Most companies spend a great deal of money training their maintenance personnel so that they can troubleshoot and correct failures of a hydraulic system. If the focus was shifted to the prevention of system or component failures, less time and money could be spent on troubleshooting. We normally expect hydraulic system failure, rather than deciding not to accept hydraulic failure as the norm. Let’s spend the time and money to eliminate hydraulic failure, rather than to prepare for it. I worked for Kendall Com­ pany in the 1980s, and we changed our focus from reactive to proactive maintenance on our hydraulic systems, thus eliminating unscheduled hydraulic failure. We will talk about the right way to perform maintenance on a hydraulic system utilizing the Main­ tenance Best Practices.

Lack of maintenance of hydraulic systems is the leading cause of component and sys­ tem failure, yet most maintenance personnel don’t understand the proper maintenance techniques of a hydraulic system. There are two aspects to the basic foundation for proper maintenance of a hydraulic system. The first is preventive maintenance, which is key to the success of any maintenance program, whether for hydraulics or for any equipment of which we require reliability. The second aspect is corrective mainte­ nance, which in many cases can cause additional hydraulic component failure when it is not performed to standard.


Preventive maintenance (PM) of a hydraulic system is very basic and simple, and if fol­ lowed properly it can eliminate most hydraulic component failure. PM is a discipline and must be followed as such in order to obtain results. We must view a PM program as performance-oriented and not activity-oriented. Many organizations have good PM pro­ cedures, but do not require maintenance personnel to follow them or hold them accountable for the proper execution of these procedures. In order to develop a preventive maintenance program for your system, you must follow the steps outlined here.

Identify the System Operating Condition

The following questions will help identify the operating condition of the hydraulic system:

Does the system operate 24 hours a day, 7 days a week?

Does the system operate at maximum flow and pressure 70 percent or better during operation?

Is the system located in a dirty or hot environment?

Equipment Manufacturer’s Maintenance Requirements

The original equipment manufacturer (OEM) usually provides complete recommen­ dations for the installation, operation, inspection, and preventive maintenance of its hydraulic system. These recommendations should be used as the basis of an effective preventive maintenance program.

System Component Maintenance Requirements

In some cases, hydraulic systems are made up of components that were assembled by the end user. In these cases, a single Operating and Maintenance manual will not be available. Therefore, the end user must rely on the manuals provided by each of the component manufacturers. As a minimum, the manuals should include the hydraulic pump, reservoir (Figure ll-l ), filters, and each of the control valves and actuators.


As in all preventive maintenance programs, we must write procedures required for each PM task. Steps or procedures must be written for each task, and they must be accurate and understandable by all maintenance personnel from entry-level to master.

Preventive maintenance procedures must be a part of the PM Job Plan, which includes the following:

• Tools or special equipment required to perform the task

• Parts or material required to perform the procedure with storeroom number

• Safety precautions for this procedure

• Environmental concerns or potential hazards

A list of preventive maintenance tasks for a hydraulic system could include the following:

1. Change the (could be the return or pressure filter) hydraulic filter.

2. Obtain a hydraulic fluid sample.

3. Filter hydraulic fluid.

4. Check hydraulic actuators.

5. Clean the inside of a hydraulic reservoir.

6. Clean the outside of a hydraulic reservoir.

7. Check and record hydraulic pressures.

8. Check and record pump flow.

9. Check hydraulic hoses, tubing, and fittings.

10. Check and record voltage reading to proportional or servo valves.

11. Check and record vacuum on the suction side of the pump.

12. Check and record amperage on the main pump motor.

13. Check machine cycle time and record.

Preventive Maintenance is the core support that a hydraulic system must have in order to maximize component and life and reduce system failure. Preventive Maintenance procedures that are properly written (Figure 11-2) and followed properly will allow equipment to operate to its full potential and life cycle. Preventive Maintenance allows a maintenance department to control a hydraulic system rather than the system controlling the maintenance department. We must control a hydraulic system by tell­ ing it when we will perform maintenance on it and how much money we will spend on the maintenance for the system. Most companies allow hydraulic systems to con­ trol their maintenance, at a much higher cost.

In order to validate your preventive maintenance procedures, you must have a good understanding and knowledge of Best Maintenance Practices for hydraulic systems. We will discuss these practices now (Table 11-1).


People say that knowledge is power. Well, this is certainly true in hydraulic main­ tenance. Many maintenance organizations do not know what their maintenance


personnel should know. In an industrial maintenance organization, we should divide the hydraulic skill necessary into two groups. In one group are the hydrau­lic troubleshooters. They must be your experts in maintenance, and as a rule of thumb they should make up 10 percent or less of your maintenance workforce. The other 90+ percent would be your general hydraulic maintenance personnel. They provide the preventive maintenance expertise. The percentages I give are based on a company developing a true preventive/proactive maintenance approach to their hydraulic systems. Let’s talk about what knowledge and skills the hydrau­lic troubleshooter needs.

Hydraulic Troubleshooter: Knowledge

• Mechanical principles: force, work, rate, simple machines

• Math: basic math, complex math equations

• Hydraulic components: application and function of all hydraulic system components

• Hydraulic schematic symbols: meaning of all symbols and their relationship to a hydraulic system

• Calculate flow, pressure, and speed.

• Calculate the system filtration necessary to achieve the system’s proper ISO particulate code.


Hydraulic Troubleshooter: Skill

• Trace a hydraulic circuit to 100 percent proficiency

• Set the pressure on a pressure-compensated pump

• Tune the voltage on an amplifier card

• Null a servo valve

• Troubleshoot a hydraulic system and utilize root cause failure analysis

• Replace any system component to manufacturer’s specification

• Develop a PM Program for a hydraulic system

• Flush a hydraulic system after a major component failure

General Hydraulic: Knowledge

• Filters: function, application, installation techniques

• Reservoirs: function, application

• Basic hydraulic system operation

• Cleaning of hydraulic systems

• Hydraulic lubrication principles

• Proper PM techniques for hydraulics

General Hydraulic: Skills

• Change a hydraulic filter and other system components

• Clean a hydraulic reservoir

• Perform PM on a hydraulic system

• Change a strainer on a hydraulic pump

• Add filtered fluid to a hydraulic system

• Identify potential problems on a hydraulic system

• Change a hydraulic hose, fitting, or tubing

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