Diaphragms are an integral part of an AODD pump – they separate the air and liquid chambers. Failure of the diaphragm is bad as it results in the pump operation ceasing as well as leakage o the fluid being transferred. Thus the selection of the correct elastomer is essential for smooth safe pump operation.
1- Chemical composition of fluid being pumped – All AODD pump manufacturers publish a detailed compatibility chart – consult these or speak to the company representative for the first steps in material selection. Remember – each fluid has unique chemical properties and react with different elastomers differently – so a thorough knowledge of this is important.
2- abrasive content of the liquid being pumped needs to be considered – as diaphragms are the softer parts of the pump and come into direct contact with the liquid being pumped – there are many elastomers that are stronger and should be used for these applications – so it is important to know the abrasion content of the fluid being pumped.
3- Flex life of the diaphragm needs to be asserted – that is the number of times the diaphragm has to flex with each stroke- and how long this would take before a mechanical failure of the diaphragm under the operating conditions occur. Ensure these are replaced in time and that a spare replacement kit is always handy.
4– Temperature: Operating temperature of the process fluid is always important because, at higher temperatures, many materials become softer and hence less abrasion resistant, whereas at lower temperatures the diaphragm flexibility is reduced and hence pumping output is lowered. Since every diaphragm has its own has a range of working temperature – do note this before selection.
5– Hygienic Applications: For pumps used in food, beverages, dairy, personal care, and pharmaceutical industries, diaphragms must meet the relevant industry standards. Do contact a technical sales representative for details.
6– Cost: Of course the basic cost of different materials vary greatly. However, the total cost of usage of a diaphragm should be taken into account. Some things to keep in mind are purchase cost, flex life, downtime of equipment etc…
Here is a list of commonly used diaphragms in AODD pumps and their properties and costs compared relatively as high and low (initial purchase) – however, each manufacturer would have these published – this provides a snapshot guideline:
|Material||Recommended use||Flex life/ Abrasion Resistance||Cost factor||Temperature range|
|Neoprene||Water based slurries/ salt water||Excellent/||Low||-18C to +93C|
|Buna N||petroleum/oil-based fluids/leaded gasolines/kerosene/turpintine||Moderate /||Low||-12c to +82c|
|Viton||Applications where extremely hot also aggressive fluids such as acids, and chlorinated hydrocarbons||Moderate||-40C to +175C|
|PTFE||Aggressive fluids such as acids/caustics/ ketones/acetates||+4 C to +107 C|
|Santoprene||Abrasion resistant/ general purpose||Excellent||-40C to +107 C|
In conclusion, it is imperative to select the right diaphragm for the job considering the factors above. Prior Experience in selection is important and once one is confident of the characteristics of the liquid being pumped – one can speak to the company’s pump engineer to zero in on the best elastomer for the job. It is important to get expert advice. This will ensure safe, efficient trouble-free operation!
How AODD pumps or diaphragm pumps are used in very many industries?
AODD pumps or diaphragm pumps use the reciprocating action of elastomeric diaphragms and ball valves to pump a fluid. There are many combinations of elastomers and wetted parts – and the fluid to be pumped would define the specific pump to be used. Depending on the flow rate required and the height to which the fluid is to be pumped, the size of the pump should be selected.
How does it work?
A simple air-valve system is used to move the diaphragm rod. Flexible diaphragms are attached at each end of the diaphragm rod. The pilot spool is pushed back and forth whenever the diaphragm rod reaches the end of its throw. This action allows air to move the air distribution valve back and forth. The air distribution rod controls air flow to the left or right air chamber, reversing on each stroke. The four ball valves are operated by pressure differences in the pumped liquid.
Types of fluids that can be pumped and why?
Diaphragm pumps are very versatile pumps and are used in the transfer of highly viscous, abrasive, semi-solid, and shear sensitive materials. These pumps are self-priming hence operation is easy. They are easy to service with fewer moving parts.
Corrosive/abrasive fluids: can be pumped by selecting the wetted parts and elastomers to withstand the types of fluid to be transferred – the pumps are available in various materials such as Aluminium, Stainless steel (withstand abrasive) and Plastics (withstand corrosive) with elastomers like Viton, Buna N, Santoprene to name a few.
Flammable fluids: Fluids like Acetone, Benzene, Petroleum etc. that easily catch fire, are possible to be pumped because AODD pumps are air driven and hence they are inherently safe for use in explosive atmospheres. However, some liquids may generate a static charge, so the pumps should be completely grounded. However, it is recommended that one should use ATEX/IECEx certified pumps for such applications.
Highly Viscous Fluids – Viscosity is the resistance to flow. In other words, we can say it the stickiness of the fluid. Depending on the viscosity of the fluid, the pump size needs to be determined – The higher the viscosity, the larger should the suction and discharge pipe size be. Due to higher frictional losses in the pipeline for high viscosity fluids, the discharge pressure will be high.
Shear Sensitive Liquids like shampoos, milk and paint when subject to shear (or churning) – whilst being transferred – can result in a change of the product characteristics. Since AODD pumps run at lower speed and hence gently move the liquid, they are ideal for use in the transfer of such liquids.
Vapour Pressure: to pump Liquids such as diesel, hydrocarbons which have low vapour pressure, we need to use a pump that runs at low speed with a limited suction lift to ensure the pump delivers the required flow.
Thus we see that AODD pumps or diaphragm pumps are extremely important in industry and one should make sure one gets the right pump for the job. For a free consultation – book an appointment with our experienced engineers at www.teryair.com by sending written email to Vinay Sawant at firstname.lastname@example.org
A Quick Intro, why not?
Teryair provides integrated engineering that connects people, applications and performances within their budget through cost-effective mechanisms. They combine technology, experience and quality to deliver transformational superior behaviour. Teryair brand intro video shows how we effectively determine quality and performance through cost control solutions that are shaping the future of various industrial sectors.
How life changes, How emotions run to highs and lows – How the world can have tremendous highs and lows.
It was 15 years ago When we at Teryair realised the importance of quality and comfort which we needed to offer our customers worldwide. So we decided to bite the bullet and undertake the task of getting ourselves ISO certified. It was a relatively new concept in India, and us being a small company at the time – took on this (what seemed like in those years) mammoth task. We were sceptical, our staff was sceptical and friends wondered if we were crazy devoting the hours in training and details of cleaning up and matching g our operations to align with ISO.
So on that day – 11th of September 2001, When we finally after gruelling hours received the coveted green signal on the ISO – we decided to celebrate with a big dinner at the Sea Rock hotel – Mumbai. The evening is so clear in my mind – it was a speciality Indian restaurant – 5 stars all the way with a Ghazal group performing. The food was delicious, and our kids – all of 4 and 5 at the time were … And then a couple of calls came in. – put on your TV set and watch the news!!! A plane has rammed into the world trade centre. I think before we reached desert – the second plane had struck. I could not believe the surreal surroundings – our Joy at certification was turned to shock and sorrow at the horror of events unfolding – whilst here at the restaurant – life went on -serene and the music played on.
On that day, the world as we knew it, changed forever. Our lives at Teryair changed too – and still, today, When we proudly say – we are ISO certified and remember our elation!! there is a part of us that hurts – that still mourns for and silently prayers for the victims of that day who suffered when we were celebrating.