16 Nov

The directional-control valve is one of the principle components of any hydraulic systems. In this post we look at the different types and how they operate:


Discrete valve: They are sometimes described as ‘bang-bang’ as they make a noise when they move from being fully open to being fully closed. This happens almost instantly, and is what controls the rapid acceleration and deceleration of fluid. The valves will move through several positions such as retract, extend and neutral to move the fluid.  Under particular conditions, the valve will create a situation known as ‘fluid hammer’. This is when there is a sound like a hammer being used inside the hydraulic system.


Digital valve: Another valve that is more basic than the directional-control valve is the digital valve. These valves operate in the mode of either being on or off. Whereas the discrete valve will achieve their positions through the use of a spool, the digital valve will make use of a poppet, plunger or a ball to create a seal with an internal seal. The seal will ensure that there is no leakage between ports.


Check valve: A check valve is a digital directional-control valve that will allow for fluid to flow in only one direction. Fluid will be stopped from flowing in the opposite direction. They usually work by having a spring-loaded check valve which will not open unless the pressure from downstream becomes more than the spring force pressure.


Spool valve: The way the spool type valve works is through a sliding action. A spool will slide between passages opening and/or closing different flow paths as the fluid is routed from or to the work ports. Spools are adaptable to a variety of spool shifting schemes, which makes it possible for them to be used in a wide range of applications.


Metering or throttling is often required by mobile applications in order for the operator to control a load slowly. It’s in these situations that the spool may have V notches so that just a small amount of fluid can flow for a smoother and slower movement. This notch or bevel is often used in industrial equipment and can be known as a soft-shifting feature.

Ports and positions of valves in hydraulic systems

When it comes to selecting a direction control valve, the amount of ports and directional states of the valve are a key decision point. Valve ports are what make it possible for fluid to flow between components. The number of positions available refers to how many distinct flow paths the valve offers.


If we take a 4 port, 3 position spool valve as an example, the ports will operate like this; One port will receive fluid from the pump that is under pressure, and another will route that fluid back to the reservoir. The final two ports will be referred to as work ports and will send fluid back and forth to the actuator.


The advantage of using spool-type valves is that they can be shifted to 2, 3 or even more positions for routing purposes. A single valve can extend, retract or be in neutral position. It’s also possible for digital valves to provide the same functions.

When it comes to naming conventions, the USA refer to the number of ports. For example, they will say 2-way, 3-way, 4-way etc. Although international standards use the word ports, they would use the term 2 way-2 position which would be known as a 2-port, 2-position elsewhere. It may be abbreviated with 2/2. 


Directional valve operators

This is the name of components such as spools, plungers and poppets. They each will apply force that shifts the elements of a valve to effect flow direction. For the best fluid system power performance, features such as timing, sequence and frequency are key factors and need to be considered and adjusted when possible.


These operators will be mechanical, electrical, electronic or pilot or may use a combination of these.


The world of hydraulic system valves is far more complex than it may initially appear, but by taking time to get to know the ins and outs of the ports and the flow, it’s possible to perfect the performance of your equipment for the ultimate results.


If you’re interested in enjoying the ease and convenience of a hydraulic power pack, contact us today.