containing the various operating mechanisms and their units, such as brakes, steering, lift cylinders, extend cylinders, and hydraulic motors.
Since an actuating mechanism is dependent on the power system, some of the troubles exhibited by the actuating system may be caused by difficulties in the power system. By the same token, a trouble symptom indicated by a unit of the power system may be caused by leakage from one of the units of an actuating system. When any part of the hydraulic system becomes inoperative, refer to the schematic diagrams located in the applicable technical manual (in conjunction with tests performed on the equipment) to assist in tracing the malfunction to its source. As previously stressed, NO UNIT SHOULD BE REMOVED AND REPLACED (OR ADJUSTED) UNLESS THERE IS SOUND REASON TO BELIEVE IT IS FAULTY.
Most hydraulic troubles can be included in one or more of the following categories: lack of fluid supply, external leaks, internal leaks, physically defective units, or related troubles caused by mechanical control linkages and electrical control circuits.
Insufficient fluid in the system results in no pump delivery or at best a sluggish or erratic operation. The reservoir must always contain sufficient fluid to till the system completely without letting the pump run dry. The proper fluid must always be used to replenish a low system. Do not mix hydraulic fluids or reuse old fluid. Make sure all replenishment fluid is properly filtered before it is dispensed into the reservoir. Remove and repair or replace defective units when there is an indication of external leakage of the unit.
If foreign particles are found when you remove and disassemble a unit, identify and trace them to the source; for example, a common source of foreign particles is found in flexible hose. Generally, the cause is improper installation or internal deterioration; either can release slivers of the lining into the system, causing units to leak or become inoperative.
To analyze malfunctions in hydraulic systems, like all other systems, you need to have a complete under- standing of the system and its operating components. Also, you need to know the interrelationship of one component to another; for instance, a complete understanding of a pressure regulator lends itself to troubleshooting the entire system as well as the regulator itself.
Pressure regulators, like all hydraulic components, are normally reliable pieces of equipment; nevertheless, the y can malfunction. Keep in mind, though, that instead of being a source of trouble, the regulator can be a fairly reliable watchdog on the other units in the system. The particular behavior of the regulator may be the only indication of leakage in places where no other indication is available. It should be kept in mind that troubleshooting the regulator is done only after the obvious steps have been taken, such as checking the system fluid level to check for external fluid loss and opening shutoff valves.
Troubleshooting the pressure regulator is done by timing the cycle of operation-from the cut-in position to the cutout and back to the cut-in position. A standard regulator operating in a normal system completes this cycle in a certain period of time. This time can be obtained from the equipment manual or closely estimated by maintenance personnel.
Since you normally use the pressure regulator only with a constant volume pump, it should take a certain definite time to buildup system pressure; for example, suppose a pump has a volume output of 6 gallons per minute, and the system requires 1 gallon of fluid to become completely tilled (pressurized). As the system takes only one sixth of the pump output to build up pressure, it should require only one sixth of a minute (10 seconds) to pressurize the system. This is true if the system is in good operating condition. But what if the system contains an internal leak? In the 10 seconds usually required to build up pressure, the pump is still delivering 1 gallon, but some of the fluid is being lost. Thus, at the end of 10 seconds, the system cannot be pressurized; therefore, the regulator cannot be cutout. The cut-in and cutout pressure of the regulator can be seen on the system pressure gauge. Once the regulator is cut out, the system should hold fluid under pressure for a reasonable length of time; however, if the system leaks, pressure drops fast and the regulator cuts in faster than normal. These indications may mean that the regulator is faulty or the other components in the system are faulty; however, by isolation techniques, such as subsystem operation, and checking shutoff valves, the problem can be located.
If the fault is the regulator, it is probably leaking at the regulator check valve or at the regulator bypass valve.
A leaking regulator check valve is one of the most common and easily recognized troubles. Again the regulator cycle is affected. With the regulator cut-in, the check valve is open, and fluid is flowing into the system.Continue Reading