Vacuum Cleaner Suction Comparisons -- Help to Normalize Air Watts vs. Inches of Lift

[John Poole]

I'm trying to compare several of Rigid's vacuums and have found there are two different sets of criteria, namely "Air Watts" and "Inches of Lift"; the model has one or the other specification, but none have both. I do not know why they use two different standards, so I tried to equate both so I have a common measure for all the units. I basically want to know how they compare in terms of suction. I have a Fein which I bought for quietness; however, it was not as powerful as my really noisy Craftsman (gave away). I basically want a powerful one for places other than my shop -- e.g. outside stuff, rain gutters.

Background

Air Watts (http://en.wikipedia.org/wiki/Airwatt) = Air Flow * Vacuum/8.5
Inches of Lift is a measure of Vacuum


My Spreadsheet

Numbers in red are calculated


URL
Catalog Number
Description
Peak HP
Air Watts
CFM (“air flow”)
Amps
Inches of lift
Computer Air Watts
Computed Vacuum


http://www.ridgid.com/Tools/WD1851-16G-Vac/EN/index.htm
Cat #31693 WD1851
16 Gallon High Performance Wet/Dry Vac With Cart
7
306
199
12
13
306




http://www.ridgid.com/Tools/WD1956-Stainless-Vac/EN/index.htm
Cat #31703 WD1956
16 Gallon Stainless Steel Wet/Dry Vac With Cart
7
294
187
12
13
294




http://www.ridgid.com/Tools/14-Gallon-Pro-Vac/EN/index.htm
Cat #18718 WD1450
14 Gallon High Performance Wet/Dry Vac
6
257
168
11
13
257




http://www.ridgid.com/Tools/RV2600B-16-Gallon-Industrial-Vac/EN/index.htm
Cat #25653 RV2600B
Industrial 2 stage 16 gallon

1235
105
12
100


100


http://www.ridgid.com/Tools/Certified-HEPA-Filtration-Vac/EN/index.htm
Cat #40048 RV2400HF
14 gallon Professional Wet/Dry w/HEPA

1235
105
12
100


100



Issue

So it should be a simple matter to convert Air Watts to Inches of Lift, e.g. the formula:


Vacuum =Air Watts * 8.5/Air Flow


But when I try to do so, the results I obtain are way off base. Here is a link to the Open Office Spreadsheet I created: http://napadata.net/misc/woodworking/Rigid_vacuum_suction_standardization.ods

I contacted Rigid about this day before yesterday and have not heard back.

Anyone have an idea of what I'm doing wrong in the conversion?

[Michael W. Clark]

Hi John,
There is not a straightforward way to convert pressure to power for a fan if you are only given one or the other.

Power is proportional to flow x pressure but there are other variables involved, of particular interest to you, the fan efficiency.

Shop vac power/performance ratings are notoriously misleading and confusing.

Mike