Tractor Hydraulics - The Basics, Part 2

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Hydraulic Basics - Part Two
by Curtis Von Fange

Part one of this article can be found here.

In the last entry to this series we gave a brief overview of hydraulic system theory, its basic components and how it works. Now lets take a look at some general maintenance tips that will keep our system operating to its fullest potential.

The two biggest enemies to a hydraulic system are dirt and water. Dirt can score the insides of cylinders, spool valves and pumps. Water will break down the inhibitors in the hydraulic oil causing it to emulsify and lose its lubricating features. Scoring of cylinder walls and breakdown of internal seals will result. It is imperative to keep these two problem areas in check.

The primary way that dirt can enter the system is through the air breather on the reservoir. As the cylinders in the hydraulic circuits are activated the oil level in the reservoir goes up and down. Air rushes in and out of the reservoir through the air breather in order to compensate for the various fluid levels. Unfortunately, this air is often contaminated with air borne dust and debris from the excavating process that the tractor is doing. The air breather is supposed to screen out this dust by trapping it in between layers of oil saturated filter material. Many times these filters are not cleaned or checked for holes or cracks thereby permitting extremely dirty air to penetrate the system. Always keep the breather assemblies clean and intact because, many times, this is the only form of protection from the dusty atmosphere.

Another way that dirt can penetrate the system is through careless repairs. Broken hoses are a main contributor to this cause. As with most farm equipment dirt, grease, and debris tends to collect around the areas that have the most oil leakage. Hose end fittings are notorious for collecting such globules of junk. When a hose breaks the usual fix is to unscrew the fitting remove the bad hose and then stick on a new hose. Many times the disconnected hoses are turned upward to keep oil from oozing out while the new hose is made at the dealer. It is during these times that small pieces of debris and dirt tend to fall off of the surrounding areas and into the open hose ends. Some folks even try to collect the drained oil and return it unfiltered to the reservoir. All of these practices can permit unwanted and potentially damaging foreign material to enter the system.

When a hose breaks it is good practice to isolate the hose ends first. Removing the hose supports so the ends can be swung away from the tractor body can do this. Then wire brush or bristle brush the ends to remove all the loose ends and debris. Remove the hose ends, drain the remaining hoses into a bucket, and then wrap them with a clean rag held in place by a twisty tie or a rubber band. Use a bungee cord to hold the hose off to the side while waiting for the new hose to come to the jobsite. When reinstalling it might be a good idea to blow some clean air through the new hose just to be sure no debris from the manufacturing process dropping inside. Reattach the hose ends and then re-secure to the tractor with the corresponding mounting brackets. It is important to always use these brackets when they are provided because it keeps the hoses and tubes from vibrating and wearing holes in them.

When examining the tractor for routine maintenance it is wise to check the hosing for certain wear characteristics. As mentioned in the last series the hydraulic hoses are a divided into high and low-pressure applications. On older hoses the outer rubber covering will, over time, react to the suns ultraviolet rays along with the heat generated from the system use. They will begin to crack and eventually peel thereby exposing the wire braiding underneath. Water penetration will start to rust the braid and safe-operating pressures will be drastically reduced. Look for these cracking and peeling signs on the hoses. Also look vigorously for vibration and moving fittings that will rub through the outer hose skin in quite short order. On low pressure hoses look for gobs of grease, dirt and sharp debris that tends to accumulate on them since they are often housed behind the tractor cowlings and sheet metal.

Other areas to check include the fitting ends. Occasionally these ends will loosen up and cause oil seepage. If the oil leaks out it could also let air and dirt in under the right circumstances. Check but dont over-tighten. Keep the oil cooler clear of dirt and debris. This area also tends to attract junk like a magnet. Reverse blowing of the cooler fins with compressed air or a low-pressure hose will keep the cooler functioning properly. Many systems now have oil filters on them. Keep these serviced on regular intervals as recommended by the manufacturer. In dirty and dusty conditions in never hurts to do it more often.

Water is the other big enemy to the hydraulic system. It usually comes into play from the humidity found naturally in the atmosphere. When the equipment sits idle the reservoir is not always what one would think as full. It might be full by the dipstick but may only be halfway full by reservoir capacity. It is like this because each double acting cylinder on the machine is divided into two chambers. These two chambers have different oil capacities. The power stroke cycle carries the most oil and generates the most power while the retraction stroke, with the ramrod in it, has less oil in the corresponding chamber. This is why the oil level vacillates so wildly in the reservoir and also explains why the capacity is larger than showing full on the dipstick. This also presents a problem in high humidity areas. The half full reservoir tends to have more exposed steel areas that can generate more surface area for condensation. The moisture collects over time to present quite a problem. Equipment that is used for many hours at a time will tend to evaporate out the moisture because of the heat generated by the hydraulic use. On the other hand, equipment that sits for long periods or is not used actively where it never warms up to an extended operating temperature will collect large quantities of moisture. Some water will be held in suspension by the moisture retardant additives in the oil. But excess water will emulsify the oil and cause internal damage to seals because the oil has lost some of its lubricating qualities. The point is to keep the oil changed according to the manufacturers specs. But if the hydraulics are used very little and never seem to reach a good operating temperature it might be wise to do it more often.

The tolerances found in hydraulic pistons and spool valves are extremely close. Even the smallest particle of dirt can score and/or groove the finely ground steel parts. Creeping cylinders and lost power invariably results. Taking the time to inspect the hydraulic system for dirt and water penetration will save mountains of dollars in repairs and will ensure that the hydraulic system on your tractor gives a long and valuable life.

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