When discussing industrial valves, technical terms come up quickly. Industry professionals may know them, but they may be less obvious to someone buying a valve or planning a new application.
What does DN50 mean? How about PN16? What are pressure drop and Kv value? And what is the difference between erosion and corrosion?
We’ve put together a glossary of common valve terms and explained what they mean in practice.
Basic Valve Terms
Ball Valve
A ball valve controls the flow of a medium using a ball with a hole through its centre. The ball typically rotates 90 degrees. When the bore is aligned with the pipeline, the valve is open. When the ball is turned perpendicular to the flow direction, the valve is closed.
Ball valves are primarily used for opening and shutting off flow. Their advantages include a simple design and quick operation.
In Maper ball valves, wearing parts such as seals and the ball can be replaced. This requires removing the valve from the pipeline.
Bottom Valve
A bottom valve is installed at the bottom of a tank or vessel. Its purpose is to allow the contents to be discharged as efficiently and completely as possible.
Maper’s bottom valve is based on a ball valve design. The ball opens or closes the flow passage at the bottom of the tank.
What distinguishes a bottom valve is therefore not an entirely different operating principle, but its design and intended application: it is specifically designed for installation at the bottom of a tank.
Read more about bottom valves.
Shut-off Valve
A shut-off valve is designed primarily to start or stop the flow of a medium.
An actuator can also be used to adjust the valve’s flow opening.
Control Valve
A control valve regulates flow within a process, for example by adjusting the valve opening.
This is the main difference between a control valve and a shut-off valve. A shut-off valve is primarily intended to stop flow, while a control valve is designed to regulate it during operation.
Not every valve is suitable for both purposes. If a valve needs to operate continuously in a partially open position, the valve type must be selected accordingly.
Valve Actuator
An actuator opens and closes a valve mechanically, without requiring manual operation.
Ball valves typically use quarter-turn pneumatic actuators. These can be double-acting, where compressed air both opens and closes the valve, or single-acting (spring-return), where a spring moves the valve to a predetermined position when air pressure is lost.
Read more about valve actuators.
Manually Operated Valve
Not every valve needs to be automated.
A manually operated valve can be a practical choice when it is operated infrequently and is easily accessible.
If the valve needs frequent operation, remote control is required, or several valves need to be integrated into an automation system, an actuator may be a more suitable option.
Technical Valve Terms
PN Rating (Nominal Pressure)
PN stands for nominal pressure. For example, PN16 is a designation indicating a valve’s pressure rating.
However, PN16 should not automatically be interpreted as meaning that the valve can withstand an operating pressure of 16 bar under all conditions.
The actual allowable operating pressure depends on factors such as temperature, material and the applicable standard. The PN designation alone does not tell the whole story.
Read our article about valve performance under demanding operating conditions.
DN Size (Nominal Diameter)
DN refers to the nominal size of a valve. Designations such as DN25, DN50 and DN100 indicate the valve’s nominal size.
However, DN does not represent the exact internal diameter of every component in millimetres. For example, DN50 does not automatically mean that the valve’s flow opening is exactly 50 mm.
This distinction matters particularly when sizing a valve. The pipeline’s DN size is a useful starting point, but the required flow rate, differential pressure, flow opening and other operating conditions must also be considered.
Nominal Pressure vs. Operating Pressure
These two terms are easily confused.
Nominal pressure, expressed as PN, is a standardised designation related to the valve’s pressure rating.
Operating pressure, on the other hand, refers to the actual pressure at which the valve operates in its intended application.
The terms are therefore not interchangeable.
Pressure Drop
Pressure drop refers to the reduction in pressure that occurs as a medium flows through a valve.
Every valve creates some resistance to flow. The more the valve’s internal design restricts the flow, the greater the pressure drop may be.
This is one reason why both valve size and internal construction matter. Pressure drop is particularly important in processes where a specific flow rate must be maintained.
Tightness and Leakage Class
Valve tightness describes how effectively a valve prevents flow when it is supposed to be closed.
A fully closed valve should not allow more leakage than is permitted for that valve under the applicable testing method.
Tightness can be tested according to standardised procedures, and different leakage classes specify different permissible leakage rates.
Tightness is not the same as pressure resistance. A valve may be designed to withstand a certain pressure, but it must also provide adequate shut-off tightness.
Flow Opening
The flow opening is the passage through which the medium travels inside a valve.
In a ball valve, this opening runs through the ball. Its size directly affects how much flow can pass through the valve and how much resistance the valve creates.
In a full-bore ball valve, the bore is close to the nominal size. This reduces flow resistance compared with a design where the flow passage is significantly restricted.
Kv Value (Flow Coefficient)
The Kv value describes a valve’s flow capacity. It is particularly important when sizing control valves.
In simple terms, Kv indicates how much liquid can flow through a valve under specified conditions.
The Kv value is not simply another way of expressing valve size. It describes the valve’s flow characteristics and can be used to compare the flow capacities of different valves and assess their suitability for a particular application.
Cavitation
Cavitation occurs when the pressure of a flowing liquid drops low enough for vapour bubbles to form. When the pressure rises again, these bubbles collapse.
This is more than a theoretical phenomenon. Collapsing vapour bubbles can create intense localised impacts, noise and vibration, potentially damaging internal valve surfaces.
The risk of cavitation is closely related to differential pressure and flow conditions. Proper sizing, valve design and material selection help manage this risk.
Erosion
Erosion is the gradual wearing away of material caused by the mechanical action of a flowing medium.
If the medium flows at high velocity or contains solid particles, it can wear down the valve’s internal surfaces.
Erosion can shorten a valve’s service life. Compatibility between the valve’s materials, construction and operating conditions is particularly important in demanding industrial processes.
Corrosion
Corrosion is the chemical or electrochemical deterioration of a material caused by its environment.
For a valve, the key question is: what medium flows through it, and how does that medium interact with the valve’s materials?
Not all materials are suitable for every process medium. The valve body material and seals must therefore be selected according to the application.
Maper uses materials such as acid-resistant stainless steel in its valves, with material selection based on the requirements of the intended application.
Traceability
Traceability means that the origin and relevant information of the materials and components used in valve manufacturing can be tracked.
In industrial applications, this is important when documented information about material properties, production batches or quality assurance needs to be available later.
Traceability is part of quality management, particularly in applications with strict material requirements.
Valve Components and Construction
Valve Body
The valve body forms the main structure of the valve and houses the key internal components that control flow.
It must withstand the pressure, temperature and process medium involved in the application. The body material therefore plays a significant role in determining the conditions under which the valve can operate.
Closure Element
The closure element is the part of a valve that opens or shuts off the flow.
Its design depends on the valve type. In a ball valve, the ball acts as the closure element. Other valve types may use a disc, plug or another type of closing component.
Valve Seat
The valve seat is the component or surface against which the closure element closes. It provides an essential sealing surface when the valve is shut.
However, the term does not refer to exactly the same structure in every valve type. In ball valves, the seat design also varies depending on the valve’s construction.
Seal
A seal prevents the process medium from leaking out of the valve or passing between components where leakage must be prevented.
A valve may contain several different types of seals. Their materials and functions depend on factors such as the process medium, temperature and operating pressure.
Maper valves are designed with replaceable seals, allowing worn seals to be replaced instead of replacing the entire valve. This can significantly extend the valve’s service life.
Stem Seal (Shaft Seal)
The stem or shaft seal prevents the process medium from escaping through the gap between the valve body and the stem or shaft.
This sealing point is particularly important in valves that are operated frequently or handle substances that may be harmful to people or the environment.
Ball
The ball is the main closure element in a ball valve. It contains a bore through which the medium flows.
When the ball is rotated so that the bore is aligned with the pipeline, the valve is open. When the ball is rotated perpendicular to the pipeline, the flow is shut off.
The operating principle is relatively simple, but the dimensions and materials of the ball, seals and valve body have a major impact on valve performance and service life.
Flanged and Threaded Connections
A flanged connection joins the valve to the pipeline using flanges. A threaded connection uses mating threads to create the joint.
The connection type affects which valve is compatible with an existing pipeline, how it can be installed and how easily it can be removed when necessary.
When selecting a connection type, factors such as pipeline construction, pressure and temperature conditions, and available installation space must be considered.
Why Does Valve Terminology Matter?
When selecting a valve, a single technical term rarely tells the whole story.
DN indicates nominal size. PN refers to the pressure rating. The flow opening and pressure drop tell us something about how the medium moves through the valve. Materials and seals, in turn, determine how well the valve can withstand the conditions of a particular application.
A valve should therefore not be selected based on one specification alone. What matters is how its different characteristics work together in the intended application.
If you have questions about valve terminology or need help selecting a suitable valve, Maper’s experts are happy to help. Get in touch!
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13.10.2026
