What is a ball valve? | ACI Industriearmaturen GmbH

Ball valves

Ball valves consist of the body, the eponymous (shut-off) ball, a shaft with bearing and seals, the ball seal and the hand lever for actuation. The shut-off ball is provided with a cylindrical bore and, when turned 90°, either releases or shuts off the passage. Ball valves can therefore be opened or closed easily and very quickly.

Ball valves are used in pipelines that are used to transport liquids or gases, such as water, oil, natural gas, compressed air, etc.

Since they completely shut off the flow, they are also the preferred choice for critical, flammable or toxic media.

Due to their design, ball valves are not suitable for flow control.

Ball-valve-one-piece-reduced-passage-floating-bearing-soft-sealing-both-side-internal-thread

Ball valve, one-piece,
reduced bore, soft-seated

Ball valves come in a wide variety of designs and can be distinguished by the following characteristics:

Size of the ball bore

According to the size of their ball bore, they are divided into two variants, with full or with reduced bore:

Ball-valve-full-bore-two-part-soft-sealing-floating-bearing-both-sides-outside-thread

Ball valve, full bore

Full bore

Full bore means that the ball bore has the same inner diameter as the pipeline. The flow losses are extremely low.

Full bore ball valves are piggable, i.e. the pipeline or the plant can be serviced with a special cleaning or inspection device (pig).

Reduced bore

With a reduced passage, the ball bore is smaller than the inner diameter of the pipeline, which can lead to large flow losses. For this reason, they are used specifically in pipelines in which the flow rate of the medium is to be increased ( jet effect).

Ball-valve-reduced-passage-one-piece-soft-sealing-floating-bearing-both-sides-internal-threa

Ball valve, reduced bore

Ball bearing

Ball-valve-floating-bearing-reduced-passage-one-piece-soft-sealing-both-sides-internal-thread

Ball valve, floating ball

Floating ball

Most ball valves are used with a floating ball. Here, the ball is held in position by the sealing rings arranged on both sides. This simple principle makes low-cost production possible. However, this bearing arrangement is not suitable for high pressures.

Trunnion mounting

The version with guided ball is more complex to manufacture. In this case, two opposite sides of the ball are fitted with journals that are mounted in the housing. This trunnion mounting means that only one sealing ring is required. In addition, these ball valves can also be used at higher operating pressures.

Ball valve-two-piece-pivot-bearing-soft-sealing-both-sides-outside-thread

Ball valve,
Ball with trunnion bearing

Type of ball sealing

Ball-valve-soft-sealing-floating-bearing-reduced-passage-one-piece-both-sides-internal-thread

Ball valve, soft-seated

Soft-seated

The "classic" ball valve is soft-seated and is still the most used today due to its versatility. The (ball) sealing rings are made of a plastic, mostly PTFE. The PTFE sealing rings are suitable for most liquids and gases and can be used up to a temperature of +200°C, depending on the additive also up to +260°C.

Soft-seated ball valves are not suitable for media containing solids or for higher operating temperatures.

Metal-seated

Metallic ball seals are used for applications with solids passing through or at higher operating temperatures. The sealing rings are made of stainless steel or other high-alloy steels, in some cases additionally hardened. Metallic sealing ball valves are suitable for operating temperatures up to approx. +650°C.

Ball-valve-metallic-sealing-pin-bearing-with-top-access

Ball valve, metallic sealing,
full bore, trunnion mounted,
top entry

Connection types

Ball valves are mainly supplied with the following types of connections:

  • Both sides with internal or external thread
  • One side with female thread - other side with male thread
  • Both sides with welding ends
  • With flanges on both sides
  • Compact ball valve for clamping between two flanges
Ball valve - female thread on both sides

Internal thread on both sides

Ball valve-compact-intermediate-flange-mounting

Compact design

Ball valve-both-sides-with-flanges

Flanges on both sides

Ball-valve-male thread on both sides

External thread on both sides

Ball-valve-welding-ends-on-both-sides

Welding ends on both sides

Body design

In terms of the body, the following types of design are common:

One-piece ball valve:

The body consists of only one component, the passage is reduced and only an internal thread is possible as a connection type.

Ball-valve-one-piece-housing

Ball valve, one-piece body

Ball-valve-two-piece housing

Ball valve, two-piece body

2-piece ball valve:

Two body parts are screwed together, versions with full bore or reduced bore possible, all connection types are feasible.

3-piece ball valve:

The ball valve consists of three parts (inlet side - middle part - outlet side). This design is particularly easy to maintain, as the center section can be easily removed to either replace it completely or to replace only the individual closing parts such as ball and body sealing rings or stem seals.

A further advantage is that the center section including ball and sealing system can be combined independently with all connection types. For example, one side can be fitted with a flange connection and the other with a threaded connection or weld-on end.

Ball valve-three-piece-housing

Ball valve, three-piece body

Three-way or four-way ball valve:

With full or reduced bore, flanged or threaded connection. Instead of a through bore, the ball is provided with an L- or T-shaped bore. This allows different switching options for distribution to one or two outlets or for mixing the flow medium.

3-way ball valve

3-way ball valve

Switch positions-3-way-ball-valve-T-version-and-L-version

Possible switching positions of a 3-way ball valve,
with T- or L-bore

Types of actuation

Like all valves, ball valves can be operated in various ways:

  • Hand lever:

    The valve is operated manually by a 90° turn of the hand lever.
    One-piece ball valves with reduced passage are often also operated with a butterfly handle.

  • Electric actuator:

    Actuation is by electric rotary actuator; rotary actuators are available for all available voltages and DC, AC or three-phase current.

  • Pneumatic- and hydraulic atuators:

    These actuators are operated by compressed air (pneumatic) or by oil (hydraulic). A distinction is made between double-acting and single-acting drives.

    Double-acting actuator:
    Opening and closing is performed by supplying compressed air or oil.

    Single-acting actuator:
    Air pressure or oil pressure opens - spring force closes the actuator;
    the reverse function is also possible: spring force opens - air / oil closes

Advantages and disadvantages of ball valves

The following are the main advantages of ball valves:

  • Due to their design, ball valves are built quite compactly
  • Opening and closing is very fast via a 90° turn
  • Ball valves with full bore are piggable
  • Ball valves are absolutely tight closing, depending on design and material even at high temperatures and high pressures
  • With full bore, very high flow rates are possible, high Kvs-value, only low pressure losses

These disadvantages are set against the advantages:

  • The sealing surfaces of the ball valves can wear out quickly.
  • At high pressures or large nominal sizes, the shaft must be journaled, resulting in higher manufacturing costs.
  • Ball valves are not suitable for flow control.
  • Pressure surges can occur in the piping system when a ball valve closes quickly.
  • In standard ball valves, the operating medium comes into contact with the so-called dead space of the ball valve. Due to the design, the medium enters the area between the body and the ball in the partially open position; this area is referred to as the dead space. In the closed position, it is then enclosed there and the medium has no possibility of expanding in the event of temperature fluctuations. This can then lead to damage to the sealing system, the ball, and ultimately to operational problems.

A ball valve can be designed to be nearly "dead space free" by means of complex machining.

Ball valve with dead space representation

Dead spaces at the ball valve

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