Hydraulic flow and pressure are all crucial parameters about hydraulic systems, their fluctuations can effectively reflect system problems and help you evaluate components efficiency.
This article mainly helps you understand specific concepts, types, and how they affect the performance of your hydraulic systems. These will help you reasonably control flow and pressure for your specific project and ensure your hydraulic equipment, especially industrial equipment, can operate stably under high loads.
What’s Hydraulic Flow and Pressure?
Hydraulic Flow
Hydraulic flow is the movement of hydraulic fluid in hydraulic systems, and it can affect hydraulic actuator’s speed. Usually its unit is gallons per minute (GPM). In hydraulic systems, hydraulic flow is generated by the output of pumps, which help convert mechanical energy into hydraulic energy and establish required pressure difference in systems. This pressure difference forces fluid flow from high-pressure areas to low-pressure areas and transfers energy to actuators. Then actuators such as hydraulic motors or cylinders can achieve linear or rotational motion.
Hydraulic Pressure
Hydraulic pressure is the force caused by incompressible hydraulic fluid within a closed hydraulic system area and can be measured in units of PSI. It is important to note that hydraulic pressure is not directly created by hydraulic pumps, the real source of it is the resistance of load to hydraulic oil flow.
In addition, pressure is also an important diagnostic parameter for hydraulic system status. Abnormal fluctuations or insufficient hydraulic pressure often indicate problems such as internal leakage, decreased pump performance or valve failure.
2 Related Factors of Flow
Flow Rate
Flow rate is a measure of flow over time, which can help quantify the amount of fluid flowing through a specific area in a given period of time. The higher the flow rate of hydraulic systems, the faster the movement and the shorter the cycle time. For example, if flow rate increases, extension and retraction speed of hydraulic cylinder piston and rotation speed of hydraulic motor will all improve.
Flow Velocity
Flow velocity is closely related to flow rate and is a microscopic manifestation of hydraulic flow, it usually refers to fluid speed when fluid passes through a certain point per unit time. Flow velocity can be calculated by the ratio of its flow rate to pipes or hoses’ cross-sectional areas.
Furthermore, flow rate is an extremely critical control parameter in your hydraulic system because it can directly affect the operating status of your hydraulic system. On one hand, excessive flow rate velocity will increase friction, which will seriously damage hydraulic system performance and components’ service life. On the other hand, low flow velocity may cause contaminants to settle in hydraulic oil and reduce operating efficiency.
Common Types of Hydraulic Flow
Reynolds number is always used to explain flow phenomena such as laminar flow and turbulent flow. Simply explained, a higher Reynolds number means turbulent flow and lower Reynolds number indicates smooth and laminar flow.
Laminar Flow
Laminar flow is often formed at a lower speed and it flows in distinct and parallel layers.
At low flow rates, laminar flow is formed due to fluid’s viscosity, which allows for smooth, orderly parallel motion. And each flow layer slides relative to each other without mixing, thus forming a stable laminar flow state. This phenomenon helps to reduce internal friction, so energy consumption and pressure loss of hydraulic systems are relatively small.
Laminar flow is an ideal flow state expected by hydraulic systems, but its stability is poor and it is easily transformed into turbulent flow due to external disturbances.
Turbulent Flow
When hydraulic fluids’ flow rate increases(high Reynolds number), the viscosity of your hydraulic fluid is relatively weakened, and turbulent flow will be formed. And you can easily find this phenomenon on bends and restrictions. Because when fluid flows too fast, local resistance to these areas will increase, which will destroy the stability of fluid and disturb their original flow path.
This phenomenon will lead to huge energy loss and significantly reduce hydraulic system efficiency. In order to reduce turbulent flow, you can use larger hoses and fittings in your hydraulic equipment, which will improve fluid stability.
Uniform Flow
Uniform flow indicates that fluid flows with constant magnitude and direction of flow velocity or its flow velocity changes very slowly during operation. Uniform flow can typically be found in long straight pipes with smooth inner walls and constant diameter. Normally, when hydraulic fluid flows through a sufficiently long straight pipe, internal fluid tends to be stable, the viscous force and pressure reach a balance, thus forming a uniform flow.
Uniform flow can ensure the smoothness and predictability of fluid transmission, significantly reduce vibration, noise and energy loss caused by drastic changes in flow rate, and provide a stable and efficient working foundation for your hydraulic system.
Non-Uniform Flow
If flow velocity or direction of the fluid changes significantly along its flow path, this phenomenon is called non-uniform flow. It usually appears in local areas such as elbows, valves, and throttles, which often causes hydraulic system vibration, noise and cavitation. More seriously, it can also damage the stability and service life of components.
There are some effective ways to help you avoid non-uniform flow. For example, you can use oil pipes with smooth inner walls and minimize pipes’ length as much as possible to avoid unnecessary bends. If flow direction must be changed, you should choose a large radius elbow instead of a sharp bend, which can help keep flow rate steady and reduce non-uniform flow.
Types of Hydraulic Pressure
Static Pressure
Static pressure reflects fluid’s pressure value in a stable static state and it can be directly measured by a pressure gauge. And it can help accurately reflect hydraulic systems’ load at a specific time.
Most importantly, you can evaluate your hydraulic systems’ operating status by static pressure. For instance, if you find static pressure continues to drop or is lower than its standard value, your hydraulic equipment may have a fault such as internal leakage or insufficient output pressure of hydraulic pumps.
Dynamic pressure
Unlike stable static pressure, dynamic pressure is instantaneous and its value may be much higher or lower than hydraulic systems’ average pressure. And it can be measured by pressure sensors during its flow.
Monitoring dynamic pressure can help you detect hydraulic equipment problems and maintain them in time. Excessive dynamic pressure means your system is at risk of cavitation, which will damage seals, pipes or wear out other components and reduce their service life.
How Pressure Affects the Performance of Your Hydraulic System?
1. Power Output
Pressure is the basis of power transmission, and hydraulic pressure is able to directly determine your hydraulic system’s power output capacity. Higher hydraulic pressure can increase power output and this advantage will help your equipment like cranes, excavators or liftings lift heavier loads.
2. Force Generation
Hydraulic pressure is a decisive factor in force generation. For hydraulic piston motors and hydraulic vane motors, as long as their pistons or vanes remain unchanged, the higher the hydraulic pressure, the greater the output force generated.
3. Internal Leakage
High hydraulic pressure can cause internal leakage in hydraulic pumps and vanes. As hydraulic pressure increases, pressure differences in hydraulic systems will become larger, which will drive hydraulic oil into gaps between components. Internal leakage will reduce volumetric efficiency of your hydraulic system, this will reduce operating speed of hydraulic cylinders.
4. Excessive Temperature
Excessive temperature is able to reduce the efficient operation of your hydraulic systems. Hydraulic pump output flow will be lost and converted into heat energy, causing thermal effects under high hydraulic pressure of hydraulic systems.
If hydraulic systems temperature are too high, hydraulic oil temperature rises and its viscosity decreases. It will also age the seals much faster and lead to leaks.
5. Responsive Speed
High hydraulic pressure means your system can quickly provide the required power without long-term power transmission, responsive speed will also be faster. However, you need precise control to avoid pressure exceeding the optimal pressure range.
Conclusion
Learning fundamentals of hydraulic flow and pressure can not only help you access hydraulic systems’ operating status, but also can maintain your faulty hydraulic system in time. We also explain how pressure affects the performance of your hydraulic systems and this reminds you to control hydraulic pressure fluctuation within their optimal range.
If you want to consult any further questions about hydraulic systems, Target Hydraulic all can provide you with effective solutions.
FAQ
Why is it important to balance hydraulic flow and pressure?
Both hydraulic flow and pressure are relevant considerations during the operation of hydraulic systems. Speed of hydraulic actuators is proportional to flow, and the force and torque output are determined by pressure. But if they don’t come into balance, there will be a lot of issues.
For example, if hydraulic pressure is very high and hydraulic flow is small, actuators will have enough power but will function slowly, be inefficient, and easily overheat. But if hydraulic flow is too large and hydraulic pressure is insufficient, actuators will move quickly but cannot overcome heavy loads.
Most importantly, this balance is the core of optimizing hydraulic systems’ energy transfer. Balancing hydraulic flow and pressure can prevent system temperature from rising and
minimize unnecessary energy loss. Stable flow and pressure can also ensure operating efficiency and service life of your hydraulic equipment.
