NAF V-port ball sector rotary control valve

NAF’s Setball SF ball sector valve offers excellent flow characteristics at a competitive price.

NAF has introduced the new Setball SF, the latest addition to its range of high performance, rotary control valves.  The Setball SF is designed primarily as a compact rotary control valve, where its V-port ball offers excellent equal percentage flow characteristics, but it can also be used effectively as a shut-off valve.  The valve combines compact size, excellent control characteristics and high flow capacity.  Its compact face-to-face dimension reduces weight and offers a clear price advantage, which makes it an ideal and cost effective choice for many applications, including erosive media such as fibres and slurries.

Development of the NAF Setball SF vs the existing Setball Range

The NAF Setball SF is designed for modulating control providing excellent equal percentage flow characteristics. Its compact size and short face-to-face dimensions significantly reduce weight, making it a cost effective choice. Together with its high flow capacity its extremely versatile and an ideal solution for a range of general control applications including erosive media such as pulp fibres or slurries.

The primary driver for the development of the new NAF Setball SF was to develop a product that follows the shorter, industry standard, face-to-face construction, which has become common in certain markets and applications. The new short dimension targets weight reduction and therefore creates the possibility to offer a robust product at a more competitive price.

Several other functional improvements were also introduced during the development of the Setball SF.  The main differences between Setball SF and Setball are:

  • A shorter face-to-face dimension.
  • A significantly reduced torque requirement (up to 50%) allowing cost-effective, smaller actuators to be fitted.
  • Increased flow capacities Cv/Kv (up to 50% higher).
  • Increased allowed maximum differential pressure from 25 bar to 35-50 bar.
  • All sizes are now rated PN40/ANSI Class 300.
  • Spring loaded PTFE stem packing and PTFE seat seal is now standard, thus resulting in a 250°C standard solutions.

Since the primary objective of the new valve is to become more competitive in the targeted application areas, the product is highly standardised with fewer options and versions. It is therefore specified in a standard configuration, which should cover most requirements.  One of the few planned additions to the Setball SF will be a soft-seated version, mainly intended for use on acids as well as for tight shut-off.

Why use a V-port ball sector valve?

The inherent valve flow characteristic is defined as the flow capacity as a function of travel at a constant pressure drop over the valve.  The Setball SF has a flow characteristic called ‘equal percentage’, which becomes linear in real applications due to pressure drop effects and pump characteristics.  By contrast, an initially linear device (ball sector valve without V-port), will tend to become quick opening when installed.

Quick opening results in high gain at low openings, which makes accurate control difficult over wide ranges and also at start up.  The V-port compensates for this to give constant gain over the entire range making control easier and vastly improving the rangeability.  Without V-port controlling small flows will result in narrow flow paths that increase velocities and add to component wear.  Addition of the V-port results in wider flow-paths which reduces component wear and also prevents dewatering in pulp applications.

Due to its high flow capability in combination with its compact size, it is a very viable economical alternative to linear control valves.  Typical applications are found in paper, board and tissue machines; fibres or slurries; water and steam operations; chemical and mechanical pulping applications; renewable fuel and ethanol plants; or any general application where a high Cv is required.

Primary characteristics

The NAF Setball SF is a highly versatile and cost-effective solution to a range of general services as well as erosive applications such as fibres and slurries.  A V-port ball sector valve designed primarily for modulating control applications, the Setball SF can also be used effectively for shut-off service. It combines a compact design with excellent equal percentage flow characteristics and high flow capacity.

The new valve offers the following features  to provide durable functionality and greater reliability for increasing process yield and plant uptime:

  • A ball sector with a V-port resulting in excellent control characteristic in combination with high flow  capacity and high rangeability.
  • A compact wafer design for weight reduction and cost savings.
  • A one-piece, leak-proof stainless steel valve body to minimise leakage paths.
  • Enhanced product integrity through a spring loaded stem seal packing that provides a long, maintenance free and safe operation.
  • Dual low friction bearings and a specially designed seat, resulting in a smooth operation and making it possible to use a small actuator.
  • A stem with a splined transmission to the ball sector for an optimum control performance.
  • Direct actuator mounting capabilities of the NAF Turnex actuator which provides a high performance, vibration resistant, compact valve package.
  • Metal seats with a rigid welded overlay of Alloy 6 to provide a higher leakage resistance over extended periods.
  • Special low flow trims for the smallest size.
  • Reduced downtime through an easy-to-service arrangement which allows for easy replacement of the seat and seat seal without the need for removing the segment and stem and actuator.

NAF Setball SF is available with double acting or fail action pneumatic actuators.  NAF Turnex pneumatic actuators can be directly mounted without any couplings or brackets.  Together with intelligent control valve positioners, this provides a high performance, vibration resistant and compact valve package suitable for precision control all ex stock in South Africa.

All valves CE-marked according to Pressure Equipment Directive (PED 97/23/EG) module H, category III.

This article was published in Volume 33, No 1 January 2017 of South African Instrumentation and Control.

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