![]() ![]() ![]() Each number represents a range, and in the example, 22 represents between 20,000 and 40,000 of the 4- μm particles in just one milliliter of fluid, even though the machine measured 22,340 particles. If you refer to the attached diagram, you can see the numbers are first expressed in 4 μm, with 6 and 14 μm following, respectively. Both numbers are rare extremes, as even new oil has infinitely more particles than 0, and if you have 2.5 million of any given particle size, you’re in a whole heap of trouble. The number of particles of each size is expressed as a single number between 0 and 28, where 0 is exactly zero particles, and 28 represents up to 2.5 million particles per ml. This allows for both easy expression and forgiving test results, as no particle counter can accurately measure every single 4-μm particle in a milliliter of fluid. To give you an idea of how fine even the largest 14-μm particle is, note that it is only just over ½ a thousandth of an inch.Įach of the defined particle sizes are expressed in a given range, rather than the actual particles measured in the test. The particle sizes are 4, 6 and 14 μm, chosen because of their potential to cause damage between moving surfaces separated by full film lubrication, such as the spool and body in a directional control valve. Based on the data collected from the machine, three sizes of particles considered most damaging in a hydraulic system are averaged out and expressed as per milliliter. The particles are measured by specialized machines using a laser to count the size and number of particles breaking the beam as they flow past. Its method has been developed to test and measure the average size and quantity of particles within a given volume of fluid, which in this case is one milliliter. ISO 4406:1999 is the current method for coding the level of contamination by solid particles, as spelled out by the International Organization for Standardization, which is more affectionately known by its acronym, ISO. This standard is world-wide, which for the fluid power industry and its plethora of global organizations, is quite astonishing in and of itself. Although the standard for oil cleanliness has changed over the years, we’re at a point in history when we all seem to agree on the method to test and express fluid contamination. We refer to the size and quantity of particle contamination when discussing cleanliness, and so that we are all on the same page, standards were created for measuring and expressing this quality. The most critical quality of hydraulic fluid you should consider is that of cleanliness. Each range of fluid is double the range below. Each number refers to an ISO Range Code, which is determined by the number of particles for that size (4, 6 and 14 micron) and larger present in 1 ml of fluid. These numbers correspond to 4, 6 and 14 micron, in that order. Cleanliness levels are defined by three numbers divided by slashes (/). ![]()
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