Going Green: Biodegradable Products for Your Hydraulic System

May 1, 2000

Waste-collection vehicles are some of the most hydraulic-intensive pieces of equipment around, easily averaging more than a thousand cycles a day. They also operate under some of the worst conditions. Although most equipment still specifies petroleum-based or mineral-based hydraulic fluid, stricter environmental regulations—and the prospect of more ahead—are raising interest in biodegradable products throughout the United States.

Of all the “green” changes a collection vehicle operator or fleet manager can make to the equipment, using a biodegradable product in the hydraulic system—prone to leaks and failures under the best of circumstances—is likely to have the greatest environmental impact. Hydraulic fluids also offer the greatest range of biodegradable options. “That’s where environmental-type fluids started, in the hydraulic arena, because that’s where a lot of the spills came from,” points out Dick Scheels, industrial product advisor for global marketing for ExxonMobil Lubricants and Petroleum Specialties Company in Fairfax, VA. “A hydraulic system’s got a bunch of hoses, and guess what? Hoses break.” Most major oil companies have developed a line of biodegradable engine oils, hydraulic fluids, and other lubricants. Some equipment manufacturers, such as Caterpillar, have developed their own biodegradable hydraulic fluid for use in their equipment.

Although the US has no laws mandating the use of biodegradable lubricants or oils, the Environmental Protection Agency is looking more closely at nonpoint-source pollution, which includes runoff from work areas and the aftermath of spills and leaks. Phase II of the Clean Water Act National Pollution Discharge Elimination System (NPDES) tightens the rules, covering smaller municipalities and industrial and commercial activities than Phase I. Municipally owned facilities that were excluded from the Phase I rule must apply for Phase II permits by August 2001.

Switching entire fleets of waste-collection vehicles to biodegradable hydraulic fluids is not yet a widespread phenomenon, however. Concerns over cost and performance are the main reasons. Oil suppliers and equipment manufacturers report customers showing interest in—but no urgency for—environmentally friendly options. “Once in a while you’ll see a bid, for municipalities especially, that says they’ll consider biodegradable,” says Pat Bartlett, chief hydraulics engineer for McNeilus Companies in Dodge Center, MN, which manufactures front-, rear-, and sideloaders, as well as concrete mixers and other heavy equipment.

Iowa is one state that has taken an earlier step than most. The state passed a bill in 1998 that provides for the purchase of biodegradable hydraulic fluids: specifically, fluids manufactured from soybeans. S.F. 2185 amends state procurement specifications so that state departments and agencies purchasing hydraulic fluids must give preference to purchasing soybean-based products, but only if two conditions are met. First, the cost of the biodegradable fluid must be within the department’s or agency’s budget. Second, the use of the fluid in the department’s or agency’s equipment must be consistent with the equipment manufacturers’ specifications.

Meeting equipment manufacturers’ specifications is where part of the problem lies, notes Erv Hooks, equipment maintenance supervisor for the City of Dubuque, IA. Some manufacturers clearly specify petroleum-based hydraulic fluid—in some cases, the manufacturer’s own brand. “If you have an oil problem, the manufacturer’s going to come in, and the first thing they’re going to ask, ‘What kind of oil are you using?’ And if you tell them soybean, they’re going to say, ‘No warranty.’ Of course, the oil people will say it’s not the oil. I guess the oil people and the manufacturer can argue it out, but the city pays for it,” says Hooks.

The oil companies themselves are familiar with the cycle that Hooks describes, and some manage to get manufacturers to approve their products for specific pieces of equipment. “This is a general industry issue. A lot of the specifications that people consider when purchasing their lubricants are geared toward mineral oils. It’s hard to change thinking on lubricants,” states Mike Dormady, director of industrial products for AMSOIL Inc. in Superior, WI. Equipment manufacturers in turn have to consider the many components of their vehicles and equipment. “Pumps, valves, and cylinders are warranted by the people who build them,” says Bartlett. “We would have to have the blessing of these manufacturers before we could recommend anything.” To counter performance concerns, AMSOIL has performed evaluations and case studies to demonstrate to fleet managers how its products will work with their equipment. “That’s something you have to show them,” Dormady says.

Using the biodegradable fluid is not mandatory in Iowa, and soybean-based hydraulic fluid has not yet caught on throughout the state. “There hasn’t been a lot of activity on that; not like we had hoped,” remarks Dennis Jeter, a sales representative with Diamond Oil Company in Des Moines, IA, which supplies vegetable-based and synthetic oils and lubricants to customers who request them. “Quite frankly, part of the problem has been short life and cost. Although I think they’re making some gains on the quality and performance of the product, I think we’re a ways away from having just totally what we need that will compete against what’s out there.”

While he’s well aware of the push to use biodegradable oils and has seen some data on their performance, Hooks, like many others responsible for maintaining equipment, would also like to see more testing of the products on different types of equipment and for different applications. For a diverse fleet like Dubuque’s—Hooks manages about 150 pieces of landfill equipment, rubbish and recycling collection vehicles, fire trucks, and ambulances—standardization is also a concern. “Is it compatible to all vehicles? And is it strictly for hydraulic systems? We have hydrostatic systems that use hydraulic oil,” he points out. Three kinds of hydraulic fluid are currently used for all of Dubuque’s equipment. “It would be confusing, when you have as many mechanics and drivers as we do, to say, ‘OK now, in your truck you have to use this, and in this truck you use this.’ Maybe down the road when they come out with something that is compatible for all, then it will be feasible to look at it.”

Counting the Cost

There are many ways of figuring the cost of switching to a biodegradable hydraulic fluid. There’s the initial cost of the product, which is almost certain to be higher than that for premium-grade, petroleum-based fluid. Vegetable-based hydraulic fluid, for example, costs two to three times the price of a high-grade, petroleum-based oil, and synthetics can cost up to six times as much. The difference is partly because of the lower volumes produced—Dormady, for example, estimates that 3-5% of the market currently uses synthetic oils of any type, biodegradable and nonbiodegradable, including engine and gear oils as well as hydraulic fluid—and partly because of the manufacturing processes themselves. Oil companies and distributors tend to agree that, while higher volume might eventually reduce prices, they probably won’t be on par with petroleum-based hydraulic fluids.

If you can find the right product for your equipment and working conditions, though, you might also find another kind of long-term savings. Better performance under extreme conditions and longer oil life—with correspondingly longer drain intervals—might help offset the price of some synthetic products. “For years the cost of synthetics has kind of deterred people from switching from a mineral oil, but now what we’re seeing is that people are actually looking at the bottom line: overall cost, longer life, less wear, better oxidation capabilities,” observes Dormady. AMSOIL introduced its first synthetic motor oil in 1972 and has a diverse line of synthetic products, some biodegradable. He believes higher performance and longer wear, not concern about biodegradability, are driving more people to switch to synthetics.

Cleanup can also figure into the cost of the type of hydraulic fluid you’re using. “We get lots of calls from people shortly after they have been fined for a spill,” ExxonMobil’s Scheels points out. Although the US currently treats most spills of biodegradable fluids similarly to those of petroleum-based products, Canada does make some distinction in how biodegradable spills are handled, which can save money and red tape when a hose breaks.

Finally, an image of good stewardship and the public relations benefits associated with “going green” make the higher cost of biodegradable fluids more palatable to some companies.

What About Performance?

Although vegetable-based hydraulic fluids are sometimes regarded as having shorter life spans and less temperature resistance, they vary widely. Scheels was part of the team that, in 1990, introduced Mobil’s EAL (Environmental Awareness Lubricant) 224H, a biodegradable, nontoxic, vegetable-based hydraulic fluid. “The product has to do its intended work,” he remarks. “224H does not have the problems that industry has seen over the years with vegetable oils. It’s as good as the best mineral oil.” He acknowledges that with any type of fluid, quality can vary tremendously. “There are vegetable oils out there that will last 15 minutes. Some of them oxidize rapidly and go rancid. There are lousy mineral-oil products too. But you can make environmentally safe vegetable oils as good as a mineral oil. And you can make synthetic environmental fluids as good as synthetic oils. It’s expensive, but it can be done.”

Choosing the right product for your environment is critical if you want to extend equipment life, notes Dormady. “In a cold-temperature environment, you’re going to get lubrication faster with a synthetic product than you would with a mineral oil. In engines and gearboxes and hydraulic systems, your biggest wear generator is start-up. So if you have a product that’s flowing at -30º versus a mineral oil that’s kind of congealed, which one do you think will provide more protection?”

Synthetics for Extreme Conditions

Thermal stability is one of the key performance indicators of hydraulic fluids, and synthetics are well known for their superior performance in this area. Jay and Kip McEwan, brothers who each own a trucking company in Alberta, have had experience with every major type of oil in harsh environments. They switched from petroleum-based hydraulic fluid to AMSOIL’s Thermally Stable Biodegradable TBI hydraulic fluid four years ago, with a slight detour in between to a vegetable-based fluid.

Jay McEwan, president of McLoja Enterprises Ltd. in Cherhill, AB, discovered a vegetable-based, environmentally friendly hydraulic fluid that, on the face of it, was just what they were looking for—until the Canadian winter set in. “We run in temperatures down to -45ºC [-49°F]. The vegetable-based oil was only good to about -28ºC [-18°F], and then it turns to margarine. It doesn’t flow through the hydraulics on our equipment, and it has a tendency to wear out pumps and cylinders.”

He prefers TBI’s performance to that of petroleum-based hydraulic fluid. “Minus 35ºC [-31°F] basically is as cold as we could go with the petroleum-based because it’s too heavy. And then you were changing out the oils to run winter and summer, whereas with the synthetic oil, we run it year-round.”

Kip McEwan, president of J & K Trucking Enterprises Ltd. in Barrhead, AB, estimates TBI to be three times more expensive than standard petroleum-based fluid. “But the life of my cylinders and pumps has increased by three and four times.” Hard use of the equipment makes high-performance oil a priority. “We put a lot of hours on the machine. If it were a regular type of oil, I would be repairing the pump or the cylinders every 24 months.”

Longer Life…But Does It Matter?

Longevity of synthetic hydraulic fluid, biodegradable or not, has always been one of its biggest selling points. “We have people who tear systems apart and look at them, and they look like they’ve never been used,” Dormady says. Jay McEwan has used the same TBI hydraulic fluid in one piece of equipment for more than 5,000 hours of operation—testing it regularly—without a change. “We’re showing a little bit of wear and tear on the oil, but it’s not degraded enough to cause us any concerns.”

Longer-wearing fluid might save money under ideal conditions, but leaks and contamination can undermine even the best of products. As Bartlett of McNeilus points out, ideal conditions are rare in the solid waste industry. “The application we’re in is quite a bit different than other applications. In the refuse industry—a frontloader being a prime example—you have a situation where the cylinders are actually working right down in the garbage. That cylinder rod extends, then it retracts again and takes a certain amount of contamination with it. Cylinders have wipers that wipe off 99.9% of the contamination. You’ve still got that one-tenth of 1% that gets into your system however.” Even with good filtration, hydraulic fluid might need to be changed more often than in other types of equipment. “If you put in an oil that’s $15 or $20 a gallon, it may last longer, but it still gets dirty,” he says.

Hydraulic fluid anywhere but in the system also thwarts the synthetic savings plan. “I’m pretty vigilant about keeping my hoses up because the oil is such an expensive item, but we still do have a failure rate of about 15-20 gallons a year of oil,” says Kip McEwan. “You blow a hose, you lose half a gallon here, or a fitting comes loose, and you lose 2 or 3 gallons there.”

Saving Cleanup Costs and Building Public Image

For the McEwans in Canada, environmental considerations rather than performance drove the change to a synthetic fluid, even though they also find the performance of the synthetic better suited to the Canadian winters. Kip often works in northeastern Alberta, home to gas and oil fields, mining operations, and lumber mills. In addition to national and provincial environmental regulations, some businesses in the area, responding to public pressure, have set even more stringent standards for those doing work on their behalf. “It was on their request that we run a biodegradable oil,” he says.

As in the US, regulations in Canada govern the disposal of biodegradable oils and hydraulic fluids just as they do for petroleum-based products. In many US states, however, spills of biodegradable fluids must be reported and treated the same as a toxic material spill. In Alberta, Kip reports, “We have a policy that we have to let them know we had a spill, but having biodegradable oil, we don’t have to have a crew come out to clean it up.” He says cleanup costs for a single spill—for which his company would pay—can easily exceed the price of a barrel of TBI.

Using a biodegradable product, he says, “eliminates about 90% of the worry about having a blown hose. I know that if I blow a hose, there’s not going to be a hundred people coming down on my neck because I blew a hose in a creek.”

Making Sure It’s All Compatible

Although most manufacturers recommend completely draining one type of fluid from the system before adding another, some fluids are more compatible with petroleum-based products and components than others. Dormady says AMSOIL’s synthetic oils are compatible with seals and components used for petroleum-based oils and even with the oils themselves. “As far as changing the oil, it’s as simple as taking out the old and putting in the new.” Even mixing different types of fluids will not cause significant problems, although he recommends completely draining the old oil first, especially if a vegetable-based fluid was the last product used. “You run into performance debilitators. You’re putting a superior product in a system, and if you have a product in there that can’t perform as well, you’re going to diminish the effectiveness of the new product. It’s like watering down your bourbon.”

Compatibility with existing seals might seem to be a relatively minor consideration when switching to a biodegradable hydraulic fluid, but it can cause big problems down the line. Polyglycol synthetics are the most likely to require seals different from the ones used with petroleum products. Other types of synthetics and vegetable fluids might be advertised as compatible, but Fred Sadock, a product specialist with Hercules Hydraulics in Clearwater, FL, advises that it’s always wise to double-check. He has worked for more than 20 years with Hercules, which supplies hydraulic seals and other components for refuse vehicles, construction equipment, and other industrial equipment. Even with his years of experience, Sadock takes nothing for granted. “There are literally hundreds of different kinds of hydraulic fluids,” and many seal materials: polyurethane, various types of rubber, silicone, fluoroelastomer, fluorocarbon, fluorosilicone, Nitrile. To ensure compatibility with the elastomeric materials in the seals, “Most of the time I have to look it up in a compatibility chart,” he says. Incompatibility with the hydraulic fluid can cause seals to swell and eventually fail.

What’s Ahead for Biodegradable Products

If the state of environmentally friendly products in other parts of the world is any indication, more legislation affecting the use of biodegradable products will eventually arrive in the US as well—perhaps as mandates, as tax incentives for companies that use green products, or as stricter penalties for spills and hazardous runoff from work sites.

“The shift, depending on where you are in the world, is occurring very slowly. It’s much more active in Europe,” notes Scheels. ExxonMobil, as the world’s largest manufacturer and marketer of lubricants for a variety of industries, deals with the environmental standards throughout the regions where its products are sold. Many European countries have stringent environmental laws regulating oils and lubricants. “Here in the states it’s a little bit different. It’s more stewardship, a program for a company that wants to be green, that wants to do the right thing for the environment.
Biodegradable Options: What’s Available and How Do They Measure Up?

If you’re considering switching to a hydraulic fluid other than the standard petroleum-based, you have several choices. Nonpetroleum-based fluids are either vegetable-based or synthetic. Not all synthetic fluids, however, are biodegradable. Additives such as oxidation, rust, and foam inhibitors (the last designed to prevent “spongy” hydraulics), as well as anticorrosion and antiwear additives, vary from product to product. Some, such as antiwear additives containing zinc, affect the fluid’s biodegradability and toxicity level.

Vegetable Oils

Vegetable-based hydraulic fluids are made from rapeseed (canola) oil and other crop-based oils, including soybean, sunflower, and castor bean. In general, these fluids have good lubricity and good viscosity but do not flow as well at low temperatures as do petroleum-based fluids. The average pour point for vegetable-based fluids is about -22°F (-30°C). (The pour point is 5°F above the temperature at which the oil shows no surface movement when inclined—a low pour point is especially important for fluid used in cold climates.) Most vegetable-based fluids tend to age rapidly and oxidize quickly, especially at high temperatures and even when antioxidants are added, leading to formation of sludge and varnish.

Vegetable-based fluids are up to 99% biodegradable, and they are usually compatible with most of the seals and other components used with petroleum-based fluids. They generally cost two to three times as much as premium-grade, petroleum-based hydraulic fluids.

Synthetic Polyglycols

Synthetic polyglycol hydraulic fluids (sometimes labeled HEPG) are among the first biodegradable fluids produced. They have good shear stability, viscosity, lubricity, antiwear performance, and resistance to aging. They also have good thermal stability, ranging from about -49° to 482°F (-45º to 250°C). Their average pour point is about -40°F (-40°C). Some polyglycols have biodegradability up to 99%, though it varies depending on the ratio of propylene to ethylene oxide. Polyglycol fluids are usually not compatible with petroleum-based fluids, so if you’re switching from one type to another, most manufacturers recommend completely evacuating and flushing the system. No more than 1% of the total fluid volume after you switch fluids should be petroleum-based—although, because petroleum-based fluid is not as dense as polyglycol, what remains in the system will float to the top and can be skimmed off.

Polyglycol fluids may not be compatible with the lining, seal, filter, and gasket materials used with petroleum-based fluids, especially with polyurethane seals. Also, because polyglycols are soluble in water, it’s important to keep water out of the system. Polyglycol fluids generally cost two to three times as much as petroleum-based products and should be changed at about the same intervals as petroleum-based fluids, or as indicated by testing.

Synthetic Esters

Synthetic esters (sometimes labeled as HEES), derived from vegetable oil or animal fat, have very good viscosity, lubricity, and antiwear performance. They age well, are more thermally stable than vegetable fluids made from rapeseed oil, and have greater oxidative stability. Synthetic esters work well in extreme temperatures and heavy-duty applications. Some tend to have low oxidation stability, which can lead to gummy deposits in the hydraulic system. Synthetic esters are up to 90% biodegradable. They can be mixed with petroleum-based oil without significant effect on performance, but the resultant mix is less biodegradable. They are compatible with most seals and other components used with petroleum-based fluids. Although they cost three to six times as much as petroleum-based fluids, they are longer-wearing and might need to be changed less often.

Both synthetic esters and polyglycols tend to remove deposits that petroleum-based hydraulic fluids leave in the system, so filters need to be checked frequently after switching to a synthetic fluid.

Biodegradability and Toxicity

How, exactly, is “biodegradable” defined? After all, even most petroleum-based fluids eventually biodegrade, although it could take several years. Many lubricants are toxic as well, and a label of “biodegradable” doesn’t necessarily mean a product is nontoxic, or vice versa.

One standard for biodegradability commonly used in the US, developed by the Organization for Economic Cooperation and Development (OECD), uses an alternate biodegradation test to measure carbon-dioxide evolution. A substance is “readily biodegradable” if it biodegrades at least 60% within 28 days. It must also meet a 10-day window that starts when it reaches 10% CO2 evolution; once it has biodegraded 10%, it must make it all the way to 60% within the next 10 days.

Companies selling their products in Europe must meet the standard developed by the Coordinating European Council, known as CEC L-33-T-82, which also measures percentage of biodegradability within a given time period. Many products sold in the US also use the CEC standard.

In an attempt to provide some consistency throughout the industry, the American Society for Testing Materials (ASTM) has issued a standard, D6046-98a, Standard Classification of Hydraulic Fluids for Environmental Impact, which classifies levels of biodegradability. To meet the highest level, a fluid must biodegrade 60% within 28 days, similar to the OECD standard, but without the 10-day window. (The standard is available through the ASTM website at www.astm.org/.)

Toxicity, a separate issue, can also be measured in several ways. The most widely recognized and used test in the US is acute toxicity to fish. This test measures the lethal concentration of the product in water that will kill 50% of fish within 96 hours. The lower the concentration, the more toxic the compound. Rainbow trout, which are extremely sensitive to many toxins, are often used as the proverbial canary in the coal mine. To be classified as nontoxic, the concentration must be greater than 100 mg/lit.

Some vegetable- and petroleum-based lubricants are classified as “food-grade” products by the Food and Drug Administration. This classification does not necessarily mean the product is not toxic to fish, algae, and other organisms.

About the Author

Janice Kaspersen

Janice Kaspersen is the former editor of Erosion Control and Stormwater magazines. 

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