Maintaining the cleanliness of your hydraulic system – and thus reducing overall component wear and maintaining its efficiency – translates directly to bottom line dollars. Chevron, for instance, says following a hydraulic system cleanliness program can reduce hydraulic fluid purchases by 20 to 25 percent.
But that’s just the start. “If you keep a hydraulic system clean, it could double the life of the system,” says Diego Navarro, service marketing manager, John Deere Construction and Forestry. And the cherry on top: The cleanliness of your hydraulic system can even be your defense in a warranty claim.
“The idea behind all of this is to slow down wear to get the best possible life out of your components,” says Pliny Smith, hydraulic product specialist, liquid filtration group, Donaldson.
What you can’t see definitely can hurt
First, let’s set the stage with what we’re dealing with. Particulate contaminates are sized by microns. For comparison’s sake, the size of a salt grain is 100 microns. The particulate matter floating around in hydraulic fluid, however, is much smaller, in the 5 to 30 micron range, far beyond what the human eye can take in.
Small is dangerous, especially with the tight tolerances of today’s hydraulic systems. “You could have millions of these particles that are not visible to the eye,” Navarro says. And the tolerances and pressures only promise to get tighter and higher as machine designers contend with all the requirements of increased productivity. Good practices today will only reap even more benefits tomorrow.
Particulate contaminates can enter hydraulic fluid at any time along the way – production, storage, machine manufacturing and transfer. “New oil is not clean,” Smith says. “The cleanest oil out there is probably an oil running in a properly maintained machine.”
In addition to particulate contaminants, there are chemical contaminants, which include heat, water and air. According to Caterpillar, these combine to break down the oil’s chemical composition, producing contamination in the form of oxidation and acids.
So what’s the definition of clean?
Cleanliness is measured by particle counts, and particle counts are reported by the International Organization for Standardization’s Cleanliness Code. The code refers to particle counts at 4-, 6- and 14-micron levels and is expressed as a ratio. Key to remember: every time you go up a level, say from 16/13 to 17/14, you double the amount of contamination in the 4- and 6-micron range. And when you go down a level, the reverse happens, and you increase your cleanliness level by 100 percent.
When you get your hydraulic oil analysis reports, check the ISO code. This code reports the result of a particle count analysis. If the contaminant levels are above the target code – for example, a 17/16/13 code on an excavator – then you need to do an immediate investigation. It may be a leak, a bad filter or a failure in progress. ISO cleanliness codes let you know both when you’ve got a problem and when your hydraulic system cleanliness procedures are working.
Remember, we’re dealing with an acceptable level of cleanliness here, a level your hydraulic system can handle without excessive wear. “With oil filters,” Smith says, “you’re trying to manage the number of particles of a given size, because you’ll never remove 100 percent.”
Even so, hydraulic systems require exceptional cleanliness. Carmen Rose, market professional, contamination control, Caterpillar, makes this analogy: Take an aspirin, crush it and divide it in half. That represents the amount of dirt you’re now going to mix into a barrel of hydraulic oil that meets an ISO 16/13 standard. Then use the mixed fluid to run a pump for 200 days, eight hours a day. When you weigh the half-aspirin’s worth of particles recirculating through the pump within those 200 days, it equals 20 pounds of dirt. Do the same procedure with an ISO 21/17 fluid, and the pump will see more than 600 pounds of dirt. “It kind of explains why pumps wear out,” Rose says.
It all starts with storage
Chevron says it’s significantly more expensive to remove hydraulic system contaminants than to prevent them from entering. While lubricant and machine manufacturers have established procedures to make sure they provide the cleanest hydraulic fluids, your part in the cleanliness chain is just as essential. You need to be a clean freak from fluid delivery to drainage.
First, make sure your hydraulic fluid delivery company is following recognized cleanliness procedures, Rose says. This means dedicated trucks, filtered product deliveries and hose management that has everything capped and in order when not in use.
All storage containers need to be under roof and out of the weather. This prevents contraction and expansion with weather-related temperature changes, which cause the air to move back and forth. “Dirt and water are introduced with the movement of air,” Smith says.
While previous recommendations had barrels placed on their sides, bung holes on top, this is no longer true, Rose says. “Storing them this way leads to a lot of leaks, and we say when you see oil coming out, dirt’s getting in.”
Instead, store the barrels upright with covers. Cat, for example, sells their own formed plastic covers, but Rose says some Cat dealers manage this using covers that resemble shower caps. Whatever their form, covers keep dirt and debris off the top of the barrel, and also prevent rust formation.
Not understanding why these procedures are essential can lead to practices that give the red carpet to contamination. As an example, Rose reports seeing barrels left open with an unfastened pump laid in the hole. “And some of these little pumps have aluminum shafts that, if not fastened, vibrate against the barrel metal, creating metal contamination,” he says. Another example from Rose’s gallery of hydraulic horrors: using dirty spout cans to top off tanks. “And that’s dealing with dirt you can see,” he says.
A prime place to introduce contaminates is when you fill a container to service a machine in the field. Since there’s not a good practical means of making sure containers are clean, Navarro says you should always have a filter interface – one when you draw the oil from tanks and another when you fill the machine. All fill nozzles should have filters, and lube trucks should have filtration on delivery. Forget the funnel – there’s no way to keep it clean enough. And make sure you periodically do an oil analysis on your storage tanks.
And all hydraulic fluids need periodic cleaning while in storage, according to Chevron. Make sure all your storage tanks have maintained breathers. Contamination control programs, such as the one offered by Cat dealers, offer tank cleaning and mobile filtration equipment that cleans stored fluids in bulk storage tanks, service truck tanks, reservoirs and equipment.
Hydraulic cleanliness is also a byproduct of environment. If you’re working in dusty or humid environments, these will force more dirt and humidity into your system. “Dirt and water get into systems in small amounts in a variety of ways, including cylinder seals and leaking valves,” Navarro says. And he warns that not all solid contaminants can be removed by the onboard filtration, such as silica and alumina, which are small enough to pass through the system again and again. These are time-dependent elements – if they’re able to enter the system at a regular rate, their numbers will increase over time.
Oil sampling – simply because it involves opening up the machine – also requires precautions. Both air and any contaminants from your technician’s hands can get into the system. There are a number of products available to help you take a clean sample.
The problem with attachments
Hydraulic attachments present significant challenges to hydraulic cleanliness. One problem is their working environment – when off a machine, they can be placed on the ground in the dirt and the mud. If the hoses aren’t capped off immediately after disconnect, excessive contamination is inevitable. Attachments can also generate increases in fluid temperature.
But by far the biggest problem attachments pose is cross contamination. One day, an attachment is working on a certain make and model of machine, the next day, it’s on an entirely different machine with a different hydraulic fluid. “The most serious issue in the field is this contamination,” Navarro says. “There are so many different products on the market today that when you mix fluids through the use of an attachment, you’ve created a new fluid.” This means when your oil analysis comes back, you’re left scratching your head – the viscosity is all over the map and the oil signature doesn’t match anything on the market. “Mixing carries consequences that are hard to pinpoint because the effects take time to show up – and when they do, they are seldom linked to mixing,” Navarro says.
Caterpillar recommends always inspecting quick couplers for damage and leaks and wiping off dirt from flush face disconnects before coupling the attachment. Protect nipples and couplers not in use with caps and plugs.
Fluid standardization across your fleet also would make life easier, but it’s not always possible, since different manufacturers specify differently spec’d fluids. Designating specific attachments for specific carrier machines is another approach. And some machines have onboard filters specifically targeted toward filtering influx fluids from any hydraulic attachments.
Is your filter up to the job?
It’s a mistake to think any filter that fits will do the job. Instead, know the filtration level your machine requires and look a filter’s micron and beta rating. “A 6-micron filter at Beta 2 means that it’s only 50 percent efficient at 6 microns, or in other words, it will only catch five out of 10 particles,” Rose explains. “But a 6-micron filter at Beta 75 catches 98.6 percent of the 6-micron particles.”
“If you buy less efficient filters,” Navarro says, “you’re killing the machine little by little because it won’t remove particles the way the machine requires. It may save you money in filters but it won’t save you money in repairs.”
Optional imbedded filter indicators, which measure the pressure drop on the downstream side of filters, are a good resource, particularly in dusty environments. “Ideally,” Smith says, “you should service a filter when it gets to 25 percent restriction, but in the real world that doesn’t happen since users want to change it when they perform other maintenance.” Since they’re usually tied into your machine’s on-board computers, these indicators give you fair warning in the cab before the filter goes into bypass, which means it’s circulating unfiltered oil. Although these indicators add about $10 to $30 dollars to the cost of a filter they also add peace of mind. “There’s really no clear way to pull a filter and know how much life it has left,” Smith says, “but with an indicator you know what’s going on.”
Synthetic media has become the standard for most construction filters. “Cellulose filters are a dying breed on hydraulic filters,” Smith says. “Synthetics get twice the life and half the pressure drop of cellulose filters.”
Reservoirs and breathers
There are two basic types of reservoirs, open and pressurized. Open reservoirs are typical on loaders and backhoes, where large cylinders cause the level of the oil in the reservoir to vary substantially.
Pressured reservoirs have two subsets – semi-pressurized and fully pressured. Semi-pressured reservoirs, seen on excavators, will reach a certain fluid level and then open via a relief valve to the atmosphere. Fully pressurized systems, common with hydrostatic transmissions, have no relief valve.
“The use of a high efficiency breather for both types of reservoirs is essential,” Smith comments. While there’s no standard for when to change a breather, Smith says they should be changed at least once a year, more often if you’re working in a dirty environment. Breathers are typically desiccant filters, although Donaldson has come out with a new wrinkle. The Thermally Reactive Advanced Protection, or TRAP breather, regenerates its water-holding capacity, leading to a much longer service life than traditional desiccant breathers, says Donaldson.
Remember that one type of hydraulic contamination is chemical – heat, water and air combining to create oxidation. Both sealed and open type reservoirs breathe to compensate for changes in volume, so water will be present in reservoirs because water is present in air. Water can also find its way into the system via cylinders, especially if the machine is on a dredging or ditch-cleaning job.
Water reduces the main function of oil – its ability to lubricate, Rose says. Moisture increases corrosion, which in turn can create acids in the oil and corresponding rust particles, according to Chevron. These particles are extremely hard and can cause increased hydraulic component wear.
Watch for overheating
The industry’s trend toward higher pressure hydraulic systems puts more stress on hydraulic fluids. “Higher pressures generate higher temperatures and higher temperatures generate more oxidation,” Navarro says. And when you go to the higher efficiency filters required by higher pressures, the pressure drop goes up and the dirt holding capacity goes down, Smith says.
High working temperatures are also a contaminant, Navarro says. “High temperatures kill the fluid and make it fail before time. For every 50 degrees above 158 Fahrenheit, the life of the fluid is cut in half,” he says. These temperatures also can break down any additives in the oil, and transform it into something else. For instance, sulfur can become sulfuric acid.
In addition to machine gauges, Navarro says there are solid physical indicators you have a problem with high fluid temperatures – the fluid gets too dark too soon and it has a foul smell.
High temperatures are usually the result of internal leaks on high pressure systems. Other culprits are inadequate air flow, including a modification to the machine that does not allow the air to move freely, altitude, and a leaking cylinder or relief valve.
Repairs open avenue to contamination
“Repairs are by far the best way to introduce contaminants into your system,” Navarro says. Whenever a machine is opened – especially in the field – contaminants are there to jump on board. Especially problematic are pump and cylinder repairs.
“After repairs, the system should be flushed at as high a temperature and flow as possible,” Smith says. The hot oil will flush through the system much more quickly, and the higher the flow, the faster it will take out contaminants. Heat and flow aids the cleanup.
Filter caddies have become an essential part of hydraulic fluid clean up. These units serve as a kidney machine, continuously filtering contaminants out of the machine fluid and then putting it back. An electric pump sucks fluid from the reservoir, passes it through a highly restrictive filter and returns it. Premium filter caddies, such as Deere’s Super Caddy, also measure particle counts and humidity, telling you exactly when the fluid is clean enough.
Caddies are not only used for after repairs, but also transferring fluids. They are typically found at dealers, but if you do a lot of your own major repairs, the $2,000 to $5,000 investment for a basic caddy could pay off in spades. “If you save the cost of one failure, you make up for the cost of the caddy several times over,” Navarro says.
An entire orchestra
When it comes to hydraulic cleanliness, Smith says, “filters are just one part of the orchestra. You have to look at everything – seals, breathers, maintenance procedures. It all works together, and if you’ve got one orchestra player out sick, you’re not going to sound good.”
Adds Rose: “We call contamination the ‘silent thief.’ We know the best operators will never notice any difference in hydraulic system reactions until they lose 20 percent efficiency. That means within seven days, they’ve lost one day’s work. And that’s just from a little dirt in the oil.”