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blowers

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Any blower has a variable output if you put a diverter in the path.  What are you burning? Coal, Charcoal, Coke, Peat, Lignite,...What country are you in?  Suggestions local to me may be VERY expensive if you need international shipping.   Basically any universal motor can be controlled by a simple old fashioned resistive rheostat.

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Here's the thing that everyone should understand about blowers .....

It's not necessary to vary the speed of the motor, in order to vary the volume of the blower.

By using a gate valve, or a damper, on the EXHAUST side of the blower, you can control the volume of air, without overloading the motor.

You will notice, as you close off the discharge of air, the motor RPM's will INCREASE, and the amperage will reduce.

This is because the load on the motor has been reduced.

 

The only time reducing the exhaust air volume can present a problem, is in the case of a blower that relies on the intake air flowing over the motor, for cooling.

In that case, a diverter gate in the exhaust, is your best option, ... but the motor will always be moving it's maximum CFM, and drawing the full amount of power required to do so.

.

 

 

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go to the big box store like lowes/Home depot get the simplest bathroom vent fan their about 15$. You can either get a light dimmer switch to control it or you can make a damper to divert some of the air blast away from the forge. 

 

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21 hours ago, SmoothBore said:

Here's the thing that everyone should understand about blowers .....

It's not necessary to vary the speed of the motor, in order to vary the volume of the blower.

By using a gate valve, or a damper, on the EXHAUST side of the blower, you can control the volume of air, without overloading the motor.

You will notice, as you close off the discharge of air, the motor RPM's will INCREASE, and the amperage will reduce.

This is because the load on the motor has been reduced.

 

The only time reducing the exhaust air volume can present a problem, is in the case of a blower that relies on the intake air flowing over the motor, for cooling.

In that case, a diverter gate in the exhaust, is your best option, ... but the motor will always be moving it's maximum CFM, and drawing the full amount of power required to do so.

.

 

 

I guess I still don't understand this Smoothbore.  I thought it was if you closed off the air *inlet* then the impellers weren't trying to push as much air and that would reduce the power used by the motor, but if you closed off the exhaust, the back pressure created more work for the motor.  I really do want to understand this because I'm designing a forced air propane forge and I have a blower from the kids bounce toy that has been in storage for a decade.  It puts out way more air than I can imagine would ever be needed for a forge, so I need to determine if it's better to restrict the intake or exhaust or if it's better to divert the excess air somewhere.

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Either way Buzzkill, block intake or outlet and the impeller isn't moving as much air so it doesn't work as hard. As Smoothbore says you can hear it, the motor speeds up and if you put a meter on it you can see the power requirements fall.

Fan impellers are "transparent" pumps there is no solid barrier to material movement in the pump. This means back pressure just keeps the impeller from moving as much material and less material moved the lower the power to do so. An propeller on a boat or airplane are examples of transparent pumps, stopping air or water from entering or leaving only results in lower resistance.

A positive flow pump is another thing entirely, a Root's Blower for instance is basically an interlocked pair of two lobe cog wheels. When they turn the material caught between them has NO choice but to move to the outlet. If blocked either the drive motor stalls, the blower breaks or whatever is blocking it breaks. When you see the bug catcher on a dragster explode this us what happened. The engine may have dropped a valve and back pressure exceeded the mechanical strength of the blower housing. Oh yes a 6,000hp engine runnning on 7 cylinders can more than drive a Root's blower to self destruction, often while blowing the heads off the engine.

A hydraulic pump or motor is a positive flow pump, interlocking gears. The bypass is in the valve body or on some occasions in the pump output manifold.

Yeah, too many years keeping the hydraulics on the drill working. As Mr. Spock said to Bones, "constant exposure results in a certain degree of contamination."

Frosty The Lucky.

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Thanks for the clarification.  I tried blocking both (one at a time) on this blower, but I guess the motor is strong enough that I could not detect a change in rpms either way.   It sounds like the bottom line is I can restrict either the intake or the exhaust without harming the motor, and that was my main concern. Now I just have to find an inexpensive way to use a solenoid (or other relay-activated electronic means) to open and close the air to set points to move on with my design.

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16 hours ago, Leon Renaud said:

go to the big box store like lowes/Home depot get the simplest bathroom vent fan their about 15$. You can either get a light dimmer switch to control it or you can make a damper to divert some of the air blast away from the forge. 

 

That's what I did and it works great.:D

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I built a sheet metal "snout" for a small squirrel cage blower that was originally designed for a air duct booster. It fits perfectly onto my forge's air pipe. I cut a 3.5" hole on the side of the housing for intake, then fabbed a "gate" of sheet metal bolted on with a 1/4-20 bolt and nylock that I can simply pivot over the intake hole to vary output. I reasoned that restricting intake would reduce the load on the motor whereas reducing output would build pressure inside the housing and work the motor harder. Plus, I saw my buddy's high dollar store bought blower and it has the air gate on the intake side as well.

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8 hours ago, Buzzkill said:

Thanks for the clarification.  I tried blocking both (one at a time) on this blower, but I guess the motor is strong enough that I could not detect a change in rpms either way.   It sounds like the bottom line is I can restrict either the intake or the exhaust without harming the motor, and that was my main concern. Now I just have to find an inexpensive way to use a solenoid (or other relay-activated electronic means) to open and close the air to set points to move on with my design.

Just make sure the motor doesn't depend on air from the blower for cooling. It's all good then. Yeah, I have an old forge blower I hooked up to a 1/3 motor and it doesn't care if I choke off either or both ports it doesn't change speed. I bet if I squirted water in it it would! :rolleyes:

Frosty The Lucky.

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Here's my home made blower. Funny thing today I forged for a couple hours and the air flow just didn't seem right. After I was finished I noticed the butterfly valve on the forge air pipe was closed the whole time! Was still able to heat the work but it was slow going. Sheesh its tough getting old. The sheet metal is riveted then I taped it for leaks. It was open on one end so I made a box to cap it, then the snout with flanges that I riveted to the box. 3.5" hole saw for the intake and a scrap of flat 18 gauge for the gate. Added a toggle switch and a 10 foot cord. Works great when the butterfly is open!

.2016-02-27%2009.42.24_zps2eyokzrl.jpg

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I just read on another site that all vacuum motors can be rheostat (Dimmer Switch) controlled. Not a week goes buy i don't see old shop vacks curb side on thrash day usually missing the hoses/attachments ,It wouldn't take much to make a nice blower out of the motor off one of these for very cheap!

 

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On 3/15/2016 at 9:53 PM, Leon Renaud said:

I just read on another site that all vacuum motors can be rheostat (Dimmer Switch) controlled. Not a week goes buy i don't see old shop vacks curb side on thrash day usually missing the hoses/attachments ,It wouldn't take much to make a nice blower out of the motor off one of these for very cheap!

 

i was wondering the same thing when i looked at the link above   one of the items was a shop vac and then it clicked all my vacs have hose ports for useing as a blower or directing air away when ive done drywalling i fire one up and put hose out the window to help keep dust down  but they get alittle hot  on the motor i will have to investigate this more

 

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Shop vac's are loud enough to require hearing protection.  As an electrician, I can't recommend "off label" uses for electrical devices out of safety concerns.  All dimmers aren't the same, many will present fire hazards if used improperly.  A vacuum draws a lot of current which would exceed the wattage limitations on most dimmers.  Anything getting used in the vicinity of water should be properly grounded, GFCI protected, UL Listed for wet use, and be connected in a manner that mitigates water infiltration.   None of that is remotely possible using off-the shelf electrical fittings, an exhaust fan, and a dimmer switch.

Take a look at bounce house blowers like this one  it's $70 bucks and it's built for exterior use.  That's cheaper than most bathroom exhaust fans and it won't take a whole lot of work to attach to your forge.

It's worth pointing out that insurance adjusters have been known to deny fire damage claims when they find anything that's not up to code, regardless of whether it caused the fire or not.

Just because a dimmer technically controls a fan's speed, doesn't mean it will behave as nicely as you'd hope.  There can be significant lag in the motor's response time.  If you don't bump the speed up to account for starting currents, the motor stalls or wallows in startup.  In extreme cases, you'll be riding the control to keep it from either burning up your stock or your motor.  The simplicity of a gate valve gives instant control without much risk.  Plus, it's good insurance to have a little air flow during "idle" to keep coal gas from working it's way into your air pipe. 

A coal gas explosion cracked my old bottom blast forge.  When I turned from the anvil to see what popped, I was just in time to see my fire landing back in the fire pot! 

 

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