Make the right choice for your selection of a flange coupling for hydrostatic machines

Are you wondering how KTR and hydrostatic drives belong together? Our following blog shows you all about hydrostatic drives, what to consider when selecting and which KTR flange coupling is the right one for your application. 

Hydrostatic drives in mobile machines

In mobile machines hydrostatics transforms the mechanical energy of the drive source (usually a diesel engine or electric motor) into hydraulic power. The effective output of a diesel engine is  converted by the hydraulic pump into fluid flow. This system is often used in construction machines because it gives a high energy density in a relatively small package. Even with the recent developments in electric drives, the hydrostatic system will continue to be a relied upon system for years to come. 

Selection of a coupling for hydrostatic drives

A flange coupling is the connection between operating source (diesel engine or electric motor) and hydrostatic drive (hydraulic pump). While selection is straight forward there are a couple items that need to be considered for a proper selection, please see the following:

First, the nominal torque of the application needs to be known. The following formula specifies the nominal torque of the system at the operating speed:

The flange coupling itself is selected through service factors added to the nominal application torque. These factors apply to drives with low load-side inertias. Our recommended factors are as follows:


After determining the minimum nominal torque of the application, the coupling size needs to be selected that has a higher nominal torque rating than the application with added service factor does. However, there are a few other factors to consider other than only torque, in order to make an optimal selection such as alignment, stiffness and assembly considerations.

Comparison of flange couplings for hydrostatic drives

For hydrostatic drive applications we offer the following flange couplings to fit these needs:

The torsional stiff BoWeX FLE-PA and FLE-PAC are aligned by the flywheel, while the torsional flexible MONOLASTIC can also be centered by the bolt pattern on the flywheel. All three flange couplings feature an axial plug-in design that enables a very short assembly length, and offer a wide variety of shaft mounting, for example for all standard SAE and DIN involute splines.

To help gather additional information on your application mounting flange of the hydraulic pump according to SAE, we have created the following questionnaire:

Questionnaire coupling selection for I. C. engines

We also offer mounting flanges for the assembly of hydraulic pumps to the diesel engine according to SAE mounting dimensions in sizes SAE 1 to SAE 6. These flanges are made of steel and cast iron for hydraulic pumps with flange connections according to SAE-A, -B, -C, -D and -E as types with 2 and 4 holes. We also offer housings for the direct assembly to the engine back plate for many engines.

„Our flange couplings are used in more than 300,000 machines and run more than 400 torsional vibration analyses annually. So, no matter if it is a standard or special design – we have always found the right coupling for your drive.“


Andreas Hücker
Product Manager Flange Couplings

+49 5971 798 357