Butterfly Valve or Ball Valve? Selection for Large Nominal Sizes
The question of the plastic butterfly valve vs. ball valve arises in almost every piping project – and as the nominal size increases, the answer becomes clearer. Whereas the ball valve is the tighter, more robust and more easily automated shut-off valve in the small and medium nominal size range, weight, face-to-face length, pressure loss and above all cost shift clearly in favour of the butterfly valve as the diameter grows. In this guide we compare both designs systematically, show the transition nominal size as a rule of thumb, explain the sizing criteria for process and industrial applications in thermoplastic material and identify the typical mistakes in valve selection for large lines.
Design and operating principle compared
The ball valve and the butterfly valve are both quarter-turn valves with 90° actuation, but they differ fundamentally in their shut-off element and therefore in flow guidance, face-to-face length and operating behaviour.
The ball valve
In the ball valve, a bored ball shuts off the flow. In the open position the bore aligns with the pipeline and – with a full bore – provides an almost unrestricted, straight flow path. The ball seals against two seat rings, usually made of PTFE or a suitable elastomer. The ball valve is thus an exceptionally tight shut-off valve with low pressure loss when open, bubble-tight shut-off and good suitability for switching duty. As the nominal size grows, however, ball mass, operating torque, face-to-face length and material use increase disproportionately.
The butterfly valve
The butterfly valve (throttle valve) has a disc-shaped flap that pivots on a shaft in the centre of the body. To open, the disc turns through 90° and aligns parallel to the flow. Sealing is usually provided by an elastomeric liner (e.g. EPDM or FPM/FKM), against which the disc edge rests. The butterfly valve has an extremely short face-to-face length (wafer or lug design), is light, saves material and, as the nominal size increases, is considerably more cost-effective than the ball valve. The disadvantages are the disc body remaining in the line (slight restriction, residual pressure loss even when open) and – depending on the design – a somewhat higher breakaway torque.
Plastic butterfly valve vs. ball valve: the transition nominal size
The decisive point in choosing between a plastic butterfly valve vs. ball valve is the nominal size. As a rough rule of thumb in thermoplastic pipework construction:
- Up to about DN 50 (2″): The ball valve is usually the first choice – compact, cost-effective, tight and easy to handle. Butterfly valves are available in this range but are rarely economically worthwhile.
- Around DN 65 to DN 100: Transition range. Here, detailed requirements such as tightness, control demand, installation space, automation and cost determine the design.
- From about DN 100 to DN 125 upwards: The butterfly valve is clearly preferred. Weight, face-to-face length, operating torque and ball valve costs rise so sharply that the butterfly valve is almost always the more economical and more practical solution at large nominal sizes.
These limits are guide values and not rigid standard specifications – the specific decision depends on the operating profile. They do, however, explain why large water, wastewater, swimming pool and process lines in plastic almost exclusively use butterfly valves, while ball valves dominate the smaller nominal size range and applications with the highest tightness requirements.
Direct comparison: butterfly valve and ball valve
| Criterion | Ball valve | Butterfly valve |
|---|---|---|
| Shut-off element | bored ball | pivoting disc |
| Face-to-face length | longer, increasing with nominal size | very short (wafer/lug) |
| Weight at large DN | high to very high | low |
| Pressure loss when open | very low (full bore) | low, but disc remains in the flow |
| Tightness | very high, bubble-tight shut-off | high, depending on liner design |
| Control / throttling | only conditionally suitable | well suited (throttle valve) |
| Operating torque | rises sharply with nominal size | moderate |
| Cost at large DN | high | significantly cheaper |
| Typical application range | small to medium DN, switching duty, highest tightness | medium to large DN, shut-off and throttling |
Selection criteria for large nominal sizes
Besides the nominal size alone, several operating parameters determine which valve is the right one in a given case. For a sound decision, the following points should be checked systematically.
1. Function: shutting off or controlling
Where the aim is purely on/off shut-off, both designs are suitable. If the volume flow has to be throttled or roughly controlled, the butterfly valve plays to its strength: its characteristic curve allows usable throttling over a wide opening range. The ball valve is designed as a pure shut-off valve and is only conditionally suitable for continuous throttling in a partly open position, because the seat rings and ball wear more heavily in intermediate positions.
2. Tightness and medium
Where a bubble-tight, long-term reliable shut-off is required – for example with hazardous or valuable media – the ball valve with its enclosing seat rings offers advantages. For water, wastewater, swimming pool water and many process media in large lines, the butterfly valve with a suitable liner also achieves tightness sufficient for the application. The chemical resistance of the liner or seat rings to the medium must be checked in both cases.
3. Pressure loss and flow
When open, the full-bore ball valve has the lowest pressure loss because the bore is unobstructed. In the butterfly valve, the disc remains in the flow path and causes a permanent, albeit usually low, residual pressure loss. With very long lines or energy-sensitive applications this difference can become relevant and should be assessed via the Kv value of the respective valve.
4. Weight, installation space and structural load
At large nominal sizes, weight is a tangible argument: a ball valve becomes heavy, needs more installation space in the line and places a greater load on the pipe support. The short, light butterfly valve considerably simplifies installation, support and later maintenance.
5. Automation and operating torque
The required torque of the ball valve rises sharply with the nominal size, which calls for larger and more expensive actuators. Butterfly valves usually require smaller actuators at the same nominal size and can therefore be automated more economically, whether pneumatically or electrically – an important factor in large, automated process plants.
6. Pressure rating, temperature and material
Both valves are available in the common plastics such as PVC-U, PVC-C, PP and PVDF. The permissible pressure rating (PN) of thermoplastics falls as the temperature rises – the material- and type-specific pressure-temperature relationship from the manufacturer’s data sheet is always decisive. The body material is to be selected according to chemical resistance to the medium and the temperature range, and the sealing materials (seat ring or liner) separately from that.
Materials and standards for plastic valves
For material selection, the same principles apply to the butterfly valve and ball valve as to other plastic valves. The body or ball material determines chemical and temperature resistance, and the sealing material complements it:
- PVC-U: standard for water and wastewater technology, good resistance to many acids, alkalis and salt solutions, limited temperature use (as a rule up to around 60 °C).
- PVC-C: similar chemistry to PVC-U, but higher temperature resistance.
- PP (polypropylene): good resistance to alkalis and many organic media, higher temperature range.
- PVDF: high chemical resistance to aggressive acids, halogens and solvents, for demanding chemical and ultra-pure media applications.
Depending on the medium, EPDM (water, dilute acids and alkalis), FPM/FKM (oils, many aggressive media) or PTFE (almost universal resistance, especially in ball valves) are used as seat or liner materials. The resistance must always be checked for the combination of medium, concentration and temperature – a pairing that is resistant at room temperature can fail at elevated temperature.
For the connecting dimensions, plastic butterfly valves and ball valves follow the established flange standards. Flange connections usually conform to the bolt patterns per DIN EN 1092 and to the pressure rating classification per the PN system (e.g. PN 6, PN 10, PN 16). The actually permissible pressure rating of the respective plastic valve results from the manufacturer’s pressure-temperature diagram and is the design pressure – not merely the flange rating.
Typical mistakes in selection for large lines
- Ball valve despite large nominal size: out of habit, a ball valve is chosen even at DN 150 or DN 200 – with unnecessarily high weight, installation space, actuation effort and cost. From the transition range onwards it almost always pays to examine the butterfly valve.
- Butterfly valve overtaxed for fine control: for precise metering in the small opening range, the butterfly valve is only conditionally suitable; here, control valves with a suitable characteristic curve are the better choice.
- Sealing material not matched to the medium: the liner or seat ring is not checked against the medium and temperature – the result is leakage and premature failure of the seal.
- Pressure-temperature limits ignored: for plastic valves the nominal pressure rating does not apply across the entire temperature range; the permissible pressure falls as the temperature rises.
- Actuator undersized: especially with the ball valve, the torque that rises sharply with the nominal size is underestimated, so that the actuator does not switch the valve reliably.
- Installation of the wafer valve planned incorrectly: wafer butterfly valves require the correct flange spacing and must not allow the disc to strike the pipe inner wall or the mating flange when opening; this must be taken into account in the installation planning.
Areas of application at a glance
In practice, both valves complement each other along the nominal size. Ball valves dominate small and medium lines, manifolds, dosing and sampling points as well as applications with the highest tightness requirements and frequent switching duty. Butterfly valves are the standard valve for large nominal sizes in water and wastewater technology, swimming pool and pool technology, chemical process engineering and everywhere that shutting off or throttling large volume flows at low weight and with economical automation is required.
Conclusion
Whether butterfly valve or ball valve – with plastic valves, the nominal size sets the direction. In the small and medium range, the ball valve impresses with full bore, high tightness and simple switching duty. As the diameter increases, the advantages reverse: from the transition range around DN 65 to DN 100, and all the more above it, the butterfly valve is lighter, shorter, cheaper and easier to automate. Anyone who systematically checks function (shutting off or controlling), tightness, pressure loss, weight, actuator torque as well as pressure-temperature behaviour and material resistance will make the right choice for every nominal size – and avoid the classic mistakes in sizing large plastic pipeline valves.
Frequently asked questions
From which nominal size is a butterfly valve better than a ball valve?
As a rule of thumb in plastic pipework construction: up to about DN 50 the ball valve is usually the first choice, between roughly DN 65 and DN 100 there is a transition range, and from about DN 100 to DN 125 upwards the butterfly valve is clearly preferred. The reason is the weight, face-to-face length, operating torque and cost of the ball valve, all of which rise sharply with the nominal size. The specific limit depends on the operating profile and is a guide value, not a rigid standard specification.
What is the difference between a butterfly valve and a ball valve?
In the ball valve, a bored ball shuts off the flow and, in the open position, provides a full, straight bore. In the butterfly valve, a disc-shaped flap pivots on a shaft through 90°; the disc remains in the flow path even when open. The ball valve is very tight and has low pressure loss, but has a longer and heavier build; the butterfly valve has a very short build, is light, cost-effective at large nominal sizes and well suited to throttling.
Can a butterfly valve be used for control or throttling?
Yes, the butterfly valve (throttle valve) is well suited to throttling and rough control of volume flows over a wide opening range – this is an advantage over the ball valve, which is designed as a pure shut-off valve. For precise metering in the small opening range, however, the butterfly valve is only conditionally suitable; here, special control valves with a suitable characteristic curve are the better choice.
Which plastic is suitable for a butterfly valve and a ball valve?
Both valves are available in the common thermoplastics PVC-U, PVC-C, PP and PVDF. PVC-U is standard for water and wastewater, PVC-C and PP offer higher temperature resistance, and PVDF is the first choice for aggressive acids, halogens and solvents. The body material is chosen according to chemical resistance and temperature range, and the sealing material (liner or seat ring, e.g. EPDM, FPM/FKM or PTFE) separately from that, based on the medium.
Why is a butterfly valve almost always installed in large lines?
As the nominal size increases, the ball mass, weight, face-to-face length, operating torque and material cost of the ball valve rise disproportionately. The butterfly valve, by contrast, has a very short build, is significantly lighter, requires smaller actuators and is more economical. That is why it dominates large water, wastewater, swimming pool and process lines in plastic, while ball valves cover the smaller nominal size range and applications with the highest tightness requirements.
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