How to Check a Blower

• Carry out a pitot tube traverse in the duct downstream of the blower.
• Obtain an average gas velocity in the duct.
• Multiply by the cross-sectional area of the duct.
• Compare it to the manufacturer's rated figures fo rthe device.

Good. I would add: start, test & run amps and volts. But remember, S.P. must be w/ in design parameters for the indoor section (almost for sure 0.33 to 0.50 " W.C.) and all doors/ panels shut, all registers (especially return (s))

100 % open. Finally, the duct size on the return must be at least 600 prefer 750 cfm. Thank you, goodnight.

Hello Guest

I don't know whether anybody else on this thread knows what you're talking about, but I'm baffled! Do you know something about this that isn't on the thread?

What is S.P. ? Static pressure?

What difference does indoor section (if any) make?

What should be almost for sure 0.33 to 0.50 " W.C. ? and why those values?

What is a register (return or otherwise) in this context?

Why should there be a duct on the return (whatever you mean by that) rather than just taking suction from the atmosphere?

It's not necessarily appropriate to have all dampers etc wide open, Need to simulate fan design conditions. If wide open gives lower than design pressure rise the blower might give 530 cfm but not be working as specified.

Cheers.....,,Codey

Buy a Fyrite cfm meter from Bacharach Instruments. If you are in India try Forbes Marshall and ask for this item.

check max. velocity of blower at inlet / outlet by anometer at duty pressure condition. Now calculate area of inlet/outlet sections.

then Flow = Area X Velocity.

To Check pressure you can use simple manometer.

Generally mfg. gives capacity and pressure at inlet conditions.

Suggestions about measuring velocity hence flow are OK, but it won't mean much unless you also know the pressure rise to compare with design figure. Flow vs pressure curve for a centrifugal blower covers a wide range.

Cheers.......Codey

Wind tunnel is the best way, but I will assume you do not have access to this. Good ideas so far, don't forget the air density levels (as well as elevation above sea level) as this will have an impact on the results. Don't forget about the 100% effective length for the duct to deter turbulence. This is typically 2.5 times the outlet area for 2500CFM and below. 3.5 times the outlet area for 3500CFM and 4.5 times the outlet area for 4500CFM, all assuming you are utilizing the duct for 100% effective length.