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Loughborough-based Flotec, a leading supplier of reliable hose and engineering solutions to rail, here discusses the benefits of applying a series of modifications and variable pitch fan technology to rail DMU trains and rolling stock.

Flotec has developed a variable pitch fan innovation for DMU rolling stock to address RTI issues.

Historically rail rolling stock DMU’s have suffered with low engine power and ‘returning to idle’ (RTI) issues during the Spring and Summer months.

This issue is commonly caused by the radiator becoming blocked by pollen, leaves and other debris which in warmer temperatures significantly hinders cooling of the engine, and the original fan pump design, which has a fixed delivery from the engine speed.

THINK Rail Passenger!

The problem ultimately creates capacity issues and train delays due to rolling stock maintenance downtime, late train arrivals and even complete cancellations to a service.

Flotec has designed an engineering solution to combat traditional rail specific complaints ensuring rolling stock fleet reliability between scheduled overhauls.

The Flotec vision is to implement products and modifications to deliver zero RTI.


THINK Rail Freight!

Let us not forget rail freight. There is an increased understanding of the necessity for freight rolling stock to transport produce in a timely manner to meet consumer demand.


The Flotec programme

Flotec’s solution overcomes the wide and varied complexities of previously designed power flow and temperature control issues associated with rail fleets.



Hydrostatic Hose

It is well known that the poor routing of hoses can lead to premature failure. Furthermore, hoses are often installed at too long a length making them weighty and hang low to the ground where damage from ballast and debris often occurs.

In this scenario, hose degradation becomes a critical issue.

Flotec installs its market leading Railtec MED2-HT EN 45545-2 fire safe hydrostatic hoses and correctly routes them with sophisticated clamping to overcome the issue of damage and frequent failure, guaranteeing a fault free life cycle between scheduled overhauls. Flotec suggests maintaining all hoses in the system.

Flotec has developed an innovative design improvement package to overcome engine overheating problems on DMU rolling stock, reducing occurrences of "revert to idle" (RTI) and engine shutdowns.


Flotec analysed the history of the problems with the cooling system and developed four packages to improve the durability and reliability of the hydrostatic system.


Hydrostatic Reservoir Overhaul

Cleaning reservoirs is often overlooked where Flotec has witnessed some DMU reservoirs not being maintained for up to twenty years. Overhauling of the reservoirs is offered as a basic level solution.

Neglecting the reservoirs can lead to a build-up of debris resulting in component contamination and failure.


Flotec can either overhaul or replace the reservoirs to ensure optimum efficiency.


Electronic Fan Control vs. Valve Thermostatic Fan Control

Original electronic fan controls proved unreliable and were replaced with valve thermostatic controls, where this became the norm.

However, these in themselves have created issues, through worn mechanical parts where they then fail to work to the correct cut in temperature thereby failing to trigger full fan speed at the precise time, resulting in RTI situations. These valve controls have become more obsolete as well as costly to overhaul.

With advancements in electronic fan control technology, Flotec recommends this as a more reliable integration.


Upgrade to Variable Displacement Pumps (VDPs)

Whilst fixed displacement pumps have been used on rolling stock for many years, and formed part of the original design, Flotec has observed some significant drawbacks. First the pump output is dependent on engine speed.


This is not too much of a problem if the gearbox change points are correct and the gearbox reverts to torque converter mode at circa 60 mph. However, if the point of change is below this the engine will lug down on an incline, resulting in lower fan speeds when higher coolant load is required.


Another issue with FDPs is that if an engine is running slow, the fan will also run slow, when a potential for full fan speed is required. This also creates a cooling inefficiency, of the engine.

Fixed displacement pumps do contribute substantially to RTI issues.


Installing a variable displacement pump (VDP) modification ensures that when cooling is not required, the pump automatically shuts down and only pumps oil around the system where necessary.

This is successful in reducing unnecessary heat generation, less wear and tear of all components, thus, creating a more optimum engine performance, and fuel savings.

Effectively, a VDP is not controlled by engine speed and alters to suit whatever cooling is required at any given time.


Variable Pitch Fan

Committed to capitalising on the latest rail technology, Flotec recommends installing a variable pitch fan as opposed to more traditional fans which is fixed to only draw in air through the radiators.

These existing fans create an efficient cooling process, but due to the one rotational direction, also pull contaminants into the radiator fins.

Blockage of the radiator through these drawn in contaminants, very quickly effects the air flow and the radiator becomes inefficient forcing the system to work harder to maintain the cooling temperature to a point where the thermostatic control engages, shutting down the engine.

The blades of the variable pitch fan rotate on their own axis to change the pitch and reverse through the cross position, this guarantees the air will always be increased and in the optimum position to produce maximum air flow when in both cooling and cleaning modes. 

Fitting a VPF effectively maintains radiator cooling efficiency by eliminating blocking contaminants and maintaining air flow through the radiator, increasing energy savings and eradicating RTI situations.

Furthermore, a hard-wired fan control system installed into the existing electronics of the train ensures that the ‘cleaning’ process is not engaged when the vehicle is either stationary or drawing into a station.

Flotec observed that the use of a traditional fan system meant that maintenance personnel had to conduct frequent high-pressure washes to the engine radiators to remove an excessive build-up of debris and contaminants.

This also resulted in potential damage to the radiator fins, thus, reducing engine temperature control competency.

Installing a variable pitch fan reduces the frequency of washing which in turn, reduces the damage to radiators and maintenance costs whilst extending their lifespan and effectiveness.




















Flotec offers rail clients a mix of different methods to get their rolling stock fleets up to speed!

The four levels of modification will suit different rolling stock operators, for their varying requirements such as geographic location or natural environments.

As an example, certain fleets may encounter hill climb ‘power’ issues due to an exceptionally mountainous terrain whilst others may encounter issues such as pollen and some may be exposed to all contributing elements.

Flotec can advise on the most appropriate option for individual clients. A breakdown of the available options is listed below:


Legacy DMU Fleets: 

Option 1

Leave the system as standard, renew the hoses, service the reservoir, check system pressure and performance check. A float of 2 reservoirs can be provided.



  • Cleaning out the reservoir of 20 years of debris, making them as new

  • Ensure system goes out fully operational

  • Cost



  • The thermo valve is unreliable


Option 2

Modify the system. Hose improvement, reservoir service, remove the thermo valve and pipework, fit electronic fan control valve, in place of thermo valve.


The components for the electronic system:

  • A Thermistor with adaptor to fit in place of thermo valve

  • A programmable CED controller, to electronically control the fan speed in relation to the engine coolant temperature

  • A wiring harness

  • A hydraulic proportional valve, to control the fan speed and limit system pressure (In event of an electrical failure the fan will revert to full speed, the thermo valve will not)



  • Removes considerable hydraulic pipework, hydraulic adaptors, and connections

  • Removes unreliable thermo valve

  • A fully programmable control of the fan



  • Initial cost (over time will be more cost effective)

  • Fan will continuously turn (pin wheel)


Option 3

  • Renew any hoses and service the reservoirs

  • Replace the fixed displacement fan pump with a variable displacement fan pump

  • Replace the Thermo valve with a thermistor

  • Fit a programmable CED controller, to electronically control the fan speed in relation to the engine coolant temperature, by varying the displacement of the new fan pump. In the event of an electrical failure the fan will revert to full speed


  • The fan will maintain speed when the engine rpm decreases

  • Removes considerable hydraulic pipework, hydraulic adaptors, and connections

  • Removes unreliable thermo valve

  • A fully programmable control of the fan


  • Initial cost (over time will be more cost effective)

  • Labour time to fit the system

  • Fan will continuously turn (pin wheel)


Option 4

The same as option 3 but also adding a reversible pitch fan. This will help keep the radiator clean.



  • The same as option 3, plus the added benefit of a self-cleaning radiator



  • The same as option 3


Option 5

A re-design of existing cooling systems

Option 6

Integration of the variable pitch fan into new build DMUs.



A Value-Added Service Provision: On-Site System Upgrade.

Flotec can conduct on-site surveys to DMU fleets and advise the best option applicable to differing needs.

Flotec is fully rail approved and holds all necessary accreditations to professionally manufacture, supply and fit the kit to rolling stock modifications to eliminate issues associated with RTIs and loss of engine power.

A comprehensive provision of all required documentation is provided to rail clients.

Picture of the award winning variable pitch fan.
Picture of the Railtec hydrostatic hose which has been proven to outperform all other hydro hoses on the market.
Picture of aa Flotec engineer working on a train.
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