Anybody know the losses associated with a "T" connection vesus a "Y",
say at angle theta? I'm sure this is a standard problem in a fluid
I notice the Lee Valley catalog ONLY carries the "Y". Woodcraft carries
"Y" and "T". Knowing the reputation of the Lee Valley staff, I suspect
they do not carry the "T" because of the large vacuum loss around the
sharp corner....and, therefore, refuse the sell it. Just a hunch.
I want to use "T" because they fit my layout better..but...hey it's
nice to have strong suction forces too.
Takes me back a long time to when I did these calculations at university.
I found a decent paper from the radon mitigation industry.
http://www.wpb-radon.com/pdf/Pressure 20drop in piping 201996.pdf
I did not expect this to include "Y" fittings, but the conclusion for the
typical 4in DC duct is
a "T" was about 22 ft of equivalent straight pipe. i.e. pressure drop is the
same as having 21 addition feet of pipe.
A sharp 90 deg (typical fitting) is almost 6 ft of equivalent straight pipe.
The radon installations are low flow compared to a DC.
In general, avoid "T" fittings. The "Y" is going to be somewhere between
the 90 and the T, but closer to the "T".
Maybe someone else will post more accurate factors.
Yes I could but that was a long time ago, not now.
Let me try a little analogy.
Remember a couple of things:
1) Crap doesn't run uphill and neither doe dust for very long.
2) There are no "T" fittings made or used in a sewer stack, only "Y"
fittings, and with good reason.
Dust collectors and sewer stacks are a lot a like.
Neither one handles sudden changes in direction well.
Enjoy you D/C equipped with "Y" fittings.
The link didn't work for me. I appreciate your answer, though. As I
mentioned in another reply, I suspect there's a cosine of theta
involved (or maybe a sine of theta)....So a T causes a 22 foot pressure
drop, then a Y of angle theta would cause, a guess:
Pressure drop = 22*sin(theta). So at 90 degrees (a T), the dropis 22
feet. At 0 degrees (straight pipe), the loss is zero.
So at 45 degrees, the loss is 22*sin(45)"*0.707 = 15.5.
I know this is back-of-the-envelop, but is it even close?
Fluid Mechanics deals with this in a number of ways. The first is
through turbulent flow or laminar flow of the fluid through a pipe or
valve. Laminar is "good" and turbulent is "bad". Laminar flow in fluid
mechanics means that the fluid is flowing in smooth layers or laminae.
The highest velocity in laminar flow is at the center of the fluid
stream and the velocities of each respective layer is linear. At the
walls of the pipe the velocity is 0 because of friction. Friction
varies from pipe to pipe and fitting to fitting.
To determine the flow characteristic you must utilize the Reynolds
Number, Darcy's Equation, Moody's Diagram, and the K Factor. Darcy's
Equation is used to calculate head loss due to friction in pipes for
both types of flow. Moody's Diagram uses the Reynolds Number and the
relative roughness of the pipe to determine the friction factor. The
"K" Factor is also known as the the Constant of Proportionality and is
used to calculate the energy losses in valves and fitting such as tees,
elbows, and bends.
So I do not think that this is as simple as you think and you are
comparing apples and oranges. The viscosity of the fluid in these
systems is also taken into account. With standard air there really is
no "viscosity" although the density of the air changes with the amount
of things that are in the air such as more oxygen than nitrogen etc.
If you utilize the Y fitting the flow of air will be much smoother and
less turbulent than if you use a T fitting. With the T fitting the air
molecules run right into a wall and then need to be reaccelerated. With
the Y fitting, even though there are frictional losses, the
deceleration of the air molecules will be much less because the change
in direction is more gradual. If you use your car for example: Would
you rather be traveling 40mph and come to a T in the road and try to
turn left or a Y? With the Y the directional change the car would
require less braking and thus less time to reaccelerate to your travel
speed. With the T you will almost have to make a complete stop.
I hope this did not confuse you but fluid mechanics do not apply here
from an engineering standpoint. However, the theories do. Let me know
if you need any more help.
<interesting response saved and snipped>
| I hope this did not confuse you but fluid mechanics do not apply
| here from an engineering standpoint. However, the theories do. Let
| me know if you need any more help.
What area of study (if not fluid mechanics) deals with air flow in a
Can you suggest some web sites that could provide some good background
in optimizing airflows? My interest is in maximizing efficiency of
solar heating panels; with a secondary interest in design of dust
DeSoto, Iowa USA
Thanks for the answer. I know this is not a simple problem but I
suspect thee are rules-of-thumb that apply. I suspect theres a cosine
of theta involved, too.
In you last paragraph, you state that fluid mechanics does not apply
but the theories do. Hmm. If the (fluid mechanics) theories apply then
fluid mechanics applies, right? Not sure what you meant by that
No so fast there.
Because of the velocity distribution you describe for pneumatic
transfer of suspended solid particulate matter,e.g. dust collection,
turbulent is good and laminar is bad. That is because the
turbulence will keep the dust suspended in the air, but laminar
flow will allow it to drop out and accumulate in the ducts. Or more
realistically, the laminar flow wouldn't pick up much dust in the first
Seems like the two 45's would sum to 90 in losses - so they would be
equivalent. I guess, there may be some non-linearities with the 90,
though that cuase linearity not to work at high angles (90 degrees for
Gerald Ross wrote:
No I don't think that and what makes you think I do? However, there are
conditions where a right angle turn makes senses.
My question is not whether "T" is better than a "Y" but by how much.
I think it would be easier to maybe buy each and see which works out best
for you. To know the percentage of how much better you need to know at any
given point, temperature, humidity, barometric pressure and volume of air
moving through the intersection.
For relative comparisions when temp, humidity,etc are held constant but
the angle of the "Y" is varied, there's got to be a rule of thumb --
say vacuum loss is proportional to the sine of the angle to the cube
Chip is the wrong descriptor.
The 1/32-1/16" thick ripped strips and end grain thingies that come off
the table and miter saw, and long, curly Forstner bit waste are what had
me pull out the grounds.
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