Low pressure valve(?) for experimental musical instrument

[Natebanton]

Hello Forum members,

I apologize if I'm intruding, as I'm definitely not an engineer. But I didn't know where to turn to for help.

I'm a professional woodwind maker, specializing in bagpipes. I'm looking to try my hand at inventing a musical instrument that would basically "plug into" the bagpipe bag. It would be "powered" by the bagpipe and be played at the same time as the bagpipe, a one-man-band sort of thing. The problem is that the bagpipe plays at about 14-16 inches of water while my "add-on" instrument plays at about half that. I need to find a way to decrease the pressure without decreasing the volume of air supplied by too much. I'm hoping there is some kind of valve that would do exactly that? I know that there are valves to decrease the pressure of propane tanks down the household use, but I'm imagining that they would be designed only for bringing high pressure (300 psi?) down the low pressure. I need something reduces from "low pressure" to lower pressure.

I have actually had a fair amount of luck using tiny styrofoam balls inside of a 3/4" tube as a crude method of reducing the pressure, but I'm hoping for some idea that would be better.

Again, I'm sorry if I'm intruding. And if there is some other place my question would be more suited I'd be happy to go there!

Cheers,

Nate

http://www.elbowmusic.com

 

[MikeHalloran]

Try a Fairchild Model 10 pressure regulator.

http://fairchildproducts.com/subcat/6/High_Precision_Pressure_Regulators.php

Better yet, call Fairchild, and have a chat.


Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

All depends on the variation in air flow.

If your secondary instrument takes a more or less constant flow of air, then a fixed orifice would probably be your best bet - simple, small and cheap.

You can get regulators to do any sort of pressure, but at low pressures the size and weight might become too big.

Just try a fixed plate, maybe even thick cardboard and gradually increase the size of the hole until you get the right mixture of air pressure and flow.

As said it all depends on the variation in air flow for your second instrument and whether this varies a lot or a little and how quickly it changes.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Natebanton]

Hi,

I had tried the "orifice" idea first. What I tried was a hole drilled through a dowel about an inch long. That didn't work. As soon as the pressure was reduced enough the amount of flow was also too low. Would the fixed plate with a hole have different results?

Yes, both instruments work with a constant pressure. More constant the better.

This will be a small instrument, so the smaller and simple the solution the better. Much thanks for the suggestions.

Nate

 

[MikeHalloran]

The orifice by itself would be roughly equivalent to the tube you've already tried.

You have to go a little farther.

To give an example using player piano technology, you could have a _big_ orifice in a flat plate, say 1/2" diameter or bigger, to provide the flow you need, and close it off with a leather- covered flapper covering the downstream side, backed up by a hairspring, set up to allow opening at an upstream pressure bias of ~7"wc. That would give you a downstream pressure more or less consistent at 7" below the upstream pressure, which is not exactly the same thing as 7" above atmosphere. You will probably have to add damping to keep it from squealing.

OR, you could use a fat u-tube manometer that blows all of its water out into a top chamber at 7"wc or so. You start with 3.5" of water in the u-tube, and let the air flow. Of course it will be sensitive to the gravity vector, and the flow will 'warble', which may be interesting or aggravating.

OR, you can use player piano tech to make a pressure regulator, just a little fancier than what I described above. Find cutaway drawings of commercial pressure regulators to get started. You still may need damping, which is present in most/all commercial regulators, but may not be easily identifiable.




Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

If you've managed to get the right pressure drop, but not the flow, just make one or two more and place them in parallel. Or make it bigger to get the right flow then place more in series to get the pressure right. Or get a bigger plate and start drilling holes. Get the pressure drop right first with the right sized hole then just drill some more holes of that size until you get the right flow.

At these sorts of flows and pressures it will be a bit of trial and error, but a long length of tubing could also work which you adjust the length and size until you get the right mix of flow and pressure drop down your tube.

As I said earlier, so long as the flow into your secondary instrument is more or less constant then these sorts of systems work well. If the flow changes a lot but you need a constant pressure then you need something which can change to adjust accordingly.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[crshears]

You might be able to receive some excellent advice by visiting

http://www.pipechat.org/

and posting your question on one of their forums; I was a member there years ago and got some very valuable feedback about the manually-operated diaphone foghorns in use many years ago around the Great Lakes.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Compositepro]

A fixed orifice will only work for a fixed flow rate. A spring or weight holding down a disc over the end of a tube will always lift (open) at the same pressure drop across the opening. You just have to calculate the area of the tube and the force closing the disc to get the pressure drop you require.

 

[1gibson]

Multiple hole slide throttle? Simple, adjustable, about the easiest thing to prototype that I can think of. Possible to make it dynamic with a little more effort?