One of the best places to get up close and personal with large hydraulic machines is at a construction site. The thing that is most amazing about these machines is their sheer size. For example, here is a medium-size shovel/excavator:
This machine weighs just over 28 tons, but it can be quite swift in its actions. The bucket can scoop out more than a cubic meter of dirt, which weighs in at approximately 1 to 1.5 tons, and move it around with no difficulty at all. Moving a person around is trivial.
To have this sort of agility, this particular shovel uses an 8.3-liter diesel engine capable of generating 340 horsepower. The engine is connected to a pair of pumps that can generate 140 gallons per minute at 4,500 psi. The hydraulic pistons have 5.5-inch-diameter faces with 4-inch-diameter shafts. In addition, there is one hydraulic motor for each track and a hydraulic motor that can spin the cab and arm at 11 rpm.
You can see from the picture that the arm has a pair of pistons working in unison at the "shoulder" -- one at the "elbow" and then one to rotate the bucket. These pistons, along with the two track motors and the rotating motor, are all controlled by two joy sticks and four pedals in the cab.
These controls send electrical signals to an electrically-operated valve block located next to the pump.
From the valve block, high-pressure hydraulic lines make their way to the cylinders.
The tracks are interesting. If you look at the tracks on any piece of large machinery, you will find that there is a hydraulic motor at one end, a free-spinning toothed wheel at the other, and then a set of rollers for the track to move over.
Here are the specifications for the Halla HE280LC shovel:
- Weight: 28.2 tons
- Length: 10.6 meters
- Width: 3.2 meters
- Height: 3.3 meters
- Ground clearance: 0.5 meters
- Bucket width: 1.3 meters
- Bucket capacity:1.1 cubic meters
- Digging depth: 7.5 meters
- Vertical digging depth: 5.7 meters
- Reach: 10 meters
- Maximum travel speed: 4.9 km/hr
- Maximum traction force: 25,143 kgf
- Swing speed: 11 rpm
- Maximum digging force: Bucket: 18 tons; Stick: 14 tons
- Ground pressure: 7.7 psi
- Cummins 6CT 8.3-C
- 8,270 cubic centimeters
- 340 horsepower at 1,900 rpm
- Maximum pressure: 5,000 psi (4,500 psi typical)
- Oil flow: 2x270 liters per minute
- Fuel: 530 liters
- Engine oil: 22 liters
- Hydraulic oil: 320 liters