Hydraulic failures rarely happen overnight. In many cases, they stem from the same preventable mistakes plants make every day — from poor contamination control and neglected reservoirs to using hydraulic fluids that can’t withstand severe operating conditions. Over time, these issues contribute to heat buildup, oxidation, varnish formation, and premature component wear that reduce system reliability and increase downtime costs.
Fortunately, many of these problems can be avoided with the right maintenance practices, formal procedures, and advanced hydraulic fluids designed to deliver long-lasting protection in demanding environments.
Here are five of the most common hydraulic mistakes plants continue to make and what can be done to prevent them.
Mistake #1: Hydraulic Pressures Are Improperly Set
On every hydraulic system there is a multitude of adjustments to be made. When a machine problem occurs, knobs on the hydraulic pump and valves are adjusted to “see” if this solves the machine problem. Unfortunately, the person doing the adjusting usually has no idea what the effect will be on the machine. Pressures in a hydraulic system typically are set too high. The thinking is that the higher the pressure, the faster the machine will run. Consider the following real-world scenario that occurred at a wood products plant:
Knobs on hydraulic pumps and valves
are often adjusted without any idea of the
effects on the machine.
A company had severe shock and leakage problems on a piece of mobile equipment. The pump was also being changed at intervals of once per month. There was an adjustment on the pump (called a compensator), which limited the maximum system pressure.
A relief valve in the system was used as an extreme safety device and a shock absorber. The recommended settings for the compensator and relief valve were 1,500 and 1,750 pounds per square inch (PSI), respectively. When the stacker started and stopped, the pressure gauge needle spiked to the maximum of 3,000 PSI, vibrated and then settled in at 1,800 PSI. This indicated that the compensator and relief valve were both set too high.
After the compensator and relief valve were reset to the recommended settings, the pressure went up momentarily to 1,750 PSI (relief setting) before settling in at 1,500 PSI (compensator setting). The difference in the force exerted on the 10-inch boom cylinder (78.54 square inches of area) with the relief valve at 3,000 PSI and at 1,750 PSI was 98,175 pounds. Once the pressures were properly set, the shock was eliminated and the life of the pump was increased. After the clamps and O-rings were replaced, the leakage stopped as well.
Mistake #2: Lack of Accumulator and Hydraulic Safety Procedures
When a machine is repaired, the pump’s electric drive motor is turned off and lockout/tagout procedures are performed. The pressure gauge is rarely checked before work is begun on or around the machine. Accumulators store hydraulic energy in the form of pressurized fluid. Most systems contain an automatic or manual dump valve that will allow the high-pressure fluid in the accumulator to dump to the tank, permitting the pressure to drop to zero. The automatic dump valves can fail closed, which will maintain the pressurized oil in the accumulator.
If a line is taken off or a component removed, an individual can become injected with high-pressure fluid. When a manual dump valve is used, the human factor enters the equation. At one plant, a young millwright was severely injured when he was injected with high-pressure oil after he failed to open the hand valve. There was no procedure in place for opening the valve before working on the system.
Many times the gauge is located on the pump side of the check valve and not the accumulator side. When the pump is turned off, the gauge will drop to zero as the oil bleeds to the tank through the hydraulic pump’s internal tolerances. The maintenance person or operator thinks the pressure is at zero and has no way of knowing if the pressurized fluid in the accumulator has been released. On systems of this design, a gauge should be installed at or near the accumulator.
Most systems have a dump valve that allows
high-pressure fluid in the
accumulator to dump to the tank,
permitting the pressure to drop to zero.
Mistake #3: Poor Troubleshooting Techniques
In our hydraulic workshops, we stress that the quickest and easiest method of troubleshooting a machine is to use a hydraulic schematic. The response from students is usually one of the following: “Management won’t give us time to troubleshoot,” “We don’t have or know where our schematics are,” or “We don’t know how to read the schematics.”
When a hydraulic problem occurs, information must be gathered to determine which component is causing the problem. A few examples include checking the pump case drain flow or checking for heat in the system. Many times the supervisor intervenes and demands that the pump, cylinder or other component be changed. At one plant, a supervisor instructed a millwright not to troubleshoot but to manually actuate a directional valve. This resulted in an accumulator discharging into a partially filled 5,000-gallon reservoir. The top of the reservoir blew off, which shut down the mill for seven days.
Hydraulic schematics are usually located inside the machine manufacturer’s manual, which is often kept in a maintenance office or storeroom. When a hydraulic problem occurs, the last thing the maintenance person wants to do is to take 15 or 20 minutes to find the manual. After all, when a machine is down, time is money. A better option is to mount larger schematics by the system under a Plexiglas cover. Smaller prints can be laminated and similarly located. If the schematic is readily available, it will be used.
The most common statement I hear from mechanics and electricians when consulting with a plant on a problem is, “I don’t know much about hydraulics.” This means they either have not been trained properly or have forgotten what they have learned. On the other hand, when I visit plants where machinery-specific hydraulic training has been conducted, I normally hear, “We use manuals and schematics all the time.” Without the proper training, you cannot expect your maintenance crew to troubleshoot effectively.
Using a hydraulic schematic is the
quickest and easiest method of
troubleshooting a machine.
Mistake #4: Poor Hydraulic Reservoir and Oil Maintenance
Reservoir maintenance, filtration, and contamination control all play a major role in hydraulic reliability, but even well-maintained systems can struggle if the hydraulic fluid itself cannot withstand severe operating conditions. Excessive heat, oxidation, and varnish formation can quietly reduce efficiency, restrict oil flow, and shorten component life long before a failure occurs.
In one Ontario log-loader application, a reservoir had not been cleaned in 17 years. After the oil was drained, technicians discovered a thick layer of sludge coating the bottom of the tank. Instead of helping dissipate heat, the contaminated reservoir was trapping heat and accelerating oil degradation.
These types of conditions often develop gradually over time. As hydraulic oil oxidizes, it can form sludge and varnish deposits that accumulate on valves, filters, strainers, and internal surfaces. Over time, these deposits can contribute to valve stiction, restricted flow, overheating, and reduced system responsiveness.
While proper reservoir cleaning and filtration remain essential, fluid selection also has a major impact on long-term hydraulic performance. Synthetic hydraulic fluids designed for severe-service environments can provide stronger resistance to oxidation, varnish formation, and thermal breakdown compared to conventional oils.
Products like AMSOIL HELIOS-VR are specifically engineered to resist varnish, sludge, and deposit formation while maintaining wear protection across a wide operating temperature range. Its advanced synthetic formulation is designed to deliver improved thermal and oxidative stability, helping hydraulic systems stay cleaner and operate more reliably in demanding environments.
Mistake #5: Component Replacements Don’t Have the Same Part Numbers
When a hydraulic problem occurs, usually one component has failed. It is essential to match the part numbers between the new and old components. Hydraulic pumps and valves that look alike are not necessarily the same. Each number or letter in the part number indicates a feature about the pump or valve. If one letter or number is different, the manufacturer’s literature should be consulted to identify the difference.
A few years ago, a plant had the main directional valve fail on its tilt hoist. The valve had the following part number: DG5S8-2C-T-50. A local vendor was called who said he had a valve with the same spool configuration and mounting pattern in his central distribution center. The valve with the following part number was flown in and delivered to the plant the next day: DG5S8-2C-E-T-50.
This image shows a tilt hoist with
a failed main directional valve.
When the valve was installed, the tilt hoist cylinders still would not extend and retract. The manufacturer of the valve was then called and given the two different numbers. The original valve (with the letter “E” omitted from the part number) was an internally hydraulically piloted and drained valve. The valve sent by the vendor was an externally piloted and internally drained valve. Since there was no external pilot line connected in the system, the new valve would not work.
To solve the problem, the valve manufacturer told the mechanic at the plant to remove the internal plug in the “P” port and install it in the “X” port. Once this was done, the tilt hoist operated normally but only after 18 hours of downtime.
These common mistakes are made primarily because of a lack of knowledge. When a machine is down, the supervisor, mechanic or electrician is going to do whatever is necessary to get the machine back online in the shortest amount of time. By making sure these top five errors don’t occur at your plant, you can reduce downtime, help your plant operate safely and improve hydraulic troubleshooting.
Bottom Line
Hydraulic reliability depends on far more than replacing failed components when problems occur. As these common mistakes demonstrate, issues such as improperly set pressures, poor troubleshooting practices, inadequate hydraulic safety procedures, neglected reservoir maintenance, and incorrect component replacements can all contribute to downtime, equipment damage, and unnecessary maintenance costs. Many of these problems are preventable with better training, proper maintenance procedures, and a more proactive approach to system health.
Fluid selection also plays a major role in overall hydraulic performance. Choosing a high-quality synthetic hydraulic oil with strong resistance to heat, oxidation, sludge, and varnish formation can help improve system cleanliness, protect critical components, maintain efficiency in demanding operating conditions, and extend service life. When combined with effective contamination control and maintenance best practices, the right hydraulic fluid can help plants reduce failures and improve long-term reliability.
