Hydraulics Troubleshooting Guide & Maintenance Hints

General
The troubleshooting charts and maintenance hints that follow are of a general system nature but should provide an intuitive feeling for a specific system. More general information is covered in the following paragraphs. Effect and probable cause charts appear on the following pages.

System Design
There is, of course, little point in discussing the design of a system which has been operating satisfactorily for a period of time. However, a seemingly uncomplicated procedure such as relocating a system or changing a
component part can cause problems. Because of this, the following points should be considered:

1. Each component in the system must be compatible with and form an integral part of the system. For example, an inadequate size filter on the inlet of a pump can cause cavitation and subsequent damage to the pump.

2. All lines must be of proper size and free of restrictive bends. An undersized or restricted line results in a pressure drop in the line itself.

3. Some components must be mounted in a specific position with respect to other components or the lines. The housing of an in-line pump, for example, must remain filled with fluid to provide lubrication.

4. The inclusion of adequate test points for pressure readings, although not essential for operation, will expedite troubleshooting.

Knowing the System
Probably the greatest aid to troubleshooting is the confidence of knowing the system. The construction and operating characteristics of each one should be understood. For example, knowing that a solenoid controlled directional valve can be manually actuated will save considerable time in isolating a defective solenoid. Some additional practices which will increase your ability and also the useful life of the system follow:

1. Know the capabilities of the system. Each component in the system has a maximum rated speed, torque or pressure. Loading the system beyond the specifications simply increases the possibility of failure.

2. Know the correct operating pressures. Always set and check pressures with a gauge. How else can you know if the operating pressure is above the maximum rating of the components? The question may arise as to what the correct operating pressure is. If it isn’t correctly specified on the hydraulic schematic, the following rule should be applied:

The correct operating pressure is the lowest pressure which will allow adequate performance of the system function and still remain below the maximum rating of the components and machine.

Once the correct pressures have been established, note them on the hydraulic schematic for future reference.

3. Know the proper signal levels, feedback levels, and dither and gain settings in servo control systems. If they aren’t specified, check them when the system is functioning correctly and mark them on the schematic for future reference.

Developing Systematic Procedures
Analyze the system and develop a logical sequence for setting valves, mechanical stops, interlocks and electrical controls. Tracing of flow paths can often be accomplished by listening for flow in the lines or feeling them for warmth. Develop a cause and effect troubleshooting guide similar to the charts appearing on the following pages. The initial time spent on such a project could save hours of system down-time.

Recognizing Trouble Indications
The ability to recognize trouble indications in a specific system is usually acquired with experience. However, a few general trouble indications can be discussed.

1. Excessive heat means trouble. A misaligned coupling places an excessive load on bearings and can be readily identified by the heat generated. A warmer than normal tank return line on a relief valve indicates operation at relief valve setting. Hydraulic fluids which have a low viscosity will increase the internal leakage of components resulting in a heat rise. Cavitation and slippage in a pump will also generate heat.

2. Excessive noise means wear, misalignment, cavitation or air in the fluid. Contaminated fluid can cause a relief valve to stick and chatter. These noises may be the result of dirty filters, or fluid, high fluid viscosity, excessive drive speed, low reservoir level, loose intake lines or worn couplings.

Maintenance
Three simple maintenance procedures have the greatest effect on hydraulic system performance, efficiency and life.

1. Maintaining a clean sufficient quantity of hydraulic fluid of the proper type and viscosity.

2. Changing filters and cleaning strainers.

3. Keeping all connections tight, but not to the point of distortion, so that air is excluded from the system.

Guidelines
The following charts are arranged in five main categories. The heading of each one is an effect which indicates a malfunction in the system. For example, if a pump is exceptionally noisy, refer to Chart 1 titled Excessive Noise. The noisy pump appears in Column A under the main heading. In Column A there are four probable causes for a noisy pump. The causes are sequenced according to the likelihood of happening or the ease of checking it. The first cause is cavitation and the remedy is “a”. If the first cause does not exist, check for cause number 2, etc.