| A hydraulic drive system utilizes a pressurized working | | | | This pump type offers a variable drive, meaning that |
| fluid to deliver power to machinery. Every system has | | | | the flow rate and outlet pressure can be regulated and |
| many common aspects. Here we will focus on the | | | | changed. These pumps are typically more complex |
| hydraulic pump. Its purpose is to pressurize the | | | | and expensive as a result. |
| hydraulic fluid that will be used to drive a machine. The | | | | Rotary vane hydraulic pumps are a higher efficiency |
| pump can be used to pressurize fresh liquid in what | | | | model than a gear pump and are suited for the middle |
| would be called an open loop system, or to | | | | pressure range (roughly 180 bar). Concentric, offset |
| re-pressurize fluid after it has driven a motor, known | | | | vanes are run in these pumps, creating areas where |
| as a closed loop system. In both cases, pump types | | | | the working fluid is forced into a smaller volume |
| are matched to certain applications and have different | | | | thereby increasing its pressure. |
| specifications to fit into any process design scheme. | | | | The ultimate pump in terms of efficiency and high |
| Let us take a look at the different types available to | | | | output is the bent-axis piston and cylinder design. Think |
| engineers and industry. | | | | of a car engine's piston and cylinder. This pump is built |
| Fixed Displacement | | | | the same way. The bent axis refers to the alignment |
| A fixed displacement hydraulic pump has a set flow | | | | of the cylinders that provide maximum efficiency and |
| through depending on the design parameters. These | | | | run at high pressures. A double action model can |
| pump types are more simple, less expensive, and | | | | increase the throughput by using two cylinders per |
| easier to maintain. These benefits come at the | | | | piston. These pumps are the most expensive, but are |
| expense of the flexibility to change the operating | | | | highly responsive. |
| parameters to meet process needs. | | | | Hydraulic pumps come in such a wide variety in order |
| The basic type is the gear pump. Pressure is created | | | | to fit into any process and any budget. Simple, fixed |
| by pushing the working liquid through a pair of gears | | | | displacement pumps work very well for a process |
| toward the outlet. These gears can be run in a line, or | | | | that does not have variable operating parameters. |
| nested within each other to improve performance and | | | | Variable displacement models are well suited for more |
| reduce noise levels. | | | | flexible processes and can also be connected to |
| A screw pump forgoes the use of gears and instead | | | | multiple machines by increasing the output based on |
| uses a pair of Archimedes spirals. These appear as | | | | the number of machines running. Even in cases where |
| screws with very large grooves. The working liquid | | | | these designs are not a perfect match, pumps can be |
| picks up pressures as it flows through the rotating | | | | run in parallel or series. Connecting two low pressure, |
| screws. These pumps are well suited for higher flow | | | | less expensive pumps in series can often work as an |
| rates at a relatively low pressure. | | | | alternative. Hydraulic pumps offer a large canvas for a |
| Variable Displacement | | | | design engineer to work with. |