The Centrisep EAPS is an all-weather, self-cleaning, fit-and-forget filtration system that protects helicopter engines against contaminants. It uses vortex separators to provide engine protection by continuously scavenging the contaminants from inlet air and expelling them overboard. This process minimizes unscheduled engine removals, keeping labor and associated costs down. It also results in greater engine reliability, increased operational availability, enhanced performance, and safer operation.

For further questions, queries, and comments, please contact us.

Q1: What particulate removal efficiency do I need to protect my engine?

Field experience, including operations in Iraq, Afghanistan and the Paris-Dakar rally, has shown that a particulate removal efficiency of greater than 96% (tested with ISO Coarse Test Dust) is more than adequate to protect the engine from erosion damage. Note that the Centrisep EAPS removal efficiency remains constant throughout its life. In contrast, the efficiency of oil wetted inlet barrier filters (IBFs) is critically dependant on a number of factors:
  • The IBF must be correctly cleaned and oiled after use. This can be difficult in the field if hangar facilities are not available.
  • IBFs are given a maximum number of cleanings because it is not possible to return the element to the original state after cleaning.
  • If a bypass door is operated, the filtration removal efficiency of the IBF is zero.


Q2: Do I need a Centrisep EAPS if I have an inlet particle separator (IPS) within the engine?

During the development of the RTM322 engine for the NH90, Merlin, and Apache helicopters, Turbomeca evaluated a Centrisep EAPS unit against the IPS system. They investigated the best system for protecting the engine's first compressor wheel, which is the one most prone to erosion. According to the Turbomeca report1: "Research has confirmed that engines protected by Vortex Separators have longer overhaul lives than those with a conventional IPS."

The engine life increase with a vortex separator compared to an IPS was two to five times, depending on the test dust used. Based on this testing, the Centrisep EAPS is the standard option on the NH90 helicopter.


Q3: The dust found in a helicopter engine is extremely fine. Can extremely fine dust be separated with a Centrisep® EAPS?

Yes. The dust particles that reach an engine intake are very fine. Large particles become disturbed and airborne by the turning rotor's downwash; these larger types of particles settle very quickly. Only the very small particles - typically from 1-150 microns - travel high enough in the air to be re-captured by the main rotor and fall on the engine intake. To validate the performances of our Centrisep EAPS, we use a standard dust called "ISO Coarse Test Dust". Field sampling, where samples of the air entering the engine were collected by means of a probe, or bag filters, has shown that the particle distribution of the actual dust in the field was very similar to ISO Coarse Test Dust. Twelve percent of the weight of this dust ranges from 0-5 µm, which is smaller than a red blood cell! We are still able to separate a significant percentage of these microscopic particles. And to address the specific problems of lime spraying by helicopters on forests suffering from acid rain, we have even tested the Centrisep EAPS with lime, with remarkable efficiencies.


Q4: In brownout conditions, the concentration of sand and dust is extremely high. Is it likely to 'saturate' the Centrisep EAPS, thus reducing its efficiency?

No. Pall has tested the Centrisep EAPS with dust concentrations of up to five grams per cubic meter of air, proving that the efficiency remains constant. (Such a high dust concentration simply does not exist in real helicopter operation). During desert operations in Namibia, dust concentrations of up to 2.5 grams per cubic meter of air have been recorded, but this was with a Puma helicopter, hovering in ground effect, for twenty minutes! So the Centrisep EAPS remains fully operational in these extreme conditions.

Defence Standard 00-34 Part 4 published by the UK Ministry of Defence defines a dust concentration of 2 g/m3 as "representative of the most arduous conditions associated with aircraft, particularly helicopters, operations."

Note: The manufacturers of oil wetted IBFs advise the following "When operating in an environment of high sand and dust levels, frequent servicing of the filter assembly may be required based on the time exposure and severity of the environment. Any operations in an environment that can result in "brownout" conditions should therefore be minimized or avoided to the maximum extent possible within the constraints of the operation."


Q5: How often does a Centrisep EAPS need to be cleaned?

The fit and forget Centrisep EAPS DOES NOT require cleaning. Contaminants are continuously scavenged overboard which means that the system has an 'unlimited dirt holding capacity'.


Q6: Does the Centrisep EAPS provide foreign object damage (FOD) protection?

Yes. The Centrisep EAPS offers formidable protection against engine FOD. (link to FOD page). It is qualified against FAR 27 and FAR29 bird strike requirements. For alternative air filter systems, recurrent fitting and removal of filter elements could create additional FOD hazards.


Q7: Why isn't the Centrisep EAPS fitted with a bypass system as a back up?

The Centrisep EAPS does not become blocked and therefore has no requirement for a bypass system and warning lights. Note that on alternative air filter systems when the bypass door is open, there is NO PROTECTION against sand and dust.


Q8: What sort of power penalties does the Centrisep EAPS create?

Power penalties vary considerably from one helicopter to another. On some helicopters, Centrisep EAPSs actually increase the amount of available power for the helicopter. This is due to the fact that the air flow and pressure distribution at the compressor entry plane is improved compared to basic helicopter engine intakes. On other helicopters, the power penalty resulting from the pressure drop and the scavenge system can be fairly high because of installation constraints. However, the penalty is still small when compared to the power loss due to early engine erosion and the pressure drop is constant so the pilot knows what performance to expect. In contrast to basic helicopter intake systems, the loss of power typically cannot be detected in hover on the latest 'state-of-the-art' Centrisep designs. The penalty may be more noticeable in forward flight, perhaps resulting in a slight increase in fuel consumption.


Q9: Does the Centrisep EAPS impact the engine TOT?

The turbine outlet temperature (TOT) is proportional to pressure drop (DP). Every filter system has a pressure drop (DP). Some are constant, some are variable. Centrisep EAPS designs have a constant DP so the pilot knows what performance to expect. In contrast, barrier filters have a variable DP. The pressure drop increases as the filter becomes blocked and hence the TOT increases.


Q10: When do I need to activate the scavenge system?

The scavenge system, whether it involves P2 air activated ejectors or electrical fans, must be ON for the Centrisep EAPS to be efficient. This means that it is extremely important that the scavenge system is energized before the helicopter encounters dusty conditions. If activated too late, the efficiency of the system drops dramatically.

In desert environments, dust can be encountered at extremely high altitudes. In these conditions, we recommend that the scavenge system be on at all times.

Scavenge is also required under heavy rain, as a fair proportion of the rain can be separated by the Centrisep EAPS to prevent engine flame out.

Scavenge is required at all times in a marine environment. A good amount of the salt can be separated to prevent engine fouling in flight and the resulting loss of power.

It should be noted that ice and snow are arrested before they get into the vortex tube, so the scavenge fan is not required in these conditions.


Q11: When I operate in a marine environment with Centrisep EAPS, how often should I flush my engine?

A: Although the Centrisep EAPS removes a fair proportion of the salt, daily flushing of the engine after marine operation is still desirable. To facilitate flushing operations, some of our Centrisep EAPSs feature built-in engine-wash connectors.


Q12: Is the air flow better with an inlet barrier filter (IBF) than with a Centrisep EAPS?

No, the air flow is better with the Centrisep EAPS. The swirling motion of the vortex tubes results in uniform, stable air flow into the engine intake. This minimizes any detrimental effects of hot gas ingestion (HGI) - link to HGI page.


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