pleas don't whistle while I work

March 18, 2009 10:41 AM

How can I stop a compressed gas regulator from whistling?

At work we use these every day to evaporate small quantities of solvents from test tubes full of sample. The evaporators are in the hood; we pipe dry nitrogen to them from a regular lab-sized size T cylinder, chained right next to the hood. The problem is that no matter how I adjust the regulator on the gas cylinder, it emits a high-pitched whine that IMO is more than just annoying -- it may pose a hazard to anyone with chronic exposure to the sound.

The evaporator requires low-pressure gas (not to exceed 2 psi), and when it's operating the flowrate is probably liters per minute. (Unfortunately I don't have a flowmeter that goes that high.) I think the problem is that most laboratory regulators are not designed to supply such high flowrates. I've tried three regulators like this one that I had lying around, all with different second-stage delivery pressures, but all of them make the same noise.

So, my questions: Is there something I can do to reduce the noise emitted by my current regulator? Or, if not, what are the magic words that I should look for in a replacement regulator?

posted by harkin banks to science & nature (8 answers total)

Well, (insert appropriate disclaimer here), but just a thought: are you entirely sure the regulators you're using are meant for such low pressures? I just had an incident in my lab where the regulator broke because we were going from full cylinder pressure to very low (15 psi) pressure... maybe you will have to look into supplier's options for additional regulator stages in your gas line.

Or if you can look into getting gas cylinders with lower pressures - we have a few different needs for helium tanks in our labs, one is for high pressure applications and the other is low, so we rotate the tanks - full = high pressure applications, half empty = lower pressure applications.
posted by lizbunny at 11:08 AM on March 18, 2009

actually, given that you appear to be using large volumes of gas, go with the additional regulators in line to step down the pressure in a few more stages than just one.
posted by lizbunny at 11:10 AM on March 18, 2009

The noise is probably a result of high velocity gas flowing through an extremely small opening. If you could arrange for most of the pressure drop to occur upstream of the regulator using something very restrictive that doesn't make noise (sintered metal filter, maybe?), this would probably help.

Perhaps you could test this theory by just barely cracking open the shutoff valve on your supply tank to restrict the flow there, just to see if this quiets down the regulator. I had to do something similar to shut up a fairly loud regulator on a welding gas tank, but that was a really long time ago.
posted by FishBike at 11:18 AM on March 18, 2009

I think the magic word might be flowmeter.
posted by Huplescat at 2:36 PM on March 18, 2009

A flow meter doesn't regulate line pressure, just flow rate.
posted by lizbunny at 2:39 PM on March 18, 2009

lizbunny: The regulator I'm using currently is rated to a delivery pressure of 0 - 15 psi, so I don't think I'm operating outside of its design parameters in terms of pressure drop. Putting an additional stage on the regulator is something that I hadn't considered.

But, my uninformed diagnosis is the same as FishBike's: gas flowing at a high rate through a small opening. FishBike, which opening were you thinking might be too small -- the one entering the regulator, or where the gas exits the regulator? Your "crack the supply valve" test seems like it would be testing if the regulator gas entry opening is too small, but not say anything about the size of the exit.

BTW, if I temporarily increase the delivery pressure to 10 psi, the whistle goes away. Don't know what that means.
posted by harkin banks at 5:42 PM on March 18, 2009

Actually I was thinking of the gas flow inside the regulator, through the valve that does the actual regulating if you see what I mean. So my thought was if you can introduce a flow restriction upstream of the regulator, that would drop the pressure on the inlet side of the regulator (only when gas is flowing of course). The regulator will then have to open its valve up farther to keep the same pressure on the outlet side and therefore the velocity through that valve will be lower.
posted by FishBike at 6:52 PM on March 18, 2009

.

Correct me if I’m wrong, but a pressure regulator on a high pressure gas tank is a fairly straightforward device, in that the only thing is does is to reduce and stabilize the outlet pressure which can be interchangeably metered as either PSI at the point of reduction or volume per time at the outlet. The later is more practical in low pressure applications, but they’re directly equivalent.
posted by Huplescat at 10:56 PM on March 18, 2009