Delta 50-850 DC

[Denny Rice]

OK someone answer this stupid question for me. A friend and I were looking at a Delta 50-850 DC and we removed the plate that takes the 6" inlet and turns it into 2-4" inlets and behold to my surprise the 6" inlet wasn't really 6" but it was 4 inches. Don't get me wrong, the pipe that was the inlet was 6" in diameter the problem was Delta had spot welded a 4" restrictor plate inside the DC so effectively taking this powerful DC unit and neutering it? Why would you do this? A couple days later I was at Menards and seen a Jet 1100 series DC and the setup is almost the same except for the color of the unit and guess what there is no restrictor plate in the Jet unit.......Why did Delta do this? Just wondering.

[Gilbert Vega]

Bump*** I'm interested in this also. My guess is to keep the motor from tripping (?).

[Rick Fisher]

Well, I can only assume that they had a problem with the motors burning up. When DC's run without restriction, the motors can overheat?

If the motor is sized too big for the impeller, the machine needs restriction to slow it down. If unrestricted, the motor overspin's and burns out.

So they likely asked to have the 6" blocked to reduce warrantly claims.

This is likely something Delta asked to have done in Tiawan.

Its likely that the Jet is made in the same factory as the Delta, but Jet didnt ask for the restrictor.

[peter de tappan]

Rick, I think you've got things exactly backwards. If the IMPELLER is too big, the motor will be overtaxed, bog down and burn out - not the other way around. Lack of restriction has no adverse effect on an induction motor. Your table saw's induction motor will run fine with no board to saw.
I think someone at the Taiwan factory just screwed up.

[alex grams]

I concur with Peter. The added resistance from the restrictor plate would make then motor run at a higher load/temp. No resistance would mean less load. The bearings would be more likely to go at a higher RPM, but that would just be bad design.

[J. Greg Jones]

I'm far from being an authority on DC systems, but here is my understanding of the dynamics of how they work, and how a load, or lack of a load, can affect the system. If the impeller is oversized for the motor, then the motor could pull more amps to attempt to drive the load and overheat, that part is accurate. But I question the part about what constitutes a load and resistance in a DC system. Lack of restriction does have an adverse effect on a motor. The example of the table saw running with no board to saw is an example of full load restriction, not a lack of load restriction. Shove a board into the blade with full force and you will have the motor running with no load restriction, and it will likely bog down and if run long enough, overheat.

Likewise, a DC fed without resistance on either the inlet, outlet, or both will be operating under full load (no resistance) and will move the maximum amount of air possible with the impeller size and design. If the motor is not sized to handle this load, the motor will be overloaded and overheat. A DC unit under full restriction (all blast gates closed, etc.) will have no load and the motor will idle comfortably, just like a table saw running with no board to saw. It's worth mentioning that the above applies to a DC, which is designed to move large volumes of air at low suction, as opposed to a shop vacuum designed to move lower volumes of air at high suction. A shop vac that is starved for air will indeed put more load on the motor.

[Chuck Tringo]

Does anyone with a 50-760 know if they did the same to this? Mine will stay in the box for about another month and I cant check it. If so I think Ill the hacksaw might have to come out .

[mike holden]

DONT remove the restrictor! The airflow is balanced between inflow and outflow - you may just end up with a spinning impeller and NO airflow!
These are not positive displacement pumps where a volume of gas/liquid HAS to move with the pump. It is a fan that relies on a balanced restriction to move the air.

If you feel you have to try and "improve" it, take measurements so you can replace the restrictor later.
Mike

[Gary Muto]

When a shop vac is starved for air you can hear the motor RPM increase. It seems to me that this is from a reduction of load similar to the DC.

[Rod Sheridan]

The restrictor plate is to reduce the airflow through the fan.

Portable collectors can run with no duct connected, which results in very little restriction. The motor does not have neough power to drive the fan with that little restriction, so the motor will overheat.

If you do remove the restrictor, you will have to make sure that the system it is connected to has enough restriction to limit the airflow to a safe value.

You will have to measure the motor current to determine if you have overloaded the motor.

Regards, Rod.

[J. Greg Jones]

When a shop vac is starved for air you can hear the motor RPM increase. It seems to me that this is from a reduction of load similar to the DC.

A DC and a shop vac don't operate quite the same way. The shop vac works by creating a change in air pressure, or a vacuum (thus the name) while a DC is designed to move large volumes of air. The shop vac operation is similar to using a drinking straw. If you suck on a straw in the air, there is very little load on the "pump" (your mouth). Stick the straw in a thick milkshake, which is similar to plugging the inlet on the shop vac, and your jaws will feel the difference as the load increases.

[Chuck Tringo]

I still fail to see how a larger opening for the DC inlet would be bad; of course I have'nt take physics in a few years: after all they have dust collectors that are wide open; they're called fans...

[Rod Sheridan]

Chuck, increasing the opening can increase the airflow through the fan.

The motor is only capable of producing so much power, overload the motor and it will burn out, or trip the overloads.

The manufacturer put the restrictor in because they knew that without it, the motor would be overloaded.

Regards