MIXING, WEIGHING & CONVEYING
USER SAFETY V. PRACTICALITY
Ivan Zytynski, director, The Spray People Group, looks at a variety of different venturi mixing systems that mix cleaning chemicals with water, and considers the trade-off between practicality/ease of use and user safety
then diluted to perform the necessary cleaning function. Using concentrates rather than prediluted chemicals saves storage and gives greater versatility because dilution levels can be varied depending on the specifics of each application. The downside of using concentrated
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chemicals is that they can be more dangerous in this form. This presents some user safety issues during the mixing process. In addition, mixing needs to be accurate and performed well to ensure a uniform and correctly diluted end product is applied. Basic principles of dilution: the standard
guidance given for the safe mixing of chemicals from concentrate follows basic common sense i.e.: • Always ensure accuracy • Ensure only trained personnel conduct the
dilution • Use the diluted chemicals right away, do
not store for later use • Wear the correct PPE • Ensure the concentrate is put back
properly to where it is supposed to be stored • Add the concentrate to the water, not the
other way around The choice of equipment to enable
accurate delivery of diluted product to where it is needed can affect all of this common sense advice. Good kit used well will enhance and meet all the advice points above but, conversely, inappropriately used equipment can be detrimental to safety and effectiveness. Below is a short guide on the various venturi mixing equipment that can be deployed. It focuses on the balance between operator safety, spill hazard, and the flexibility of the mixing system. A venturi mixer will use the venturi principle
to automatically mix concentrate with a water stream. The venturi principle states that when a fluid is forced through a narrow opening it accelerates and this will result in a loss of fluid pressure. This localised low pressure can be utilised to create a suction effect where fluid will naturally move from an area of higher pressure to the generated low pressure area. This siphoning effect can be used to
24 MAY 2021 | PROCESS & CONTROL
leaning chemicals, be they sanitisers, caustics, or acid cleaners are often stored in a concentrated form. This is
automatically mix cleaning chemicals with a water flow. The amount of suction can be controlled by throttling the siphon tube and by controlling the flow rate of the water. Venturi mixing offers a practical, safe and
inexpensive way to dilute chemicals from concentrates to their ready-to-use form. As venturi mixing requires no pumps, power or moving parts, it is a robust and commonly deployed alternative to the manual dilution of cleaning chemicals. It has a further advantage in that the concentrate will typically be well mixed in the hose, resulting in a very even mixing without the need for further stirring. A concentrate poured into a container of water may often require a secondary agitation to ensure it is fully mixed. Venturi systems will provide natural agitation as the fluids move together through the hose system. Options for venturi systems: these systems can be deployed in 4 main configurations:
1. Mix to container These systems will be wall mounted mixing
stations that are designed to deliver the required diluted chemical into another container. This container will then be moved elsewhere to be used. These systems replace the need for manual mixing and stirring. As such they offer greater user safety when mixing. As only the diluted liquid is moved
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completely inaccessible to the end operator. Only the diluted product can be dispensed in a predetermined dilution. These systems offer the ultimate in safety. However, they come at the price of practicality. As the diluted solution needs to be moved in a container to where it will be used, this may present problems in terms of time and effort.
2. Mix at wall These systems will mix the concentrate
straight into the wash down hose that is being used in the cleaning operation. This means that only the diluted cleaning solution is ever under fluid pressure. The automatic mixing at point of delivery means that only the required amount of concentrate is used. This eliminates the potential for wasted diluted chemicals being made or running out of dilute part way through a job. They are versatile and easy to use whilst maintaining high safety standards.
3. Mobile mixers around
the factory, the risk of a hazardous leak of the concentrate is eliminated. The
Pic: 2
concentrate used in such systems can be locked away if necessary and so is
These venturi mixing stations are a hybrid system somewhere between the mix at wall system and the mix at gun system. The mixing occurs at a wheeled, mobile mixing station which will be hooked up to a suitable water supply. This means venturi mixing can be
“delivered” to any part of factory and will eliminate the need for long hose
runs from fixed wall mounted units. In terms of safety and chemical security
they are also somewhere in between.. They have the safety advantage of the chemical being in a large container, and the concentrate is stored some distance from the operator. This reduces the risk of operator
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