Considering all the maintenance items that need regular checkups on today's refuse trucks — diesel particulate filters, engine oil, engine coolant, tires, brakes and batteries — it's easy to see how hydraulic systems can get lost in the mix. For starters, their maintenance intervals tend to be longer than many key components on a refuse vehicle chassis. Though every truck and refuse body manufacturer develops its own maintenance schedule, and operating patterns influence the schedule tremendously, the typical maintenance intervals outlined below put hydraulic oils at the high end of the spectrum:
- Engine Oil — 250 hours
- Automatic Transmission — 500 hours
- Standard Transmission — 1,000 hours
- Rear Differentials — 600 hours
- Power Steering — 1,000 hours
- Antifreeze — 1,000 hours
- Hydraulic Oil — 1,000 hours
"There's so much concentration on the truck PM [preventive maintenance] schedule that the body and its hydraulic system tend to get overlooked," says Darry Stuart, president of Wrentham, Mass.-based DWS Fleet Management Services, a firm specializing in fleet management issues. "Hydraulic oil might last longer than engine oil, but it's far more critical because the hydraulic valves, seals and pumps have tolerances around zero. That's why the hydraulic oil cleanliness is even more critical than that of engine oil."
Hydraulic cylinders used to operate the trash compactor on the refuse body as well as front-loader forks are regularly worked hard, and are exposed to grime and other contaminants that can get into the system, Stuart adds.
Chafing and wear on hydraulic hoses are other issues that need close monitoring, says Darryn Wallace, senior technical service specialist with Superior, Wis.-based lubricant maker AMSOIL Inc. "I have seen hose failure occur due to the driver snagging the hydraulic line on a tree branch, rubbing a building or light post while making a tight turn, damaging the pump by running into something, or stressing the hydraulic system trying to lift a container frozen to the ground," he says. The standard hydraulic sump on a refuse truck holds 40 to 50 gallons, and the typical hydraulic system flows at a rate of at least 30 gallons per minute. Once a line is ruptured, it can take less than two minutes for all of the fluid to drain out of the system.
When replacing hydraulic hoses, fleets must accurately gauge the length of hose required, Stuart says. "You must be exact when replacing hoses, as a difference of an inch or two in length could mean a year or two less in life," he says.
Finally, there are the electronics to consider. "There are a tremendous amount of electronics — joystick controllers, relays, switches, wires and the like — involved operating the hydraulic equipment," Stuart says. "That's why the batteries are so important to the hydraulic system. Many times what seems to be a breakdown in the hydraulics is actually an electronic issue."
Knowing Your Oil
One of the most crucial components of the hydraulic system isn't even a "component" in the literal sense. Yet putting the right kind of hydraulic oil into a refuse truck's hydraulic system can dictate everything from operational effectiveness to life cycle cost.
"Most hydraulic oils have sufficient capability to handle the heat generated by a garbage truck hydraulic system, provided it meets the appropriate viscosity requirements for the temperatures it is operating in," Wallace says. Petroleum-based hydraulic oil may need to be changed based on the seasons. Because of their higher viscosity index, synthetic hydraulic oils can be used without the need to change for the climate of a given season.
Most refuse truck hydraulic systems do not need additional oil coolers to handle high temperatures, Wallace adds. "Considering the harsh operating environment they work in, adding more components to the truck will increase the odds of something getting damaged," he says.
Oil analysis is another critical part of maintaining the hydraulic system for the long haul. "It's just as important to hydraulic oil as it is to engine oil, transmission fluid, etc.," Wallace says. "Rather than looking for elevated wear metals like in engine oil, oil analysis of a hydraulic system is primarily concerned with seeking any levels of contamination, such as water and dirt."
Particle counting is the most common type of analysis performed on hydraulic oil because it can measure the number of particles in specific sizes. Other types of analysis can be performed to determine if the hydraulic oil pump is approaching the end of its useful life by detecting and identifying the size and type of wear particle that the hydraulic system is generating.
Synthetic hydraulic oil may have another advantage over petroleum-based oils in terms of allowing the system to perform more efficiently. "A good quality synthetic hydraulic oil meeting maximum efficiency hydraulic fluid specifications can lower energy costs and/or increase productivity in the equipment by 6 to 15 percent," Wallace notes.
Eye on Maintenance
As is the case with the rest of the vehicle, maximizing the uptime of a refuse truck's hydraulic system comes down to regular care. That includes inspecting the entire vehicle on a daily basis and using quality greases and oils, says Tom Price, product engineering manager for Chattanooga, Tenn.-based Heil Environmental.
"Simple things, such as watching the hydraulic fluid pressure, will tell you when the filter is getting clogged," Price says. "The more pressure it takes to push oil through the filter, the more it is clogged. At some point, the oil bypasses the filter through a relief valve. That means dirt and contaminants are getting into the system."
In a white paper that it produced, truck leasing firm Beacon Funding Corp., Northbrook, Ill., states that cost should never get in the way of maintaining your equipment. "The cost of a good preventive maintenance program will always pay for itself over the long run," the white paper says. "Also, calculate how much your truck earns for you in a day. Keep this figure in mind so that you'll know just how much unproductive downtime costs you."
In the paper, Beacon stresses that fleets should train their drivers to always watch gauges for signs of trouble and then immediately notify a mechanic about any problems that they think the vehicle might have. Doing so could head off more expensive repairs and excessive vehicle downtime.
For example, Beacon poses the example of a seal leak on a refuse truck's hydraulic pump. If the problem had been identified and handled in a preventive maintenance program, the seal would have quickly been spotted as leaking. This more than likely changed within a couple of days and would have kept the loss of oil to a minimum. The only costs that would have been incurred would be the hydraulic pump seal, which, more than likely, only would have been around $40 plus the cost of the labor. The labor to remove the pump, replace the seal and reinstall the pump should not take more than three or four hours.
Assuming four hours labor at $65 per hour, the labor cost would have been $260. Thus the total bill would have amounted to $300.
But if the seal had been left leaking without replacement, it would have eventually burned up due to lack of oil, the company explains. Not only would a new pump have to be purchased — at a cost of over $600 — but also the owner would have used more oil as the seal continued to leak (approximately $2.50 per gallon). Even more costly would be a pump failure during an important job, when the truck is fully loaded, Beacon says.
Stuart stresses that regular maintenance combined with quality hydraulic oil and grease can head off many problems. "Good grease and good oils are the cheapest maintenance in the world," he says. "When budgets get tight, like they are doing now, it's tempting to buy the cheapest product you can find in the belief that you are saving money. But if that leads to an increase in parts failures and more downtime for repairs, it's costing you far more money than you are saving."
Sean Kilcarr is a senior editor of Fleet Owner, a sister publication of Waste Age.
For more stories on waste fleets, click on the Trucks & Bodies link at the top of the page.
Protecting the System
Unfortunately, maintenance personnel often decrease the lifespan of a hydraulic system and its oil, according to Darryn Wallace, senior technical service specialist with Superior, Wis.-based lubricant maker AMSOIL Inc. The many ways in which maintenance workers can wreak havoc on a hydraulic system include:
- Failing to inspect and tighten loose hydraulic connections.
- Not replacing leaking seals on hydraulic rams.
- Using the wrong viscosity hydraulic oil for the temperature range in which the truck is operating.
- Failing to remove dust or debris that has built up around seal areas and joints.
- Not changing oil-tank breathers on schedule or using the wrong type of breather.
- Over- and underfilling the hydraulic fluid level.
- Not tightening the oil tank cap properly.
- Failing to prevent dirt or debris from settling on the hydraulic oil tank.
- Incorrectly pressure washing the truck. Water could get forced past the seals in rams or through the tank cap if careful procedures are not followed.
- Misapplication of fluids added to hydraulic system.
- Not changing primary hydraulic filters on a regular schedule or using an inappropriate oil filter.
- Not greasing the pins and bushings on a regular basis.
— Sean Kilcarr
Stop and Go
Hydraulic systems now are being used to help power refuse trucks themselves as well as their trash compactors. Houston-based Waste Management (WM) is one of a handful of refuse firms to begin field-testing parallel hydraulic hybrid waste collection trucks.
In its Fort Worth, Texas, market, WM is testing four Peterbilt Model 320 hybrid-diesel collection trucks equipped with a hydraulic launch assist (HLA) system developed by Cleveland-based Eaton Corp. While the HLA and hydraulics powering the compactor are completely separate systems, they share similar components and characteristics for easier maintenance.
The HLA system, which adds about 1,000 pounds to the vehicle, captures and stores energy during braking, then transfers it to help accelerate the vehicle to the next pickup location.
Laboratory testing shows the HLA system cuts fuel consumption anywhere from 25 percent to 33 percent, reduces wear on the engine and improves brake pad life by at least 50 percent. WM's field tests are designed to see if those numbers hold up under real-world conditions.
"Though development is in early stages, we are optimistic that the investment we are making now will lead to a reduction in greenhouse gases, and ultimately benefit both manufacturers and users of heavy vocational vehicles," says Eric Woods, WM's vice president of fleet and logistics.
— Sean Kilcarr