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Unfortunately all of that is still based on a misunderstanding of the performance charts. The ratings are not for unimpeded flow - they are based on standardized levels of restriction, ranging from no restriction to zero airflow. I do agree with your last point though - It would be nice to have...

Thankfully Ametek is pretty transparent about their products. You go to their website, enter the model number into the search box, then click 'Datasheet', and it's all right there. I think you might be misunderstanding the performance charts though. Those are performance levels for various...

Guessing it was an internal short that caused it. The motor had a few thousand hours on it, so a good life for a motor of its type and implementation. Full power consumption and performance details are given in the spec sheets of both of the motors. The new one uses more power at any given...

Well, prove us wrong then. Eliminate those variables and add some consistency to your measurements and let's see the effects. Obviously the amount of air going in is equal to the amount of air going out, so the only answer to the question of "why am I measuring a difference" is that your...

My central vacuum's rotor burned out, and considering the cost of just a replacement rotor or a similar motor, it made sense to upgrade the motor for a bit more performance (moving from an estimated 384 air watts to to 700). I saw that the 8.4" generally have the same mounting pattern as the...

You're still talking about 10%+ difference in cross section just from your orifice estimates. Add in the leaks mentioned earlier and imprecise measuring and it really isn't surprising. It seems like at this point, plenty of valid potential answers have been presented, and to figure out exactly...

1/8" difference could explain a lot of what you are seeing, depending on which side is larger. I don't know how big those ports are, but a 1.125" diameter circle has over 26% more surface area than a 1" circle. Add in leaks and imprecise measurements and I don't think there's much mystery. If...

Well if your armature is good and happens to be a 215330, I have a 7.2" motor (115334) that is only missing the armature that I'm giving just for shipping cost. I can't tell what type of motor that is, don't see a serial number or any other identifying info. I'd guess you have something closer...

You have the model number of the vacuum/motor? Any idea what the problem with the motor is?

It seems like you are saying that central vacuums are bad because they have too little power because of system losses... but they are also bad because too much power reduces performance. Regarding motor information - I'm always a fan of companies being more transparent, but in this case I think...

Definitely going to have higher losses in a central vacuum, but those losses decrease as air speed decreases. As you mentioned, peak airflow rates on a wide open system aren't a very good indicator of actual cleaning performance. I'd be surprised if, given the same cleaning head and method of...

Central vacuums can have HEPA level filtration, and plenty of installations have interior exhaust. I'd say the level of filtration needed depends on what you are vacuuming and your proximity to neighbors. I personally don't have any nearby neighbors, so I wouldn't mind the minimum filtration...

Looks like I have some more modifications to plan.

That's interesting about the bag - is the difference just that the SilentMaster has the bag on top? Or is there something that keeps the bag from the sides of the housing?

Yea central vacs win me over for the external exhaust option if nothing else. But the motor technology definitely does seem to have lagged behind more portable options, probably because you don't have the pressures of weight reduction or energy efficiency driving improvement. I wish there were...

True haha. When I was browsing I was more looking at peak performance than efficiency, but I definitely saw some that did not justify the amount of power they used. I looked around more on Ametek's site and found the 122661 that uses 17.5 A with a 2" orifice. Nice CFM rating at that operating...

Does Ametek still make 20 A motors (or 240 V ones around 10 A)? I feel like I went through every 7.2" and 8.4" one on their website and only saw ~15/7.5 A max.

The value, in my mind, would be in selecting a replacement motor. Obviously a little late if you don't have a currently working motor like me, but if you were able to see that your system presents a resistance that is equivalent to, for example, a 5/8" orifice plate, then when when looking for a...

I think you could get a decent approximation of an equivalent orifice size for a system with just a pressure gauge. Set everything up, including the cleaning head to cleaning surface interface, so that it closely replicates your normal use. Turn the vacuum on, and measure vacuum pressure as...

Thanks for the info, Just bought the 122501 from MD. That's interesting about the thermistor - I actually had one picked out to add to the control circuit for soft starting. Although I believe the ones that came preinstalled were kept in series with the motor throughout operation, while the one...