Hydraulic Accumulators, Filters , Valves & Pumps
Hydraulic Valves
What is a directional control hydraulic valve, and for which application do you need it?
Directional control valves regulate the start, stop, and change in the flow direction of a pressure medium, such as hydraulic oil, which is why they are also called switching valves. These valves come in various types, including spool, poppet, and rotary slide valves. However, rotary slide valves are less common today due to their limited operating pressure (up to 70 bar). Directional control valves without proportional control are typically referred to as switching valves.
Directional control valves control the start, stop and change in the flow direction of a pressure medium
The function of a directional control valve is defined by the number of working ports (excluding control ports) and the number of spool positions it has. Typically, a directional control valve includes a minimum of two spool (switching) positions and two working ports. The most widely used type is the 4/3-way valve, which indicates the valve has four working ports and three spool positions, in accordance with DIN ISO 1219 standards.
Directional poppet valve
What is a directional control poppet valve and for which hydraulic application do you need one?
Directional poppet valves can handle operating pressures up to 1,000 bar. These valves are a type of directional control valve designed to fit into housing bores with threaded connections, earning them the name hydraulic cartridge valves. They use movable seating elements like balls, poppets, or plates.
The design allows for a tighter seal as operating pressure increases. However, cartridge valves have limited maximum flow compared to spool valves. To accommodate larger flows, larger cartridges would be needed, but the threaded connection may not support these larger sizes.
Directional spool valve
What is a directional spool valve and for which hydraulic applications do you need one?
Directional spool valves consist of a moving spool inside the valve housing. When the control spool is actuated, it connects or separates the channels within the housing to regulate fluid flow. These valves are known for their high switching power, low actuation force, and versatility in control functions.
They can be either direct-operated, using solenoids, levers, rollers, or hydraulics/pneumatics, or pilot-operated, depending on the force required to move the spool. The type of operation is determined by the flow rate and size of the valve. At higher system pressures, particularly above 350 bar, leakage losses around the spool and housing become important factors to consider. These losses are influenced by the gap size, hydraulic fluid viscosity, and system pressure.
Check valve or non-return valve
What is a check valve or non-return valve and for which hydraulic applications do you need one?
A check valve, also known as a non-return valve, is the simplest directional control valve in hydraulic systems. It allows fluid to flow in one direction while preventing reverse flow. These valves are commonly used as prefill, bypass, or pre-tensioning valves, and to protect components from pressure surges.
Typically spring-loaded, check valves use a ball or plate to seal flow in one direction. Designed with seats, they effectively prevent leakage. Variations include line rupture valves, which prevent accidents by closing when flow spikes from a ruptured line, and pilot-operated check valves, which allow bi-directional flow when activated by external pressure. Shuttle valves, another special type, enable free flow at the highest pressure.

What is a pressure control valve? For which hydraulic applications do you need it?
Each pressure control valve operates by switching or regulating at a specific, preset pressure level. This switching pressure is usually adjustable directly on the valve. The valve’s position (open or closed) changes either gradually through control or abruptly through switching. Pressure shut-off valves and pressure sequence valves have a fixed throttle, while relief and reducing valves are equipped with a variable throttle mechanism.
Pressure valves are hydraulic valves that gradually (control) or suddenly (switch) change in position.
The most widely used pressure control valves are pressure relief valves and pressure reducing valves. Pressure relief valves manage system pressure by diverting part or all of the flow back to the tank. Pressure reducing valves, on the other hand, lower the pressure supplied to a specific sub-system within a hydraulic system. Sequence valves control the flow to a secondary circuit, while unloading valves direct the flow to the tank once a pre-set system pressure is reached.
Pressure valves, relief function
Pressure relief valve for hydraulic system
Pressure control valves come in two types: pressure relief valves and pressure reducing valves. Pressure relief valves generally have higher flow capacities because they need to handle and direct the entire flow to the tank. In contrast, pressure reducing valves manage flow at a lower capacity.
Pressure valves, reducing function
What is a pressure reducing valve and for which hydraulic applications do you need one?
Unlike pressure relief valves, which regulate the input pressure from the pump into the hydraulic system, pressure reducing valves control the output pressure delivered to a subsystem, such as an actuator.
These valves adjust the input pressure (primary pressure) or maintain a specific output pressure (secondary pressure) that is lower than the fluctuating pressure in the main hydraulic circuit. This allows for a reduced pressure in one part of the circuit compared to the system pressure.
Note: Pressure control valves are typically in a normally open position.
Pressure valves, fixed throttle
What are sequence and unloading valves, and for which hydraulic application do you need one?
Pressure control valves can change position—either opening or closing—gradually through control or abruptly through switching. Valves designed for switching tasks are known as pressure valves with fixed throttles, such as sequence valves and unloading valves.
Sequence valves manage the flow to a secondary circuit, allowing it only when the primary circuit reaches a predetermined pressure. Unloading valves, on the other hand, are remotely controlled pressure shut-off valves that redirect flow to the tank once a specified pressure is achieved in a particular part of the hydraulic circuit.

What is a proportional hydraulic valve and for which hydraulic applications do you need one?
Proportional hydraulic valves can regulate the flow opening in a proportional manner, unlike standard hydraulic valves that adjust flow gradually. The most basic form of a proportional hydraulic valve is a variable throttle operated by a manual lever. For applications that demand precise flow control, hydraulic valves can be outfitted with advanced electronic controls, incorporating integrated measurement and feedback systems for enhanced accuracy.
Proportional control valves are hydraulic valves that give you very accurate control of flow and pressure.
Proportional directional control valves
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Proportional pressure control valves
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Proportional flow control valves
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What is a flow control hydraulic valve and for which hydraulic applications do you need one?
Flow control valves regulate the flow by adjusting the size of the opening at the throttling point, which in turn controls the speed of actuators. The most basic form of a flow control valve features a needle or longitudinal slot placed within the pipeline, connected to a screw that alters the opening at the throttle point. Known as throttle valves, these devices have a fixed throttle, allowing them to modify the flow rate depending on the load conditions.
Use flow control valves to influence the speed of movement of hydraulic actuators in a hydraulic system.
The flow rate through a throttle valve at any given setting is determined by the pressure difference (Δp) before and after the throttling point. If the pressure drop across the throttling point stays constant, the flow of oil through the valve also remains consistent, enabling operation at steady speeds regardless of changes in load. Pressure-compensated flow control valves are designed to maintain a consistent pressure drop across the throttling point, ensuring uniform flow.
Flow controls, pressure compensated valve
What is a pressure compensated flow control hydraulic valve and for which hydraulic applications do you need one?
A pressure-compensated flow control valve ensures constant flow at any pressure. In two-way valves (series valves), the pressure reducing valve and throttle are in series, while in three-way valves, they’re in parallel. The key difference is that excess oil in three-way valves is diverted through the valve itself, unlike two-way valves where it’s routed through the pump’s safety valve. Three-way valves are more efficient, as system pressure only meets the load requirement, whereas two-way valves allow the pump to keep running until the preset safety pressure is reached.
Flow controls, throttle valve
What is a throttle valve and for which hydraulic system application do you need such a flow control?
Throttle valves come in piston and needle designs, as well as turn plugs with axial or radial grooves. Grooves offer more precise control compared to pistons but can be less consistent. Needle throttles require significant force to adjust slightly.
The flow through a throttle is determined by the pressure difference (Δp), so in systems with varying pressures, the flow rate will fluctuate.
Non-adjustable throttles are used to manage excessive pressure surges and are also common in control systems
