QUOTE(nathansnathan @ Aug 1 2012, 10:01 AM)
30r9 is the SAE rating for the high pressure. 30r7 is the equivalent low pressure version. They have a flourolastemer (sp) (like silicone) lining. I bought some of the low pressure stuff in 3/8 for maybe $60 for 25'. It's too bad the EU doesn't have such crappy gas or we could get it in metric.
I wonder what they use in Brazil? ... nevermind
Actually 30R7 and 30R9 are different mainly in that 30R9 is lined to resist the oxygenated fuels, 30R7 is not. these ratings are by the SAE (Society of Automotive Engineers)
30R9 also has a considerably lower permiability to gasoline than 30R7 i think it was something like over thirty times less permiable to gasoline vapours. Hence 30R7 is not allowed to be used as a replacement on newer smog controlled cars. use of 30r9 reduces the hydrocarbon smog problem. even when a car is just sitting, it is polluting by outgassing of the fuel. 30r9 reduces the hoses role as a source for this pollution.
30R7 will degrade in high oxygenated gasoline. 30R7 used to be specified for FI pressures. now we are starting to see 30R7 marked as unsafe for FI pressures. that is because the new fuels will weaken 30R7 over long exposures and can cause it to fail at high pressure.