Dust Collector Question

[Sean Troy]

I've always thought I should have the blast gate to the machine open and a second one for best performance of my DC. Does it matter where the second open blast gate is located? Closer to the dc or farthest from the machine I'm using? Thanks, Sean

[David Kumm]

The second gate theory is only valid if the gate is much smaller than the main and the collector needs additional make up air to keep the velocity of the main up ( 4" gate and 6" main ). You will certainly lose cfm at the machine when you open a second so be careful when doing so. The second gate if needed should be placed so the additional air is available to the larger pipe. Opening one near the collector is the worst of both worlds. Dave

[Sean Troy]

My main runs are 6" and all drops from them are 4"

[Jim Dwight]

Two 4 inch tubes have less area than one 6 inch. So the 4 inch drops is cutting the air in the main run. But the suction at the drop you want to use will decrease if you open a second port. But airflow in the 6 inch line will increase. If dust is collecting in the main, it could make sense to open a second drop (further away from the DC). But if you want more airflow at the drop you are using, opening a second drop will not help. You need a bigger drop, possibly branching at the tool with a Y fitting.

[Jim Becker]

Dust collection is all about airflow, not "suction". The more air that can move, the better the efficiency. As Jim D mentioned, opening another gate will help fill the 6" main, but it's going to benefit collection at the machine you're working with nearly as much as equipping it with a larger hood so you can enlarge the drop to 5" or 6" for maximum airflow. A 4" pipe can only pass about 400-450 CFM under best circumstances with a typical blower simply because that's all the air that can fit through it. A 6" pipe can get nearly 4x that much air through under best circumstances with a typical blower because the space is there to do so. The more air you can move in a given time period, the better the dust and chip collection.

[Ole Anderson]

Run with just one drop open to maximize airflow and collection at the tool. As (if) you get a buildup, the airway will narrow, velocity will go up and maintain an adequate airway. Self healing if you will. If that concerns you, just open a second gate occasionally to flush any accumulated debris out of the duct. Remember, velocity needs to be higher in vertical runs than horizontal ones. Sometimes we overthink these things.

A corollary is dust buildup in the bottom of your TS cabinet. Why worry as long as it doesn't affect the airflow at the blade.

Has anyone ever seen a major buildup in their ducts?

[Sean Troy]

What I found seems to work best is, if I half way open the next gate inline furthest from the DC.

[Larry Frank]

I think the answer is that it depends...dust collector cfm, static pressure,layout of ducts, gate size, etc,etc...

I think the best way given all the variables is to try it out...

[Sean Troy]

I think the answer is that it depends...dust collector cfm, static pressure,layout of ducts, gate size, etc,etc...

I think the best way given all the variables is to try it out...

I tried several ways and find having the second blast gate open half way works best.

[Alan Schaffter]

An optimum DC setup should move the max CFM that the motor/blower is capable of providing through the existing duct work, at the machine. You are trying to move as much air and capture as much dust as possible at the machine.

Opening a second gate, even partially, is a non-starter- there is absolutely no valid reason to do it!!!!! It won't improve CFM or SP at the machine. Quite the contrary- depending on location of the second gate, CFM (and SP) at the machine could be reduced by half or more with two gates fully open. Some folks would have you believe that opening two gates improves separation performance in a cyclone- not so. By opening a second gate you increase total CFM available at the blower but that will not result in an in increase in the air velocity- separation in a cyclone depends on velocity and velocity is dependent on impeller RPM (and duct and cyclone diameter.) Remember, a DC won't slow down, it will run at something a little less than the design speed of the motor (3450 RPM, etc.), so the velocity through the blower will almost never change. It will increase slightly (and result in an over-current- pop the breaker) if there is no ducting attached to the blower. Velocity is determined at each point in the system only by the diameter of the ductwork. Also, unless you have a commercial shop with two or more machines being used at the same time and a big honking DC, there is no reason to reduce the size of your drops- run the same size duct all the way from DC to machine. As for dust not making it up a vertical drop or settling in horizontal ducting- if that is happening you either have leaks, poorly designed ducting, woefully undersized DC (for the size of the ducting), or clogged filters.

[David Kumm]

As you have read, dust collection is complicated. Every system and every impeller will be different so the impact of opening gates can only be guessed. It will never increase velocity or cfm at the machine. It may improve separation in the cyclone. Although the impeller isn't changing speed, the amount of cfm entering the cyclone does affect the velocity in the inlet pipe. Every cyclone is designed to separate within a given velocity range at the inlet so ensure the particles spin enough times and at enough speed. Too slow or too fast will both send fines into the filters. You really need to measure cfm and velocity to know a correct answer for your set up. Dave

[Kurt Kintner]

The inlet to my ShopFox 2hp is 6 inch.... I reduced that down to 4 inch at that point, and ran 4 inch stove pipe around the ceiling, with drops to my machines, each with a blast gate. In my one man shop, this system works very well, even using 90 degree elbows.... I have a planer, which everyone knows, produces a lot of chips/dust. It clears that easily....

[Sean Troy]

https://www.pennstateind.com/store/TEMP1425S.html This the DC I have. The only difference is mine is the slightly older Red colored version and has 6" outlet.

[Jim Becker]

The inlet to my ShopFox 2hp is 6 inch.... I reduced that down to 4 inch at that point, and ran 4 inch stove pipe around the ceiling,

The thing is...4" duct can't provide more than about 400-450 CFM. You can't physically fit more air in there at the velocity the blower moves the air. 6" duct can carry nearly 4 times that much air at the same velocity. Dust collection is a matter of moving air in volume at low pressure. I'm not suggesting your system isn't working well for you, but it's also not working to its full potential. Again...'just trying to be clear about how duct diameter affects things.

[Ole Anderson]

An optimum DC setup should move the max CFM that the motor/blower is capable of providing through the existing duct work, at the machine. You are trying to move as much air and capture as much dust as possible at the machine.

Opening a second gate, even partially, is a non-starter- there is absolutely no valid reason to do it!!!!! It won't improve CFM or SP at the machine. Quite the contrary- depending on location of the second gate, CFM (and SP) at the machine could be reduced by half or more with two gates fully open.

Thank you Alan, I completely agree. Are we more interested in keeping the inside of the duct squeaky clean or maximizing airflow at the machine in an effort to keep our lungs squeaky clean? I vote for the latter.