To understand how ISO cleanliness classes operate and what is displayed on HYDAC’s FCU 1000, it’s necessary to use ISO 4406, which is the most common particle counting method.
The FCU 1000 is a portable service unit designed for short term measurement of particle contamination, humidity level and fluid temperature.
The cleanliness classes as per ISO 4406 are determined by the cumulative counts in the size bands >4µm(c), >6µm(c) and >14µm(c).
To comply with the ISO-standardisation process, particle sizes have been redefined. Particle sizes are now displayed as µm(c).
Meaning of numbers 18/16/13 on FCU 1000
If the numbers 18/16/13 flash up on the FCU 1000, they indicate a typical cleanliness class.
The number 18 represents all the particles that are 4µm or larger, 16 represents all the particles that are 6µm or larger, and 13 represents all the particles that are 14µm or larger.
This would change if the number displayed read 20/17/15, with the numbers correlating to 4µm, 6µm and 14µm.
At times only two numbers are displayed on fluid samples: this is a 5µm and 15µm reading for manual determination only.
Code to break down particles in a sample
There is a code to break down how many particles are in a sample.
Using 18/16 /13, 4µm equates to 18. This is greater than 130,000 particles, but less than 250,000 particles that are
4µm or greater.
This can be applied to 16, which is 6µm, and 13, which is 14µm.
The next illustration shows a 100ml fluid sample magnified 100 times. The gradients are 10µm apart.
ISO 4406 is equivalent to an SAE AS 4059 and NAS 1638 standards. Therefore, different standards can be equal across different ranges.
How clean should fluid be?
Another question commonly asked is how clean fluid should be?
The answer to that is as clean as possible.
It’s also important to look at the equipment in a system, and the equipment most sensitive to contamination, with particle count matching that.
The table shows that an applicable target cleanliness class and a matched filtration rating is required dependent on the pump, drive, valves, and bearings etc. in a system.
The target cleanliness for a gear pump, cylinder and proportional valve would be 17/15/12 or better. However, this is only applicable for less than 140 bar. As a higher pressure than this is achieved, the cleanliness class decreases, meaning that a cleaner fluid is required.
This is because as pressure is increased, tolerances within parts decrease, necessitating less of the larger particles or just less particles travelling through a system.
This means less potential for particles to cause damage within a system. And that is indicated at the top of the screen.
For more specific fluid care such as target cleanliness classes at higher pressures or what other ISO classes look like under a microscope, consult HYDAC’s Fluid Control Contamination Handbook, which can be downloaded for free from the web.
