Most of us have watched one of the popular reality-TV shows involving fishing, mining, logging or trucking. Without fail, there seems to be some dramatic mechanical failure that keeps us in suspense during the commercial break. Failures involving hydraulic systems often happen in cold temperatures. Many of us can sympathize with the guy on the show; he’s shown lying under the equipment with no gloves on his hands, snow is falling and his jacket is covered in oil. The drama provides great entertainment, but also a great example of the significant time and money lost every year in hydraulic equipment operated in cold temperatures.
So why do these guys always end up facing hydraulic equipment failures in the middle of the winter? Most often it is due to poor maintenance, poor startup procedures and continued use of a cheap hydraulic fluid that gets too thick in cold temperatures.
Completing scheduled hydraulic system maintenance throughout the year can significantly reduce cold-temperature downtime. Unfortunately, tight schedules, remote job sites and the need to keep equipment running at all costs can mean that badly worn hoses, leaky seals and other maintenance items go unchanged for extended periods. The colder the ambient temperature gets the more likely a catastrophic failure of one of these weak points will occur, and poor-quality hydraulic oil may accelerate the failure.
Hydraulic oil must protect moving parts from excessive wear, keep the system clean and free from varnish and transmit energy to complete a number of different jobs such as moving mountains of dirt and cutting trees off at their bases. To do these jobs, it’s critical that the hydraulic oil stay within range for thickness regardless of the outside temperature. This is especially important during cold temperature starts, when damage and accelerated wear can occur quickly if the oil gets too thick.
Damage and wear can be caused by starving the inlet side of the hydraulic pump (pump cavitation). This can occur during cold weather when oil becomes so thick that the pump is unable to pull fluid from the reservoir fast enough for continuous lubrication supply. Instead, the pump pulls air, components become starved of lubricant and metal-to-metal contact occurs. Overly thick oil also contributes to pressure spikes that blow hoses, filters and other critical components.
To help prevent this condition, most equipment manufacturers include hydraulic oil viscosity recommendations in their operator manuals and will often recommend thinner oil for cold ambient temperatures. This is one way to help solve the problem, but we all know that synthetic lubricants provide a solution through higher viscosity index. High-viscosity-index synthetic hydraulic fluids remain much more fluid in cold temperatures while maintaining a protective layer of fluid in high temperatures. The higher the VI, the less the fluid’s viscosity will change due to temperature fluctuations.
The importance of this can be illustrated by comparing a cheap mineral oil with a high-VI synthetic hydraulic oil. Both oils have the same thickness of 32 cSt at 40°C (ISO 32). But, the synthetic hydraulic oil has a VI of 160 and the mineral-oil-based hydraulic fluid has a VI of 90. When both oils are cooled to 10°F, the low-VI mineral oil thickens much more than the high-VI synthetic oil. Even though the oils are classified as having the same ISO viscosity, the high-VI synthetic oil will flow much better at 10°F. This means better lubrication for the pump and less chance of a pressure spike, damaging cavitation or blowing neglected weak points in the system.
Bottom line: Fluids with a higher viscosity index provide better protection in cold temperatures than fluids with a lower viscosity index.
On the other end of the spectrum, hydraulic oils need to fight varnish and sludge buildup most often associated with high-temperature, high-pressure industrial environments. Not all hydraulic oils are designed to provide effective resistance to varnish and sludge in these environments, and varnish and sludge are directly responsible for sticking valves and other operational issues. As temperatures increase, hydraulic oils thin out. In excessive temperatures, some do not provide the required oil thickness to adequately protect against wear. Additionally, oils not formulated correctly for these extreme applications allow varnish to form after continual operation at high temperatures, and sensitive operationally controlled valves begin to malfunction. Just like motor oils, not all hydraulic oils are created equal, and that is especially evident in cold-temperature applications.
AMSOIL synthetic hydraulic oils can greatly reduce cold-weather problems. They also provide outstanding oxidation resistance for longer fluid life and significantly better resistance to harmful varnish that plagues many hydraulic systems operating in hot industrial environments. AMSOIL has the hydraulic products to keep customers running smoothly in both extreme cold and in hot industrial environments.
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