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 which 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 con-tinuous vibration, excessively high operating pressures, or faulty or careless assembly. Exter-nal leaks usually have little effect on the opera-tion of equipment other than a steady draining of the oil supply; but 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 any of the following causes: 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 loss of pressure and failure of equipment. While large internal leaks can usually be located by installing pressure gages in various parts of the equipment, the location of small leaks generally requires disassembly and visual inspec-tion of the parts. Internal leaks may result from worn or scored valves, pistons, valve plates or bushings, or improperly fitted or damaged gaskets.

The symptoms of trouble in a hydraulic system are frequently unusual noises. Some noises are characteristic 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 the noises which 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 suc-tion 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 par-tial 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 per-sists 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 adjustment.

The term HYDRAULIC CHATTER is sometimes used to identify noises caused by a vibrating spring-actuated valve, by long pipes im-properly 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.