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!