Care and attention should be key watchwords when it comes to hydraulic equipment. Watch out for the effects of contamination in your hydraulic systems. Don’t overlook the most common causes of hydraulic system contamination. Do what you can to clean up any contamination that gets through defenses. Ignoring the problem could result in catastrophic system failure.
Why do hydraulic systems fail?
Common causes for mobile hydraulic system malfunction are related to contamination and valve issues (damage-causing spools to stick, or dirt stopping them from opening and closing smoothly). Any hydraulic system maintenance training should cover diagnosing and addressing these issues. Hydraulic system contamination by insoluble particles can cause slurry build-up. These particles can be generated within the system during operation (for example, by wear and tear on metal edges or flexible seals) or can gain entry from the surrounding environment through openings or leaks. Solids in high-velocity hydraulic fluid flows can be deposited in nooks and crannies throughout the system, causing blockages and/or interfering with the smooth operation of valves.
Why does this seem like a new problem?
Years ago, it was common practice to drain hydraulic oil into any old container when, for example, fixing a hose. Once the job was done, the oil would be poured straight back into the tank. This didn’t cause major issues because machinery was comparatively primitive, with simple gears and levers. Yes, the system would eventually suffer from the gradual build-up of dust and dirt in the fluid, but it wasn’t nearly as sensitive as today’s precision equipment. The hydraulic system maintenance culture of the time was forgiving, and crucially, less costly.
These days, contamination of a hydraulic system is a much larger concern. Parts and tolerances are minute. Systems operate with greater precision, which means they are more sensitive to deviations. For example, electronically-controlled pressure valves in pilot circuits produce hydraulic forces tuned to moving a proportional directional valve spool to the required flow opening. These valves may move less than a millimeter to produce the exact forces required. Typically used as the first layer of control in massive hydraulic systems, or to control steering, pilot valves can be incapacitated by a single particle of the right dimensions. A jammed pilot valve could render a machine inoperable. In a worst-case scenario, safety functions that depend on functioning valves could fail if oil is contaminated. Filtering out different types of hydraulic contamination such as dust, rust, worn metal, and rubber is essential to guarantee the reliable functioning of a complex system.
How does a hydraulic system become contaminated?
Some hydraulic system contamination is generated by the system itself, and some get in through gaps in the system’s defenses. For example, water can be absorbed from the air if the system is left open, or it can seep in through leaky valves or other structural weak points. This can result in rust, or iron oxide particles which are particularly tough contaminants.
Common opportunities for hydraulic system contamination to occur include:
- When fluid is being added or replenished
- During system operation, from component wear-and-tear
- Through quick couplers on lines
- Through breather caps
- Through leaks around worn or damaged seals and gaskets
- When the system is open to the atmosphere during repairs and maintenance
Contaminated fluid
Even fresh fluid can bring hydraulic contamination with it. This contamination may come from the manufacturing processes for the oil itself, or from the containers, it was stored in. Even careless filling of containers can mean that pristine product going into a spotless receptacle winds up contaminated! Good filtration and cleaning procedures should be incorporated into the filling process to avoid hydraulic system contamination.
Beyond the factory, oil can be contaminated by exposure to the atmosphere or other external contaminant sources during transport and storage. This is particularly an issue if the oil is repeatedly opened and closed, or if it’s decanted between different containers.
While filling your system, the method of using an open container and funnel is best left in the past. Use a filter-transfer pump to draw fresh fluid and pump it directly into the system through a coupler on the tank, which reduces opportunities for most types of hydraulic contamination to enter the system. The Donaldson filter cart can offer a convenient portable mode of off-line kidney loop filtration, flushing, and fluid transfer.
Breather/filler caps with a porous mesh will only keep out the largest contaminants. Trying to fill the system quickly by pouring fluid through the breather port is a prime opportunity to introduce hydraulic system contamination.
If using quick couplers on your lines to attach accessories, or to provide points for testing or filling, clean them rigorously before making a connection. Any contaminants on the surface of a coupler are likely to be driven into the system.
Hydraulic system contamination with metal
Metal and rust are among the most common types of hydraulic contamination.
Metal fillings are a by-product of many of the processes used when manufacturing metal hydraulic tanks, including drilling and threading. Tiny particles of metal may also break off due to friction between moving parts during machine operation – this is a particular issue when the hydraulic oil you’re using is too thin. Gears grinding against the inlet side of a gear pump housing may create metal shavings, and the pistons of long-stroke cylinders in lift machines can rip off metal slivers and filings from the cylinder’s internal surface.
Another opportunity for hydraulic system contamination with metal particles is when a hose that includes wire reinforcement is cut to length. Use a compressed-air-driven cleaning projectile to ensure the ends are clean before crimping.
Cavitation occurs when excess pressure is applied to tiny pockets of vapor on metal surfaces inside your hydraulic system. These vapor pockets can be formed if, for example, the inlet flow to a pump is restricted. When the pockets implode under pressure, the generated shock waves erode the surfaces on which they formed, fracturing off metal fragments.
Although softer metals are more prone to cavitation damage – think aluminum or bronze – it’s not an uncommon problem for tough metals such as steel.
Cavitation is a problem, and a side effect, that leaves you with metal particles dispersing through your system causing contamination. These mobile metal particles can compound erosion problems in the system, as they traverse valve spools and port edges at high velocity.
Research suggests that solid particles in hydraulic oil may even contribute to the formation of further cavitation bubbles, creating a vicious cycle of hydraulic system contamination. So, you can see how critical it is to control the level of particle contaminants. Use high-quality hydraulic oil and be careful to avoid introducing external contaminants with the oil; use high-quality filtration, such as that provided by Donaldson, to protect machinery during operation; and perform system flushes when warranted to eradicate sludge.
Hydraulic system contamination from fiber and other environmental factors
The most common type of hydraulic contamination after the metal is fiber contamination, followed by a variety of other environmental factors.
There are many sources for fiber contamination in hydraulic fluid. Paper towels or rags used to clean components during installation or maintenance can shed tiny fibers. Sawdust and woodchips from a dirty operating environment can find their way in when the system is opened for inspections, repairs, and fluid top-ups. Hoses, seals, and O-rings shed elastomer particles as they deteriorate. While these types of hydraulic contamination are softer, they can still cause damaging blockages. Harder contaminants include silica particles: these come from topsoil, sand, dust, and rock minerals in concrete floors and roadways. Mobile machinery, in particular, tends to be exposed to these hard, sharp-edged particles, which can cause catastrophic failures if they get into valves.
Protect your system
You’ll never eliminate all types of contamination from your hydraulic system. Whether the contamination is built-in, manufactured, or introduced, it is a fact of life. That said, if the system isn’t protected correctly, or if it’s deployed in a dirty environment, you’re inviting additional problems unnecessarily. Using filters and learning how to clean your contaminated hydraulic system won’t make up for ineffective maintenance. It is always more cost-effective to prevent a problem from happening than it is to clean/ fix it afterward.
If system analysis shows excessive hydraulic system contamination on an ongoing basis, consider hiring an independent filtration and contamination control expert. Donaldson has several authorized hydraulic filtration specialists who can help identify the source of hydraulic system contamination. They may also help re-design your maintenance regimen or identify filtration products better suited to your equipment and operating environment. To maximize system performance and life span, establish processes to control hydraulic system contamination build-up, and follow them rigorously and consistently.
Establishing a complete picture of contamination control means keeping an eye on the exceptional events as well as the day-to-day. If your system overheats periodically during operation, this may be contributing to sludge developing in the fluid, or excessive abrasion and wear on metal parts as the hydraulic oil thins in the heat.
Teamwork is key
All stakeholders with an interest in your hydraulic system, from the equipment owners, supervisors, operators, and maintenance technicians, should be informed and attentive when it comes to hydraulic system maintenance. Everyone who comes into regular contact with your systems should know the tell-tale signs and be on the lookout out for different types of hydraulic contamination. If your machine operators are responsible for carrying out filter changes or for replacing worn hoses, ensure that their training extends beyond the mechanics of the task to cover hydraulic system contamination control strategies, too. Understanding the consequences of hydraulic fluid contamination contributes to better vigilance and ultimately higher system reliability.
