TYPES OF HYDRAULIC PUMPS

  BRACT, Vishwakarma Institute of Technology, Pune

TY. B. tech

Mechanical Engineering Department

HMAFP - Home Assignment - TYMEA, Batch 2, Group 5

Guided by - Prof. Sachin Komble

Group Members/Authors - 

Nivedita Bhagwat - RN 31

Pranjali Bhople - RN 38

Vedant Bhosale - RN 41

Harsh Bhutada - RN 44

Chhavi Kumari - RN 52

 

Introduction

Hydraulic pumps are used in hydraulic drive systems. A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy. It generates flow with enough power to overcome pressure induced by a load, any load at the pump outlet.  This mechanical energy is taken from what is called the prime mover (a turning force). 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.  

Classification of Pumps

All pumps may be classified as either positive-displacement or non-positive-displacement. Most pumps used in hydraulic systems are positive-displacement.

Gear Pumps

A gear pump is used in many hydraulic systems because of the simple design and widespread availability. It has only a few moving parts, works smoothly, and operates very well at pressures around 210 bar. In a gear pump, the displacement chambers are formed between the housing of the hydraulic pump and the rotating gear wheel (or gear wheels, depending on model or hydraulic pump design). Gear pumps are hydraulic pumps that are available in many different types.

External gear pumps

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.
 

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.

Internal gear pumps

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.
 

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 the operation to be exceptionally quiet with a constant flow.

Gear ring pump 

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 traversing 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.

Screw Spindle Pumps

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.

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.

 

Piston pumps

Hydraulic piston pumps can handle large flows at high hydraulic system pressures. The piston pump is a hydraulic pump that delivers optimum efficiency and reliability while maintaining a compact size with a high power density. 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 which makes it possible to operate at high pressures with low fluid leakage. 

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. Applications are mobile and construction equipment, marine auxiliary power, metal forming and stamping, machine tools and oil field equipment.

Axial piston pump

Fixed displacement

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.

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.

Variable displacement

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.

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). 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).

Radial piston pump

Fixed displacement, variable displacement

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 an 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.

Vane pumps

Vane pumps are hydraulic pumps that operate at very low noise levels. 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 of up to 3,000 rpm.
The hydraulic vane pump finds its use in die casting and injection moulding machines in industry, as well as in land and road construction machinery. The operating pressure of vane pumps does normally not exceed 180-210 bar. However, in specially designed vane pumps the operating pressure may go well over 200 bar and up to 300 bar.

Vane pumps, variable displacement

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

Vane pumps, fixed displacement

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 setup 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.

Conclusion

Hydraulic pumps convert electrical energy into fluid pressure by using an electric motor to drive the pump. Gear pumps and vane pumps are used in low and medium pressure industrial applications. Piston pumps specifically are used in medium and high pressure industrial applications. Axial piston pumps find application in medium and high pressure applications. With special features, these pumps become power saving units and reduce system heating. In short, a pump is the heart of any hydraulic system.