Vacuum piping questions
Vacuum piping questions
(OP)
Hello all,
This is my first post so please bear with me. I am trying to calculate how much vacuum I will have in a series of branching pipe system. My first question is can I use the same formulas and calculations from "branching pipe flows" for pumps or do I need equations from ductwork systems with FTP and FSP?
Next, my vacuum section looks like this:
/-- /-- /--
V---|-------|-------|
\-- \-- \--
I do not know the specs on the vacuum yet but I intend on finding it. The desired suction on each branch is 8 inches of WC. I know the lengths but the pipe size is need to be designed. Sorry if I left anything out, let me know. I would appreciate any insight or help.
Thanks,
mecheHOG
This is my first post so please bear with me. I am trying to calculate how much vacuum I will have in a series of branching pipe system. My first question is can I use the same formulas and calculations from "branching pipe flows" for pumps or do I need equations from ductwork systems with FTP and FSP?
Next, my vacuum section looks like this:
/-- /-- /--
V---|-------|-------|
\-- \-- \--
I do not know the specs on the vacuum yet but I intend on finding it. The desired suction on each branch is 8 inches of WC. I know the lengths but the pipe size is need to be designed. Sorry if I left anything out, let me know. I would appreciate any insight or help.
Thanks,
mecheHOG





RE: Vacuum piping questions
We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer
RE: Vacuum piping questions
You'll find the attachment too a interesting read !!
RE: Vacuum piping questions
Pumping equations are not going to help much, you need to go to gas-flow arithmetic. All of the predominant equations (e.g., Isothermal Gas, AGA Fully Turbulent, Panhandle A, and Weymouth) assume incompressible flow which requires that downstream pressure be a reasonable proportion of upstream pressure (most people use 90%). If your suction is 8 inH2O at sea level (about .3 psia) then if upstream pressure is more than about 9.1 inH2O you have violated that assumption.
There is a compressible-flow equation in the GPSA field data book called the Spitzglass Equation (equation 17-29 in V12) that purports to be appropriate for vacuum flows, but I've never had occasion to compare its results to field measurements. I would probably start there, but it has the limitation of assuming a constant temperature of 60°F.
Beyond that you might want to look at HVAC references.
David
RE: Vacuum piping questions