Why new hydraulic oil still needs filtering before use?

It is a popular belief that technicians and operators of equipment that has hydraulic oil that is brand new and freshly extracted out of the bulk container or drum is safe and ready to use straight out of the container. It appears fresh and clean. It smells clean. The manufacturer claims it is in compliance with ISO standards. Why would anyone want to remove it from the filter before placing it in the hydraulic system?

The key to knowing the meaning of "new" actually lies in the area of cleanliness of hydraulic fluids and how recalcitrant the modern systems of hydraulics are to even tiny contamination.

New oil isn't the same as clean oil

This is the most important idea to comprehend. The new hydraulic oil has been refined. It's not filtered to the level of cleanliness that components of precision hydraulics require.

When manufacturing is taking place, the base oils are mixed with additives such as antioxidants, anti-wear and viscosity index enhancers, as well as corrosion inhibitors and other additives. Every stage of the blending process introduces the possibility of contamination by particulates. Metal particles from equipment used in processing dust, dust from the manufacturing process, as well as additive particles that aren't completely dissolvable—each of them could be incorporated in the end product.

The majority of the new hydraulic oil that is used as it is removed from the refinery or mixing facility has the ISO 4406 cleanliness code of about 18/16/13 or less. The most modern hydraulic equipment, especially ones with servo valves, proportional valves, and high-pressure piston pumps, require oil to be 16/14/11 or more clean, and many of the more sensitive systems require 14/12/9 or higher. The difference between the oil that is within the drum and that which your system requires is significant and real.

The path of contamination from refinery to the machine

Even if the oil that was used to make it came out of a refinery completely in good working order—and it's not—the trip from the blending facility to your reservoir for hydraulics can present multiple potential sources of contamination.

Tanks for storage at the distribution level are not always sealed according to the standards that hydraulic systems need. Bulk oil is stored in huge tanks that breathe when temperature alters, pulling in air as well as any particles transported through any vent or filter that is fitted—and the majority of storage tanks for bulk storage are not equipped with breathing filtering.

Transfer operations cause additional contamination. Filling a drum using a bulk tank, moving the drum, then filling up your system with the drum—every transfer point provides an opportunity for particles to get into the oil. Pumps used to transfer oil, hoses and fittings, funnels, and containers that are contaminated—all of them can allow particles, water, or other incompatible substances into what is supposed to be clean oil.

The drum isn't an unclean container according to the standards of hydraulics. New drums can contain manufacturing residues or rust particles that have accumulated on the surface of the interior or residual contaminants from drying. Drums that are classified by the term "new" or "clean" in commercial terms generally do not meet the standards of hydraulic systems.

What kind of particles are in the hydraulic device?

Understanding the significance of incoming filtration is a matter of understanding the precise tolerances of the hydraulic parts. The spools of servo valves have clearances ranging from one to four microns. Hydraulic pump pistons as well as bores of cylinders function with clearances of 5-20 microns. Proportional valve components are in the same range.

A particle that measures between 10 and 15 microns, which is inaccessible to the naked eye and smaller than a human red blood cells -- is the right size for it to get trapped in a servo valve's clearance and cause scoring, stiction, or even a complete seizure. It's also the ideal size to function as an abrasive with three bodies between a piston in a pump and the bore, which causes additional wear particles that circulate and can cause more damage.

This is the cause of most of the premature failures of hydraulic systems. It's not a dramatic event. It's a gradual accumulation of damage to particles that reduces performance, causes leakage, decreases efficiency, and ultimately leads to component failure, often months after the initial contamination. The cause is often found to be in commissioning in the event that a system was contaminated with oil that had not been removed prior to usage.

Water contamination in the new oil

Particulate contamination isn't the only issue when it comes to new oil. Water that is free and dissolved can be present in the process of blending by condensation within storage tanks or by inhaling humid air during storage and transport.

Hydraulic oil containing water causes an acceleration in the oxidation process of the oil itself, which results in decreased strength of films and their lubrication efficiency as well as the development of microbial growth in some types of oils as well as corrosion of metal surfaces in valves, pumps, and cylinders, as well as a reduction of additive efficacy.

Hydraulic systems that are operating with very small amounts of water pollution—as low as 0.05 percent to 0.1 percent free water—will experience significant wear and a shorter life of the component. The process of filtering the new oil through a kidney loop using water-absorbing components prior to filling eliminates this possibility.

The real-world argument for pre-filtration

The rationale behind filtering new hydraulic oil prior to use is not purely theoretical. It is backed by the maintenance data of industrial facilities that track the life of components as well as oil cleanliness across large fleets of equipment.

Systems that use pre-filtered, verified-clean oils with ISO 16/14/11 or higher generally have a longer life of the pump and fewer valve replacements. longer intervals between oil changes and fewer breakdowns that are not planned for during the initial phase of operation, which is the time when commissioning contamination can cause the most severe harm.

The procedure for pre-filtration is easy. New oil must pass through a portable filtration device, often referred to as a kidney loop or filter cart loop, equipped with elements that are rated between 3 and 6 microns of absolute. The oil circulates until the particle counter is able to confirm that the cleanliness of the oil is within the specifications of the system. This isn't a lengthy or complex process, but it is a matter of careful preparation and the appropriate equipment.

For systems that are large or with strict cleanliness requirements Many operators are now requiring that the oil they purchase must be approved to meet a cleanliness requirement by the seller prior to delivery. This is done with documentation along with the delivery. This does not substitute the pre-filtration on-site; however, it serves as an acceptable baseline for quality and cuts down on the amount of time needed for filtration prior to the oil achieving specifications for the system.

Pre-filtration as a an integral part of the standard procedure

The price of a cart for filtering, the time it takes to run new oil through it prior to filling, and the price of replacing filter elements are less than the cost of a malfunctioning hydraulic system, stuck valve or servo, or a sudden shutdown within a production setting.

The pre-filtration process for new hydraulic oil must be considered a mandatory step in any commissioning or maintenance procedure and not as an option to follow best practices. Each hydraulic system that has been designed with care to precise tolerances, each variable displacement pump that is high-efficiency, and every proportional valve that has precise spool clearances—each of these components is dependent on the oil that regulates and lubricates them to achieve the purity level that tolerances require.

The oil that is new and has not been purified cannot be presumed to meet the standards. The only way to be sure that the oil is clean enough is by filtering it and testing its cleanliness using a particle counter prior to when the oil is put into the system.

This one step, if followed regularly, is among reliable and cost-effective techniques in the maintenance of hydraulic systems.