Hydraulic System Care and Inspection
by David Doyle, CLS, OMA I & II
General Manager
, Tribology

Routine inspection between major maintenance schedules can prevent manageable issues from becoming major problems with the operating reliability of any hydraulic system. Ensuring a system is regularly monitored will allow the hydraulic fluid to perform its task of transmitting power, provide proper cooling, control contaminants and wear, protect against rust and corrosion, and proper sealing against leakage for valves. Most routine inspections can be performed by visual examination, a check list, and a little time.

Temperature control is one of the most important factors in optimizing hydraulic fluid service life. A normal temperature range for most systems is 110-140F / 45-60C. High temperatures could be due to impaired relief valve operation or improper settings, or issues with the oil cooler. Using an infrared thermometer is very useful for checking components such as drive motors and servos valves. Temperatures above 150F / 65C can be an indication of sticking valves. Cleaning hoses regularly in dirty environments will help decrease hydraulic fluid temperatures.

Visually inspect all system hoses, pipes, and pipe connections for leaks or worn fittings and couplings. This is another common problem that can be recognized by routine visual inspection. Hydraulic fluid leakage reduces power, allows contaminants to enter, and slows down movement of components.

Regular reservoir inspection is an important practice. Check fluid levels. Confirm the site glass is configured properly if one is installed. When topping off fluid keep the fill area clean and pre-filtering when adding new fluid is recommended. Do not mix oils unless the compatibility and viscosity impact has been investigated. Breather caps and breather filters should be inspected. Visually inspect the reservoir and site glass for changes in color and odor and signs of aeration and foaming.

Critical systems should have monitoring gauges for temperature and filter or pressure differential installed in the correct locations.

Mechanical components should be inspected. Listen for abnormal noise from motors or pumps that could be signs of oil starvation or cavitation. A plugged suction filter can cause cavitation or oil starvation in a pressure pump. Take time occasionally to verify hydraulic motors are running at the correct RPMs. Visually inspect cylinder rods for any pitting, dents, scoring (common problem with dirt lodged in seal area), or other damage that could allow fluid to bypass, thus resulting in a loss of pressure and power.

Safety equipment and features should be inspected regularly. This would include railings, relief valves and high pressure hose fittings. Accumulators should be precharged to half the system maximum pressure and oxygen should never be used as a recharge gas. Prior to working on or opening up a pressurized area in a hydraulic system verify the pressure has bled down.

Oil sampling for laboratory analysis is an important aspect of monitoring critical hydraulic systems to maintain optimal equipment and fluid performance. Testing should provide information on the existence of fluid oxidation, contaminants, wear, and cleanliness as a minimum. Fluid sampling procedures should be standardized for consistency of data, ensure safe practices, and ensure the most optimal location for representative data. Returns line carry the most information. Areas of turbulence, such as bends in piping, provide the most homogenous samples. Avoid sampling after filters, areas of low flow and dead ends. When taking a sample for analysis flush sampling ports prior to obtaining a sample and avoid sampling from the very top or very bottom of the fluid reservoir level.

For further information on ALS Tribology testing services please contact one of our regional laboratories or email us.