I have been in search of a simple steam trap testing description for the 5 basic types of steam traps. All I want is as follows:

Contact the downstream side of an inverted bucket steam trap and you should hear ____________ (hold/discharge, hissing, rattling, no sound etc...) if it is functioning properly.

Same for all aother trap types.

Does anyone have a sound pattern description for each type of trap they can share?

Not a direct proceedure, but several app notes available on the net:
http://uesystems.com/news/peultra.pdf
UE also has a sound gallery of sound samples from varies types of steam traps:
http://uesystems.com/tech_support_gallery.asp
SDT 170MD equipped with contact probe sound file indicates this trap has failed mechanically and is not performing its function:
http://www.sdtnorthamerica.com/wav/TChatter.wav
We offer a wide variety of Ultrasound inspection systems from a number of manufacturers.

Isn't an IR scan one of the most efficient methods to inspect steam traps?

IR is a very efficient way of testing steam traps but not all traps can be tested (they may be lagged etc.) I've also found that some traps leak thru by design and therefore the heat signature isn't as pronounced as one would normally expect. We've found the best method is to combine ultrasound with IR for trap testing.

Dasteve, I agree with your opinion. Because I have seen IR results to be too conservative that one team must always stay tuned to "traps".

One more thing I think is mentionable that flash steam downstream of steam trap should not be taken as problematic trap. You people may disagree.

When we test traps we use both ultrasound and IR. You need to hear what the trap is doing, which is only half the picture. Then you need to know what the temps are, together you get the whole picture.