Efficient Construction Machine Cooling: How Variable Displacement Pumps in Fan Motors can Finally be Cost-Effective This solution only generates the energy that is actually needed

Energy prices are on the increase – and this has a direct impact on large construction machine cooling. If you work with hydraulic fan motors, this mostly involves the use of inefficient fixed displacement pumps. They are inefficient because they produce more energy than is needed. They constantly provide the maximum flow rate, although this is needed in very few load cases. The alternative is variable displacement pumps with electronic load-sensing, but these pumps are costly and the valves needed for the pump control are excessively complex and expensive. But not any more – HYDAC has an innovation that makes variable displacement pumps more cost-effective: the PPDB08PZ-01 combination valve.

All-in-One: HYDAC Combination Valve for Electronic Load-Sensing

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What Pump should I Use to Cool my Fan Motors?
Fixed displacement pumps are inefficient.

For thermal management in construction machines, hydraulic fan motors are installed that can provide precisely the cooling capacity that is needed via a variable rotational speed. A fixed displacement pump combined with a proportional bypass controller is the wrong choice here. This combination is a real energy guzzler, as it diverts the flow that is not needed for the fan motor through a bypass valve, resulting in high throttle losses. But the low costs speak for themselves, as pressure-controlled pumps and their complex pump control are too costly. It's no wonder that people tolerate the inefficiency of the fixed displacement pump. 

The Innovation that makes Variable Displacement Pumps in Fan Motors a SuccessCost-effective at last: variable displacement pumps with the HYDAC combination valve

The advantages of pressure-controlled pumps are plain to see: lower energy consumption, power supplied as needed, greater efficiency – and reduced diesel engine exhaust emissions, as the media being cooled can function at an optimal operating temperature. All of these are important factors which make using your construction machines more sustainable and energy-efficient. This was previously only possible with load-sensing controls and external pilot valves, but HYDAC now has a valve that can do it all. 

Our latest development: to operate your variable displacement pump with electronic load-sensing, you now only need one valve. Our electroproportional swivel angle control valve is compact, inexpensive and highly efficient. That's why it makes sense to rethink the variable displacement pump – with the lower valve costs and reduced energy consumption, you will find that pressure-controlled pumps quickly pay for themselves. With energy prices constantly increasing, this means you can be well prepared for the future. 

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How the HYDAC PPDB08PZ-01 Combination Valve WorksThings are going to get a little technical now

  • Closed-loop control of the pump pressure: The combination valve measures the pump outlet pressure and uses direct control of the pump swivel angle to achieve closed-loop proportional control of the pump pressure. 
  • Setting the pump pressure mechanically: The valve has an inverse performance curve. This means that at zero solenoid current, the pump pressure is at its maximum value. You can set this value at the valve mechanically. 
  • Pressure measurement & setting flow rates: A cartridge valve replaces the load-sensing control and the external remote valve. It measures the pressure at the pump connection and directly alters the pressurisation of the swivel angle actuator to set the required flow rate. 

Your Advantages
How you Benefit from the HYDAC Combination Valve

Icon: plant held in someone’s hand – symbolising energy efficiency and sustainability.


Thanks to the use of pressure-controlled pumps and the HYDAC combination valve, only the volume of flow that is needed to generate the correct cooling capacity is produced. This means you can avoid wasting drive energy across the board. 

Icons of people with change-over arrows – symbolising the comprehensive customer support we provide with our combination valves.


Innovation is highly valued at HYDAC – as is comprehensive consultations with our customers. That's why we'll actively support you in making your construction machine cooling process even more efficient. 

Icon: Footprint with the text CO2 – symbolising reduced energy requirements thanks to pressure-controlled pumps.

Lower Emissions

As the pump’s flow rate is adjusted, less energy is required. Thanks to the electronic load-sensing, you can reduce your energy requirements and costs. 

Increase your Cooling System's Efficiency

Find out about our innovative pump control – our experts are on hand to help.

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