There are many types of hydraulic compressors that are used for various functions. These may include piston compressors, rotary vane compressors, axial flow compressors, liquid ring pumps and rotary screw compressors. Most hydraulic compressors are used to increase or decrease the pressure of a liquid or gas using physical processes. The variety of hydraulic compressors is a result of the many tasks that require changing gas or liquid to a specific pressure.
Piston compressors are often considered one of the basic types of hydraulic compressors. In these, a crankshaft moves a piston within a confined chamber, and a liquid or gas is compressed by this piston into a smaller space. In the past, piston compressors were often used for pressurized hand tools and may still be used for certain kinds of tools. Many piston compressors are used in oil or natural gas systems, because they are considered simple, effective and versatile.
Rotary vane compressors use rotating, fan-like blades called vanes to compress hydraulic materials. Often considered one of the oldest forms of hydraulic compressors, rotary vane systems come in many different shapes and sizes and with various functions. The size and shape of the vanes usually determine how strong the pressure can be. Multiple vanes also can be combined to make more complex rotary vane compressors of virtually any size.
Axial flow compressors, for instance, use multiple vanes to increase the compression capabilities of a machine. The design of these compressors means axial-flow systems are often used when compact pumps are required. An axial flow hydraulic compressor also might be used in high-volume situations where a single rotary vane may not be sufficient.
A liquid ring pump, often powered by a motor, is similar to rotary vane compressors. These types of hydraulic compressors make use of the positive displacement principle. Liquid is compressed to form a seal inside a chamber, a process that creates room for hydraulic compression between the vanes connected to the rotor. Centrifugal acceleration plays an important role in this kind of compression, and liquid ring pumps often must work in stages as a result.
Rotary screw compressors use a combination of helical screws to change the pressure of gasses and hydraulic materials. Helical screws are often designed to withstand significant speeds or extended use, and are often preferred for permanent hydraulic systems. As hydraulic material passes through the screws, it is usually forced into a smaller space, which increases the pressure.