You can use hydraulic machines - equipped with a pump - to do different types of work such as lift, lower, open, close or rotate components.
Hydraulic pumps are sources of power for many dynamic machines. Hydraulic pumps are capable of pushing large amounts of oil through hydraulic cylinders or hydraulic motors. In this fashion, the pump converts the mechanical energy of the drive (i.e. torque, speed) into hydrostatic energy (i.e. flow, pressure).
Hydraulic pumps operate according to the displacement principle. This involves the existence of mechanically sealed chambers in the pump. Through these chambers, fluid is transported from the inlet (suction port) of the pump to the outlet (pressure port). The sealed chambers ensure that there is no direct connection between the two ports of the pump. As a result, these pumps are very suitable to operate at high system pressures and are ideal for hydraulics.
Selecting the appropriate hydraulic pump for your application is always a challenge because of different ranges and capabilities. DTA can help you select the correct pump within a reasonable price range and within your budget. Contact DTA for your hydraulic pump needs today!
DTA has extensive expertise in pump technology and carries a substantial inventory of pumps from several different vendors. Depending on your requirements, DTA can supply high-quality hydraulic pumps, taking a wide variety of functional and hydraulic system requirements into account.
Hydraulic pumps are manufactured depending on different functional and hydraulic system requirements, such as operating medium, required range of pressure, type of drive, etc. A large range of design principles and configurations exists behind hydraulic pumps. Consequently, not every pump can fully meet all sets of requirements to an optimum degree. Three different types of hydraulic pumps exist:
Hydraulic Gear Pumps
Hydraulic Vane Pumps
Hydraulic Piston Pumps
Note: while gear pumps operate with fixed displacement volume, vane and piston pumps may operate with fixed or variable displacement volumes.
A gear pump is used in many hydraulic systems. It has few moving parts, works smoothly, and operates very well at pressures up to 250 bar. The displacement chambers are formed between the housing of the pump and the rotating gear wheel (or gear wheels, depending on model).
External gear pumps are used in industrial and mobile (e.g. log splitters, lifts) hydraulic applications. Typical applications are lubrication pumps in machine tools, fluid power transfer units and oil pumps in engines. These pumps have some unique features:
In an external gear pump, only one of the gear wheels is connected to the drive. The other gear wheel rotates in the opposite direction so that the teeth of the rotating gear wheels interlock. With use of a bearing block, the gear wheels are positioned in such a way that they interlock with the minimum clearance. Volume is created between the gear tooth profiles, housing walls and surfaces of the bearing blocks.
Typical parameters are:
Internal gear pumps are primarily used in non-mobile hydraulics (e.g. machines for plastics and machine tools, presses, etc.) and in vehicles that operate in an enclosed space (electric fork-lifts, etc.). The internal gear pump is exceptionally versatile and also capable of handling thick fluids. Key features are:
In an internal gear pump, the gear rotor is connected to the drive. When the gear rotor and internal gear rotate, volume is created between the gear ring profiles, housing walls and filling piece. The space between the gear tooth profiles increases relatively slowly over an angle of about 120°. This causes operation to be exceptionally quiet with a constant flow.
Typical parameters are:
The gear ring pump is primarily used as a pressure lubrication system for machines and combustion engines. They are also used in hydraulic power steering systems.
This pump is often assembled with a high pressure pump, e.g. radial piston pump. The rotors of the gear ring pump can be directly built into the housing of the high pressure pump, which makes it possible to build very compact units. Such small double-pumps are often used for rapid traverse on large presses and tensioning equipment.
The rotor has one tooth less than the inner stator. Planetary movement of the rotor results in compressing and decompressing of the displacement chambers within the housing.
Similar to internal gear pumps, screw pumps possess an extremely low operating noise level. They are therefore used in hydraulic systems in such places as theatres and opera houses.
The displacement volume of the screw spindle pump is the largest of all gear pumps. Screw pumps contain 2 or 3 worm gears within the housing and therefore also referred to as worm gear pumps.
Typical parameters are:
The worm gear that is connected to the drive has a clockwise thread. Rotary movement is transmitted to further worm gears, which have counter-clockwise threads. The displacement chamber is formed between the threads and the housing of the screw pump.
The vane pump finds its use in die casting and injection moulding machines in industry, as well as in land and road construction machinery.
Hydraulic vane pumps operate with much lower flow pulsation, i.e. constant flow. As such, vane pumps produce less noise while maintaining a relatively high speed.
Key features of the vane pump:
The operating pressure of vane pumps does not normally exceed 175 bar. However, in specially designed vane pumps the operating pressure may go over 200 bar and up to 300 bar. Hydraulic vane pumps are available as single chamber vane pumps or double chamber vane pumps.
Both types use the same parts, i.e. they comprise a rotor and vanes. The vanes may be radially moved within the rotor, and the centrifugal force of the rotor pushes the vanes out to touch the housing. The difference between the two types is in the shape of the stroke ring that limits the stroke movement of the vanes.
Typical parameters are:
In a single chamber vane pump, the stroke movement of the vanes is limited by a ring with a circular internal track. The position of this so-called stroke ring is off-centre with respect to the rotor, resulting in change of volume in the displacement chambers. The displacement chambers are created by the rotor, two vanes, the internal surface of the ring and the control discs on one side.
In a single chamber vane pump, the system pressure is only on one side of the rotor. This causes a significant load on the bearings. To reduce this load, the forces acting on the rotor must be in balance. This is the reason why double chamber vane pumps were designed, as mentioned below.
For double chamber vane pumps, the process of filling the chambers (suction) and emptying is in principle the same as for single chamber vane pumps. In this case, however, the stroke ring (i.e. stator) has a double eccentric internal surface. The rotor can be placed in the axis of the stator because of these surfaces, which differentiates them from single chamber vane pumps.
This set up causes each vane to carry out two strokes per rotation of the shaft. All radial loads on the rotor are now neutralized (two pressure ports on each opposite side). The end result is that two pumps have been built together as one. Due to the twin cam forms of the stator, two displacement processes occur per revolution.
Only the single chamber vane pump is available as a variable displacement volume type. By moving the stator (stroke ring) with an adjustment screw, it is possible to adapt the size of the displacement chambers. When the axis of the rotor is in the centre position of the stroke ring, all formed chambers are of equal size and the outflow of the pump is nil.
Three positioning devices may be used:
The outflow of the pump may be controlled and adjusted mechanically (i.e. directly with an adjustment screw on the pump). You can also control the outflow by other means, such as a combination of hydraulic and electrical control.
Hydraulic piston pumps can handle large flows at high hydraulic system pressures. Typical applications are mobile and construction equipment, marine auxiliary power, metal forming and stamping, machine tools and oil field equipment.
In these pumps, the pistons accurately slide back and forth inside the cylinders that are part of the hydraulic pump. The sealing properties of the pistons are excellent.
Key features of hydraulic piston pumps are:
Hydraulic piston pumps operate at very high volumetric efficiency levels due to low fluid leakage. The plungers may consist of valves at the suction and pressure ports or with input and output channels. Piston pumps with valves at the ports are better suited to operate at higher system pressures due to better sealing characteristics.
The design of an axial piston unit is based on two important principles. First, the design of the axial piston pump may be based on the swash plate principle or bent axis design. Secondly, hydraulic system parameters have to be taken into account: whether the usage is to take place in an open or closed loop circuit is of great importance.
Axial Piston Pumps - PV-plus Variable Displacement | Parker Hydraulics
In closed loop circuits, the return line (i.e. the suction line of the pump) is under pressure. This must be incorporated in the design of axial piston units used in closed loop systems. It is also imperative to have a variable displacement volume hydraulic pump in operation in these systems. In fixed displacement volume configuration, the axial piston unit can be used both as pump and as motor.
In bent axis design, the displacement volume is dependent on the swivel angle: the pistons move within the cylinder bores when the shaft rotates. In swash plate design, the rotating pistons are supported by a swash plate; the angle of the swash plate determines the piston stroke.
Typical parameters are:
Radial piston pumps are used in applications that involve high pressures (operating pressures above 400 bar and up to 700 bar), such as presses, machines for processing plastic and machine tools that clamp hydraulics. Radial piston pumps are the only pumps capable of working satisfactorily at such high pressures, even under continuous operation.
Radial piston pumps are available in two different configurations. With eccentric cylinder block, the piston rotates within the rigid external ring. Eccentricity determines the stroke of the pistons. Or, with an eccentric shaft, the rotating eccentric shaft causes radially-oscillating piston movements to be produced. Most models have an odd number of pistons to reduce the flow pulsation.
Typical parameters are:
Speed n [rpm] is the mechanical equivalent of the hydrostatic parameter flow Q [L/min], and pressure p [bar] is the hydrostatic equivalent to the mechanical parameter torque τ [Nm]. It is the relation between these variables that allows tuning the pump outflow to hydraulic system (i.e. load) needs.
When you use a pilot-operated, electro-hydraulic controlled pressure or flow regulator, the outflow of the pump depends on system pressure, flow or a combination of both (i.e. power control). The example below illustrates the use of a pressure-controlled hydraulic piston pump.
If the hydraulic system pressure reaches above a predetermined pressure setting, the flow of the pump returns to zero and the system pressure is maintained constant. By doing so, the power lost in the system is low and the energy consumption of the drive system is minimal at maximum pressure.
Note that a combination of flow and pressure regulation permits designing very economic drives (e.g. load sensing).