The function of a pump is to convert mechanical energy into hydraulic energy. It is the heart of any hydraulic system because it generates the force necessary to move the load. Mechanical energy is delivered to the pump using a prime mover such as an electric motor. A partial vacuum is created at the inlet due to the mechanical rotation of pump shaft. Vacuum permits atmospheric pressure to force the fluid through the inlet line and into the pump. The pump then pushes the fluid mechanically into the fluid power actuated devices such as a motor or a cylinder.
Classification of pump
Pumps are classification into three different ways and must be considered in any conversation of fluid power equipment:
1. Classification based on displacement:
- Non-positive displacement pumps (hydrodynamic pumps)
- Positive displacement pumps (hydro-static pumps).
2. Classification based on delivery:
- Constant delivery pumps
- Variable delivery pumps
3. Classification based on motion:
- Rotary pump
- Reciprocating pump
Non-Positive Displacement Pumps
Non-positive removal pumps are essentially velocity type units that have a lot of clearance among turning and fixed parts. Non-uprooting siphons are described by a high slip that increments as the back weight increments, so the outlet might be totally shut without harm to the siphon or framework.
Non-positive pumps do not build up a high weight however, move a huge volume of liquid at low weights. They have basically no attractions lift. In light of enormous freedom space, these siphons are not self preparing. As such, the siphoning activity has a lot of leeway space to seal against atmospheric weight.
The uprooting between the bay and the outlet isn’t sure. Therefore, the volume of liquid conveyed by a pimps relies upon the velocity at which the pump is worked and the opposition at the release side. As the obstruction develops at the release side, the liquid slips once more into the freedom spaces, or at the end of the day, follows the easiest course of action. At the point when the opposition gets to a specific worth, no liquid gets conveyed to the framework and the volumetric effectiveness of the pump drops to zero for guaranteed speed. These siphons are not utilized in liquid force industry as they are not able to do withstanding high weight.
Their most extreme limit is constrained to 17–20 bar. These kinds of pumps are basically utilized for moving liquids, for example, water, oil, and so forth , from one area to another extensive separated area. Execution bends for positive and non positive removal pumps are appeared in Fig.1.1. The two most normal kinds of hydrodynamic pumps are the radial and the pivotal stream propeller pumps.
Advantages and disadvantages of non-positive displacement pumps
The advantages are as follows:
- 1. Non-displacement pumps have less moving parts.
- 2. Starting and support cost is low.
- 3. They give smooth consistent stream.
- 4. They are appropriate for taking care of practically a wide range of liquids including slurring and sledges.
- 5. Their activity is straightforward and solid.
The disadvantages are as follows:
- 1. Non-displacement pumps are not self-preparing and consequently they should be situated underneath the liquid level.
- 2. Discharge is a function of output resistance.
- 3. Low volumetric efficiency.
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Positive Displacement Pumps
Positive Displacement Pumps, conversely, have next to no slips, are self-preparing and it should pump against extremely high pressures, yet their volumetric efficiency is less. Positive Displacement Pumps have a very close clearance between rotating and stationary parts and hence are self-priming. Positive displacement pump discharge a fixed measure of liquid into the water driven framework per insurgency of the pump shaft. Such pumps are equipped for beating the weight coming about because of mechanical loads on the framework just as the obstruction of stream because of rubbing. This equipment should consistently be secured by help valves to forestall harm to the pump or framework. By a long shot, a larger part of liquid force pumps fall in this classification, including including gear, vane and piston pumps.
Positive displacement pumps are classified based on the following characteristics:
1. Type of motion of pumping element:
Based on the type of motion of pumping
- Gear pumps and vane pump pumps.
2. Displacement characteristics:
Based on displacement characteristics,
- Fixed displacement pumps.
- Variable displacement pumps.
3. Based on type of pumping element.
The advantages of positive displacement pumps over non-positive displacement pumps are as follows:
- They can operate at very high pressures of up to 800 bar (used for lifting oils from very deep oil wells).
- They can achieve a high volumetric efficiency of up to 98%.
- They are highly efficient and almost constant throughout the designed pressure range.
- They are a compact unit, having a high power-to-weight ratio. They can obtain a smooth and precisely controlled motion.
- By proper application and control, they produce only the amount of flow required to move the load at the desired velocity.
- They have a great flexibility of performance. They can be made to operate over a wide range of pressures and speeds.
Constant Delivery Pumps
Constant Delivery Pumps consistently convey a constant amount of liquid in a given time at the working rate and temperature. These pumps are commonly utilized with moderately basic machines, for example, saws or drill presses or where a gathering of machines is worked with no particular relationship among their relative paces. Force for responding actuators is frequently given by constant volume pumps.
Variable Delivery Pumps
The output of variable delivery pumps may be varied either manually or automatically with no change in the input speed to the pump. variable delivery pumps are habitually utilized for rewinds, constant tension devices or where a group of separate drives has an integrated speed relationship such as a conveyor system or continuous processing equipment.
Difference between positive displacement pump and non-displacement pump
Positive Displacement pump
- The flow rate doesn’t change with head.
- The stream rate diminishes with head.
- The stream rate isn’t greatly influenced by the thickness of a liquid.
- Efficiency is almost constant with head.
Non-Positive Displacement pump
- The flow rate change with head
- The stream rate diminishes with the thickness
- Effectiveness is practically consistent with head Efficiency increments with head from the start and afterward diminishes.
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