Hydraulic systems are everywhere, with common examples including the following:
• Garbage trucks
• Mobile cranes
• Snow plows
• Forklifts
• Dump trucks
• Excavators
• Front-end loaders
• Mobile shears
• Backhoes
• Mobile well-drilling and core-sampling equipment
• Skidders
• Piling rigs
• Street sweepers
• Mobile hydraulic power units
• Bucket trucks
• Tow trucks
• Feller bunchers
• Scissor lifts
Hydraulic Systems
Hydraulic systems can look complex and intimidating, but most are relatively straightforward, consisting of a sump, a pump, hoses, valves and either pistons or hydraulic motors.
Sump – The hydraulic system’s sump responsible for holding the oil, providing time for the transferring of heat, and a place for contaminants, including water, to settle.
Pump – The hydraulic system’s pump produces the fluid flow that creates pressure. In most cases, it is the most expensive part in the system. Hydraulic oils are subjected to pump tests to prove their ability to protect pumps under normal operating conditions. Hydraulic systems can have many different types of pumps, but the three most common are gear, vane and piston pumps. Gear pumps are often found on lower-pressure systems and are relatively simple and reliable. As positive displacement pumps, they pump a fixed amount of fluid for every revolution. Although variations exist, a good example is an automotive oil pump. Vane pumps are common on mobile equipment and can be variable or constant displacement. Piston pumps can be found on higher-pressure applications and are more complex and sensitive to contamination than vane or piston pumps.
Hoses – Hoses carry hydraulic pressure and flow to various components, and are perhaps the weakest link in any hydraulic system. Maintenance is often ignored until a problem develops. Hoses fail due to heat, cold, repeated flexing, physical damage and exposure to the elements.
Valves – Valves control the route of the hydraulic flow within the system, sending flow and pressure to components in order to operate them. Pulling a lever back may route fluid to one side of the hydraulic system, causing it to extend a piston, while pushing it forward may cause it to retract. Varnish presents a major problem with valves, causing them to stick or not allowing them to seal properly.
Pistons/Hydraulic Motors – Pistons and hydraulic motors convert the hydraulic flow and pressure into work. Pistons provide linear motion, allowing bulldozer blades to lift and backhoe buckets to tip, while motors convert hydraulic flow and pressure into rotational force, allowing drills to operate. Common issues associated with pistons and hydraulic motors are internal or external leakage. External leakage results in loss of fluid and possible contamination issues, while internal leakage results in lost efficiency. For example, a bottle jack with its valve only partially closed requires furious pumping to lift an object off the ground and won’t be able to keep it there.
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