classic | mobile


SA Instrumentation & Control Buyers' Guide

Technews Industry Guide - IIoT 2018

Technews Industry Guide - Maintenance, Reliability & Asset Optimisation


Slurry control valves for level control
July 2018, Level Measurement & Control

In order to improve the froth level control at a flotation concentrator in Rustenburg, eDART was recently commissioned to replace the froth level control valves on the secondary cleaner.

Froth level control is extremely important on flotation machines as it directly relates to efficiency of the plant. If the froth level is too deep then the grade of the concentrate will increase and at the same time recovery drops off. When the froth level is too shallow the recovery will improve but a lot more concentrate will be produced at a lower grade. The aim is to produce concentrate at the optimum grade, which will result in the highest efficiency of the plant.

From a control point of view, the most efficient point of a control loop is when the level is on setpoint and there is no error. Where error is recorded there is an opportunity to improve the control. The Rustenburg customer is using an advanced controller to control the froth level at the flotation plant. As flotation froth levels are influenced by more than one variable, a simple PID controller cannot offer the good control results required which more modern controllers do.

A human operator will give the setpoint a step change and then leave it constant for a long period, and the signature of the more advanced controller is the gradual change to the setpoint point. As the advanced controller considers multiple variables in calculating the valve position, it can respond a lot quicker than a standard PID controller. If the output, or valve signal, represented by the blue line, is compared to the level signal (PV) represented by the red line, it can be seen that the ratio of the output signal to the process signal is approximately 2 to 1; this is the gain of the loop. With conventional PID controllers, the gain of the loop is seldom greater than 1. With the use of the advanced controller, the valve responds at least twice as fast to bring the level back to setpoint.

This is one of the major advantages of advanced controllers over standard PID controllers, in that they are 100%–200% faster than the best a simple PID controller can achieve. If the gain on any control loop is too high, it will lead to instability of the control loop, as the level will overshoot/undershoot the setpoint.

The final control element, or valve in this case, in any control loop is the limiting factor on how good the control can be. The valve has to be correctly sized. Looking at this trend it can be seen that the valve is approximately 45% open on average to maintain the control, which is evidence that the valve is correctly sized for the application. Any valve problems will result in a drop off in performance of the control loop. As the advanced controller is adjusting the setpoint continually, so the control valve is responding rapidly to keep this control loop in control.

eDART has developed their range of slurry control valves to meet the exacting demands of modern advanced controllers, the end result being vastly improved plant performance for their customers.

For more information contact Afrivalve, +27(0)11 791 1411,,

Supplied By: eDART Group
Tel: +27 11 791 1411
Share via email     Share via LinkedIn   Print this page

Further reading:

  • Contents measurement in silos
    January 2019, Morton Controls, Level Measurement & Control
    Each industry provides its own challenges with regard to accurate process control. In the mining and metal processing industry, accurate level measurement is a challenge due to the increased volume of ...
  • A wavelength for all situations
    January 2019, Endress+Hauser, Level Measurement & Control
    113 GHz: the best fitting radar frequency for every level application.
  • Innovative vertical gravity samplers delivered by eDART
    December 2018, eDART Group, News
    To meet the requirement of an international customer, eDART Slurry Valves designed, tested and manufactured a vertical gravity sampler assembly (VGSA) for application within the minerals processing sector. Duane ...
  • SIL2 for UWT’s rotating paddle ­series
    October 2018, Morton Controls, Level Measurement & Control
    The terms ‘functional safety’ and ‘safety integrity level’ (SIL) have occurred more frequently since the publication of the international standard IEC 61508/IEC61511. Particularly in systems with hazard-causing ...
  • Level measurement is becoming more sophisticated
    October 2018, KROHNE, Level Measurement & Control
    Since radar was developed and deployed during WW II, its use has expanded enormously. As technology advances, these uses are also advancing. For example, radar technology is used in the motor industry ...
  • The right wavelength
    September 2018, Endress+Hauser, Level Measurement & Control
    113 GHz: the best fitting radar frequency for every level application.
  • SIL2 for rotating paddle level switch
    September 2018, Morton Controls, Level Measurement & Control
    The terms functional safety and safety integrity level (SIL) have occurred more frequently since the publication of the international standard IEC 61508/IEC 61511. Particularly in systems with hazard-causing ...
  • Pushing the pulper towards maximum efficiency
    August 2018, VEGA Controls SA, Level Measurement & Control
    Non-contact measuring methods have become well established in the paper industry.
  • The benefit of head-guided plugs on slurry valves
    August 2018, eDART Group, Valves, Actuators & Pump Control
    “Good guiding of the plug head with three or more guide bars offers better benefits to valve performance than otherwise offered by the conventional method of fitting guides around the shaft,” commented ...
  • Reliable wastewater treatment
    July 2018, Siemens Digital Factory & Process Indust. & Drives, Level Measurement & Control
    To update and optimise its wastewater disposal system, the authorities of the City of Edmonton in Alberta, Canada, opted to use level measurement technology from Siemens. Installing the Sitrans LUT400 ...
  • Through-air radar for level measurement
    June 2018, VEGA Controls SA, Level Measurement & Control
    Radar is one of the most common level measurement technologies in the instrumentation market. Whether measuring liquids or solids, from chemical plants to wastewater facilities to ready-mix cement manufacturers, ...
  • Enhanced pressure vessel level measurement
    May 2018, EOH Process Automation Solutions, Level Measurement & Control
    The traditional approach to level measurement in a pressurised vessel, such as a boiler, has been to use a conventional differential pressure (DP) transmitter with external water-filled ‘wet’ legs connecting ...

Technews Publishing (Pty) Ltd
1st Floor, Stabilitas House
265 Kent Ave, Randburg, 2194
South Africa
Publications by Technews
Dataweek Electronics & Communications Technology
Electronic Buyers Guide (EBG)

Hi-Tech Security Solutions
Hi-Tech Security Business Directory

Motion Control in Southern Africa
Motion Control Buyers’ Guide (MCBG)

South African Instrumentation & Control
South African Instrumentation & Control Buyers’ Guide (IBG)
Terms & conditions of use, including privacy policy
PAIA Manual


    classic | mobile

Copyright © Technews Publishing (Pty) Ltd. All rights reserved.