Could my nanofilter be loading up already?

[James Gunning]

Randall,

I did notice something to consider with fitting an SDD to your blower. The impeller in your Powermatic appears to spin clockwise, (when viewed with the impeller horizontal and the motor on the top side-viewed from above). The SDD is set up with a CCW spin. (as viewed from above) If you couple them closely together like I did on my build, the airflow spin will have to reverse direction going into the blower. It will still work, but will result in some loss of efficiency. If you are able to put a longer duct between the blower and SDD, it may help that problem somewhat, but may result in too tall a unit in your confined space. The solution is an air straightener. Simply, a set of vanes in an "X" pattern in the center tube of the SDD. Essentially dividing the center tube into quarters. That stops the airflow from swirling and feeds the impeller with the smooth airstream it needs. It's a similar issue as the recommendation to have a few feet of smooth pipe feeding into the intake of the SDD (or any DC for that matter). It reduces turbulence in the airflow which will increase the efficiency of the blower.

I would say, in general, try to avoid using flex pipe to the extent possible and the amount of twists and turns for the airflow. Pretty much the same as a duct system design.

[Randall J Cox]

Wow, I never would have noticed that... Just my luck. Nice catch! Now I have something else to mod. Better to know now than later after it's all back together. Thanks again! Randy

[Andy Giddings]

1 PSI is about 27.7 inches of water, Randy. Google is your friend :-). I suspect you are not getting the filter fully clean when blowing which is why the drop is small. Not sure there is much you can do about it but might be worth giving Wynn a call to see if there is a better method

[Randall J Cox]

Randall,

I did notice something to consider with fitting an SDD to your blower. The impeller in your Powermatic appears to spin clockwise, (when viewed with the impeller horizontal and the motor on the top side-viewed from above). The SDD is set up with a CCW spin. (as viewed from above) If you couple them closely together like I did on my build, the airflow spin will have to reverse direction going into the blower. It will still work, but will result in some loss of efficiency. If you are able to put a longer duct between the blower and SDD, it may help that problem somewhat, but may result in too tall a unit in your confined space. The solution is an air straightener. Simply, a set of vanes in an "X" pattern in the center tube of the SDD. Essentially dividing the center tube into quarters. That stops the airflow from swirling and feeds the impeller with the smooth airstream it needs. It's a similar issue as the recommendation to have a few feet of smooth pipe feeding into the intake of the SDD (or any DC for that matter). It reduces turbulence in the airflow which will increase the efficiency of the blower.

I would say, in general, try to avoid using flex pipe to the extent possible and the amount of twists and turns for the airflow. Pretty much the same as a duct system design.

X vanes in top of SDD. Makes sense. Have you done? Kind of scary as they are right close and subject to being sucked into the spinning metal impeller (as I plan to mount the motor impeller up top, connected directly to the SDD). They would have to be made of something strong and anchored to the side of the SDD with pop rivets or something similar. Don't want drag so maybe sheet metal which is thin. How long would they have to be? Anybody out there done this, if so how? Thanks. Randy

[James Gunning]

Randy,

I haven't done it yet, but will be one of first chores when it cools down this fall. (un-airconditioned summer shop working in FL isn't much fun). My plan is to make the air straightener out of sheet metal, either aluminum or steel (It could also be plastic). It would want to be the same length as the center tube of the SDD. I was thinking of either pop rivets or screws to secure it to the center tube. I have the same concern about it going into the impeller, so the mounting wants to be secure.

The actual shape of the pieces I plan on is two flat rectangular pieces, each with a slot in the bottom center running halfway up the length. Slip them over each other and you have an X. If I use sheet metal I would probably solder the center joint. Then some trimming until it slipped into the center tube of the SDD. Tabs on the top of the x would fasten to the center tube. Difficult to get at the bottom of the center tube, so would likely only fasten at the top. It would not have to be airtight, nor a perfect X to work. All we're looking for is to stop the rotation of the airstream going up the center tube.

I can't remember where I saw it, but I've also seen this done with a cluster of flexible plastic tubes (about 1" diameter) filling the center tube as well. I'm sure it worked well, but I was concerned that method might be more apt to clog if longer stringy bits of wood got sucked into it. The X could get stuff sticking to it as well, but that seemed to me less likely.

[Randall J Cox]

Wow, I guess 3 in of water isn't much pressure. My SDD arrived today so my teardown of existing single stage system begins and the new configuration then will start. My first order of business is the vanes in the SDD. Randy

[Tim Campbell]

Hi Randall,

Of what it's worth, I reckon the whole line about having to match cyclone rotation with fan rotation and how straightening vanes will counteract this effect is a myth. I used to believe this myth myself, and set off to do some testing to determine what the effect of mis-matching fan and cylone rotations using 2 near identical cyclones connected in turn to my 2 HP fan. I then added flow straightening vanes and repeated the tests to see inf this made any difference. As you can see from the plotted data below, there's very little difference between the 3 different configurations.

Attached below are pictures of the two cyclones, the straightening vane in the cyclone outlet tube and the plotted data. The cyclone on the left is the MK 1 prototype which matches the fan rotation direction, the one on the right is the Mk 2 with opposing rotation. One note about the data, our domestic power supply is 50Hz which will result in airflows of around 20% less than what you would be expecting to see, but i think the relativity between the data whould still be applicable.

Cyclones x 2.jpgIMG_0185.JPGCyclone fan curves.JPGCyclone system curves 2.JPG