Why there is no pressure regulator on helium/hydrogen tanks? So I've had people filling party balloons for me with helium tanks which had no regulators. Lately I've also seen local meteorologists filling large weather balloons from hydrogen cylinders (180 atm) which also didn't have a pressure regulator.
Are they doing a really bad thing, or is no regulator not a danger for such cases where you aren't doing other things at the same time and can control the flow rate as needed? 
And why?
 A: Usually it's not quite true that there is no regulator - typically these types of cylinders have a pressure reduction valve that doesn't look like much. There's nothing to "regulate" but they reduce the pressure from 100+ bar to something that makes sense for filling balloons.
A similar thing is used in scuba diving: the "primary regulator" takes the pressure from the tank down to something that is just a bit above the water pressure, after which the demand valve (the thing in your mouth) can be used to get the pressure just right for breathing under water. Again there are no knobs to turn - there is a diaphragm that "senses" the water pressure and provides just enough counter force to allow air to flow, but not to create excess pressure.
See diagram (from http://www.best-scuba-gear.com/images/unbalanced-diaphragmw.jpg):

These things can look like just a valve, but they don't allow the output pressure to get above a certain value. The ratio in area of the diaphragm compared to the area of the valve determines how insensitive the output pressure is to the input pressure.
Here is a picture of a "rental" helium tank (zoomed just on the pressure reducer). You don't see a gage - but I'm pretty sure that the inflator body has just this kind of mechanism in it (from http://www.craigswarehouse.com/web_images/Helium1a.JPG)

A: For filling balloons - whether for parties or research - it's not so important to control pressure. In fact having a regulator in line would only slow down the process. There are compatible gas regulators for nearly every gas including He and H. Some require special materials - such as Viton O rings for oxygen compatibility. Regulators are used more often for reducing the cylinder or plant pressure to a more appropriate level for controlling smaller flows or setting a pressure.
