Valves in building services applications: types, functions and selection

What is a valve?

In plant engineering and, in particular, in piping technology, valves are defined as components that influence the flow of fluids by opening, closing or partially obstructing the passage of the fluid flow or by diverting or mixing the fluid flow. 

What are the different types of valves?

In general, valves are distinguished by their design features into the basic designs of gate valve, globe valve, ball valve, butterfly valve and diaphragm valve. 

Gate valve

A gate valve is a valve whose obturator moves in a straight line and, in the seating area, at right angles to the direction of flow.

Globe valve

A globe valve is a valve whose obturator moves in a straight line and, in the seating area, in the direction of flow.

Ball valve

A ball or plug valve is a valve whose obturator rotates about an axis at right angles to the flow direction; in the open position, the fluid flow passes through it.

Butterfly valve

A butterfly valve is a valve whose obturator rotates about an axis at right angles to the flow direction; in the open position, the fluid flow passes around it.

Diaphragm valve

A diaphragm valve changes the flow passage as a result of the deformation of its flexible obturator.

Check valve

A check valve opens automatically when flow passes through the valve in a specified direction; the valve automatically prevents flow in the opposite direction.

Strainer

A strainer filters undesired solids from the fluid handled.

Valves are further categorised by the functions they perform (e.g. shut-off and safety valves, control valves, mixing or distribution valves) and by the applications they are used for (e.g. power station, heating, gas or foodstuff valves). Valves can also be distinguished by their type of actuation: manually operated valves, electrically, pneumatically or hydraulically actuated valves and process fluid controlled valves (e.g. flow limiters, differential pressure regulators, safety valves, etc).

Key characteristics

Being aware of the key characteristics helps in using valves successfully and safely. Here is a brief overview: 

Nominal size

The nominal size (code DN from the French "diamètre nominal") in building services refers to the inside diameter of a pipe. It is composed of the letters DN and a number linked directly with the physical size of the connections (in mm). Example: DN 32

Pressure

Pressure (code p) is defined as the force exerted per unit area.

Nominal pressure

The nominal pressure (code PN from the French "pression nominale") is a reference value. It indicates the design pressure in bar at room temperature (20 °C). It is composed of the letters PN and the highest permissible pressure. Example: PN 10

Volume flow rate

The volume flow rate (code Q) refers to the quantity of liquid or gas that flows through a pipe in a specified time unit.

Resistance coefficient

The resistance coefficient (code ζ, zeta) indicates the resistance of valves or other fittings in pipes acting in the direction opposite to the flow direction. The larger ζ, the higher the pressure loss. Good to know: The ζ value applies to the valve in fully open condition.

Pigging

Pigging is the cleaning of a pipe with a pig or another cleaning device travelling through the pipe.

Flow coefficient

The Kv value and Kvs value are also known as the flow factor or flow coefficient. They are used for comparing, selecting and dimensioning valves. The value is specified in m³/h.
The Kv value corresponds to the water flow through a valve at:

• Differential pressure of 1 bar
• Temperature between 5 °C and 30 °C.

There is an associated Kv value for every degree of opening (actuator stroke, actuator angle).

Plotting these Kv values over the stroke provides the characteristic curve of the valve. The Kv value is calculated as follows, where r [kg/dm³] is the density factor of the fluid, Q [m³/h] is the volume flow rate and [bar] is the differential pressure.

Kv = Q ∙ √ r/∆p 

→ for water with r = 1, the following results:

Kv = Q / √∆p 

Kvs value → Flow through a fully opened valve (100 % degree of opening)

→ A valve has only got one Kvs value but several Kv values.

In 10 steps to the right valve at the example of a data centre

The best way of finding a suitable valve that is also the most efficient choice is by employing a systematic approach. Follow these step-by-step instructions to find a valve meeting your requirements. You will automatically eliminate the valves that are unsuitable for your project. This is illustrated at the example of a cooling circuit for supplying a heat exchanger in a data centre. The volume flow rate in the example is 200 m3/h, which leads to the recommended nominal size of DN 150.

1. What function is to be fulfilled?

We require a valve for the shut-off task (OPEN/CLOSED). Examples of other functions are measuring, throttling or controlling.

Suitable valves:

Gate valve / globe valve / ball valve / butterfly valve / diaphragm valve

2. What is the fluid that will flow through our valve?

What chemical properties has the fluid got? Is the fluid corrosive and/or abrasive? Does the fluid contain solids or could it also be explosive? It is important that the valve material is resistant to the fluid handled. The fluid in our example is cooling water used in a closed circuit.
Suitable valves:

Gate valve / globe valve / ball valve / butterfly valve / diaphragm valve

3. What are the temperature requirements?

The fluid temperature and ambient temperature also play a major part in selecting the right valve. Examples of some key temperature limits are -50 °C / -30 °C / -10 °C / +60 °C / +120 °C / +350 °C. These are values at which, usually, a different material has to be chosen. In our example, the fluid temperature is +6 °C and the ambient temperature is +20 °C. We are in an indoor environment.
Suitable valves:

Gate valve / globe valve / ball valve / butterfly valve / diaphragm valve

4. What are the pressure requirements?

How much pressure does the valve need to seal to atmosphere? What is the pressure or differential pressure to be decreased by our valve between the inlet and outlet?
In our example, the system pressure is approx. 8 bar. The planned nominal pressure class of the piping is PN 16.
Suitable valves:

Gate valve / globe valve / ball valve / butterfly valve / diaphragm valve

5. What standards, regulations and acceptance criteria need to be met?

In our example, the safety requirements of Annex I of the European Pressure Equipment Directive 2014/68/EU (PED) for fluids in Groups 1 and 2 apply. In addition, the valve is to be maintenance-free.
Suitable valves:

Gate valve / globe valve / ball valve / butterfly valve / diaphragm valve

6. Resistance coefficient ζ, zeta

Since we would like our system to be as efficient as possible, we are looking for a valve with an extreme (very low) resistance coefficient. This is where one of the valve types is eliminated in our example.
Suitable valves:

Gate valve / globe valve/ ball valve / butterfly valve / diaphragm valve

7. How much space is available for the valve?
For us, space is very limited. The more compact the valve installation, the better. In the case of a 1:1 replacement for existing valves, identical design is important. In our example, this means two further valves are no longer in the race.
Suitable valves:

Gate valve / globe valve/ ball valve / butterfly valve / diaphragm valve

8. What is the free passage required?

This is linked with pigging and with whether solids have to pass through the valve. This is not the case in our example.
Suitable valves:

Gate valve / globe valve/ ball valve / butterfly valve / diaphragm valve

9. Are there any hygienic requirements to be met by the valve?

This is particularly important for drinking water installations and in the foodstuffs industry. Our example has not got any such requirements.
Suitable valves:

Gate valve / globe valve/ ball valve / butterfly valve / diaphragm valve

10. The price/performance ratio
Projects are governed by budget planning and the investors' desired security. What counts is: as cost-efficient as possible while meeting the requirements. Availability and interchangeability are further key criteria. A ball valve in DN 32 or DN 50 would be cheaper than a butterfly valve that has to be flanged into the piping. However, this option is not suitable for the flow rate of 200 m³/h (DN 150) in our cooling circuit example. We require a valve meeting DN 150. This eliminates the last option in the selection.

Suitable valves:

Gate valve / globe valve / ball valve / butterfly valve / diaphragm valve

CONCLUSION:

The systematic approach has led us to the right valve for our project: a butterfly valve.

Looking for the right valve? KSB is here to help

Every year, KSB manufactures almost a million industrial valves. Industrial valves from KSB are used in power stations, buildings, on ships and in process and water engineering systems. Alongside globe valves, gate valves, butterfly valves, ball valves, diaphragm valves and control valves, the industrial valve product range also includes actuators and positioners. Contact us – We’ll be pleased to assist you.