Central vacuum recommendations?

[Hatsuwr]

Last week, just after reaching 50 years, the rotor burned out on my NuTone CV350. I'm not sure I want to spend $250+ on a replacement motor. I'll try rewinding it at some point, and will keep an eye out for units that are being scrapped to pull a rotor from, but even if it gets fixed it will probably be relegated to garage use.

So, I'm looking for a replacement. My main priority is performance, although I'm not sure how I would balance CFM and suction - leaning towards giving more weight to CFM right now. Bottom-emptying is much preferred, although I can work around that if there's enough to justify it.

I'm not at all concerned about noise or cleanliness of exhaust air, since it will be installed in my utility room and exhaust will be routed outside. I haven't read much about cyclonic systems yet, but it seems like they might be a good fit to eliminate the cost of bag changed and maybe have a smaller impact on performance as it becomes loaded.

Here is a spreadsheet I threw together for MD, Cyclovac, and Flo-Master (also has the info for my old NuTone). Let me know if you'd like to see any other brands or more points of comparison here:


The Cyclovac 725 Hybrid is at the top of my list right now. It seems to be the best value among the mid-to-high performance models (as far as air watts per dollar). It can be operated with or without bags. One strange thing is that it's air watts rating is 6% lower than the A700tv2, despite having a 2% higher CFM rating and <1% lower water lift rating.

 

[cheesewonton]

Last week, just after reaching 50 years, the rotor burned out on my NuTone CV350. I'm not sure I want to spend $250+ on a replacement motor. I'll try rewinding it at some point, and will keep an eye out for units that are being scrapped to pull a rotor from, but even if it gets fixed it will probably be relegated to garage use.

So, I'm looking for a replacement. My main priority is performance, although I'm not sure how I would balance CFM and suction - leaning towards giving more weight to CFM right now. Bottom-emptying is much preferred, although I can work around that if there's enough to justify it.

I'm not at all concerned about noise or cleanliness of exhaust air, since it will be installed in my utility room and exhaust will be routed outside. I haven't read much about cyclonic systems yet, but it seems like they might be a good fit to eliminate the cost of bag changed and maybe have a smaller impact on performance as it becomes loaded.

Here is a spreadsheet I threw together for MD, Cyclovac, and Flo-Master (also has the info for my old NuTone). Let me know if you'd like to see any other brands or more points of comparison here:


The Cyclovac 725 Hybrid is at the top of my list right now. It seems to be the best value among the mid-to-high performance models (as far as air watts per dollar). It can be operated with or without bags. One strange thing is that it's air watts rating is 6% lower than the A700tv2, despite having a 2% higher CFM rating and <1% lower water lift rating.

Air Watts are an instantaneous measure of vacuum motor power. As the size of the orifice changes airflow and suction values change. Thus for each orifice size there is an associated air watt value. Each motor will have a combination of airflow and suction at a certain orifice size that yields the maximum air watt value. It may be that A700tv2 manages to achieve that combination of airflow and suction that yields a higher max air watt value than the 725 can achieve. Remember it requires both suction and airflow working together to achieve air watts.

 

[Hatsuwr]

Air Watts are an instantaneous measure of vacuum motor power. As the size of the orifice changes airflow and suction values change. Thus for each orifice size there is an associated air watt value. Each motor will have a combination of airflow and suction at a certain orifice size that yields the maximum air watt value. It may be that A700tv2 manages to achieve that combination of airflow and suction that yields a higher max air watt value than the 725 can achieve. Remember it requires both suction and airflow working together to achieve air watts.

Would be nice if they posted the air flow vs water lift curves!

 

[cheesewonton]

If you have the model number of the motor you can usually find them on the Bison-Ametek website.

https://www.bisonametek.com/product...696&utm_content=312471696&utm_source=hs_email

 

[Hatsuwr]

If you have the model number of the motor you can usually find them on the Bison-Ametek website.

https://www.bisonametek.com/products/find-a-product?utm_campaign=2024 New Website Launch&utm_medium=email&_hsmi=312471696&utm_content=312471696&utm_source=hs_email

Yea Ametek is good about that, just gotta get MD, Cyclovac, and Flo-Master on board!

Speaking of Ametek though, I was able to find the rotor, it's part #215330. Best price I've found so far is about $125 with shipping... Not too bad.

Alternatively, I also found that there are a great many motors that seem to be more or less drop in replacements for mine, and with better performance. These range in price from $200-$400. I didn't want to just replace the whole motor with an identical one when it was only the rotor at fault, but replacing with an upgraded one doesn't seem like a bad idea.

Here's what I've narrowed the list of potential motors to:



And here are their air flow vs suction curves:

 

[panasonicvac]

The CycloVac you're thinking of is a good option. They do offer an extended 25 year warranty.

 

[Hatsuwr]

The CycloVac you're thinking of is a good option. They do offer an extended 25 year warranty.

I just discovered today that I can probably fit an 8.4" motor into my old vacuum. I would probably need a little adaptor that I can 3D print since the bottom of the 8.4" ones have a sort of cone shape instead of being flat like my 115334.

The 122501-00 seems to be what is used in the A715h and DB8000, and I'm debating seeing if I can make one of them work.

 

[ultralux88]

My personal opinion would be the MD M715h. Being honest though, I am an MD dealer. But its extremely powerful, and my experience is that the support bag design does lead to better airflow, which is why I prefer the MD, FloMaster, and SilentMaster lines of theirs where the bag is in the top of the unit held in the outer cloth bag.

 

[Hatsuwr]

My personal opinion would be the MD M715h. Being honest though, I am an MD dealer. But its extremely powerful, and my experience is that the support bag design does lead to better airflow, which is why I prefer the MD, FloMaster, and SilentMaster lines of theirs where the bag is in the top of the unit held in the outer cloth bag.

I decided to go ahead and get the bigger motor (the same one used in the M715h if I'm not mistaken). Waiting to hear back from a cheaper retailer on Monday, and will hopefully have it within a week.

I'm curious how the performance will compare. I have a good quality vacuum gauge to measure no flow vacuum pressure. I imagine that will be lower that on newer vacuums just because of random small leaks everywhere than I have yet to seal up. I'm not sure how I would measure CFM... I have a cheap anemometer, but I'd have to build some sort of expansion adapter to decrease the velocity quite a bit. I doubt that would be accurate enough to even be worth it though.

 

[cheesewonton]

I decided to go ahead and get the bigger motor (the same one used in the M715h if I'm not mistaken). Waiting to hear back from a cheaper retailer on Monday, and will hopefully have it within a week.

I'm curious how the performance will compare. I have a good quality vacuum gauge to measure no flow vacuum pressure. I imagine that will be lower that on newer vacuums just because of random small leaks everywhere than I have yet to seal up. I'm not sure how I would measure CFM... I have a cheap anemometer, but I'd have to build some sort of expansion adapter to decrease the velocity quite a bit. I doubt that would be accurate enough to even be worth it though.

Use the anemometer to measure airspeed at the center of the hose connection. No duct. Move the anemometer around until you get the highest airspeed reading. Calculate the area of the hose opening in cubic feet. It will be small, on the order of 0.006 something to 0.008 something square feet. Go out four decimal places. Multiply the airspeed by the area in cubic feet then multiply that by 0.8. That last factor is a rule of thumb factor used for calculating turbulent airflow since, if you could measure airspeed all across the diameter of the opening you would find airspeed at the center is much higher than airspeed at the outside of the hole. The air along the sides of the tubing doesn't flow as fast due to friction.

 

[panasonicvac]

My Beam had it's original motor replaced to a bigger one, there's a slight bit of increase from the performance but definitely for certain it has now outlasted the other motor. So yeah if you're able to get away with putting in a 8.4 motor in your NuTone, that's WAY cheaper than buying a brand new unit. I wish NuTone was still making their CV units, they were the best ones.

 

[centralvacs1928]

My Beam had it's original motor replaced to a bigger one, there's a slight bit of increase from the performance but definitely for certain it has now outlasted the other motor. So yeah if you're able to get away with putting in a 8.4 motor in your NuTone, that's WAY cheaper than buying a brand new unit. I wish NuTone was still making their CV units, they were the best ones.

Y'know, I've never been NuTone's biggest fan, but seeing all these failed VX and PP units does give me a fresh appreciation for how solid the previous CV models were. The CV350 and 353 used big 7.2" motors (two and three stage respectively) which would deliver pretty decent performance and very long life. Their dual motor CV450, with smaller 5.7" motors in air series, could be a real beast especially if installed on a dedicated 20 amp circuit! Good life expectancy too as long as nobody placed their spare bags on top of the unit and blocked off all the cooling air...

 

[centralvacguru]

As the manufacturer of the Modern Day M715, I can tell you that the 8.4" motor has had tremendous success! The earlier versions had a thermistor installed and it had quite a few infant mortality problems. Once that was removed, the motor has been bullet-proof! With 154" waterlift you will clearly feel a tremendous difference between this and your old Nutone 350! Nutone has not been very visible since it was bought out by Drainvac. It appears that they took a few of their models and put Nutone labels on them. These are usually sold through distribution warehouses and electrical supply stores. I agree with Cemntralvacs1928 that the Nutone 450 had great waterlift but unfortunately running the two motors in series did put excessive heat on the second motor and it failed prematurely.

 

[Hatsuwr]

As the manufacturer of the Modern Day M715, I can tell you that the 8.4" motor has had tremendous success! The earlier versions had a thermistor installed and it had quite a few infant mortality problems. Once that was removed, the motor has been bullet-proof! With 154" waterlift you will clearly feel a tremendous difference between this and your old Nutone 350! Nutone has not been very visible since it was bought out by Drainvac. It appears that they took a few of their models and put Nutone labels on them. These are usually sold through distribution warehouses and electrical supply stores. I agree with Cemntralvacs1928 that the Nutone 450 had great waterlift but unfortunately running the two motors in series did put excessive heat on the second motor and it failed prematurely.

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 I would be installing would be bypassed after the first second or so after startup is finished.

Do you know what the cause of failure was? Just the NTC burning out, or was it maybe causing overheating related damage to the motor?

 

[centralvacguru]

The issue was related to the porcelain coating on the outside of the thermistor. When the unit was located in a cold atmosphere (think garage or basement in the winter) and the unit would turn on, the instantaneous heat in this device was excessive and it would actually crack the porcelain and then the thermistor would fail. Amazing a field cure would be to simply bypass the thermistor that was tye-wrapped to the side of the motor under the carbon filter.

 

[panasonicvac]

I really liked the CV450 that a neighbor of mine has I used to go over and vacuum for. One of the motors did in fact fail one time so I couldn't use it for a while and had to use their other vacuum which was a purple Vax X5. Nonetheless, if NuTone was still selling that model, I would've recommended it. But personally, I'd rather have a Vacuflo DB7000/Maxum 7 over it like what this one person did as I'm sure it would've not been priced at $399 anymore today. I brought the Vacuflo up because it's specs are very similar to the CV450.



According to industrialsewingmachineman.com, NuTone had some amazing deals on their CV units. I wonder if part of the reason was because they were made up in Canada or elsewhere? Either way, for someone like me that's rather frugal, I would've easily bought one back in the day. Especially the CV850 unit at $529, I don't know how much the SilentMaster S5 (240 volt) was sold for back in the day but I think that's an incredible value for a dual motor 240 volt unit and because of it I think I would've bought a CV850 over the S5. I brought the S5 up because it's specs are very similar to the CV850 not to mention they both use dual motors that are parallel.

NuTone CV-850: 890 Air Watts, 138 Waterlift, 195 CFM
SilentMaster S5/S900r2: 866 Air Watts, 136.4 Waterlift, 190 CFM

https://www.industrialsewingmachine...dpZmORfZb5Xw56lByVMoBr0Ksvn38PWEQs1cpjO5qQoD7

 

[ultralux88]

NuTone CV-850: 890 Air Watts, 138 Waterlift, 195 CFM
SilentMaster S5/S900r2: 866 Air Watts, 136.4 Waterlift, 190 CFM


I will say, they basically use the same motors, the NuTone just has horned exhaust motors rather than radial. These two units feel the same until the bag in the NutOne starts filling up, and the lack of anything to keep the bag away from the outside of the can starts changing things...

 

[Hatsuwr]

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?

 

[centralvacs1928]

The MD tapered cloth support bag is the key to keeping airflow strong as the bag fills, as it allows much more of the disposable bag's surface area to be used for filtering. The more common "bag in a can" design means that the side walls of the bag are in close contact with the enclosure, and no air can flow from these areas.

One of my first realizations of what a difference this made was years ago servicing a customer's system. She had NuTone inlets and, fortunately, a newer "C-Vac Pack" hose and tool set. I was running the system and heard the distinctive sound of a 115334 motor, but noted that the performance seemed very good for a Nutone CV-350 (usually kind of anemic in my experience).

A short time later I went to the basement to check the machine and found, not a NuTone CV-350, but an old MD Model A (private labeled as an Air-Flo, but in an unusual single motor configuration). Same 115334 motor, but with an open-top disposable paper bag supported by a tapered cloth bag, suspended from the top rim. Noticeably stronger airflow from a unit with the same specs on paper.

 

[centralvacguru]

That would have been the same as the Modern Day Model B power unit. but for Nick at Central Vac in Chicago we private labelled it as his AirFlo Model A We first built those in the 1960's with the 115334 motor. The larger version can was the Model E that stood for "Extra Large". Eventually we made a FloMaster M34 with the "34" standing for the last two numbers of the Ametek Motor. You are correct that the tapered cloth bag is a key to the MD units sustaining the airflow over longer periods of usage.