KSB butterfly valves with a proven track record

Benefits of a butterfly valve from KSB

• Short face-to-face length, low weight and resistance to many fluids
• Versatile use thanks to diverse connection options and robust materials
• Reliable sealing and resistance with specially developed elastomer liners 
• Easy to automate: available with manual, electric, pneumatic or hydraulic actuators

Butterfly valves in a nutshell

This is how butterfly valves work

Shut-off butterfly valves serve to control the flow of fluids or gases in pipes. Butterfly valves are generally characterised by their short face-to face length and simple design. And like other shut-off valves they are employed to completely stop the flow in a pipe. The difference is that KSB butterfly valves can also be used as control or throttling valves within the operating limits and hydraulic data.

A distinction is made between centred-disc and offset-disc butterfly valves. 

A centred-disc butterfly valve is defined by a soft-seated butterfly valve with the disc moving at a right angle to the direction of flow of the fluid, rotating around its own axis by 90 degrees. The centre of rotation is in the centre of the seat. In the closed position, the valve is sealed by the edge of the disc being pressed into the liner, which is made of elastomer or plastomer. In the open position, the fluid flows on both sides of the valve disc. The advantage of a centred-disc butterfly valve is its versatility, e.g. it can be clamped between flanges, it can be used for downstream dismantling or as a "dead-end valve".

KSB produces centred-disc, soft-seated butterfly valves up to nominal diameters of 4000 mm. The maximum pressure classes depend on the nominal size and are available up to 25 bar. Depending on the liner quality, fluid handled and pressure, this design is suitable for temperatures of up to 200 °C.

There are three different types of offset-disc butterfly valves:

• Single-offset butterfly valve: The centre of rotation of the valve disc is offset from the seat centreline but remains on the pipe centreline.
• Double-offset butterfly valve: In addition to the above, the centre of rotation is also offset from the pipe centreline.
• Triple-offset butterfly valve: In addition to both of the above, the rotational axis of the seat is neither parallel nor symmetric to the pipe centreline.

Centred-disc butterfly valves are also available in different variants, with two main designs:

The disc and shaft of the butterfly valve are two separate components. This means that a single-piece body with an elastomer liner can be used.
The disc and shaft form a single unit. For this reason, the body has to be made of two pieces. Here too, the liner can be made of a plastomer, reinforced by an elastomer."

KSB butterfly valve – matching body types for every requirement 

• Butterfly valve with wafer-type body: This type is only suitable for being clamped between two flanges.
• Butterfly valve with semi-lug body: This design enables downstream dismantling for a short time.
• Butterfly valve with U-section body: The throughholes and threads enable simple clamping or flanging of the valve.
• Butterfly valve with full-lug body: The threads enable the valve to be easily bolted to and removed from a flange. In the case of a butterfly valve clamped between flanges, only pressure is applied to the body; the force is transferred from flange to flange through the bolting. A flanged butterfly valve additionally absorbs piping forces.

For all body types of butterfly valves, flanged connections to different standards such as EN, ANSI and JIS are possible.

Easy to automate thanks to variable actuators

Butterfly valves can be operated manually or with automated actuation. Designed with a 90 degree swivelling movement and with shaft ends and actuator flanges standardised to EN ISO 5211, butterfly valves are easy to automate. For the correct selection of a suitable actuator for butterfly valves, the following parameters have to be known:

• Actuating torque of the butterfly valve
• Lubricating or non-lubricating fluid
• Required actuation: pneumatic, hydraulic or electric
• Function: open/closed or control tasks

The minimum actuating torque for a manually operated butterfly valve is stipulated in EN 12570. The size of the actuating element must be selected for the valve to be able to be closed manually at maximum differential pressure. Butterfly valves can be operated manually with a lever or handwheel. Up to nominal size DN 150 a butterfly valve is usually operated with a lever. Levers can either be continuously adjusted or set by means of a ratchet disc; they are fitted in such a way that they indicate the valve disc position.

To reduce the actuating forces, butterfly valves with a larger nominal size are fitted with gear units. The gear units are grease-packed and maintenance-free. A position indicator informs the user of the valve disc position.
If butterfly valves are frequently to be operated remotely, pneumatic, hydraulic or electric actuators are used. All variants can be employed for both open/closed and control tasks.

Pneumatic actuators for butterfly valves

Pneumatic actuators are very common as they are suitable for potentially explosive atmospheres (for example in systems in which compressed air is available as auxiliary energy); they are also much safer than electric actuators. A distinction can be made between double-acting and single-acting actuators:

• Double-acting actuators: The valve is opened and closed by compressed air.
• Single-acting actuators: The compressed air only operates the valve in one direction while loading a spring stack. In the other direction, the recovery forces of the springs actuate the valve. Single-acting actuators can either be closed by spring force or opened by spring force. Actuators that are closed or opened by spring force move the valve disc into the required fail-safe position if the air supply fails.

Solenoid valves, positioners and mechanical or inductive limit switches can be externally mounted on the actuators. Also, innovative all-in solutions are available with all components assembled in a box. This box is directly connected to the actuator of the butterfly valve. This does away with the need to connect the tubing and wiring of the accessories to the actuator.

Reliable sealing by elastomers from KSB 

The liner is the most important component of a butterfly valve. It ensures tight sealing at the flanged line connections, the seat/disc interface and the shaft passages. By being compressed between the body and the line flanges, the liner provides tight sealing at the flanges. Optimum chemical resistance to the fluid handled is provided by a comprehensive range of elastomers which have been developed by KSB for the liner:

• EPDM: resistant to heat, chemicals, hot water
• NBR: resistant to fuels, mineral oils, lubricating greases, vegetable or animal fats, oils, water, drilling emulsions 
• Viton®: resistant to oil and chemicals, high heat resistance, high resistance to ozone, ageing and weather, high flame retardancy, low gas permeability
• Hypalon®: resistant to chemicals (especially to fluids with an oxidising effect)
• Silicone: resistant to heat, ozone, ageing and chemicals (almost unchanged mechanical properties over the entire temperature range)
• Epichlorhydrin: resistant to mineral oil, weather and ozone
• HNBR: resistant to oil and petrol. Like NBR but with a higher resistance to temperature, ageing and weather (physical properties also at high temperatures)
• Nitrile, carboxylated: resistant to abrasion, pneumatic transport of solids, also suitable for the food processing industry
• PFA (Teflon®) perfluoroalkoxy copolymer: properties similar to PTFE but with a denser structure, resistant to chemicals (almost all organic and inorganic chemicals)

Strengths and applications of KSB butterfly valves

A centred-disc butterfly valve is robust and adaptable and mainly designed for the following applications:

• Water management and drinking water supply
• Water treatment
• Seawater desalination
• Cooling water transport
• Hot water circuits
• Shipbuilding
• Waste water treatment plants from the secondary treatment stage onwards
• Chemical and process engineering
• Steel industry
• Biofuel production
• Sugar industry
• Pulp and paper industry
• Surface treatment technology
• Food industry
• Beverage industry
• Mining