Why Machine Design Maters: Choosing the Best Dosing Technology
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A brief description of each dosing technology discussed in this blog
Piston Dosing – A piston is driven inside a cylinder, moving a set distance to displace the liquid or paste.
Flowmeter – The flowmeter measures the volume of liquid that passes through it. In this blog we will focus on mass flowmeters.
Gear Pumps – Two intermeshing gears sit inside a housing, and one of the gears is driven, which in turn drives the other gear, transporting the fluid between the gear teeth and the housing.
Screw Pump – A spiral ‘rotor’ turns inside a stator or casting, as the rotor turns within the stator a progressive contacting of the rotor with the stator transport material through the pump.
Peristaltic Pump – Rollers in a peristaltic pump compress a tube against the housing as they rotate, creating a vacuum which draws fluid through the tube.
PTFE Diaphragm Pumps – the diaphragm reciprocates back and forth, as it retracts it seats the outfeed check valve and opens the infeed check valve drawing material into the chamber, and as it expands it close the infeed check valve and opens the outfeed check valve displacing the material from the chamber.
When would you use Piston Metering?
Piston metering is very versatile and can handle a broad range of viscosities from liquids to dense pastes. Whilst the specifications will vary to suit the required maximum dose size, viscosity range, desired dosing speed and accuracy requirements – the same fundamental dosing methodology is pretty much suitable for any type of dosing requirement.
A limiting factor is the maximum single dose size is limited to the maximum displacement of the metering cylinder, and then a reload cycle is required, however in most instances the metering unit can be sized larger than the maximum required dose size.
When would you use Flowmeters?
Flowmeters offer a fantastic solution for liquid filling and metering, they are highly accurate, can offer a continuous flow, and have minimal fluid contact parts with a smooth fluid path – making purging or flushing through liquids very easy.
A limiting factor is viscosity – typically only suitable for lower viscosity liquids.
When would you use Gear Pumps?
Gear pumps can handle a relatively broad range of viscosities (dependant on pump sizing and system design).
Limiting factors – Gear and Lobe pumps are not 100% efficient – there is some slippage or by-pass – the efficiency is a factor of the size of the pump, the liquid it is handling, and the speed it is running. Which necessitates cross-checking and compensation when changing between different liquids or speeds.
Gear and Lobe pumps have tight internal tolerances and contacting metal surfaces, therefore handling abrasive and non-lubricating fluids can be problematic, causing premature wear and failure.
When would you use Screw pumps?
Screw pumps are particularly useful for thicker pastes that are shear sensitive (Non-Newtonian i.e. their viscosity changes when subjected to force and movement), or for liquids that have large solids/particles.
Limiting factors – the correct sizing and configuration to suit a material or range of similar materials and application is important to get the best results, therefore, they tend to be limited to specific applications, and the technology is costly both in terms of initial outlay and spare/wearing parts.
When would you use Peristaltic Pumps?
Peristaltic Pumps are useful for small and accurate dosing, minimum fluid contact parts and the ease of changing the hose makes for easy maintenance.
Limiting factors – the nature of the pump necessitates the hose to have elastic properties, limiting the options for hose materials and therefore material compatibility with certain liquids.
When would you use PTFE Diaphragm Pumps?
PTFE Diaphragm Pumps are useful for small dosing of highly reactive and aggressive chemicals.
There are of course other types of filling technology which we haven’t covered in the blog – for example many millions of bottles are filled under gravity, vacuum and pressurised technology in high throughput industries like beverage filling – so we chose to just focused on the above-mentioned filling technologies which Grunfeld offers.
Summary
In the context of the systems we offer and the markets we serve, Piston Metering is the most common technology, its versatility is vital to many filling operations.
Coming in at second place is flowmeter filling, for liquid filling applications it presents fewer moving fluid-contact-parts and a continuous flow (especially attractive for filling large jerry cans, drums and IBC.
The other filling technologies we have covered are typically used in more specialist applications, where they are chosen for their particular merits.
To find out which dosing technology is best for your filling operation, get in touch today.