DC questions

[Jeff in Acton]

I have a 1hp dc and I assume its normal for the motor to slow a bit when the 4in hose gets cut down to 1 1/2 in as it does when I hook it up to my bandsaw.Is this normal and will it hurt the motor over time?

[William Young]

I had a 1HP first and now a 2HP but neither one ever slowed down even if I temporarily block the hose off completely. It dosn't sound normal to me but maybe it is common to your particular make and model. Worth checking out and seeing what others have to say about it.
W.Y.

[Bryan Cowing, Innerkip On]

I think you are hearing the volume of air slow down because of the restriction.

[Jeff in Acton]

Your right Brian the air volume is decreasing,but doesn't that also mean the motor is slowing down and laboring to pull the full amount of air that it is designed to pull.Thanks for your input,Jeff

[Lee Brubaker in Edmonton]

the only time the motor should perhaps sound different is when it is asked to deal with the DC trying to handle more air than it was designed for, or when there is a restriction and the DC is gasping for air. Frankly, I don't think the motor should "sound different" under either of the above conditions, but there will be a difference in motor amp draw, and the sound related to air velocity. I think I would check with the DC manufacturer.

[Ken in Regina]

Jeff, you will normally hear a change in the apparent motor speed when the air is restricted, but it will speed up. You can test this by simply using your hand to block the hose on your DC or shop vacuum. When you restrict the air flow, the motor speeds up.

This seems the opposite of what you might expect, but it's just really basic simple physics at work. When you reduce the amount of air flow, you reduce the amount of work the motor has to do. That is, the less air flowing through the hose, the less air the impeller has to move, therefore the motor is able to spin faster.

This will only be a problem for the motor if it depends on the air flow for cooling and you restrict it to the point that it's not cooling properly for long enough to do damage.

The only other problem will be that your DC hose needs a certain volume of air flowing through it to carry the chips and dust. If it doesn't have the necesary air flow, it won't work as effectively.

If your motor is actually slowing down when you restrict it to 1 1/2" there must be some other problem. Are you sure the motor is slowing down, or is it maybe just the change in sound from the lower volume of air flow, do you think?

[Dave In Cavan]

Right on. If you have a clamp on ammeter or know and electrican who does you will see that the motor amps will drop when you restrict the input or airflow. Which means the motor isn't working as hard as cfm have dropped. This only applies to centrifugal fans and pumps not positive displacement type. The only way you can check out the motor is to have an electrician put a mega-ohmmeter on it. This gets expensive. Keep a close nose to the motor and see if you can smell the insulation cooking or breaking down or the motor windings over heating.
Dave

[William Young]

[Wayne in Red Deer]

This info doesn't have to do with your motor sound but more with the air volume at your machine. I was having problems with my 1 HP unit giving me sufficient flow when reduceing to 2 1/2 in or less for certain applications, I couldn't get enough flow to draw away hardly any sawdust. The problem was I was reducing at the machine, the solution was to reduce at a point not much more than a foot from the inlet on your DC and run the appropriate sized suction line to the machine you are working with. This may not help with the motor if you have a problem there but it sure improves the suction on small attachments

Wayne

[Dave In Cavan]

As Ken pointed out it's all about cfm. and velocity. The volume of air entering through the 2 ins dust port slows down dramatically once it gets into the 4ins line and the dust will precipitate out of the air stream. This is the principle of the cyclone separator. By running the 2 ins line back to the fan the air velocity is kept high enough to carry the dust. I have a 2hp system with 4 ins lines. When I use a piece of machinery with 2 ins port I open up 2 or 3 other ports further down the line to provide sufficient volume of air to the system to maintain velocity.
Hope this helps.
David

[Chester Van Ness]

Jeff: Whils it's true that you will get better velocity in a smaller Dia. line, the machine you have is not meant to suck on a 2 1/2" line. the smallest line that you should use is 3". DC's don't have the clearances that vacs do and if you starve it for great lengths of time you will even notice that the fan housing will start to heat up. the main header in your shop should be the same size as the inlet to your DC and i mean after you remove the plastic "Y" thingy if yours has one. By kepping the header the same size you areable to provide the volume at the machine your sucking from and then you run a short piece of 3" to the machine using a tapered reducing adapter at the machine.Hope this helps. Chester