How many motors for a given cfm/ depression?

[John Doney]

Hey guys,
I'm new here and was wondering if there is a loose relationship between the number of motors put into a bench, and how many cfm can be moved at a given depression. I'm looking to build a bench that can test a big block chevy head of around 400 cfm at 28" of water. I don't see myself needing much more than that.

Any thoughts?

[Brucepts]

On a PTS style flowbench it uses a 28" test pressure and 16" differential pressure (DP) so adding those 2 together gives you 44" of total pressure. Taking that number and looking up the vacuum motor data chart, find the cfm flow at 44", divide your 400 (or total cfm needed) by that number and it will give you the total motors required, not totally exact but it gives you a pretty good idea. I would always go a motor or two over that for a safe margin. If you plan to use a different test pressure or DP just do the same math.

The motors are the life of your flowbench, in the long run it pays to go with the best motors you can buy, if you have to try and save $$$'s for a build look somewhere else for that savings, in my opinion.

[Tony]

Welcome to the Forum John.

What limits most of us is the available mains power.
As you keep adding motors, the current to run them all can add up to become surprisingly high.

A fairly average typical 400 CFM bench might require about 25 Amps at 230 volts, or 50 amps at 110 volts.
You can do slightly better than that, but it requires being absolutely fanatical about motor efficiency.
What is your power availability ?

[ivanhoew]

or use a big single motor like we do tony ,and get more cfm/amp?

[John Doney]

Well, I am hoping to build a bench that will run off of 110-120 volt. 220-230 volt is very hard for me to get access to.

[Tony]

How much current do you have to run the bench ?

[John Doney]

Well, as luck would have it, I did end up finding a way to get access to 230v. I think the max amps would be around 50 or so but I'm not 100% sure.

[Tony]

Well, as luck would have it, I did end up finding a way to get access to 230v. I think the max amps would be around 50 or so but I'm not 100% sure.

If you do have 50 amps available, even the crappiest motors will get you about 8CFM per amp, or say 400 CFM.
Try really hard, and buy the most efficient motors available, could get close to 16 CFM per amp and a whooping 800 CFM.

Something in excess of 600 CFM should be dead easy, a bit either side of 700 CFM most likely.

[Hotz]

Welcome john family PTS
You is already being advised by the best ...
Here you can find some accessories for your project if you have not looked.
http://www.flowbenchtech.com/store.html

Cheers.

[RACEPUMPER]

That's pretty true Aldowin, with a big bench you cry when the bill comes
Welcome to the forum


Jim