Polypropylene pumps are a suitable low cost alternative to SS pumps Also suitable for Good for acids and alkalis But not suitable for HOT Liquid transfer.  While Stainless Steel AODD Pumps best sutable for HOT LIQUID transfer also usefull for ACIDIC and ALKALI Liquid transfer.  And  Aluminium AODD Pumps most commonly used for pumping of water and water based liquid, oily fluids. Not suitable for ACIDIC or ALKALI higher concentration. But can be used for diluted acidic or alkali concentrations liquid.