Agricultural machinery is up against a variety of harsh environmental conditions, so proper protection of the hydraulic systems is necessary.
By Josh Cosford, Contributing Editor
The agricultural industry is unique in many ways, not the least of which is the source of nourishment for billions of people, which is not something mining or forestry can claim. When it comes to the design and operation of agricultural machinery, the operating environment creates unique challenges that fluid power designers must overcome to ensure machines are effective and reliable.
The challenge of eliminating contamination in ag hydraulics is a daily struggle, as the ambient environment assaults machinery with every possible ilk of damaging stressor. A late-spring Sunday drive in the country could yield vistas of dust clouds as tractors work dry fields or, conversely, nothing at all as machinery sits idle in the rain. And even during heavy rain when fields are inaccessible, there’s always work to be one on the farm, such as livestock care and handling of seed, feed and fertilizer.
Hydraulics at risk in dusty environments
Sometimes, the plumes you see stem from dry-spread fertilizers and nutrients. Using hydraulic conveyor and spinner motors to hurl dry nutrients across the field, granular and powdered fertilizers are still relatively common. Lime is used to adjust soil pH, gypsum to improve soil structure, and phosphate fertilizers may be periodically spread on fields, each of which can be dusty.
Because hydraulic systems need to respire during the operation of differential area cylinders (those with a single rod), the reservoir fluid volume lowers during cylinder extension and rises during cylinder retraction. To prevent vacuum or pressure inside a reservoir, a breather cap is installed atop the filler hole in most cases.
However, because farm equipment sometimes operates within a swirling cloud of grit, that reservoir interior needs protection from contaminant inhalation. The filler cap on most reservoirs doubles as a breather device, allowing air to enter while filtering a great deal of the particles doing their best Trojan Horse impersonation.
Despite this common barrier to contamination ingression, there are caveats to the commonly used breather cap. The off-the-shelf twist-lock designs you can buy at the tractor supply store are neither terribly efficient nor configured appropriately to store very much dirt. We rate a filter’s capacity to store contaminants by its Dirt Holding Capacity, and such inexpensive breathers may only hold a few grams of dirt and dust before becoming clogged.
Additionally, the budget-friendly breather designs have a poor beta ratio, which describes a filter’s efficiency at trapping particles in a single pass. Contrary to the low micron number claim by breather cap manufacturers, the efficiency of these designs is poor. When you factor in the construction method using either mesh or foam, you might agree that a 4-micron rating from a $4 breather will offer some compromises.
A high-end machine deserves high-end contamination control equipment, so farm machines should use low-micron, high-efficiency breathers. Many manufacturers offer synthetic media with ultra-fine mesh down to 3-micron or lower, and the penalties of back pressure are nominal when flowing only air. Additionally, synthetic media’s dirt-holding capacity is exponentially higher than that of inexpensive materials, allowing the element to hold over 100 grams of dirt when so equipped.
Farmers must be mindful of their environment and the potential for quickly loading a breather cap with dirt, even when using high-capacity elements. Spin-on breathers are quick and easy to replace, but they should be replaced regularly. The effects of a clogged breather are often challenging to detect, and the damaging consequences can occur without notice. A pump may cavitate more quickly should air not quickly replace the reservoir’s fluid, as reservoir vacuum occurs when a differential cylinder extends. Here, it’s always best to follow the manufacturer’s service frequency recommendations.
Keep water at bay
Of course, there are perhaps just as many chances where rain is the prevailing issue on any given day, depending on climate, of course. Rain presents its own challenges regarding reservoir respiration since mobile hydraulic systems aren’t friends with water. Water, even in the form of humidity, creates a range of problems for hydraulic components, including corrosion, fluid degradation, and increased microbial growth, among others.
OEMs have been diligent in avoiding reservoir design and placement in such a way as to allow and encourage free water to enter around the filler-breather location. A well-planned location and installation of a breather riser will prevent pooling water from dripping into the tank, but humidity is a serious concern for outdoor machinery.
To combat excessive humidity inside the reservoir, which can be absorbed by hydraulic oil, OEMs now use desiccant breather caps to leech away water in addition to particles. Although expensive compared to traditional breather caps, the protection they provide for the lifeblood of your tractor is invaluable.
The desiccant breather cap is nearly universally a transparent plastic shell with colored silica gel beads. These small beads provide exceptional surface area for the best chance of capturing water molecules as they pass. Modern breathers use methyl violet or iron salts that change the color of the beads when they’re saturated, providing a visual signal to change the breather.
Older technology used a chemical called cobalt chloride, although such versions have been phased out in the farming industry because of environmental concerns. Cobalt chloride is blue when dry but turns pink when saturated. Meanwhile, the modern chemicals, as previously discussed, are more inert and appear orange when dry before changing to green when saturated. When shopping, be sure to locate or ask for the orange desiccant.
High-end machines take contamination prevention to another level by incorporating sealed reservoirs. A reservoir capable of a moderate positive pressure allows for differential volume control while avoiding any chance of cavitation or contaminant entry. These systems are exponentially more expensive than breather caps but are impervious to even the most biblical dust cloud.
Farm equipment experiences more trouble outside of reservoir humidity, of course, since they’re exposed to the elements. In many cases, farms may lack space in the machine shed for all the required equipment, so infrequently used or older machines may sit outside. Besides the obvious filler cap, water can invade through poorly maintained and uncapped quick couplers (Pioneers), damaged cylinder rod seals and from condensation inside the reservoir.
Each of the above options results in free water, which can damage the hydraulic system in ways more severe than humidity alone. Free water can create localized pools of rust as machinery sits for extended periods, which could rust and create iron oxide particles. Those particles could break away during machine startup and create havoc on sensitive components.
In cold climates, water will also freeze, leading to possible physical damage depending on its location. When water freezes, its volume expands with such strength that even steel parts may be damaged. The worst damage may occur in late fall and early spring when the mercury waxes and wanes thermoclastic. If the freeze/thaw cycle is strong enough to heave asphalt and concrete, imagine how easily a seal could be blown out.
Older machinery and implements pose unknown risks
Another form of contamination common in agricultural hydraulics originates from an unexpected source: implements. Few farms are fortunate enough to commission only brand-new equipment, and farmers frequently buy, sell and trade to secure the fleet that suits their needs.
Many hydraulic-heavy farm implements consist of various hydraulic cylinders and/or motors. Folding disks, silage wagons, large balers, and auger wagons are machines frequently used by most farms, and with so many hydraulic functions, the machine as a whole stores many gallons of hydraulic fluid. Cylinders, motors, valves and plumbing contain hydraulic fluid, and when buying old machinery, the condition of such fluid is often unknown.
Auction houses often list equipment as-is, so no guarantee is offered to the state or quality of the hydraulic fluid or the components it’s meant to lubricate and protect. Simply hauling your new-to-you self-propelled sprayer home and connecting up the hydraulics without first purging everything could invite hoards of damaging contaminants into your expensive tractor.
Your tractor is worth far more than some hydraulic oil (or the implement), so be sure to drain all used fluid and then refill and bleed air as required. You dramatically decrease the opportunity for contamination while ensuring your actuators begin their stay with you enjoying fresh oil.
This next part is for the veteran farmers reading. Up until now, the article risks appearing fluffy and irrelevant because we all know farmers with old, rusty equipment who use them every three years with no issues despite looking like a bombed-out armored personnel carrier. Also, I like to indulge in the random YouTube videos that appear in my feed with titles like “This Excavator Hasn’t Run in Twenty Years. Can We Get It Started?” Clearly, old machines have the capacity to work and run, but that doesn’t make them ideal.
If old equipment works for you and your farm and hasn’t hindered your production capacity, then who am I to tell you to focus your time on contamination control rather than putting up hay or caking cows? However, the reality for commercial farming is that productivity, reliability, and automation are necessary to remain profitable with ever-tighter margins. But when advanced, 7-figure machines are expected to make huge returns on investment, being casual about contamination control is not an option.
