interesting read. Took up my Sunday evening.
I'm sure someone was thinking it when they showed that dry soil on the plate...where's Ron! That wasn't from any vacuum. If it was, buy another one.
What we're taught is that 80% is dry soil. Dry vacuum it out. There's pretty much all your weight difference right there.
The remaining 20% is stuck on the fibres with oils, etc and require some chemical/mechanical means to break that bond. So I wouldn't put much stock in that weight testing. However, IF no dry vacuuming is performed, HWE would remove more than VLM since there is actually a "vacuum" system, except for Dry powder, since they are essentially dry vacuuming,
I've often been cleaning a carpet, using HWE, and evaluating how the wand is performing and wondering how well a VLM system would have worked on it. Now, I'm not using the old style wands which flood and suck, I'm using a angled jet wand so I can see it flushing the carpet. I've thought that running a pad across this carpet would remove that surface soil, the shampoo would break that bond, but it wouldn't be giving it that flush, esp on berber. The reason I use HWE, and spend $1000's to buy and set up my busn to use that equipment ( and right now with all the BS I'm going through with a new install the VLM is looking very attractive ) I still find it to be the best way to clean a carpet. You can believe I'm not spending the money because of any ego! Can I make it look clean with the other methods? You bet. Just put in the prep steps and it'll look beautiful. Don't have to worry about propane, or carrying water, etc etc. But I know I'll be leaving something behind.
I offer VLM, but only in highrises or inaccessible areas, or for budget reasons, or certain soiling conditions. There may come a time when there might be water rationing, ie our reservoir isn't exactly full this year, where a VLM method may be the only way. When that time comes I'll simply explain that this is the best method "available". But as soon as there is water again, HWE is the best method available.
Gee, start to finish, I think I spend an hour on this thread!