By Josh Cosford, Contributing Editor
From selecting the right fluid to keeping machines clear of snow, regular cold weather hydraulic preparation and maintenance will ensure smooth and consistent machine operation from start-up.
As I sit here writing this article about cold weather hydraulic maintenance, the temperature in my Canadian city hovers around 77°F (25°C). Usually, this is no big deal since we get plenty of ninety-degree days in the summer. However, being mid-Autum, there are talks of records falling today.
Nevertheless, Autumn is a good time to remind you to prepare for the cold months, when they eventually and inevitably come. It’s easy to get complacent on days like today, and I’m guilty myself. Last week, a neighbor casually quipped, “You finally closed your pool, eh Josh?” as he walked by with his dog. We like to swim in October … so what?
When a Canadian pool closes for the winter, the process is more than turning off the pump and throwing a cover over the pool. You first have to add a chemical cocktail and then pump antifreeze into the lines surrounding the pool (but not the pool water itself). Without this care for fall maintenance, you risk funky pool water come spring, and that’s only if the lines didn’t first freeze and damage the pump, filter or heater.
Extreme cold temperatures and moisture can wreak havoc on a hydraulic system, but proper design and maintenance can sure reliable start-up and operation.
Operating hydraulic machinery in the cold is inevitable in Canada, the Northern USA, and much of Europe. A solid cold-weather maintenance program should be implemented to not only improve the reliability and efficiency of your machinery but also allow them to even run at all in some cases.
Hydraulic fluid considerations
It’s no surprise that hydraulic fluids thicken in cold temperatures. In fact, some oils will appear to behave more like liquid honey when the temperature drops much below freezing. High-quality hydraulic oil with a decent viscosity index should be suitable for machinery operating with a small window near freezing, but true arctic conditions require something more.
Because cold, thick hydraulic fluid flows poorly, it creates excessive backpressure just for the pump to move the fluid through the plumbing. Thick oil also offers reduced lubrication, which, of course, leads to increased wear as the fluid is no longer able to provide either full-film or boundary lubrication. Indeed, when the mercury drops to below zero (-18°C), special Arctic oil is pretty much mandatory.
Screw Plug Heaters from Warren Electric consist of tubular elements that are brazed or welded to a screw plug and provided with terminal enclosures. They are screwed directly into a tank wall or through a matching pipe coupling. Image courtesy of Motion
Appropriately enough, most manufacturers make their “Arctic” hydraulic oils blue in color, and have properties that make it suitable for icy wastelands. With an extremely low pour point, low viscosity and excellent viscosity index, these fluids ensure every cold weather machine starts and runs efficiently no matter how cold the ambient environment. Changing to arctic oil before the cold hits keeps you from being caught off guard.
Before moving on to other cold weather maintenance practices, you might be wondering if Arctic oil must be replaced again in the spring. The answer depends on your latitude, but if you’re anywhere it gets hot in the summer, you definitely want to store your artic oil for the season and replace it with something more hot-weather suitable.
Cold-start issues are common, so pre-warming the hydraulic fluid before heavy operation helps prevent issues or damage from cold, thickened fluids. You don’t need hot fluid, but it should be warm enough to be within the operating window for the given oil and system components. For example, although a hydraulic system will function between 10-1,000 centistokes (mm²/s), the ideal operating viscosity might be 16-36 centistokes, for example, and should be geared toward the most sensitive component.
And don’t confuse viscosity grade with operating viscosity. Anti-wear oil is tested and rated at 40°C (105°F), but AW32 will still be over 1,000 centistokes at freezing. This shows the importance of synthetic Artic oil, which, although with an insanely high viscosity index of 160 or more, still sits well over 300 centistokes at freezing. Drop the temperature to –30°F, and even Arctic oil will be nearly unpumpable.
Heating systems
Oil heating systems range from tank heaters to liquid-to-liquid heaters or to preheat hydraulic circuits. Tank heaters could be mounted to the reservoir surface but are not quite as efficient as in-tank heaters, which can be programmed to maintain temperature using a thermostat. However, since only 60-80% of the system’s oil resides within the reservoir, supplementary heating could also be used.
Liquid-to-liquid coolers can piggyback off the machine’s engine coolant system, which heats up more rapidly than a hydraulic system can. In all likelihood, the engine block may also be heated to improve its own cold-weather startup efficiency.
If an electric power source is unavailable because of the remote nature of the machine location, sub-circuits can be designed to simply run fluid through a heating process consisting of a single 2-way, 2-position valve leading to a moderately low-pressure relief valve. You want that relief valve to operate at low pressure to prevent excessive, localized heat generation, which can oxidize the fluid. And, of course, all three heating options may be combined if the environment is extreme enough or you require a short startup period.
If your machine runs a closed-loop pump and motor combination, such as many mobile machines do, installing a charge pressure reduction system will make turning over the engine and starting the pump an easier affair, even with a tank heater. The system simply reduces incoming charge pressure temporarily so that it’s easier to crank against a lower load. If you’re unfamiliar with closed-loop pump technology, the charge pump is a smaller fixed displacement pump that directs makeup fluid into the inlet of the pump and ensures there is always positive pressure.
In the same vein, electronically controlled pumps can run at reduced pressure until the oil is heated. It’s not rare for mobile machinery power units to run in the hundreds of horsepower, and even just an idling pump can emit significant heat through its case drain. Once up to operating temperature, the machine controller can permit full pressure once again.
Think about your rubber components
Standard synthetic rubber seals and hoses become brittle in cold temperatures, increasing the risk of leaks or failure. Cold-resistant materials, like polyurethane or certain elastomers, should be used. Consideration should be made for clearances and extrusion gaps, especially if the metal parts being sealed shrink and open up possible extrusion gaps for the seals to push through during startup. Look for material with high thermal stability, especially in the low range.
Continental’s Arctic high-pressure hydraulic hose can be used in construction, forestry, surface mining, oil and gas, waste handling, utilities and other applications where lower temperature can impact performance.
Hydraulic hoses may also need to be replaced for use in extreme cold, especially NBR (Buna-N), which could become brittle or crack. Pay special attention to the bend radius of a hydraulic hose, which could be reduced as the mercury drops. Some manufacturers have developed advanced compounds, such as copolyester, which handle the frigid extreme while remaining flexible.
Snow and cold means moisture
Cold environments can lead to condensation inside hydraulic systems because of the hydraulic oil’s capacity to either retain humidity when hot or condense free water when cold. Regular fluid checks and water-absorbing filters are critical to prevent water-related issues like corrosion or reduced system efficiency.
Of course, pay special attention to machinery operating in cold rain or snow. As a machine comes up to operating temperature, any snow left on the machine may melt and find its way into the hydraulic circuit. Just as with your vehicle, do your best to blow or brush snow off the machine to prevent free water from being ingested around the breather cap. If necessary, consider a desiccant breather cap to absorb any moisture before it can hit the oil. However, if the machine was designed for operation in rain, you should be okay here.
If possible, store your machinery in a warm or insulated location when sitting idle. This will prevent fluids from reaching excessively low temperatures but also ease the start and warmup procedure. If you live in the snow belt and garage your car, you know how easy it is to get in and go while you point and laugh at the people who brushed off a gun slit on their windshield and went on their way on a snowy morning.
Even if you have a storage space without insulation or heat, you’d be surprised at how much the machine’s residual heat from the previous day’s operation will melt any ice or snow that was left on the machine after the shift. Heck, even a tarp over the machine will help reduce startup time the following day when you’re in the middle of a blizzard.
You want to ensure your operator is toasty and cozy for a relaxing day of snow grooming or tree felling, so don’t forget to pay attention to cab maintenance. I know it’s not hydraulic-related, per se, but it requires attention nonetheless. Ensure the wipers are functioning, defrosters are working at full capacity, and all the various heaters (and there could be many) haven’t kicked the bucket since the previous season.
If you’ve had the pleasure of traveling to the extreme North, you know they take their weather seriously. If you haven’t, let me put it this way: public parking lots have block heater hookups. If you yawn into the open air when it’s -20°F, you will start choking. Your breath vapor can cause your eyelashes to stick to your skin. Under these cold extremes, you can forget about operating your hydraulic machine unless you’re dedicated to cold-weather maintenance.
Filed Under: Engineering Basics, Trending
