How can I build a better pulsed pressure generator?

Sorry I will try again. Ditch the compressor. Use a blower. Delta BFB1224GH-AF00 4PSI static pressure and 65 dB (digikey). You may need a receiver tank.

To define a pulsed pump requires specs for pressure (PSI) , flow (CFM) and load impedance and pulse rate if really necessary and noise level specs.

Without this implementations will only match your requirements by accident.

Continuous air pressure depends on load profile of the fan vs load. Will any fan work? Depends on above specs.

pulsed pressure? Is this essential? Then you need a silent valve (rectifier) and an oscillating pump (e.g linear solenoid or better a reciprocating tiny piston).

I did :-)

I wish I knew where I can find electrically operated ones. They don't have to last forever, it's not for production. The plastic one I tried to kludge lasted only minutes, became hot ... gone.

Thanks. Maybe I'll call them because I can't find any electrically operated ones (with solenoid). Or I need to get a big enough solenoid.

[...]

--
Regards, Joerg 

http://www.analogconsultants.com/

That really looks like it wuold turn into a science project for me :-)

The linear actuators in there look like they may burn up if I use them for compression.

--
Regards, Joerg 

http://www.analogconsultants.com/

Nah, that really wold be too much work for just this one task.

--
Regards, Joerg 

http://www.analogconsultants.com/

how about one of them big rotating solenoid, aka. a DC motor ;)

shouldn't be a big problem to find one with the power you need

motor + 2 clevis bearings and a pneumatic cylinder (or maybe a bellow made from an inner tube)

might even be possible with a pneumatic rotary actuator

-Lasse

I recently fixed my Expresso machine pump. It used a spring loaded AC solen oid rated for 3 minutes duty and ran from a single diode off AC. The pump o scillates each half cycle and supplies high pressure water at 2 cups per mi nute into the boiler. It uses an integrated nylon valve to control the flo w and costs about $60 for my Rancillio machine. They all use similar solen oid pumps.

That essentially what we have now, less the cylinder, using a valve switch instead. All you need is a powerful motor (in my case that is an electric drill) and a sort of poor man's bell crank. An alternative might be a wiper motor for trucks or large aircraft which already has the bell crank. But this only allows sort of sinusoidal excitation, not real arb-style. Does solve the compressor noise problem though.

--
Regards, Joerg 

http://www.analogconsultants.com/

What about those breast pumps ?

Aww, rats! I knew I should have kept the parts of our old Saeco espresso machine when it died. Now we went back to lowtech, the old Italian stovetop cookers. But we do have one fancy version in polished stainless steel.

Thanks, this is a good idea.

--
Regards, Joerg 

http://www.analogconsultants.com/

don't use the full rotation, servo the motor like in the woofer thing

some of those big RC servos for big helicopter and such can do

60deg/0.08sec and the through a gear box, though the probably probably don't have the power you need

-Lasse

It is very tough to get enough gusto out of that, even if I had a big stepper plus gearbox.

Maybe I could try to obtain one for a drone. But then I'd have some unmarked cars sitting in front of the house soon :-)

--
Regards, Joerg 

http://www.analogconsultants.com/

I don't know the unit mmH2O but this converter says 4psi is about 2800mmH2O:

The blower doesn't even come close and derates substantially for airflow.

--
Regards, Joerg 

http://www.analogconsultants.com/

[...]

I think a device powered by a couple of AA cells will be a few orders of magnitude off in the power we need :-)

--
Regards, Joerg 

http://www.analogconsultants.com/

How about a big woofer on the big end of an exponential horn? About 15 years ago the fellow I worked with built an exponential horn with cardboard and paper mache, I have no idea of the pressure at the end of the horn, but it would knock over paper targets at 20 ft. Mikek

do you need a gear box?

1/50 gallon ~= 75cm^3 -> 40mm piston x ~60mm stroke

3psi ~= 21000 pascal

21000 * 20mm^2*pi ~= 27N

if the crank is only ~60mm you only need few N/m

I think that is doable with a stepper

-Lasse

It is, but only if you have a serious stepper like this one:

And then one has to hope that the forward-reverse acceleration can do the 1Hz bas and 25Hz small excursions. When you go this fast stepeprs can lose oomph.

--
Regards, Joerg 

http://www.analogconsultants.com/

It's unlikely going to work because in order to create pressure in the

1Hz spectrum it would have to compress the whole big column of air in the horn. That's a lot, and speakers do not have enough excurion for that. Also, it would not solve the problem with the failing surrounds.

--
Regards, Joerg 

http://www.analogconsultants.com/

the big one still has 3Nm at 1000hz

and if you used a dual action cylinder you could "preload" the other side with 3psi so that you only need half the force

though the inertia of the rotor/piston etc. might be the limiting factor not the force from pressure

-Lasse