Scubapro chrome plated brass regulators...

[Open Ocean Diver]

Plumbing the vacuum cleaner to the flowmeter. Just came up with this, modified my vacuum cleaners suction release collar and it give me a range of 5-25 CFM on the meter.

Next I’m going to try a gate valve teed-off the suction line, instead of a ball valve. Hoping for smother control and better range.

 

[rsingler]

How about a shot 90 degrees from the picture you have above.

Here you go @couv

 

[Couv]

Thanks @rsingler

With the system open as pictured: Can you show zero flow on the rotameter or do you have to slow the vacuum motor down with the dimmer switch? I ask as I'm not going to use a dimmer on my vacuum (nothing to do with safety BTW.) If zero flow cannot be attained, I'll have to incorporate another valve inline with the vacuum.

 

[lexvil]

Thanks @rsingler

With the system open as pictured: Can you show zero flow on the rotameter or do you have to slow the vacuum motor down with the dimmer switch? I ask as I'm not going to use a dimmer on my vacuum (nothing to do with safety BTW.) If zero flow cannot be attained, I'll have to incorporate another valve inline with the vacuum.

While I don’t know if Rob can get 0 flow with the pump on full speed I can’t imagine with that ball valve full open that he couldn’t, somewhere around 1/2 open should do it.

 

[Open Ocean Diver]

With a one inch tee and ball valve opened, mine will go to zero without varying the vacuum motor. Problem with mine is the one inch ball valve I have is hard to turn in small increments. Not sure if it’s just a bad ball valve.

 

[rsingler]

With my smaller tee and ball valve, I can't get close to zero flow with the valve open. Perhaps because I chose a tiny, but supposedly powerful shop vac. I have to use my dimmer, and zero flow is at about 15% rpms with the valve open.
I mostly use the ball valve as a way to modulate the low SCFM half, for reasons the engineering experts alluded to above: with a slowly advancing dimmer switch, the motor is silent, then kicks in, albeit at a 15% rpm rate. But with the ball valve closed, that lowest rpm immediately generates 5 SCFM, which I can eliminate with the valve.

A smaller vac motor and a larger PVC pipe and valve prior to the 3/4" rotameter opening will probably do the trick without a dimmer, however.

And I'll bet that it makes a difference which flow path the rotameter is plumbed into - straight in vs at a right angle. You might even be able to get more creative in making the rotameter arm less efficient (read: lower flow) with a Y-fitting instead of a tee.

 

[Angelo Farina]

You should not us a normal dimmer for controlling the speed of a fan. You need another type of circuit (technically not a dimmer, also if commercially they give it this improper name) for that, which can buy cheap on Ebay: 220V 4000W Variable Voltage Controller For Fan Speed Motor Control Dimmer Tool | eBay

 

[Open Ocean Diver]

That’s a lot of power, most electric ranges here in North America run on 220V in and around 3000 to 5000 watts. Our vacuums and shop vac’s usually are 120V plugged into 15 amp circuits. Most light dimmers here are between 300 and on the high side maybe 1000 watts.

The eBay unit is a larger phase controlled variable voltage supply, same as our smaller household light dimmers, works on the same principal. Where as a variable transformer (Variac) will not change the shape of the AC waveform.

 

[rsingler]

The eBay unit is a larger phase controlled variable voltage supply, same as our smaller household light dimmers, works on the same principal. Where as a variable transformer (Variac) will not change the shape of the AC waveform.

So this 110v version is still not better than my cheap dimmer?

Should I look for a cheap Variac? I just want it so @couv won't yell at me...

I'm not sure his smile is worth the $62 difference...

 

[Open Ocean Diver]

Haha

The cheeper one is only better than your little dimmer because it will handle the full circuit potential and then some if you believe the rating. I don’t know many household 120 V plugs rated at 4000 W. The second one will be better for a variety of loads and capable of using the full circuit potential 20amps is perfect for home use, has fewer components to fail and you will have it for a lifetime. A true industry standard. $72 is well worth it you’ll have it forever, truly a robust piece of equipment, no electronics to fail and mimics exactly what’s coming out of your plug at a reduced voltage.