Fan Drive Solutions
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Fan Drive Solutions 


Reversing the Impact of Engine Emission Regulations


Improve machine efficiency and operating costs with hydraulic fan drive systems using proportional fan speed control and reversing. Pre-engineered manifolds provide these important fan drive functions. 

applications fan drive group 

Family of pre-engineered Reversing Fan Drive (RFD) HICs designed to counter the impact of engine emissions.


 applications fan drive schematic

Put all the critical fan drive control functions into a compact remote-mounted manifold.


applications fan drive circuit 1 

RFDE-40-000, RFDE-80-000 & RFD-120-000

Piston/Piston Example: Variable pump provides fan speed control. HIC provides reversing and over-pressure protection/anti-cavitation.



applications fan drive circuit 2 

Gear/Gear Example: HIC provides fan speed control, reversing and over-pressure protection/anti-cavitation.



Product Information

Fan Drive Datasheet

Fan Drive HICs Product Section


The best way to reverse the impact of global engine emission regulations is to transition from a mechanically-driven fan to a hydraulically-driven fan. With the new emission-designed engines consuming power that machines had prior to the legislation, machine designers need to find ways to get that power back. Mechanically-driven fans run continuously as a ratio of the engine speed. These fans are sized to handle the maximum cooling required and will run whether there is demand for cooling or not. This overcooling condition is wasted power that could be allocated to more useful work or can save on fuel and operating costs. To understand the potential impact, as a general rule of thumb, reducing a fan’s average fan speed by 10 percent can reduce fan power consumption by as much as 27 percent.

Hydraulic fan drive systems, in comparison to mechanical, provide cooling-on-demand, precise fan speed control, reversing for fan cleaning, reduced noise, and design flexibility to place the cooling system anywhere on the vehicle. Most off-highway vehicles already have hydraulic systems and electronic controllers, so a hydraulic fan drive system can be a relatively easy addition with a high return on investment.

A basic hydraulic fan drive system consists of an open circuit hydraulic pump and motor sized to meet the maximum cooling demand. To then get cooling-on-demand, add proportional fan speed control, electronic temperature sensors (engine charge air, hydraulic cooler, engine coolant, etc.) and an electronic controller to manage it all. Adding reversing functionality to clean the cooling system is easily accomplished by integrating a directional control into the motor or remote manifold. For high power fan requirements, a closed-circuit hydrostatic system—which inherently includes reversing—can be used.


Fan Speed Control

Proportional fan speed is controlled using a normally closed proportional relief valve (PRV), regulating fan speed by controlling the pressure drop across the fan motor. The valve can be integrated into an open circuit piston pump (pilot control), in the fan motor (full flow) or in the remote manifold (full flow). When there is no demand for cooling, 100% of the command signal is applied to the valve. This allows the flow to bypass, providing minimal flow to the motor/fan. As the machine starts to work and the demand for cooling increases, the command signal decreases, thus increasing the pressure and, subsequently, the fan speed. This is the heart of the cooling-on-demand functionality. 

Another important feature is the fail-to-full-speed function provided by the normally closed PRV. With fan drives, it is important to keep the machine from overheating, so in case of signal loss to the valve (due to cut wire, loss of connection, etc.), the fan would go to full speed. This allows the machine to keep operating and remain productive until the problem is fixed.

The fundamental purpose of the PRV valve is to increase the fan speed as cooling is demanded, but some of the key benefits occur when there is no cooling demand. This is where the true savings takes place. In addition to power savings, there is an inherent average noise reduction as the average fan speed decreases. European regulations require that a vehicle with a belt driven fan be operated at maximum fan speed during the test for noise.  European Directive 2000/14/EC states if the vehicle has a variable fan speed capability; it can be operated for the noise test at 70% of maximum fan speed.  This can reduce the fan noise by about 8 dBA and help a machine sold in Europe pass the stringent noise requirements.


Why Reversing?

Working in dirty environments can cause debris accumulation around a vehicle’s cooler and radiator, thus decreasing the efficiency and increasing the power needed to cool. Keeping the cooler clean and free from debris allows the system to operate at peak performance, making more power available for useful work. A reversing fan drive system provides this essential function, making it an important addition to any vehicle operating in these conditions. 

Purging, or de-clogging, the cooler can prevent vehicle overheating caused by extreme debris build up. This can also reduce the manual cleaning typically needed for these applications, while decreasing the amount of high pressure water spray around the engine compartment and near the costly electronic components. 

Common applications that can benefit from a reversing hydraulic fan drive system include, but not limited to: construction & road building (wheel loaders, excavators, skid steer loaders, road rollers, dozers, asphalt pavers, motor graders, backhoe loaders, articulated dump trucks, mobile crushers & screens), agriculture (any harvesting machine, tractors, sprayers), material handling (forklift trucks - combustion, telehandlers, aerial lifts, cranes), buses, forestry machines and landfill compaction equipment. For many of the vehicles listed, reversing could be an optional value-added feature - depending on the end application. For example, not all wheel loaders are going to work in a dirty environment, so fan cleaning would be an option end customers can select when ordering the vehicle.

There are different options for managing the reversing function. The machine microcontroller, like Danfoss Power Solution’s PLUS+1™ with a Fan Drive Subsystem Application, can be configured to reverse at a certain frequency (e.g., once per hour, once per day) depending on the application environmental conditions. A reversing switch can provide additional flexibility, allowing the operator to clean on demand. The complete reversal cycle is managed by the software and offers the ability to modify the timing of each of the following steps: 1) decelerate to minimum speed, 2) reverse the fan, 3) accelerate to reverse maximum fan speed, 4) cleaning time, 5) decelerate to min speed, 6) reverse the fan, and 7) accelerate back to cooling state.


Pre-Engineered HICs

With decades of experience in fan drive systems, Comatrol, along with TurollaOCG and Danfoss Power Solutions, have applied their combined knowledge and experience into pre-engineered fan drive Hydraulic Integrated Circuits (HICs). The product line is called RFD (Reversing Fan Drive) and is built around the PRV10 and PRV12 proportional relief valves that have been applied in fan drive systems since 2005 with over 100,000 valves in the field. The valves have been optimized for fan drive control for precise and repeatable fan speed. 

Additional functionality integrated into the RFD designs includes reversing, dual shock valves and anti-cavitation. The HICs are configurable to allow selection of needed flow range, pressure setting(s), voltage, port size, with PRV, and without PRV. To meet the numerous fan drive system needs, three flow ranges are available – 40, 80 and 120 LPM (11, 21, and 32 GPM). A motor drain connection is standard, helping to eliminate a hose going back to reservoir.

A key component for reversing a fan drive is an open-transition spool on the 2-position, 4-way valve. Because there is always some amount of flow going through the valve when shifting (i.e., the fan is always turning), the open-transition spool reduces pressure spikes during reversals. Additionally, minimal pressure drop across the directional valve is critical because it can reduce fan speed and performance if too constricting. Traditionally, reversing systems have been designed using a CETOP valve (D03/NG6 or D05/NG10), but the D03 has high pressure losses for even the 40 LPM, while the D05’s large size adds weight, cost and requires a large manifold for the 80 LPM range. Comatrol has moved away from CETOP and optimized the new RFDE-40 and RFDE-80 designs around a new DV15 directional valve piloted with a solenoid valve. The RFD-120 design uses a solenoid to pilot two 2-position, 3-way valves to get the same reversing functionality for the high flow demands. 

“Our customers were seeking more efficient and compact designs than our existing 40 and 80 LPM HICs using CETOP valves,” said Rocco Marella, Account Manager (EU). “They needed lower pressure drop through the HIC to improve the efficiency of the fan drive system and a much slimmer design to fit around the tight space constraints in the engine compartment.  We worked closely with product development, leveraging Comatrol’s computational fluid dynamic capabilities, to design and optimize a solution that met these stringent requirements.”

The result of this development work includes a 79 percent reduction in pressure drop of the 40 LPM HIC, from 24 bar (348 psi) to 5 bar (73 psi) at 40 LPM (10.6 GPM), while reducing the overall HIC size by 30 percent.  The pressure drop for the 80 LPM is equivalent to the previous design, but comes in a more compact build with an overall reduction equaling 60 percent.  The RFDE-40, RFDE-80 and RFD-120 come in both the ‘PRV’ (open circuit gear system) and ‘000’ (variable piston pump system) designs, supporting the most common reversing and modulating fan drive solutions in the industry.  For commonization of design, the 40 and 80 solutions are the same size but are optimized for their respective max flow capacity.

Moving away from CETOP produces additional gains with the coils. The Comatrol PRV and solenoid valve(s) come standard with Robust Coils, which are designed to handle the extreme environments of an engine compartment, including ambient temperatures. The integrated Deutsch connectors are IP69K rated for best-in-class sealing against water and dust ingression. The coils are also PLUS+1 Compliant, meaning they are designed for installation on machines that use Danfoss Power Solution’s PLUS+1 hardware, ensuring they are compliant out of the box.

The dual shock valves with anti-cavitation checks are standard on the RFD’s to protect the fan motor. The shock valves trim the maximum motor torque by absorbing pressure spikes (shock effects) at the work ports. This is necessary during reversing, especially in case of a reversal at full flow. The anti-cavitation feature allows additional flow to the motor through the tank port when the motor overruns the pump. Using our PVLP shock valves provide both shock and anti-cavitation in one valve, creating a compact design in the manifold.

“As a result of the demands of continued emission regulations, Comatrol is focused on meeting the needs of our customers who are looking for products that assist in improving overall machine efficiency,” said Mark Mahony, Product Application Engineer (US).  “Our updated family of fan drive HICs allows the engine to run more efficiently, thus improving fuel economy and reducing emissions.  Comatrol will continue to help customers meet emission regulations while addressing productivity and cost requirements.” 

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