For continuous processing and in-line blending, when it’s necessary to dispense a constant, accurate amount of product every time, they are essential.
But while most positive displacement pumps are capable of dosing, progressive cavity (PC) pumps are fast becoming the dosing pump of choice for customers looking for superior performance.
Dosing pumps are specified when accurate control of dispensing ingredients or products is required. Examples of applications within the food and beverage industry include: adding strawberry flavour to milk; adding sauces to ice cream; adding botanicals to spirits; or adding colourings or flavourings to food products.
Within the water treatment industry, accurate dosing of chemicals is vital for efficient wastewater treatment and for potable water quality. In all these examples, it’s essential that the ingredients or products being added are dispensed at a constant, proportionate rate to ensure even mixing and distribution, in order to guarantee a high-quality product and to control costs.
However, many traditional dosing pump designs such as piston pumps, air diaphragm pumps and peristaltic pumps have a pulsating action. This pulsed flow means that once the pump has dispensed a product, there is a pause before it can dispense again.
This results in a gap in the process and can cause uneven distribution of ingredients. Furthermore, some of these pump designs require check valves; if solid or viscous particles get caught behind the valves it can cause them to stick, blocking the pump and halting the process.
Products of differing viscosity or solidity can be dosed by a single pump, since the flow rate of PC pumps is not affected by pressure or product viscosity. They can also handle harsh, abrasive chemicals
PC pumps are virtually pulsation-free. They use a rotor/stator pumping action which delivers a continuous flow into the product stream, compared to the start/stop action of piston or other positive displacement pumps. In the case of Seepex’s PC dosing pumps, this produces a stable flow rate with a linear accuracy of +/-1%.
A sticky situation
Another benefit of PC dosing pumps over the alternatives is their ability to handle highly viscous products, sticky materials and those that contain solid particles. Rather than just dispensing simple, free-flowing liquids such as sauces and flavourings, PC pumps can dose sauces containing herbs and spices, ice cream with hard biscuit inclusions, and even abrasive pastes directly onto dough sheets.
The action of PC pumps is low-shear and can therefore dose traditionally difficult-to-pump solid, semi-solid or shear-sensitive materials without damaging them, such as: buttermilk, yogurt, ice cream, polymers and flocculants.
In fact, a variety of different products of differing viscosity or solidity can be dosed by a single pump, since the flow rate of PC pumps is not affected by pressure or product viscosity. They can also handle harsh, abrasive chemicals, such as ferric sulphate dosing at wastewater treatment plants or anaerobic digestion facilities.
Just as importantly, due to the constant, pulse-free action of PC pumps, the use of flow control valves and ball valves is not required. This means that they can be used in complex applications, such as dosing into and from chemical tanks. Chemical particles can settle at the bottom of tanks and block valves, preventing other positive displacement pumps from doing their job, but not so in the case of PC pumps.
Right first time, every time
The benefits to manufacturers and processors of using PC pumps for dosing are multiple. By providing an accurate, linear flow they dispense the correct amount of ingredients every time, maintaining product quality.
This accuracy also reduces wastage and means that overdosing, often required with pulsating pumps, is not needed, helping to keep down the costs of raw materials. As an automated process, it also saves on labour and forms part of a system that can help to control an inventory. In addition, dosing pumps provide traceability – essential for today’s manufacturers.
What’s more, as flow valves, ball valves and pulsation dampeners are not required, installation and maintenance costs are reduced compared to alternative solutions. System costs are also lower, as the lack of pulsation reduces the wear on pipework. And as PC pumps can be wall-mounted or installed vertically, horizontally or even upside down, they are suitable for almost any site, including those with a small footprint or an unconventional layout.
It’s important to keep in mind the impact that Industry 4.0, or the connected factory, is set to have on UK manufacturing in the near future.
They are also highly flexible and can be specified according to customer demand. For example, the Seepex D range of PC dosing pumps is not only modular – meaning it can be scaled up or down as required – it can also be specified to handle extremely viscous products; tailored for hygienic or industrial applications; or be made from chemical-compatible materials, depending on the final use.
Pumped up about Industry 4.0
Whatever your reason for specifying a dosing pump, it’s important to keep in mind the impact that Industry 4.0, or the connected factory, is set to have on UK manufacturing in the near future. There’s a general misconception that enhanced connectivity, smart manufacturing and Industry 4:0 are for big operations with ultra-sophisticated data capture strategies but all processes, no matter how simple, can benefit from preparation for future proofing – and this includes when selecting a dosing pump.
To this end, Seepex’s range of PC dosing pumps includes a Smart Dosing Pump (SDP). Users input just one parameter – the proportional flow ratio – and the pump, featuring an integrated PLC monitor, will then make any necessary adjustments automatically. Once set, the flow rate is monitored and controlled entirely by the pump drive, which adapts to variations in operating conditions to ensure accurate, repeatable dosing. In addition, dry running and over-pressure sensors feed back to the drive to protect the pump from damage, helping to increase service intervals and the lifespan of the product.
Despite its enhanced capabilities, the SDP is surprisingly easy to operate, comprising a PC pump with an intelligent inverter drive which is programmed either locally via an HMI or centrally via a fieldbus interface. It can also be controlled via analogue/digital I/Os, either locally or remotely by a PLC. Ultimately, it provides all the benefits of a PC dosing pump with enhanced control options, future proofing your dosing system as we move towards the fourth industrial revolution.
The sweet taste of success
Successful cider making depends upon accurately dosing ingredients to produce the correct flavour and colour profile for each cider product, from variable raw materials. Heineken in Hereford produces 65% of the cider sold in the UK and after becoming unhappy with their existing diaphragm pumps, they wanted to make improvements to their ingredient dosing process to ensure high product quality. The diaphragm pumps, which dosed acids, sweeteners and colours into their cider, were difficult to maintain and recalibrate due to the pulsating nature of the flow, so Heineken turned to Seepex, who recommended hygienic PC dosing pumps to deliver all the ingredients required – even those with a high viscosity – directly into the product pipeline.
The PC pumps have eliminated the problems caused by sticking ball valves and the high maintenance requirement, and Heineken have found the flow calibration simple and changes to the flow easy to make. Labour costs on maintenance and calibration have been reduced, downtime is lower, and spares costs have also dropped. Dosing control and accuracy have improved so much that Heineken has since replaced all its remaining diaphragm pumps with hygienic PC pumps.
Lesley Eaton is business development and marketing manager, Seepex