Hydraulic hose assembly cleanliness – part 3

Published:  09 October, 2015

This is the third and final part of a short series of articles based on the British Fluid Power Association’s recommendations and best practice for hydraulic hose assembly cleanliness. This month, we look at some of the main hydraulic hose assembly processes and contamination zones.

Various methods and types of machinery for the cleaning of hose and hydraulic hose assemblies are used during both the main manufacturing processes to reduce contaminants prior to connectors’ installation and, more importantly, at the end of assembly process, which is then validated for final assembly cleanliness.

Care must be taken to ensure methods and fluids used in cleaning/flushing (and drying) of hydraulic hose assemblies have to be such that the rubber hose tube is not scoured and/or abraded by the process, or that the cleaning/flushing fluid does not remove or extract components of the rubber damaging the hose tube. If in doubt contact the hose supplier/manufacturer for advice.

Risk assessment

Risk assessment shall be carried out on all types of flushing/cleaning (and drying) processes, and machinery, to prevent health and safety risks to operators and other people within the vicinity. Machinery manufacturers’ recommendations shall be followed at all times. Relevant personal protective equipment (PPE) shall be worn.

Air blowing combined with extraction during cutting

Compressed air filtered at point of use to ≤ 5 μm is applied to both ends of the cut hose piece. Methods of applying the air must give protection to operators. Eye protection is required for all compressed air methods. Typical methods used are:

a) By pushing each end of the cut piece of hydraulic hose against a fixed concave cone shaped trigger nozzle to start a timed air blast.

b) By using a hand held trigger operated, compressed air gun fitted with a concave cone to produce an air blast for a set time.

The use of a concave cone allows the full length of the hose to be cleaned. A convex cone penetrates the hose bore for a small depth thus the air expelled misses a small section. For this reason the hose is blown in both directions. In both cases above, the opposite hose end should be pointed in a downwards direction or into a collection chamber to prevent direct exposure to other operators and general environmental contamination. Air Blowing methods are usually complemented by local extraction systems that are fitted directly to the hose cutting machine to prevent/reduce cutting debris entering the hose bore. A typical extraction rate of 3m/second should be maintained. This system should contain a filtration system to remove and collect particles and general debris. This (these) filtration system(s) shall be regularly maintained to ensure its continued effectiveness. Note: Spark Arresters shall be fitted between the hose cutting machine and the extraction filter to prevent ignition of collected rubber particles in the filter.


Air Blowing a projectile (also known as ‘pellet’ or ‘pig’) through the cut length of a hose using a pellet launcher/gun, attached to a compressed air supply, can remove a number of contaminants generated by the process. These include cutting and skiving debris, residual contaminants such as mandrel release agent from the hose manufacturing process, and lubricants used on the mandrel of the skiving process. A range of pellets are available for removing specific contaminants.

The above process shall be repeated from both ends of the hydraulic hose cut length to ensure that the location area of the compressed air pellet nozzle, on the first pass, is cleaned on the second pass of the pellet. This cleaning process must be repeated until the blown projectile is visually clean. Note that it is important to verify the projectiles have passed through the hose. Advanced launchers are available with a projectile verification system. Note also that projectiles shall not be re-used.

The above information has been edited from the British Fluid Power Association’s guidance document BFPA/P111 ‘Recommendations and best practice for hydraulic hose assembly cleanliness’. The full document contains further information and clarification on a number of the points referenced above. For more information about the document and how you can obtain a copy, please contact the Association at info@bfpa.co.uk, or Tel: 01608 647900.

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