Displacement, flow and efficiency are crucial indicators, which can be used to evaluate the operating status of your hydraulic pumps. From this article, you can learn more about specific meanings about them, factors affecting flow, important hydraulic pumps efficiency types and you will know practical methods to increase hydraulic pump efficiency.
What’s the Displacement of Hydraulic Pumps?
Hydraulic pumps’ displacement is one of the most core parameters of your hydraulic pumps. They are volumes of discharged hydraulic fluid after a complete revolution of pump shafts and usually be measured by milliliters per revolution(ml/r).
You need to note that displacement is hydraulic pumps’ theoretical output and has nothing to do with actual working pressure or efficiency. In addition, displacement can also directly affect theoretical flow rates that the system can generate at a specific speed.
Hydraulic Pumps Classification by Displacement
Hydraulic pumps can be divided into fixed displacement and variable displacement hydraulic pumps according to whether their displacement is adjustable during operation. Below we will explain their different working conditions to you.
Fixed Displacement Hydraulic Pump
When the model and structure of fixed displacement hydraulic pumps are determined, they will have constant fluid pressure volume after each complete pumping cycle and can’t be adjusted arbitrarily. These hydraulic pumps’ output flow depends only on their drive shafts rotation speed. If their drive shafts’ speed is faster, more fluid will be output.
Fixed displacement hydraulic pumps usually have relatively simple structures and they can be easily maintained, which make them have long service life. Internal and external gear pumps are typical fixed displacement hydraulic pumps. This type of hydraulic pumps are suitable for consistent speed or simple working conditions applications such as material handling and light load lifting platform.
Variable Displacement Hydraulic Pumps
Fluid volume of variable displacement hydraulic pumps can be changed to fit for your various hydraulic systems’ requirements without changing their drive speed. For example, you can adjust hydraulic piston pumps’ internal components like pistons’ stroke to change fluid volume.
Variable displacement hydraulic pumps have excellent energy saving performance. They can accurately match the flow required by their system actuators and avoid providing unnecessary fluid volume. This type of hydraulic pumps can be applied in high automation level, control accuracy and low energy consumption applications like injection molding machines, presses.
What’s the Hydraulic Pump Flow?
Hydraulic pump flow indicates fluid volume delivered by your hydraulic pumps within a specific time and is usually measured in liters per minute(L/min). Flow is a key performance parameter to measure hydraulic pump’s delivery capacity. In order to help analyze the performance of your hydraulic pumps, usually flow can be divided into actual flow and theoretical flow.
Theoretical flow refers to the flow obtained under ideal conditions and is only related to pumps’ structural parameters and speed. Actual flow refers to fluid volume actually output by your hydraulic pump during actual operation. Under normal circumstances, actual flow is always less than theoretical flow due to unavoidable internal leakage and wear.
Key Factors Affecting Flow
1. Pump Displacement
When hydraulic systems’ rotation speed is constant, the displacement of hydraulic pumps directly determines their flow. Hydraulic pump flow will become greater as hydraulic pump’s displacement increases. Although actual flow is less than theoretical flow due to internal leakage, larger displacement pumps can still have much greater actual output flow than smaller displacement pumps.
2. Rotational Speed
Rotational speed of drive shafts is the most critical external driving factor to affect hydraulic flow. For fixed displacement hydraulic pumps, theoretical fluid volume discharged is fixed during each pump shafts’ revolution. But rotational speed can determine how many times pump shafts will rotate within a specified time. Therefore, when hydraulic pump displacement is fixed, the higher the rotational speed, the greater the total output flow.
3. System Temperature
Hydraulic systems with high temperature cannot directly affect hydraulic pump flow, they reduce hydraulic fluid’s viscosity to increase the risk of internal leakage, which can reduce hydraulic pump flow. For example, as your hydraulic system temperature rises, low viscosity hydraulic fluid will aggravate the leakage of internal moving components’ gaps such as hydraulic gear pumps’ teeth side clearance or between hydraulic piston pumps’ cylinders and valve plates. Due to these serious internal leakage, actual output flow will continue to decrease.
However, when hydraulic systems’ temperature is too low, fluid’s viscosity will increase sharply and resistance to hydraulic oil flow will also increase. This will not only cause low flow, but will also increase internal wear of your hydraulic pump and even shorten its service life.
In general, both too high and too low system temperatures cannot maintain a stable flow of hydraulic pump. You need to install a temperature control or cooling system to ensure the normal operation of your hydraulic system.
Types of Hydraulic Pump Efficiency
Volumetric Efficiency
Volumetric efficiency is a key performance indicator to measure internal leakage status of hydraulic pumps. This indicator is the ratio of actual output flow to theoretical output flow.
If volumetric efficiency value is high, it means that your hydraulic pump’s internal sealing is good and the risk of internal leakage is small. A volumetric efficiency value of 85% or more indicates that your hydraulic system is operating normally.
The core factor affecting volumetric efficiency is operating pressure. High operating pressure can increase pressure difference, which will increase internal oil leakage and reduce volumetric efficiency. In addition, any factor that increases oil leakage will reduce volumetric efficiency of hydraulic pumps.
Mechanical Efficiency
Mechanical efficiency is used to evaluate hydraulic pumps’ energy wasted caused by internal mechanical friction during operation. It is the ratio of theoretical input power to actual input power. And the level of mechanical efficiency can directly reflect your hydraulic pumps’ effectiveness of overcoming mechanical friction during pumps’ energy conversion process. The higher the mechanical efficiency, the smaller the friction loss. Hydraulic pumps will also need less additional energy to be driven. You also need to know that hydraulic pumps’ normal mechanical efficiency range is above 80%.
Total Efficiency
Total efficiency of hydraulic pumps can be used to reflect overall pump performance. It is the ratio of actual output power to actual input mechanical power. Total efficiency can help reflect the extent of all energy losses in hydraulic pumps, including volume loss due to internal leakage and mechanical loss due to mechanical friction.
This indicator can also be calculated by multiplying hydraulic pumps‘ volumetric efficiency and mechanical efficiency. So the total efficiency will be affected by both efficiencies. Total efficiency of 70% or more indicates well-maintained hydraulic systems.
Tips for Increasing Hydraulic Pump Efficiency
Tip1: Using Appropriate Hydraulic Fluid
Using appropriate hydraulic fluid can greatly improve efficient operation of your hydraulic pumps. You need to choose suitable hydraulic fluid with proper viscosity according to your hydraulic system requirements. Proper viscosity hydraulic fluid will have stable fluidity and reduce hydraulic pumps’ operating resistance, which will maintain mechanical efficiency.
Most importantly, appropriate hydraulic fluid can also reduce the risk of internal leakage and avoid a decrease in volumetric efficiency.
Tip 2: Ensure Proper Filtration
Ensure proper filtration not only maintains high efficiency but also extends service life of hydraulic pumps. Efficient filtration can help remove solid particle contaminants from hydraulic oil and this will greatly reduce the wear and tear of your hydraulic pumps. Clean and impurity-free oil can help improve the mechanical efficiency of hydraulic pumps and enhance their operational efficiency.
Tip 3: Regular Maintenance
Regular maintenance is essential for hydraulic pumps and it mainly includes leaks inspecting, filters cleaning and hydraulic oil changing. Regular inspection and replacement of worn seals also needs to be considered.
For one thing, regular maintenance is able to reduce unnecessary oil leakage and increase
volumetric efficiency. For another, it can also ensure hydraulic pumps always operate in the high efficiency range.
Tip 4: Choose Variable Displacement Pumps
Variable displacement pumps have excellent power adaptability and they can automatically reduce their displacement to precisely match pumps’ specific flow requirements. But fixed displacement pumps always have excess flow and lead to a lot of energy waste. Luckily, variable displacement pumps can avoid these problems and achieve energy-saving, efficient operation during the entire working process.
Conclusion
After reading this article, I guess you must have a deep understanding about hydraulic displacement, flow and various types of efficiency. And you will be able to maintain your hydraulic pump properly and improve your engineering efficiency. If you are looking for a hydraulic pump partner, Target undoubtedly can be your good choice.
FAQ
Does high total efficiency mean high operating efficiency of hydraulic pumps?
Yes, this conclusion is right. The higher total efficiency of hydraulic pumps, the higher operating efficiency of hydraulic pumps. Total efficiency is the ultimate performance of your hydraulic pumps and it combines all energy losses within pumps. In addition, high total efficiency means lower operating energy consumption and less economic losses.
Therefore, the single volumetric efficiency and mechanical efficiency cannot reflect the overall operating status of your hydraulic pumps. You need to pay attention to the total efficiency.
