The overall efficiency of the hydraulic installations used to control or drive auxiliary machines is basically dependent upon the size, oil pressure, speed, and stroke of the hydraulic installation. The efficiency of the hydraulic speed gears and the components of the system will depend upon the care that is given to them. Except for piping and fittings, major repairs of hydraulic gear are generally done in a naval shipyard or by the manufacturers. This section will deal primarily with troubleshooting and preventive maintenance of hydraulic systems, including external hydraulics. Hydraulic transmissions are sturdy, service-proven machines, inspected and tested with such care that casualties seldom occur. When casualties do occur it is usually the result of faulty assembly, installation, or maintenance. A correctly installed hydraulic system, operated regularly and serviced with proper care, will retain its design characteristics of power, speed, and control. The need for costly repair and replacement will seldom occur if the equipment has been maintained properly.

TROUBLESHOOTING

Troubleshooting an electrohydraulic system involves the systematic elimination of the possible causes, one by one, until the actual cause of a casualty is found. In attempting to locate the source of any trouble in an electrohydraulic system, remember that all troubles fit into one of three categories. It is either hydraulic, electrical, or mechanical. Isolating a trouble into one of these categories is one of the main steps in finding the source of trouble.

Hydraulic Troubles

Casualties in a hydraulic system are generally the result of low oil levels, external or internal leakage, clogged lines or fittings, or improper adjustment of valves and other working parts. Do NOT disassemble a unit unless you are certain that the trouble exists within that unit! Unnecessary disassembly may create conditions that lead to additional trouble, since dirt may enter an open system.

Leaks are a frequent cause of trouble in hydraulic equipment. Generally, leaks are a result of excessively worn parts, abnormal and continuous vibration, excessively high operating pressures, or faulty or careless assembly. External leaks usually have little effect on the operation of equipment other than a steady draining of the oil supply. Even a small leak wastes oil, and the resulting unsightly appearance of a machine is indicative of poor maintenance procedures.

External leaks may result from improperly tightened threaded fittings; crossed threads in fittings; improperly fitted or damaged gaskets; distorted or scored sealing rings, oil seals, or packing rings; scored surfaces of working parts; improperly flared tube ends; or flanged joints not seating squarely.

Internal leaks usually result in unsatisfactory operation of the equipment. Large internal leaks are signified by a loss of pressure and the failure of equipment. While large internal leaks can usually be located by installing pressure gauges in various parts of the equipment, the location of small leaks generally requires disassembly and visual inspection of the parts. Internal leaks may result from worn or scored valves, pistons, valve plates or bushings, or improperly fitted or damaged gaskets.

The most common symptom of trouble in a hydraulic system is an unusual noise. Some noises are characteristics of normal operation and can be disregarded, while others are evidence of serious trouble. Even though the exact sound indicating a specific trouble can be learned only through practical experience, the following descriptive terms will give a general idea of which noises are trouble warnings. If popping and sputtering noises occur, air is entering the pump intake line. Air entering the system at this point may be the result of too small an intake pipe, an air leak in the suction line, a low oil level in the supply tank, cold or heavy oil, or possibly the use of improper oil.

If air becomes trapped in a hydraulic system, hammering will occur in the equipment or transmission lines. When this occurs, check for improper venting. Sometimes, a pounding or rattling noise occurs as the result of a partial vacuum produced in the active fluid during high-speed operation or when a heavy load is applied. This noise may be unavoidable under the conditions stated and can be ignored if it stops when speed or load is reduced. If the noise persists at low speeds or light loads, the system needs to be vented of air. Air in a hydraulic system can also cause uneven motion of the hydraulic motors.

When a grinding noise occurs, it can usually be traced to dry bearings, foreign matter in the oil, worn or scored parts, or overtightness of some adjustments. The term hydraulic chatter is sometimes used to identify noises caused by a vibrating spring-actuated valve, by long pipes improperly secured, by air in lines, or by binding of some part of the equipment. Squeals or squeaks indicate that the packing is too tight around some moving part or that a high-frequency vibration is occurring in a relief valve.

Electrical Troubles

Even though troubles occurring in electrical equipment are the responsibility of the Electricians Mate, the Engineman can help maintain the equipment by making a few simple checks when electrical troubles occur. Failure to have a switch in the ON position will cause unnecessary delay in operating electrical equipment. If the switch is closed and the equipment still fails to operate, check for blown fuses or tripped circuit breakers. Troubles of this type are usually the result of an overload on the equipment. If a circuit breaker continues to cut out, the trouble may be caused by damaged equipment, excessive binding in the hydraulic transmission lines, or faulty operation of the circuit breaker. Check for visual indication of open or shorted leads, faulty switches, or loose connections. Do not make repairs to the electrical equipment or system. Do not open enclosures of electrical equipment, but do report evidence of possible electrical failure to the Electricians Mate.

Mechanical Troubles

When electrohydraulically driven auxiliary machinery becomes inoperative because of a mechanical failure, a check should be made. Look for improper adjustment or misalignment of parts; shearing of pins or keys; or breakage of gearing, shafting, or linkage. Elimination of these causes should be done according to the manufacturers instructions for the specific piece of equipment.

MAINTENANCE

The principal requirements necessary to keep a hydraulic transmission in satisfactory operating condition are regular operation, proper lubrication, and the required state of cleanliness of all the units and their fluids. Regular operation of hydraulic equipment prevents the accumulation of sludge and the freezing of adjacent parts. Regular use also aids in preventing corrosion. The necessity for proper lubrication and cleanliness cannot be too strongly emphasized Detailed instructions on the maintenance of a specific unit should be obtained from the appropriate manufacturers technical manual, but the following general information will also be useful.