When most people think about preventative maintenance and ensuring the reliability of their hydraulic systems, the only thing they consider is regularly changing filters and checking oil levels. When a machine fails, there is often little information about the system to look at when troubleshooting. However, appropriate reliability checks should be performed under normal operating conditions of the system. These checks are critical to preventing equipment failures and downtime.
Most hydraulic filter assemblies have bypass check valves to prevent element damage from clogging with contaminants. The valve opens whenever the pressure differential across the filter reaches the valve spring rating (typically 25 to 90 psi, depending on filter design). When these valves fail, they often fail open due to contamination or mechanical damage. In this case, the oil will flow around the filter element without being filtered. This will lead to premature failure of subsequent components.
In many cases, the valve can be removed from the body and inspected for wear and contamination. Refer to the filter manufacturer’s documentation for the specific location of this valve, as well as proper removal and inspection procedures. This valve should be checked regularly when servicing the filter assembly.
Leaks are one of the biggest problems in hydraulic systems. Proper hose assembly and replacing faulty hoses is one of the best ways to reduce leaks and prevent unnecessary downtime. Hoses should be checked regularly for leaks and damage. Hoses with worn outer casings or leaking ends should be replaced as soon as possible. “Blisters” on the hose indicate a problem with the inner hose sheath, allowing oil to seep through the metal braid and accumulate under the outer sheath.
If possible, the hose length should not exceed 4 to 6 feet. Excessive hose length increases the likelihood of it rubbing against other hoses, walkways, or beams. This will lead to premature failure of the hose. In addition, the hose can absorb some of the shock when pressure surges occur in the system. In this case, the length of the hose may change slightly. The hose should be long enough to bend slightly to absorb shock.
If possible, hoses should be routed so that they do not rub against each other. This will prevent premature failure of the outer hose sheath. If the hose cannot be routed to avoid friction, a protective cover should be used. Several types of hoses are commercially available for this purpose. Sleeves can also be made by cutting an old hose to the desired length and cutting it lengthwise. The sleeve can be placed over the friction point of the hose. Plastic ties should also be used to secure the hoses. This prevents relative movement of the hose at friction points.
Suitable hydraulic pipe clamps must be used. Hydraulic lines generally do not allow the use of conduit clamps due to vibration and pressure surges inherent in hydraulic systems. Clamps should be checked regularly to ensure that the mounting bolts are loose. Damaged clamps should be replaced. In addition, the clamps must be positioned correctly. A good rule of thumb is to space the clamps about 5 to 8 feet apart and within 6 inches of where the pipe ends.
The breather cap is one of the most overlooked parts of your hydraulic system, but remember that the breather cap is a filter. As the cylinder extends and retracts and the level in the tank changes, the breather cap (filter) is the first line of defense against contamination. To prevent contaminants from entering the tank from the outside, a breathing filter with an appropriate micron rating should be used.
Some manufacturers offer 3-micron respiratory filters that also use a desiccant material to remove moisture from the air. The desiccant changes color when wet. Replacing these filter components regularly will pay dividends many times over.
The power required to drive a hydraulic pump depends on the pressure and flow in the system. As the pump wears, the internal bypass increases due to increased internal clearance. This leads to a decrease in pump performance.
As the flow supplied by the pump to the system decreases, the power required to drive the pump decreases proportionately. Consequently, the current consumption of the motor drive will be reduced. If the system is relatively new, current consumption should be recorded to establish a baseline.
As system components wear, the internal clearance increases. This results in more rounds. Whenever this bypass occurs, heat is generated. This heat does no useful work in the system, so energy is wasted. This workaround can be detected using an infrared camera or other type of thermal detection device.
Remember that heat is generated whenever there is a drop in pressure, so there is always local heat present in any flow sensing device, such as a flow controller or proportional valve. Regularly checking the oil temperature at the inlet and outlet of the heat exchanger will give you an idea of the overall efficiency of the heat exchanger.
Sound checks should be carried out regularly, especially on hydraulic pumps. Cavitation occurs when the pump cannot get the required total amount of oil into the suction port. This will result in a sustained, high-pitched howl. If not corrected, the pump’s performance will decline until it fails.
The most common cause of cavitation is a clogged suction filter. It can also be caused by the oil viscosity being too high (low temperatures) or the drive motor speed per minute (RPM) being too high. Aeration occurs whenever outside air enters the pump suction port. The sound will be more unstable. Causes of aeration may include a leak in the suction line, low fluid levels, or a poor shaft seal on a non-regulated pump.
Pressure checks should be carried out regularly. This will indicate the condition of several system components, such as the battery and various pressure control valves. If the pressure drops more than 200 pounds per square inch (PSI) when the actuator moves, this may indicate a problem. When the system is operating normally, these pressures should be recorded to establish a baseline.
Post time: Jan-05-2024