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Larox Flowsys explains how to select the best control valve for flotation column and cell control.

According to the company, froth depth in a flotation cell is an excellent indicator of flotation cell performance.

The thicker the froth, the more concentrate is entrained within.

There are several factors that influence control, such as air addition rate, flocculant dosing rate and pulp flow rate.

Balancing the circuit is almost impossible without accurate and reliable control.

There are a various types of valves that can be utilised in flotation column and flotation cell control.

The type of valve used on flotation columns may vary from a flotation cell.

For example, dart valves have been traditionally used on flotation cells.

In larger mining operations, the sizes of flotation cells have grown and so must the size of the valves.

In certain designs, the dart valve may require an external box built onto the exterior of the flotation cell, which may be large and costly to manufacture.

Another hindrance is that the containment box may need to be drained to enable maintenance work to take place on the dart valve.

However, there are alternative types of valves that do not require the dart valve containment box, which may allow for a less expensive total assembly and provide the accurate and reliable control of the flotation cells.

But the low driving head in flotation cells may create challenges in choosing the control valve size.

For this reason, control valve sizing on flotation cells requires the user to pay more consideration to piping effects.

Inlet and outlet velocities from the cells as well as any 90deg turns or elbows at the outlet may play a significant role in decreasing the driving head and thus force the selection of a larger-diameter control valve.

Control valve sizing in flotation cells requires the user to pay more consideration to piping effects owing to the low driving head.

The goal is to achieve accurate flow control to maximise pulp retention time and to minimise downtime.

Some manufacturers have developed special sizing programs that automatically calculate the decreased driving head caused by elbows, bends and inlet and outlet tank effects.

Pinch valves have been utilised successfully in small and large sizes to eliminate the need for external boxes and additional material costs.

The pinch valve provides very accurate flow control and a long service lifetime.

In the image above, the depicted valve is located at the LKAB iron ore mine and has been continuously operating without a rubber sleeve change for 22 years.

This is the oldest known reference for a Larox valve installed on flotation control.

To ensure the last valve will not cavitate, the piping is shaped like a ‘J’ before it departs to its final destination.

This ‘J’ section creates a few feet of head pressure to ensure that the full pressure drop is not taken across the valve.

Cavitation can cause short sleeve lifetime and unpredictable control owing to pulsing effects.

In flotation columns, the design of the outlet piping may or may not have severe effects on the control valve utilised to control the level in the column.

If the column is 30ft in height, the driving head is the pressure created by the head multiplied by the specific gravity.

In most cases, the driving head is sufficient enough that a simple calculation can be made to determine the size of valve required and Cv without any special sizing program to calculate downstream piping effects.

However, if the valve is required to take the full pressure drop across it, there is a high risk of cavitation.

Again, the ‘J’ tube arrangement should be employed to create some backpressure on the control valve to limit the amount of pressure drop the valve must take and to prevent cavitation from occurring across the valve.

In a flotation column, a ‘J’ tube that is 50 per cent of the column height with a vacuum breaker at the top will provide adequate protection to prevent cavitation.

According to Larox Flowsys, the rule of thumb with a pinch valve is to limit the pressure drop across the valve to 50 per cent of the inlet pressure to the valve.

If this is done, in most cases the valve will not cavitate.

Larox Flowsys Pumps and Valves Take Flow Control Technology to New Heights.

Larox Flowsys is the preferred supplier of industrial valves and pumps. They focus on abrasive, corrosive and other demanding shut-off, control and pumping applications serving a wide range of process industries worldwide. Their solutions offer substantial savings through improved performance, longer service lifetime and lower maintenance costs.

With decades of experience in flow control and elastomer technology, Larox Flowsys is at the forefront in addressing customer needs and making customers’ processes more competitive. Larox Flowsys valve and pump solutions have proven their suitability for a wide range of industries and applications. They work in partnership with clients to specify, design and deliver the optimal solution.

Larox Valve and Pump Products Include: Automatic Pinch Valves, Manual Pinch Valves, PVEG Valves, Heavy Duty Knife Gate Valves, Valve Sleeves and Peristaltic Pumps for Transferring Duties (LPP-T), for Dosing Duties (LPP-D) and for Accurate Metering (LPP-M).

LArox Flowsys has recently alunched a new series of progressive cavity pumps to supplement its peristaltic pump family. Larox Progressive Cavity pumps are engineered for the most demanding industrial slurry and paste pumping applications. Due to pump’s unique features and patented design, high efficiency and high pressure are acheived in a shorter construction.

Larox Flowsys’ international sales and service network covers over 55 countries. More than 600 qualified manufacturer’s representatives provide service you can count on. Larox Flowsys was the first pinch valve manufacturer in the world to get awarded the ISO9001:2000 Quality Certificate in 1997.

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