Smooth and Quiet

Floating Cup machines are extremely efficient. Tests of the Technical University of Eindhoven have shown peak overall efficiencies of 97%. The new control valve for variable displacement pumps and motors furthermore strongly reduces the losses of the control system. The Floating Cup principle almost completely eliminates metal-to-metal contact friction, which also improves the durability and reliability of the pumps and motors

Floating Cup motors can deliver high torque outputs, even at zero or close to zero rotational speeds. Since friction losses are almost eliminated there is no stick-slip effect. Furthermore, having a large number of pistons, the torque output is nearly constant. The usual torque variations due to a limited number of pistons are avoided. Floating Cup pumps and motors are designed for heavy duty operation at rated pressures of 500 bar.

Floating Cup pumps and motors are smooth and quite. The number of pistons is about 3 times as high as of conventional piston pumps and motors. The high number of pistons fundamentally changes the behaviour of hydrostatic pumps and motors in terms of noise, pressure pulsations and torque output. The double, mirrored configuration strongly reduces the load on the main bearings and also the structure borne noise.


Automotive production


The Floating Cup is a general principle. It can be applied in pumps and motors, both variable and constant displacement, as well as in hydraulic transformers. Floating cup machines can be applied in a wide range of operating conditions. Difficult operating points, such as start-up at full load, are not an issue anymore. The floating cup machines can also be operated at high rotational speeds, due to reduced flow losses and the low centrifugal forces of the cups.

The Floating Cup principle is ready for cost effective, automotive production. The pistons and cups require a extremely narrow tolerance, which can be realized by means of sorting after the production. Automotive bucket tappets are produced in a similar way. Since the ‘floating’ cups are free to position themselves, there is no further tolerance chain.

The floating cup design is well protected. Patents have been granted on the basic floating cup principle in the United States, Europe and Asia. Subsequent patents have been granted on the variable displacement design as well as on some other design details. New patents have been applied on the hydrostatic bearing and the pump control. The technology has been proven by industries and research institutes and is now ready for production and licensing.

exploded view rotation group Floating Cup pump



barrel plate

roller bearing

port plate

fixed pistons

roller bearing


free "floating" cups

barrel plate

free "floating" cups




port plate

fixed pistons

The principle

Piston and cup

Balanced cup

direct conversion

The Floating Cup principle is named after the cup-like cylinders which are carried and supported by a rotating barrel plate. The cups are hydrostatically balanced: they ‘float’ on the barrel plate. Each cup is paired with a piston having a ball shaped piston crown. The piston crown has a cavity. The dimensions of the cavity are chosen as such that the expansion of the piston crown equals the expansion of the cup.

The ball shaped piston crown has the same outer diameter as the inner cylinder of the cup. The resulting sealing line is always and by definition perpendicular to the main axis of the cup, irrespective of the tilt position of the piston. Consequently, the radial pressure load on the cup is equal in all directions. The cup is therefore completely balanced and does not create a hydrostatic load on the piston, which minimizes friction and wear.

Whereas the cups are floating, the pistons have no possibility to move. They are press fitted into the rotor, onto the main shaft. The oil column creates a hydrostatic force on the piston, having the same tilted position as the cup. The shaft torque is created by the radial components of these piston forces. The conversion of hydraulic power to mechanical output power is direct: there are no moving interfaces or linkages. As a result there are also no principle losses.

Multi piston

many, mirrored pistons

Many advantages

Self priming

The Floating Cup design allows for a much higher number of pistons in the same envelope. This fundamentally improves performance. More pistons allow for reduced flow and pressure pulsations. The mirrored design allows to balance the high large hydrostatic forces, resulting in low bearing load.

There are many advantages to a high number of pistons. It offers new opportunities for noise reduction, the pressure and flow pulsations are reduced, and the shaft torque is becoming almost constant. When operated as a motor, a high number of pistons deliver a torque which is unequalled in terms of smoothness and start-up performance.

Having 24 pistons, there are also 24 barrel ports resulting in a large flow area. This minimises flow restrictions in the pump. The short stroke avoids high acceleration and velocity of the oil going in and out of the cups. Together, the short stroke and large flow area minimise the risk for cavitation, and allow for higher operating speeds, even without pre-charging the supply side.



pistons avoid deformation

control pistons

create pure torque

Identical parts

Minimal deformation

Low friction control

Floating Cup can also be applied in variable machines. Most rotation group parts are identical to the fixed unit. The same low cost pistons and cups are also used for bias and control pistons.

Added to the rotation group are two swash plates. These enable the variation of the pump displacement.

The swash plates are designed as such that the deformation is reduced to a few micron, even at the highest pump pressures. Furthermore, the load on the swash plate bearings is minimized. this increases the durability and life-time of these bearings.

Two control pistons, one on the front side and one at the rear are used to control the swash plates. This way there is no additional axial load of the control pistons on the swash plate. The pair of control pistons only generate a torque load. A new control, explained below, strongly reduces the losses compared to conventional pump controls.

new control


Patented control system

Floating Cup pump control is compatible with existing conventional control systems. However, we wanted to avoid the high losses that are currently connected to pump control, in which a continuous leakage flow is accepted. In conventional pumps, these losses can reduce the total pump efficiency with up to 20%. Therefore a new valve and control circuit is developed, which strongly reduces these losses.

The new valve system can take advantage of the

 hydrostatic balanced swash blocks, which only need minimal control force, and, due to the small angle of the principle, minimal control flow. The patented control system allows for a very accurate and precise control, without efficiency losses.


smooth torque

Low friction control

Full torque at startup


In the floating cup design we managed to avoid highly loaded sliding interfaces. This not only reduces friction and wear, it almost completely erases stick-slip effects, which deteriorate controllability at low speed.

This results in having no minimum operating speed for floating cup pumps and motors, no stick-slip behaviour and hardly any torque loss at breakaway. Floating cup machines greatly improves hydraulic winches and other applications were dynamic load control is needed.

The diagram shows a comparison of measured torque efficiencies for different hydrostatic principles at extremely low rotational speeds (< 1 rpm). The torque of a floating cup motor is almost equal to the theoretical maximum. The test results also show a very small torque ripple for floating cup motors. This is one of the advantages of the high number of pistons. Compared to the bent axis motor, the floating cup motor delivers about 20% more torque at start-up and breakaway. Compared to the radial piston motor, the torque efficiency is even twice as high.

The high number of pistons of the floating cup principle results in an extremely smooth torque output. This opens new markets for the hydraulic industry, especially for those applications where NVH is of importance. An example are the recent developments of hydraulic hybrid transmissions for passenger cars and other vehicles.



low friction PISTON head

fixed pistons with cavity

hydrostatic bearing

The pistons in the floating cup principle have a ball shaped piston crown. The cup slides and pivots around this ball shape. The sealing line between the cup and the cylinder is always standing perpendicular to the cup axis. As a result the cup is hydrostatically balanced in all radial directions. The cups can not create a side force on the piston. Hence the friction losses and wear are extremely low.

In the floating cup design the pistons can not move: they are press fitted into the rotor. Unlike other axial piston designs, there are no ball joints or slippers and therefore no additional friction losses, leakage or wear. The leakage between cup and piston is negligible. This is due to a cavity in the piston crown. The cavity is made as such that the piston expansion matches the cup expansion, thereby always closing the gap between the piston crown and the cup, even at very high pressures.

A new hydrostatic bearing is developed for the sealing area surrounding the barrel ports. The new design strongly reduces the friction and the wear of the interface between barrels and port plates.

Floating Cup pump mounted on the Innas test bench

Industrial Property

Manufacturing & Licensing


Floating Cup technology is protected by patents and patent applications covering several patent families. The basic principles for fixed and variable machines are covered, and the protection is meanwhile extended with important improvements.

The geographical area covers Europe, the USA, Japan and recently also China.

The Floating Cup technology for pumps and motors is released for licensing. Next to patent licensing, also know-how and technical assistance is an important part of the licensing arrangement. The market introduction of the first Floating Cup pumps and motors of our licensees is being prepared.  Licensing-in is still possible. Please contact us for more information.


Relevant data on the technology, the performance and recent development status is available through our download page. Hardware testing is allowed under an evaluation program. It is open for OEM's and (hydraulic) industries with a relevant strategic interest. Please contact us for further details.

Copyright 2015 - INNAS BV