Multi-grade viscosity hydraulic fluid: What goes in it & what you get out of it

In business, every cent counts towards a company’s bottom line. This is especially true when the business in question relies on the use of excavators, backhoes, forklifts and other heavy machinery: every cent that isn’t spent on repairing equipment is another cent that can go toward profit. The potential for generating profit increases exponentially when heavy equipment can be kept running longer and be made more resilient to avoid the need for offline maintenance.

Of course, managers must consider which maintenance costs are worthwhile. After all, there’s not much point to spending money on aging equipment that may suddenly break down. But cutting corners on such resources can hurt a company’s bottom line more that in can help. Case in point: choosing between a multi-grade viscosity hydraulic fluid versus a lower-quality and less expensive alternative.

Perils of poor quality

It is not uncommon to hear operators rev an engine on startup, especially when they’re using older equipment that is acting sluggish. What they are doing is using increased RPM to compensate for the thinning of the equipment’s hydraulic fluid, in order to get the engine to do the same amount of work as it ordinarily would if it had a higher-quality hydraulic fluid. Regardless of whether the equipment is powered with diesel or electricity, that operator is paying an energy penalty when they increase RPMs. But if the viscosity of the hydraulic oil were to retain its grade, then the engine could do the same amount of work with less energy –?i.e., the operator wouldn’t have to rev the engine.

Sluggish starts and performance are just a couple of symptoms related to lower quality hydraulic fluids. Another major indicator can include excessive chatter and vibrations as the equipment’s actuator is being engaged. This is often caused by cavitation, or a lack of sufficient oil in the pump. Cavitation results from a lack of fluid going into the pump and is usually attributed to poor viscosity – either because heat has caused the hydraulic fluid to become too thin to provide enough protection, or because cold temperatures have caused the fluid to thicken to the point that it doesn’t adequately flow. Cavitation results in excessive wear in the pump and greatly increases the potential for catastrophic equipment failure.

Varnish buildup can also have a dramatic effect on equipment performance. Varnish starts as a sticky soft residue tenaciously clinging to metal. The sticky-soft nature of the varnish actually attracts wear debris while preventing anti-wear additives in the oil from attaching to the metal, both of which dramatically increase wear. Varnish buildup leads to a chain reaction within the hydraulic system that results in erratic operation, increased wear on valves and pumps, shorter fluid life due to increased oxidation, less fuel efficiency and increased down time.

Another issue relating to hydraulic fluid quality relates to leaks. Leaks often result from seal failure and ruptured hoses, both of which can be caused by excessive operating temperatures. Seals and hoses are both made from rubber, which crystalizes and becomes brittle when exposed to excessive heat. Excessively high temperatures can be avoided by maintaining correct volumetric pressure – and the best way to modulate that is by using fluids that maintain their viscosity in extremely hot conditions.

Formula for success

It’s important to identify the signs indicating inferior-quality hydraulic oils, but knowing what to look for in a superior hydraulic oil can keep managers from being put in that position in the first place.

Viscosity is the single most important criteria when evaluating a hydraulic fluid for performance. Viscosity is a fluid’s resistance to flow – after all, hydraulic systems are all about flow: keep the lubricants flowing and the equipment pumps more efficiently, delivering better and more consistent hydraulic performance. A fluid’s viscosity changes as temperatures increase or decrease – the higher the temperature, the thinner the oil and, consequently, the lower the viscosity. Cold temperatures have the opposite effect of thickening the oil and raising viscosity. This change in viscosity in a given fluid determines its viscosity index (VI). Hydraulic fluids with a high VI will maintain the same viscosity over a wider range of temperatures, resulting in better efficiency, less fuel consumption, and decreased maintenance – all of which contribute to keeping the equipment running more efficiently with less required downtime.

Another key attribute in high-quality hydraulic fluids is the use of a superior base stock. Fluids that utilize a higher-quality base stock have inherently higher VI ratings, so they’re less likely to lose viscosity as operating temperatures increase. As a general rule, synthetic hydraulic fluids will always provide a higher VI than petroleum-based fluids. Even the best petroleum-based hydraulic fluid will not have as high a VI as a synthetic fluid, due to the nature of the molecular structure of the base stocks involved. There are few, if any, practical applications for hydraulic fluids with low VI ratings: they’re simply an inferior product available at a low price point. A company may save some money when purchasing them, but it’s almost certain to result in eventual equipment failure. It’s simply not worth the risk.

Not all multi-grades are alike

Hydraulic fluids can be made into multi-grade products with the inclusion of high-molecular weight polymers. The molecular structure of these polymers resembles tiny springs, which are chemically calibrated to expand and contract depending on the temperature to which they are exposed. The molecular nature of the polymer causes the oil to adhere to its surface, but the adhering qualities vary depending on operating temperature. When it’s hot, the coil expands, and in extreme heat it expands dramatically, resulting in an increase of surface area. When the oil molecules adhere to the increased surface of the polymer coil, it causes the oil to thicken just enough maintain its grade (as opposed to thinning.) Conversely, when temperatures drop, the polymer’s coil shape contracts, resulting in less surface area and causing the oil to thin, again maintaining its grade.

While multi-grade fluids can provide superior performance, it’s important to note that not all multi-grade fluids are equal. This is because the majority of fluids utilize polymers that are essentially plastic in their composition –?and because they are plastic, they tend to break down after repeated cycles through a system’s pump, which literally fractures and shatters the polymer after extensive use.

By contrast, a multi-grade product that is shear stable,?such as Schaeffer’s HTC Extreme Performance with DYNAVIS?, is engineered to withstand such punishing conditions. Shear-stable products are formulated with polymers that are more like rubber than plastic in nature; rather than shattering or breaking apart when cycled through a pump, these polymers will instead bend and flex, returning to their normal shape upon exiting the system. The result is a product that doesn’t break down as quickly, providing longer operating life while requiring less maintenance.

The performance benefits of shear-stable fluids really shine when it’s subjected to the three biggest risk factors: heat, pressure and time. When heavy equipment is in operation, conventional fluids gets hotter, causing it to thin out; this is when hydraulic system performance begins to suffer, straining to keep up with output. Picture a forklift operator lifting a heavy load. As his equipment begins to strain, he’s forced to increase RPMs by revving the engine to complete the work, consuming more energy in the process. As this goes on, it takes more time to do the job, and more fuel is consumed. However, a multi-grade shear-stable fluid is able to stabilize viscosity at a wider range of temperatures, allowing operators to increase performance and do more work without increasing fuel consumption.

The bottom line

Superior multi-grade hydraulic fluids provide an enormous number of performance benefits while improving efficiency and prolonging equipment life. Industry studies provide documented evidence that users who put their faith in multi-grade viscosity hydraulic fluids experience substantial energy savings through reduced fuel and energy usage. Ultimately, the best proof for even the most skeptical user will be seen in their bottom line. It’s hard to argue against a product that consistently delivers savings in the form of less fuel consumption, better energy savings and less equipment downtime.