Volume Flow

Volume flow, a fundamental quantity in hydraulics, describes the volume of fluid flowing through a specific cross-section per unit of time. It is crucial for the speed of actuators and the performance of hydraulic systems. Precise control of the volume flow enables accurate positioning and movement of cylinders or motors in industrial applications.

Basics of volume flow in hydraulics

Volume flow is a physical variable that indicates how much volume of a fluid is transported through a specific cross-section per unit of time. This is of central importance in hydraulics, as it directly influences the working speed of hydraulic cylinders and hydraulic motors. A higher volume flow results in faster movements, while a lower volume flow enables slower, more precise movements.

Definition and formula symbol

The volume flow is usually denoted by the formula symbol Q. The base unit in the International System of Units (SI) is cubic meters per second (m³/s). In practice, especially in hydraulics, liters per minute (l/min) or cubic centimeters per second (cm³/s) are often used to obtain more manageable numerical values.

The basic formula for calculating volume flow is:

Q = V / t

Where:

• Q = The volume flow
• V = The volume of the fluid
• t = The time

Another important relationship exists between the volume flow, the cross-sectional area, and the flow velocity:

Q = A * v

Where:

• A = The cross-sectional area through which the fluid flows
• v = The average flow velocity of the fluid

This formula illustrates that, with a constant cross-sectional area, an increase in flow velocity directly leads to a higher volume flow and vice versa.

Significance for hydraulic systems

In hydraulic systems, the volume flow is the primary parameter for controlling the speed of working cylinders and hydraulic motors. A hydraulic pump generates a volume flow, which is then directed to the consumers via valves and lines. The size of the pump and its speed determine the maximum possible volume flow in the system.

Precise control of the volume flow is crucial for the functionality of many machines and systems. For example, in machine tools, construction machinery, or lifting devices, it must be possible to precisely adjust the speed of movements in order to achieve optimal working results and ensure safety.

Measurement and control of the volume flow

Accurate measurement and control of the volume flow are essential for the efficient and safe operation of hydraulic systems. Various methods and components are used for this purpose.

Volume flow meters

Various measuring devices are used to measure the volume flow in hydraulic systems. The selection of the appropriate measuring device depends on the application, the required accuracy, and the operating conditions.

Common types of volume flow meters are:

• Turbine flow meters: These devices use a turbine wheel that rotates in the fluid flow. The speed of the wheel is proportional to the volume flow and is recorded electronically. They are suitable for a wide range of applications and offer good accuracy.
• Gear flow meters: Here, the fluid is passed through two intermeshing gears that rotate. Each revolution of the gears displaces a defined volume. The number of revolutions per unit of time provides information about the volume flow. They are particularly robust and suitable for highly viscous media.
• Ultrasonic flow meters: These non-contact measuring devices use ultrasonic waves to determine the volume flow. They measure the time difference between ultrasonic signals sent with and against the fluid flow. Ultrasonic flow meters are ideal for applications where no mechanical parts are desired in the fluid flow.
• Coriolis mass flow meters: Although they primarily measure mass flow, they can also derive volume flow if the density of the fluid is known. They offer very high accuracy and are insensitive to changes in viscosity.

Volume flow control valves

Volume flow control valves are hydraulic components that serve to control and maintain a constant volume flow in a system, regardless of pressure fluctuations. They are crucial for the precise control of actuator speed.

There are different types of volume flow control valves:

• Throttle valves: These valves create resistance in the fluid flow, which reduces the volume flow. They are simple in design and inexpensive, but their control is pressure-dependent. This means that the volume flow also changes when the pressure in the system changes.
• Flow control valves: These valves maintain a constant volume flow regardless of pressure fluctuations. They consist of a throttle point and a pressure balancing piston. The pressure balancing piston ensures that the pressure drop across the throttle point remains constant, which also keeps the volume flow constant.
• Flow dividers: Flow dividers divide a supplied volume flow into two or more partial flows. They can operate either proportionally or independently of each other. Proportional flow dividers divide the volume flow in a fixed ratio, while independent flow dividers allow the partial flows to be adjusted individually.

Factors influencing the volume flow

Several factors can influence the volume flow in a hydraulic system. Understanding these factors is crucial for the design and operation of efficient systems.

Pressure and pressure losses

The pressure in the system and the associated pressure losses have a direct influence on the volume flow. Higher system pressure can lead to a higher volume flow with the same pump output, provided there are no throttles. Pressure losses caused by friction in pipes, valves, and other components reduce the pressure available for the work to be performed and can thus reduce the volume flow to the actuators.

Fluid viscosity

The viscosity of the hydraulic oil plays an important role. A high-viscosity fluid causes greater friction losses in pipes and components than a low-viscosity fluid. This can lead to a lower volume flow at the same pump output. Temperature fluctuations have a significant effect on the viscosity of the oil, which is why the operating temperature of the system is often regulated to ensure constant viscosity and thus a stable volume flow.

Cross-sectional areas and pipe dimensioning

The dimensioning of the lines and the cross-sectional areas of the components are decisive for the volume flow. Narrower cross-sections result in higher flow velocities and thus greater pressure losses for the same volume flow. Optimal pipe dimensioning minimizes pressure losses and ensures that the desired volume flow reaches the consumers. Insufficient pipe dimensioning can lead to cavitation and overheating of the fluid.

Leaks

Internal and external leaks in the hydraulic system can reduce the effective volume flow to the actuators. Internal leaks occur, for example, in pumps or valves, where part of the fluid flows past the working circuit. External leaks are visible leaks at seals or connections. Both types of leaks lead to a loss of volume flow and thus to reduced system efficiency.

Applications of volume flow in B2B hydraulics

Volume flow is of crucial importance in numerous industrial applications where precise movements and high forces are required.

Construction and agricultural machinery

In construction machinery such as excavators, wheel loaders, and cranes, as well as in agricultural machinery such as tractors and harvesters, volume flow is essential for controlling the working functions. The speed at which an excavator arm is moved or an attachment is lifted depends directly on the volume flow supplied to the corresponding hydraulic cylinders or motors. Precise volume flow control enables sensitive and efficient work processes.

Machine tools and production equipment

In modern machine tools and automated production systems, the volume flow is used for the precise positioning of workpieces and tools. Hydraulic clamping devices, feed drives, and tool changers require precisely defined volume flows to ensure high accuracy and repeatability. Control is often via proportional valves, which can continuously adjust the volume flow.

Lifting and conveyor technology

In lifting and conveyor technology, for example in forklift trucks, elevators, or crane systems, the volume flow is decisive for the lifting and lowering speeds. Controlled supply and removal of the hydraulic oil enables smooth starting and braking of the loads, which both increases safety and reduces component wear.

Energy generation and offshore applications

Volume flow also plays a central role in energy generation, particularly in wind turbines for rotor blade adjustment or in offshore applications for controlling drilling rigs and underwater vehicles. These applications often require high forces and precise movements under extreme conditions, which can only be achieved with reliable hydraulic volume flow control.

Future developments and trends

Developments in hydraulics are aimed at making systems even more efficient, precise, and intelligent. This also applies to the area of volume flow.

Energy efficiency

A key trend is the increase in the energy efficiency of hydraulic systems. This is achieved through the use of speed-controlled pumps that adjust the volume flow according to demand. Instead of constantly generating the maximum volume flow and throttling excess energy via valves, these pumps only deliver the volume flow that is actually required. This significantly reduces energy consumption and heat generation in the system.

Digitalization and Industry 4.0

The integration of sensor technology and digital control enables even more precise monitoring and control of the volume flow. Intelligent valves with integrated electronics can dynamically adjust the volume flow and provide data on the operating status. This data can be used for predictive maintenance and process optimization, which improves the reliability and availability of hydraulic systems.

Miniaturization and integration

The trend toward miniaturization and integration of hydraulic components is leading to more compact systems that require less space and are easier to install. This also applies to volume flow control valves and sensors, which are becoming smaller and more powerful. Such integrated solutions enable new applications in areas where space requirements were previously a limiting factor.