Static Pressure Loss Calculation

[John Williamson]

I have a question on a Static Pressure calculation that I hope I can put into words. :o

I'm trying to get an accurate calculation on the SP loss for the duct I want to run to my jointer. It starts at the DC and then runs along the ceiling into a wye connector. The angled part of the wye drops a branch to the table saw and the straight part of the wye feeds on to the end of the run that connects to the jointer.

The question is do I need to calculate the wye at the table saw branch drop as a loss for the jointer even though the run is basically a straight shot through the wye connector heading back to the DC??:confused:

[Steve Roxberg]

My guess, and how I would do it is no. Not for the straight portion assuming the other direction is blocked off when you are running the jointer. My guess is worth what you paid for it.

[Eric Gustafson]

My guess has a much value as Steve's. I would not think the branch to the saw would affect SP unless that gate was open while you are using the jointer.

Perhaps someone smarter than me has a better answer.

[Rob Luter]

Good rule of thumb - any time the air has to accelerate, decelerate, change directions, change from smooth flow to turbulent flow, or otherwise change behavior; assume a static pressure loss.

If the air travels through the wye without changing speed, direction, or other flow characteristic, ignore it. I'll bet however that as the air travels over the open wye going to your saw the smooth flow is interrupted and some turbulence is created. Depending on velocity, this could be as significant as if it were changing directions.

If it was me, I'd account for some static loss at a value somewhat less than a regular wye.

[Joe Chritz]

I am by no means a fluid mechanics expert nor did I stay at a Holiday Inn express but in my research on DC you only count changes in direction.

Everything in the pipe will effect the movement of the air, even the screws holding them together. The difference is how much it effects it and if it is worth bothering. Just like a straight run increases static pressure.

Short answer, only count direction changes. i.e. a 45 counts as 3 feet of straight pipe. That isn't an accurate number just an example.

Joe

[alex grams]

post the size (assuming PVC) and the flow rate (CFM) you expect through the pipe and i could run a quick program to give you an answer. In all honesty, if you are going through the straight part of the wye and the other branch is closed, the pressure drop you will experience will be very minimal (effectively insignificant).

[John Williamson]

post the size (assuming PVC) and the flow rate (CFM) you expect through the pipe and i could run a quick program to give you an answer. In all honesty, if you are going through the straight part of the wye and the other branch is closed, the pressure drop you will experience will be very minimal (effectively insignificant).


Looking for around 500CFM and it's 4" PVC. It will be running through the straight part of the wye with the other branch closed. I thought that there would be some turbulence caused by the opening in the wye even with the other branch closed but couldn't find any SP loss value anywhere.