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Help figuring out static pressure for my 6" PVC duct run

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Forum topic by RonGoldberg posted 09-16-2013 12:30 AM 952 views 1 time favorited 10 replies Add to Favorites Watch
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RonGoldberg

33 posts in 1083 days


09-16-2013 12:30 AM

Can anyone help with this calculation. I have come up with different numbers each time I use someone elses charts for static pressure. Please, respectfully, don’t refer me to Bill Pense’s web page. He rocks and is an amazing resource. What I would like is for someone to just check my work, that is it.
Total:
18 feet of 6” diameter PCV
4, 6” 45 degree elbows
1 blast gate
2 feet of 4” flex hose.

Can responses show me that math that you are using.

Grateful,
Ron G


10 replies so far

View crank49's profile

crank49

3481 posts in 1696 days


#1 posted 09-16-2013 02:23 AM

That’s not enough information.
I assume you are looking for the static loss for that duct system, but the loss of pressure is related to the velocity, and hence the volume of air going through the system.
Are you running 6” PVC from a collector to a blast gate and one 4” flex hose. Why?
You didn’t mention any WYEs or TEEs.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

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RonGoldberg

33 posts in 1083 days


#2 posted 09-16-2013 12:07 PM

Michael,
Thanks for your quick response. I read/was told that to figure out the SP, I should look at my longest run from the cyclone and base the calcuations on that run. I will ultimately have 5 machines connected (running only 1 at a time). Machines are: 2 HP TS w 4” port, 2 HP BS w 4” port, 13” planner with 2.5” port, 6” jointer w 4” port and lastly router table with 2.5” port. All the machines will be fairly close to the cyclone inlet (ie, TS will be about 5’) I hope to have a main trunk line (that is 12 feet long w Wye’s coming off, nowever, I thought I was just to look for the run that would potentially have to most SP—that is the one ending in the band saw). I would keep blast gates closed while operating the BS. Can I email you a diagram? So, there is the 12 foot trunk line that drops with two 45 degree elbows, followed by a vertical piece of 4 foot 6” pipe, followed by two more 45 degree elbows, then 1 more foot of straight 6” pipe, then blast gate, then 2 feet of 4” flex hose. Does anyone know how to take a powerpoint pic and post it so everyone can see what I mean? All responses welcome.
Thanks,
Ron

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RonGoldberg

33 posts in 1083 days


#3 posted 09-16-2013 12:17 PM

Michael,
By the way, just read the tag line as your signature. Now that is FUNNY and certainly true!

View RonGoldberg's profile

RonGoldberg

33 posts in 1083 days


#4 posted 09-16-2013 12:48 PM

I hope this works….above are the pics of my layout.

Ron

View bigblockyeti's profile

bigblockyeti

1739 posts in 445 days


#5 posted 09-16-2013 01:06 PM

The static pressure will be the same for any run to any of the tools you have connected, assuming the air in the ducting is in fact static. It will depend solely on the performance of your dust collector.

View RonGoldberg's profile

RonGoldberg

33 posts in 1083 days


#6 posted 09-16-2013 02:17 PM

OK, now I am super confused. I am trying to figure out WHICH cyclone to purchase based on size and set up of my workshop. Basically, I could go ahead and get a 5HP Clear Vue and spend big bucks or I can get a smaller system with less CFM rating. Say for example, I get the PSI 2HP portable cyclone. It is IDEAL for my low ceiling height basement and I just want to make sure it is powerful enough. Here are the manufacturers specs on the unit:
•Small height and small footprint: 7ft tall with a 27 1/2” x 21-1/4” footprint
•1025CFM dust collection through the cyclone for ultra-fine filtration
•14” aliuminum impeller provides superior aerodynamic performance
•.5 micron filter with 350 sq ft of surface area keeps fine dust out of your shop
•Includes our exclusive Re-Circulating cleanout system that eliminates the filter can and need to clean it.

The guy, Bill, that is helping me at Penn State is extremely nice, knowledgeable and pleasure to deal with, but I just wanted to get a 2nd opinion. See the diagram in above post.
Thanks,
Ron

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bigblockyeti

1739 posts in 445 days


#7 posted 09-16-2013 03:05 PM

So you’re looking more for the pressure loss at a given air flow rating it sounds like? Pressure is one component to be considered but CFM is what will equate to air velocity necessary to keep the dust and shavings suspended in the air back to the collector verses falling out of suspension into the bottom of your trunk line. I would be less worried about the longest line you have identified as it looks like it would only be connected to the mortise or bandsaw, neither are going to produce tremendous amounts of large shavings. The planer is going to be your biggest problem. If you are going to be planing any boards close to the max width of your planer, I would strongly recommend a 4” hose instead of a 2 1/2” hose as it could clog very quickly. My DW734 would clog a 2 1/2” hose planing only 6” wide boards regardless of what was trying to draw the shavings out. With a 4” hose ~ 5’ long straight into a 1hp dust collector (even with fairly plugged filter bags) the problem of clogging was gone. I know it’s a bit subjective, but I think you could get by with the 2hp PSI with no problem given the size of your shop and what you’re trying to accomplish, so long as you keep the four lines you’re not using blocked off some how while not being used.

View mummykicks's profile

mummykicks

57 posts in 527 days


#8 posted 09-16-2013 07:01 PM

http://www.engineeringtoolbox.com/duct-friction-pressure-loss-d_444.html
can be used to calculate friction drop. The 45 elbows won’t hurt it too much.
Using your values I get 1.27” for 18’ of 6” and 1.1” for the 4” section, so 2.3” of water total pressure loss.

Power requirement to push 1025cfm through this is calculated as follows:
Q = cfm
P = pressure – in of water
d = density of air .076 lb/ft^3

Power = Q(P)/(6350 x d) in horsepower

So:
1025(2.3)/(6350 x .076) = 4.8hp

Generally speaking the fans will be rated at a given cfm for a given pressure. The 5 hp version says it does 1400 or so cfm, which is probably the no load flow rate I’m guessing.
They should have a fan curve for that blower that you could get to better estimate what power you’d need for that flow rate.
Based on the above you’d get something like 500cfm with a 2hp system and obviously half the flow velocity.

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MarkwithaK

370 posts in 1903 days


#9 posted 09-17-2013 12:59 AM

Agreed with many of the above statements in that you are most likely NOT looking for static pressure. It can get confusing. This is a rather decent article on the subject:

Static Pressure

-- If at first you don't succeed then maybe skydiving isn't for you.

View djg's profile

djg

104 posts in 887 days


#10 posted 09-26-2013 09:08 AM

use Bill Pentz static pressure calculator. It works perfectly for this. just search the web for staticcalc.xls enter your information and it will calculate what you need.

DJG

-- DJG

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