Constant Displacement Pump

A constant pump is a hydraulic pump that provides a continuous flow of hydraulic fluid in hydraulic systems, generating constant pressure. It is primarily used to provide the base load in hydraulic systems and is known for its reliability and ease of maintenance.

Functionality and design of constant pumps

Constant pumps are designed to deliver a virtually constant volume flow at a given speed. This distinguishes them from variable displacement pumps, whose delivery volume can be adjusted to the respective demand. The function of a constant pump is based on the displacement principle, in which a fixed volume of hydraulic fluid is transported per revolution of the drive mechanism.

The displacement principle in hydraulics

The displacement principle is fundamental to the function of constant pumps. It means that the pump moves a defined amount of fluid from the suction side to the pressure side with each revolution. Since the delivery volume per revolution is fixed, the actual volume flow depends directly on the speed of the drive motor. A higher speed results in a greater volume flow, while a lower speed reduces the volume flow.

Components of a constant pump

Typical constant pumps consist of a housing, a drive mechanism, for example gears, vanes or pistons, and the corresponding inlet and outlet openings. The choice of materials and the precision of manufacture are crucial for the efficiency and service life of the pump. Seals and bearings also play an important role in minimizing leaks and ensuring smooth operation.

Types of constant pumps

Various types of constant pumps are used in hydraulics, differing in their design, performance characteristics, and preferred areas of application. The choice of the appropriate type depends on the specific requirements of the hydraulic system, such as the required pressure, volume flow, and type of application.

Gear pumps as constant pumps

Gear pumps are one of the most commonly used types of constant pumps. They are characterized by their robust design, simple construction, and high reliability. In gear pumps, the hydraulic fluid is transported by the rotation of two intermeshing gears. The fluid is conveyed from the suction side to the pressure side in the spaces between the teeth.

Features of gear pumps

Pressure range: Gear pumps can generate pressures of up to approximately 350 bar.
Volume flow: They offer a constant volume flow that depends on the speed and size of the gears.
Applications: Ideal for applications that require medium pressure and a constant volume flow, such as in machine tools or mobile machinery.
Advantages: Cost-effective, robust, easy maintenance.

Vane pumps as constant pumps

Vane pumps are another common type of constant pump. They consist of a rotor with radially movable vanes that rotate in an eccentrically arranged housing. The vanes are pressed against the inner wall of the housing by centrifugal force or springs, thus forming chambers that transport the hydraulic fluid.

Features of vane pumps

Pressure range: Similar to gear pumps, vane pumps can reach pressures of up to approximately 350 bar.
Flow rate: They deliver a low-pulsation flow rate, resulting in quieter operation.
Applications: Often used in applications where low noise levels and a consistent volume flow are important, such as in plastics processing or elevators.
Advantages: Low noise, good efficiency, compact design.

Axial piston pumps as constant pumps

Axial piston pumps are among the most powerful constant pumps and can generate very high pressures. In this design, several pistons are arranged parallel to the drive shaft. The pistons move axially in cylinders and are driven by a bevel gear or a crankshaft.

Features of axial piston pumps

Pressure range: Axial piston pumps can generate pressures of 500 bar and above.
Flow rate: They offer a high flow rate and high power density.
Applications: Ideal for demanding applications that require high pressures and large volume flows, such as in heavy industry, mining, or large construction machinery.
Advantages: High power density, high efficiency, long service life with proper maintenance.

Areas of application for constant pumps in the B2B sector

Constant pumps are indispensable in a wide range of B2B applications, where they ensure the base load in hydraulic systems. Their reliability and ability to deliver a constant volume flow make them a preferred choice in many industries.

Constant pumps in machine tools and production equipment

In machine tools such as lathes, milling machines, and presses, constant pumps are essential for supplying hydraulic drives. They ensure that the power and speed required for machining processes are continuously available. This is particularly important for precise movements and high repeatability in manufacturing.

Constant pumps in mobile work machines

Constant pumps are also widely used in mobile machinery such as excavators, wheel loaders, and cranes. Here, they supply the hydraulic cylinders and motors that are responsible for moving the working equipment and the chassis. The robust design of constant pumps is a major advantage in the often harsh operating environments.

Fixed displacement pumps in agriculture and forestry

In agriculture and forestry, constant pumps are used in tractors, harvesters, and forestry machines. They drive hydraulic attachments such as plows, seed drills, or wood splitters, thus ensuring efficient operation.

Fixed displacement pumps in energy generation and distribution

In the field of energy generation, for example in wind turbines or hydroelectric power plants, constant pumps are used in cooling systems or to control flaps and valves. Their reliability is crucial here for the safe and uninterrupted operation of the plants.

Advantages and disadvantages of a constant pump

The decision for or against the use of a constant pump depends on the specific requirements of the hydraulic application. It is important to carefully weigh the advantages and disadvantages in order to find the optimal solution.

Advantages of constant pumps

Cost efficiency: Constant pumps are generally less expensive to purchase than variable displacement pumps.
Simple design: Their simple design results in high robustness and lower maintenance requirements.
High reliability: Due to their uncomplicated mode of operation, constant pumps are very reliable and have a long service life.
Ease of maintenance: Their simple design makes them easy to replace in the event of defects, especially if they are externally flanged.
Constant volume flow: Ideal for applications that require a steady and uninterrupted flow of hydraulic fluid.

Disadvantages of constant pumps

Energy efficiency: Energy losses can occur during partial load operation or fluctuating demand, as the pump always delivers the maximum volume flow and excess energy must be dissipated via throttle valves.
Heat generation: Throttling the volume flow causes the hydraulic oil to heat up, which can affect the service life of the oil and components.
Noise: Throttling can generate noise that may be disruptive in certain environments.
Limited adaptability: Constant pumps cannot adapt their volume flow to changing requirements, which limits their use in systems with highly variable demand.

Maintenance and servicing of constant pumps

Regular maintenance and careful servicing are crucial for the longevity and efficient operation of constant pumps in hydraulic systems. Preventive measures can minimize downtime and reduce operating costs.

Regular inspections of the constant pump

It is important to regularly check constant pumps for external damage, leaks, and unusual noises. A visual inspection can often provide initial indications of potential problems. Look for discoloration of the housing, which could indicate overheating, or vibrations, which could indicate imbalance or bearing problems.

Monitoring the hydraulic oil

The quality of the hydraulic oil has a direct impact on the performance and service life of the pump. Regular oil sampling and analysis are essential to monitor contamination, water content, and the condition of the additives. Contaminated or aged oil can lead to increased wear and premature failure of the pump.

Filter replacement and system cleaning

Hydraulic filters must be changed regularly in accordance with the manufacturer’s specifications to keep the system free of particles. Clean hydraulic fluid protects the sensitive components of the pump from abrasion and corrosion. If necessary, the entire hydraulic system should be flushed and cleaned to remove deposits.

Bearing and seal inspection

The bearings and seals of a constant pump are wearing parts and should be checked at regular intervals and replaced if necessary. Defective seals can lead to leaks and pressure loss, while worn bearings can impair the efficiency of the pump and lead to increased noise.

Fixed pump vs. variable pump

The choice between a constant pump and a variable pump is a fundamental decision when designing a hydraulic system. Both pump types have their specific advantages and disadvantages and are suitable for different requirement profiles.

Feature	Fixed displacement pump	Variable pump
Delivery volume	Fixed delivery volume per revolution.	Variable delivery volume that can be adjusted to suit requirements.
Adaptability	No adjustment of the volume flow to requirements possible.	High adaptability to changing load conditions.
Energy	Lower energy efficiency at partial load, as excess fluid must be throttled.	High energy efficiency, as only the fluid that is actually needed is delivered.
Cost	Lower acquisition costs.	Higher acquisition costs.
Complexity	Simple design, low maintenance.	More complex design, higher maintenance costs.
Applications	Base load supply, simple systems with constant demand.	Systems with varying demand, energy-efficient solutions, precise control.

The decision to use a constant pump often makes sense when a constant volume flow at a relatively constant pressure is required and the acquisition costs play an important role. For systems with highly fluctuating demand or high energy efficiency requirements, variable pumps are the better choice, even if they require higher investments.

What is a fixed displacement pump in hydraulics?

A fixed displacement pump is a hydraulic pump that provides a continuous flow of hydraulic fluid in hydraulic systems, generating a constant pressure. It is primarily used to provide the base load in hydraulic systems and is known for its reliability and ease of maintenance.
How does a fixed displacement pump work?

Fixed displacement pumps are based on the positive displacement principle. With each revolution of the drive mechanism, they transport a fixed quantity of hydraulic fluid from the suction side to the pressure side. The actual volume flow depends directly on the speed of the drive motor.
What are the main types of fixed displacement pumps?

The most common types of fixed displacement pumps are gear pumps, vane pumps and axial piston pumps. Each type differs in its design, performance characteristics and preferred areas of application.
What are typical areas of application for fixed displacement pumps in the B2B sector?

Fixed displacement pumps are often used in machine tools, manufacturing plants, mobile machinery (such as excavators and cranes), agriculture and forestry as well as in power generation (e.g. cooling systems in wind turbines). cooling systems in wind turbines) where a base load supply with a constant volume flow is required.
What are the advantages of using a fixed displacement pump?

Advantages include cost efficiency in purchase, a simple and robust design, high reliability, low maintenance requirements and the ability to deliver a constant volume flow, which is ideal for applications with constant demand.
What are the disadvantages of fixed displacement pumps?

Disadvantages include lower energy efficiency at partial load operation (as excess fluid must be throttled), possible heat generation in the hydraulic oil due to throttling, potential noise generation and limited adaptability to widely fluctuating performance requirements.
How does a fixed displacement pump differ from a variable displacement pump?

A fixed displacement pump delivers a fixed volume flow per revolution, while a variable displacement pump can adjust its delivery volume to the respective demand. Fixed displacement pumps are simpler and cheaper, but variable displacement pumps are more energy efficient with variable demand.
What maintenance work is important for fixed displacement pumps?

Important maintenance work includes regular inspections for damage and leaks, monitoring the hydraulic oil quality, changing hydraulic filters in good time and checking and replacing bearings and seals if necessary.
What pressure range do gear pumps and vane pumps achieve?

Gear pumps and vane pumps can generate pressures of up to around 350 bar.
What pressure range do axial piston pumps achieve?

Axial piston pumps are among the most powerful fixed displacement pumps and can generate pressures of 500 bar and above.