24 Nov 2021

Cleanliness Inspection of Hydraulic Actuators

Six years ago Oliver Valvetek changed its method of cleanliness inspection of hydraulic actuators and has not looked back.

Flush cleaning of actuators involves passing clean hydraulic fluid through an actuator at a sufficient flow rate to ensure turbulent flow is achieved.  Turbulent flow is when the Reynolds number exceeds 4000, the Reynolds number is calculated using the flow and the physical properties of the hydraulic fluid.

Originally during flushing of gate valve actuators with hydraulic fluid, in-line particle analysers were used to monitor the number and size of particles against a the NAS 1638 standard.  However, the analysers were poor at differentiating air bubbles and could give no indication as to the type of particles.

The NAS standard was superseded by ISO 4406 and SAE AS 4059F all of which clearly list the maximum contamination limits for cumulative particle counts.

For comparison and understanding of particle sizes, the analysis process and acceptable limits of SAE AS 4059F look at particulates in the process which are approximately 1/10th of the thickness of a human hair or 6um and bigger !!

In 2015, Oliver changed from in-line analysers to the far more sensitive optical analyser method.  The Pamas Fast Patch 2 Go system was chosen and provides the level of detail needed to ensure the cleanliness levels called for by our customers is met.  Since its installation over 6000 patches have been analysed.

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