Improved Closed Loop

Contrary to a conventional closed loop system, with the Improved Closed Loop or Integrated  testing/cleaning system, the hydraulic oil is continuously cooled, filtered, degassed and dehumidified. This system is a standard feature of all hydraulic equipment of Sun Test Systems.

The result is regenerated clean and de-aerated hydraulic fluid in the aircraft after hydraulic testing. Also maintenance time on the hydraulic system of the aircraft is reduced (less leakages, less replacement of hydraulic fluid, less waste) and operational reliability will increase and handling of the aircraft is improved.

With the Improved Closed Loop system the complete content of the reservoir continuously circulates through the filter and cooling system and through the vacuum system. From this circuit the aircraft system is fed and the polluted aircraft oil is being guided through the return pipe to this cleaning circuit. Also through the mixture with degassed hydraulic oil the volume of dissolved gas in the aircraft hydraulic system is being decreased which results in a safer aircraft. This system can be found in all Sun Test Systems hydraulic test trolleys and is suitable for all types of aircraft and helicopters.

The advantages of our Improved Closed Loop system one by one:

  • Continuous and fully cleaning of the hydraulic oil
  • Continuous and fully degassing and dehumidification of the hydraulic oil
  • Maximum cooling of the oil through continuous passing through the heat exchangers. This especially is an advantage when working inhot climates and/or if low oil temperatures are required.


Reliable determination of the level of free gas: the AA-GIO® system

In spite of all the measures taken in the past, there was still no accepted method for checking  (i.e. controlling by measurement) whether or not the aircraft really was ‘clean’ from free gas in the hydraulic system. For the German Air Force, Sun Test Systems developed an advanced aircraft measurement technique called
AA-GIO®.  This system is being used by the German Air Force to determine if, and how much, free gas is present in an aircraft hydraulic system, and approx where in the system this gas is located. AA–GIO® is in use on the Tornado, Transall, SeaKing and CH53 helicopters.  It is applicable and useful to all fighters since those aircraft especially are at risk due to their flight manoeuvres and high dependency on uninterrupted hydraulic pressure.


Depending on the product the following functions are incorporated (or can be incorporated):

  • Two hydraulic systems, including hydraulic fluid de-aeration and super-cleaning
  • Aircraft power supply 115V, 400Hz
  • Aircraft power supply 28V DC
  • Hand tool power supply
  • Pneumatics
  • Tower lighting
  • Pressurised air system
  • Air start capability
  • Nitrogen generator
  • Nitrogen bottles
  • Engine compressor wash
  • Fuselage washing
  • De-icing
  • Computerized or manual operated.