaust emission factors. In addition, electric vehicles (EVs) were found to be 24% heavier than equivalent internal combustion engine vehicles (ICEVs). As a result, total PM10 emissions from EVs were found to be equal to those of ICEVs. PM2.5 emissions were only 1-3% lower for EVs compared to ICEVs.

Therefore, EV's will likely not have a great effect on PM levels. Non-exhaust emissions already account for over 90% of PM10 and 85% of PM2.5 emissions from traffic. These proportions will continue to increase as exhaust standards improve and average vehicle weight increases.

The (peer reviewed) article can be found by clicking here.


The Dutch newspaper De Volkskrant published an article on the outcome of the study. The article "Ook elektrische auto is fijnstofbron", was written by Bard van de Weijer, on May 9th, 2016, page 20, (in Dutch). Please click here for a copy.


Floating Cup

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