Merits of mechanical and digital options in dosing pumps

Nita Karume
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Merits of mechanical and digital options in dosing pumps

Dosing pumps play an important role in many industries from mining and wastewater treatment to pharmaceuticals and food production – and are available in a growing range of mechanical and digital options.

“Choosing the right pump starts with understanding the respective areas where mechanical and digital dosing pumps excel,” says Tshephang Sithole, sales engineer – water treatment at global pump specialist Grundfos. “While high flows and high pressures might be prioritised in some applications, for instance, other users need to focus on accuracy or remote-control functionality.”

Sithole points out that many industrial applications such as water treatment plants or mining will tend to need a robust solution that delivers large volumes of water at pressures of up to 150 bar. There are still certain automatic functions, though, depending on the configuration.

Tshephang Sithole, sales engineer – water treatment at global pumping specialist, Grundfos.

“While Grundfos’s basic range of mechanical dosing pumps requires an operator for most functions, our analogue relay (AR) range has additional features such as an automatic stop when the chemicals are depleted,” he says. “Furthermore, the D-range has servomotors to automatically set the stroke length, thereby adjusting the dosing flow.”

This is done with a 4-20 mA signal that can be remotely transmitted from a SCADA system or other digital input. Variable speed drives (VSDs) can also be fitted to these pumps, and the frequency can be adjusted up or down to vary the dose.

READ: Switzerland grants US $4M for water and sanitation in Niger

Digital dosing pumps, by contrast, come with a range of features that make them most suitable for automated plants or where higher levels of monitoring and control are required, including remote functions. Grundfos has been a pioneer of digital dosing for over 20 years.

“Automation functions are particularly valuable for companies who have plants in different parts of the country,” he says. “If loadshedding leads a pump to trip, for instance, an alarm will notify the user, and they can remotely reset and restart the operation.”

Grundfos smart digital installation
A Grundfos smart digital installation facilitating accurate dosing of Sodium Hypochlorite (NaOH) at one of the major breweries in South Africa.

They are also preferred where accuracy of dosing quantities is prioritised, or where dosing volumes are very small. Some digital dosing pumps boast high turn-down ratios as low as 1:3,000, and can deliver pressures of down to 0,002 bar.

“They can even pick up leaks in the line, and will help prevent liquid losses by automatically alerting the operator,” he says.

The automatic de-aeration function is another valuable element in advanced digital dosing pumps, allowing them to detect and remove bubbles from a line. This is important as bubbles will impair the accuracy of dosing.

Thermoplastic Valves and Actuators: All you need to know

Staff Writer
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Thermoplastic Valves and Actuators: All you need to know

The Pump Industry has a diverse number of operations that require the control of the flow of various fluids in different processes.

For over 50 years, thermoplastic valves have been growing in acceptance as an effective choice over metal valves in many applications. The advantages of thermoplastic valves include:

  • Thermoplastic valves are dielectric, so they do not support an electrical charge. This enables them to be immune from the electro-chemical corrosion that occurs with metal valves.
  • Thermoplastic materials are immune to microbiological-influenced corrosion that leads to rust and pitting in metal valves.
  • Interior walls are moulded with a smooth finish that enables high flow coefficient and consistent performance over an extended service life.
  • Up to 50% lighter in weight than metal valve counterparts. This allows for lower freight and handling costs, and ease of installation.

Thermoplastic valves have the advantage of being lightweight, corrosion resistant, chemical resistant and non-toxic. They also will not scale or rust and have low thermal conductivity. Commonly used in municipal and industrial chemical feed systems, thermoplastic material is rugged and well-proven for industrial applications when used within the range of the material’s specifications. Thermoplastic valves fitted with electric or pneumatic actuators also allow for automated control and remote access by operators.

Thermoplastic valve materials
The most common materials used in thermoplastic valve manufacturing are PVC, CPVC, GFPP and PVDF. Both materials inherently perform differently at the same operating temperature, pressure, impact and UV exposure.

The thermoplastic valve body is precision moulded from the base material. Thermoplastic valve assemblies additionally have smaller components made of different material that also interact with the liquid process. All of these materials require careful attention during valve selection due to potential chemical compatibility. Incorrect material selection, especially of O-rings and liners, can lead to premature valve failure.

Ball valves use elastomer O-rings made of EPDM or FMP. These are located in the end connections and stem to create a sealing surface between plastic components. PTFE seats on either side of the ball provide a smooth travel and sealing surface for the ball to ride and seat against. Thermoplastic butterfly valves have an elastomer liner that the disc seals into and O-rings made of EPDM, Viton or Nitrile. A thermoplastic butterfly valve also has a stainless steel or titanium shaft that holds the liner and disc assembly in place within the valve body.

When specifying a valve for a potentially corrosive application, consulting a chemical resistance chart for the thermoplastic and elastomer material chemical compatibility will ensure correct material selection. EPDM rubber is an elastomer recommended for water, steam, dilute acids, dilute alkalis and alcohols.

All thermoplastic material operating pressure decreases as temperature increases. Maximum operating pressure of a 2-inch ball valve can be 250 psi at 70°F, non-shock. The pressure and temperature curves are different for PVC and CPVC. The same schedule 80 PVC ball valve will have a max pressure of 130 psi at 145°F.

READ: Thermoplastic valves manufacturer, Asahi, acquires its Southern Africa distributor

A valve actuator is the device that “actuates,” or moves, a valve open or closed. It attaches to and works in conjunction with two parts: the valve body and the valve pilot.

Types of actuators

When considering actuating a thermoplastic valve, the following points need to be identified:

  • Valve type: ball, butterfly, diaphragm, three-way ball
  • Valve size
  • Valve operation: on/off, throttling (modulating 4-20 mA), 3-position
  • Installation: indoors or outdoors

Electric or pneumatic
Pneumatic actuators require plant-supplied air and come as either double-acting or spring return. Options include solenoid (AC or DC), air filter/regulator, positioner (4-20 mA), auxiliary limit switches, visual indicator and declutchable manual override.

Actuator cycle time is the time it takes an actuator to travel from open to close and is important for preventing water hammer resulting from a valve opening or closing too fast. The cycle time of Hayward’s HRSN2 electric actuator for a 4-inch ball valve is approximately 9 to 13 seconds. Cycle time for a 12-inch butterfly valve is approximately 39 seconds. For electric actuators, this speed is fixed.

Speed of a pneumatic actuator is governed by a solenoid assembly that opens or closes on command and regulates the flow of air into and out of the actuator piston cylinder. Double-acting actuators have air supplied to both the open and close cylinders. On loss of supply air, a double-acting valve will remain in the last position. Fail-safe spring return actuators are used in applications that require a valve to travel to either a full-open or full-close position in the event of loss of air supply. The fail-safe position is selected when specifying the actuator but can be changed in the field, if needed.

Electric actuators –These types of valves are among the most common and the most dependable. They’re capable of quickly operating some of the largest valves, and they’re powered by a single or three-phased electric motor that drives a combination of level gears and spurs. Subsequently, these gears and spurs drive a stem nut, which engages the stem of the valve to open or close it. They often include a declutching mechanism and a hand wheel that allows for manual operation in the event of a power failure.

Manual actuators – Manual actuators use levers, wheels, and/or gears to facilitate movement. Manual actuators differ from automatic actuators, as automatic actuators have an external power source providing the force and motion needed to operate a valve automatically or remotely. For many valves, manual operation isn’t an option, either because the application includes valves in remote pipelines or due to the sheer force required for operation. Additionally, manual actuators aren’t a practical solution for valves located in toxic or hostile environments, and they’re not as useful in applications requiring the safety precaution of allowing for immediate shutdown.

Conclusion
When choosing valve actuators, usage factors are a significant consideration. For example, electric actuators, by nature, require electricity to operate. Pneumatic actuators can operate in temperatures ranging from -4 to 150° F (-20 to 70°C), or in some cases in the range of -40 to 250°F (-40 to 121°C), provided the right seals, grease, and bearings are in place. Electric actuators can operate in temperatures ranging from -40 to 150°F (-40 to 65°C).

Pneumatic actuators are often preferred in hazardous or toxic environments due to their explosion-proof nature, but if there’s a lack of compressed air or a pneumatic actuator is unable to meet other operating specifications, electric actuators may be used.

Full-service capability vital for reliable pump supply

Martina. A
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Full-service capability vital for reliable pump supply

Even the best quality pumps need to be supported with a full range of aftermarket services, according to Jordan Marsh, sales manager at Integrated Pump Technology.

“Reliable pumping is the life-blood of many sectors in our economy, making the choice of pump supplier a strategically important one,” says Marsh. “This applies even when customers have specified the best pumps available.”

He highlights, for instance, that Integrated Pump Technology is so confident of its Grindex range that it offers a 36-month warranty on all new pump units purchased. The expected lifespan is, of course, much longer than this, he says, and the company is well equipped to ensure customers long and reliable performance.

“Our full-service offering includes a comprehensive stock of all critical spares across the range, with a service centre and experienced staff to maintain units to OEM standards,” he says. The necessary equipment and expertise are on hand to look after the complete range of pumps, from the 0,4 kW units right up to the large 90 kW Grindex Bravo Mega pumps.

Integrated Pump Technology also supplies and supports Faggiolati slurry pumps and Leybold vacuum pumps, and can even service and test other brands of submersible pumps.

READ: IPR REBUILD gives unreliable water pump new life

Among the technical services in the company’s quality-accredited workshop is its test tank, which allows comprehensive testing of pumps with motors up to 150 kW. According to workshop manager Fred Slabbert, the continual investment in workshop capability means that customers can benefit from a six-month warranty on refurbishments and repairs. The workshop can even conduct full refurbishments.

“Pump users can bring us their equipment for a professional assessment by our skilled technicians,” Slabbert says. “After careful examination, we generate a condition report which gives all the details necessary for an informed decision, and customers are assured of aftermarket services to OEM standards.”

Underpinning the company’s high service levels is a dedicated workshop sales administrator, providing a strong link between customers and the workshop and spares store.

“We prioritise quick and efficient turnaround times on all spares sales, repairs and quotes, keeping customers informed at each step in our relationship,” he says. In the unlikely event of a customer needing assistance on site, the workshop is also equipped to provide trouble-shooting assistance on most mechanical or electrical issues.

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