3D printed Lamb 7.2" -> 8.4" adapter.

[Hatsuwr]

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 7.2", but they have a sloped bottom instead of the flat bottom of the 7.2". This makes sealing against an existing housing a bit more complicated. You can see the difference below:



I figured an adapter would be pretty easy to make. It would need to have a flat bottom to sit against the vacuum housing, a groove around the bottom outer circumference for an o-ring to assist in sealing against the housing, a flat ring on the top to interface with the flat outer circumference of the bottom of the motor for primary weight bearing, and a slope that closely follows the slope of the motor for secondary weight bearing and sealing. I also added some walls that go up the sides of the motor for better sealing there.

Here is the cross section of what I ended up with:



And the whole part, with some softened corners:



I only have undyed filament, so it's a bit hard to see much detail of the actual part with a picture. I also need to tune my printer a bit more to give a nice finish. I printed in ABS with 20% infill. Total filament used, including supports, was about 180 grams, so a material cost of ~$4.

The part turned out quite close to what I wanted, with a couple exceptions:

1. The inner diameter of the thin walls going up the side of the motor is right around 1 mm too large. Better too large than too small for the first print though, and it's easy enough to seal that gap up.
2. The sloped part that interfaces with motor wasn't sloped quite enough. This made it so that weight bearing was happening around the hole in the motor for air intake instead of around the rim. I'm again glad the error was in that direction though, since some careful heating with a heat gun allowed me to sort of mold it against the motor. Still a bit of pressure being applied around the air inlet, but much less. Plus, ABS is flexible and will creep a bit over time. On a reprint I might lower the inner part of that slope very slightly - less than a millimeter to start with.

I tried attaching the file for the model, but I don't think its format is allowed on the site. If it doesn't work and if anyone wants it, just send me a message and I can email it.

 

[Vacuum Facts]

Why did the rotor burn out? I noticed the electrical power consumed by the motors weren’t mentioned. How many Watts do they both burn through? I ask, of course, since in earlier discussions we’ve established the best cleaning performance can be achieved with just a few hundred Watts with the most superior designs, and I was interested.

Given that, if you use a more powerful motor, how do you know it isn’t going to get too hot either to be harmful to its own lifetime (following Arrhenius) or a danger to its surroundings if its temperature gets too high with your modifications? Or is it suck it and see?

 

[Hatsuwr]

Why did the rotor burn out? I noticed the electrical power consumed by the motors weren’t mentioned. How many Watts do they both burn through? I ask, of course, since in earlier discussions we’ve established the best cleaning performance can be achieved with just a few hundred Watts with the most superior designs, and I was interested.

Given that, if you use a more powerful motor, how do you know it isn’t going to get too hot either to be harmful to its own lifetime (following Arrhenius) or a danger to its surroundings if its temperature gets too high with your modifications? Or is it suck it and see?

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 system restriction, but is more efficient and has a better cooling system.

I wouldn't necessarily agree with the statement about best cleaning performance. It will definitely depend on tool size and geometry, and the surface being cleaned. The low hundreds of watts definitely isn't at the point where gains in performance stop though.

All that said, cooling of the motor definitely isn't a concern. As long as you don't obstruct the motor's air intake/exhaust and have a separation between the two to prevent hot air recirculation, then it's operating within intended parameters.

 

[Vacuum Facts]

Can't easily find the spec sheets. Could you state what their motor powers are?

Edit, I found them. The electrical power consumed is always hidden and rarely volunteered...and it's clear why: ~1.4 and 1.8 kW respectively! Comparable to a winter room heater, but less than some of the most wasteful mains machines.

Earlier, I meant performanced measured reputably and independently to formal industry test standards.

Incidentally, motor airwatts listed (~384/700) are not the same as airwatts present at the cleaner head (the only location relevant for cleaning) in a given situation (varies in use), since air resistance in different parts of the air circuit varies. They'll be relatively greater under identical use conditions for the second motor though, and therefore suction pressure will be greater (equations). Hopefully there's no head clamping.

Interesting project though. I can't see the typical user doing this kind of thing though.

 

[Hatsuwr]

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 system restriction values. Overall system restriction is modeled by using an orifice plate of varying diameter for consistency and repeatability. From what I have read, Ametek believes that most central vacuum installations roughly equate to a 0.625" orifice. I estimate my system (taking into account some future modifications) will probably be closer to 0.750"-0.875", which was one factor in choosing the 122501.

So those air watt ratings do relate to what is present at the cleaner head... you just have to figure out which row corresponds to your system in a given configuration. If you wanted to know what orifice diameter your system configuration (including or excluding any hoses or cleaning heads) equated to, you could figure it out pretty easily by measuring the vacuum produced while operating in that configuration. A certain vacuum pressure created will necessarily relate to a certain air flow rate.

 

[Vacuum Facts]

The airwatts values on their spec sheet are peak values associated with fluid flow in a pipe of optimal diameter (air resistance). Such values vary in use so the performance charts represent the system response. Airwatts are only a measure of the above-floor cleaning potential associated with a hose tool in relatively unimpeded flow and not a measure of carpet cleaning potential. The hose tools themselves modify the net air resistance and equivalent orifice size.

The effective airwatts at the cleaner head are likely lower than peak motor airwatts the spec sheet reports since resistive load is dynamic and quite high due to the different floor surfaces. Suction is the parameter of relevance for carpet cleaning, not airpower, as this drives the speed of air in the flow that imparts force on particles. Suction is not fundamentally a function of airpower (airwatts); it is a function of both the maximum pressure the motor can produce—referred to as waterlift in the spec sheets—and the net relative resistance at the cleaner head depending on the properties of the flooring at the time (see equations). Head suction is the primary indicator of cleaning performance potential on carpets. Since other factors influence how well high air speed is distributed within pile, driven by the suction, only the directly measured cleaning performance is relevant, and that has to be empirically quantified very precisely, as discussed.

Cleaning performance can't be accurately inferred, other than in a relative qualitative way, by motor properties. The Ametek Lamb 115334 motor rates its airpower as 384 aW and waterlift as 110", whereas the 122501 Lamb vacuum motor lists 710 aW and 151.9", which is an 85% increase in peak airpower and 38% increase in maximum suction. Above floor cleaning potential and carpet cleaning potential increase respectively by those amounts. How much of that maximum potential is actually met will need to be empirically quantified with statistical significance, but it will almost certainly be less due to other factors at play associated with the tools and cleaner head design. Also, again, if resulting cleaner head suction is too high, you'll get clamping, and it will become impractical to even achieve that potential performance increase.

Edit: Shocked by its mere 900-1,200 hour claimed lifetime. The most advanced motors associated with vacuum cleaners I'm aware of have been tested for over 20,000 hours. Very crude motor technology—slow and energy guzzling.

 

[Hatsuwr]

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 some good brushless options, although motor life isn't really high on my list of reasons why. 1,000 hours will last most people a decade or more, and being so simple, they are easy and usually cheap to repair. In my case, it was a $110 part that failed after a few decades of relatively heavy use).

I did look for brushless motors when assessing replacement options, but there weren't any with the level of performance I was looking for. Hopefully when my replacement fails in the next few decades there will be!

 

[Vacuum Facts]

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.

Sorry, I wasn't clear. Those motor performance charts are acquired using the standard orifice plate technique (e.g. ASTM F558 / IEC 62885) modelled on established old science. The plate allows the pressure drop across it to be easily measured so the Bernoullie equation can be used to determine airflow, thus allowing a calculation of airpower, which is the product of the two. The plots produced reveal the system's response to air resistance and can also identify peak airpower, which the motor datasheet specs report although don't mean much on their own.

Everything after that I discussed above still then applies. Airpower is relevant to determine above floor cleaning potential, but open hoses represent relatively unimpeded flow—so that peak airpower won't likely apply. Under resistive load on carpet, only the suction matters anyway, since it directly determines air speed and thus force imparted on particles in the flow and is not fundamentally a function of airpower (it's a function of net air resistance and maximum motor pressure). Suction pressure represents the carpet cleaning potential, since there are other factors that affect airspeed on a given flooring associated with the head design. Cleaning performance can only be quantified empirically, not from other parameters. The earlier calculation shows the maximum potential improvement you could see, although it won't be realised for many other reasons associated with dirt removal from carpets, which is a first order system and so gradual.

Still an interesting pet project, but one I suspect most people wouldn't choose to adopt for the cleaning chore.

 

[Hatsuwr]

There is an orifice diameter that will roughly match a system in any configuration you want - hose or not, cleaning head or not. There's not really any way around that fact. In a particular configuration, you will achieve a certain amount of airflow. With a fully open orifice plate, if you gradually decrease the diameter, you will eventually attain that same airflow. That orifice diameter is a simple representation of the configuration in question. It's really just a consolidation of all combined system restrictions into a single repeatable metric.

 

[Vacuum Facts]

Yeah. Quantifying it doesn't directly quantitatively relate to carpet cleaning performance though, for the reasons above, so peak airpower isn't worth fixating on (except for above floor cleaning) since it's so indirect. Will be interesting to see how you determine non-subjectively how much cleaning performance improves with your new, more energy guzzling motor.

 

[cheesewonton]

I have looked at upteen Ametek Performance Bulletins for their suction motors and it strikes me that most of their motors produce their peak air watts at an orifice somewhere in the neighborhood of 0.75 inches, give or take a quarter inch. That corresponds pretty closely to the working orifices of most vacuums. Not 100% but pretty close and I have to assume that is not accidental.

 

[Vacuum Facts]

Yes, it maximises above floor cleaning potential. That's what the curves represent—along with the particular system's response to varying resistance in use. Ultimately, what counts is representative empirical measurements of actual cleaning performance (ideally to industry test standards). I'm tempted to soon start measuring input power-normalised performance.