Thread Number: 16499
Thoughts on Trebor's Sanitaire modification.
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Post# 176027   4/5/2012 at 19:50 (2,924 days old) by Sanifan ()        

I think many of us recall a thread where Trebor suggested a modification for the Sanitaire upright that improves its performance. The modification involves drilling two 1/8" holes on the back walls of the air-intake nozzle in order to increase airflow and reduce the clamping effect Sanitaires are known for.

Well, I finally found time to do this mod. Here are my thoughts:

After drilling the holes, the suction across various spans of carpet seems more consistent. Before, the vacuum seemed to suck more onto the carpet at points where the nap was raised somewhat. Conversely, it would suck onto the carpet less where the wood subfloor was uneven, breaking the seal. The modification results in a consistent feeling suction that doesn't feel like its clamping onto the carpet.

Suction around the perimeter of the nozzle seems reduced. Before the modification, the VGII brushroll would bounce dirt and debris up and down in front of the nozzle. The suction and airflow would pull the dirt in from a good distance around the perimeter of the nozzle. Post modification, the VGII still bounces the dirt, but the nozzle has to be nearly on top of the dirt before it sucks into the vacuum. I suppose this is to be expected as some of the airflow is diverted through the little holes. There is simply less air moving directly under the bottom of the nozzle because of it. I still feel that there's plenty of airflow and suction under the nozzle. It's just a matter of covering the entire carpet surface with the nozzle in order to suck in dirt.

Of course, I think this mod is a compromise. That is, if the nozzle clamps onto the carpet as Sanitaires are prone to do, airflow is choked off resulting in reduced cleaning. This mod insures that the clamping does not happen. So this is very good in this situation. But because the holes divert some of the air, the amount of air entering directly under the bottom of the nozzle is lessened. Given that there's enough clearance for airflow in the first place, there will be less pull underneath the and around the nozzle.

So it seems that this mod is especially good for those vacuuming on medium to high nap carpet where clamping can be an issue. In my building I have low nap commercial carpet, so maybe this mod isn't as useful. I like the consistent feel of the suction that the mod provides, but seeing less dirt get sucked into the nozzle at a distance gives the impression that the vac is cleaning less effectively. That is probably not true, but one does get that feeling not seeing the bouncing dirt get pulled in from as far away.

One caveat with my observations is that I inadvertently poked two different diameter holes in my Sanitaire. That is, I was using one of those conical stepped bits. I started with 1/8" tip but realized I went in too deeply. The result is that the hole on the outside surface of the nozzle's wall is 1/8". The hole on the inside surface is 3/16". I don't know if this makes a difference or not as the ultimate aperture is 1/8". It just expands out to 3/16" on the side that faces the brushroll.

I'd be interested in hearing your observations about this modification. I'll report back as I use the vacuum more.

Thanks to Trebor for a useful modification.

Post# 176049 , Reply# 1   4/6/2012 at 02:32 (2,924 days old) by tolivac (Greenville,NC)        

I have the Sanitaire SC883 Contractor model and it is performing pretty well on my deep carpet.It would be interesting to get another similar machine and do the Trebor mod to it-then compare them.My Sanitaire hasn't "clamped" to the carpet yet.Sometimes Kirbys can do this--"G" models.I do see an excellent "airlift" effect on my carpet when using my Kirbys,Sanitaire,Royals,and Riccar Radiance,Brilliance vacuums.Maybe the clamping is when the whole carpet is fastened to the subfloor instead of the edges as mine is.

Post# 176064 , Reply# 2   4/6/2012 at 06:43 (2,924 days old) by twocvbloke ()        

A simpler modification:

Replace the 6-position Dial-a-nap knob with an 8-position Dial-a-nap knob, that gives you them two heights that are inbetween the "too high" and "too low" ones on the 6-pos. one, works great for me... :)

Post# 176092 , Reply# 3   4/6/2012 at 12:14 (2,924 days old) by Trebor ()        
What makes the modification effective...

is the fan is fed more air, which in turn causes the agitator to keep spinning. As to the matter of dirt moving from further away before the mod: part of the vibration is caused by the machine breathing intense little gasps of air due to the tight seal against the carpet. Post modification the airflow is somewhat continuous. If you were to graph the airflow the pre-mod graph would be high low spikes, the post mod would be more wavelike and stretched out a bit.

If the machine is used on flat-glue down carpet over concrete, the agitator should have brushes ONLY, no beater bars at all, in which case the mod can help performance, depending on the texture of the weave.

The used of a beater bar on carpet over concrete is very hard on the machine (think jackhammer) because the housing and frame absorb the shock.

This mod have been around for awhile. Kirby use to place a bleed valve in their rug nozzle, under the hood. They stopped with the Tradition. I installed one in my H1. Two 3/8 holes, and one pinhole for the pivot. It should work in G series as well. Open the holes just a tiny crack and no more clamping to the carpet. All the way open, and even cotton shag throw rugs do not get sucked in.

By the way, the hole drilled as you describe (wider on interior side) should be even better. It allows expansion of the air as it is sucked in.

Post# 176102 , Reply# 4   4/6/2012 at 13:34 (2,923 days old) by Sanifan ()        

That makes sense the way you described it, Trebor. It's helpful to visualize what's happening with the beater and the fan. Sometimes you forget the two are linked.

The airflow does feel more continuous. It's hard to say how the modded machine cleans after one use, but I'm sure it will do fine.

I understand about the concrete. The building we have is quite old and has wood subflooring. So no worries about the machine shaking itself apart.

As I understand it, the Turbo Brush for the older Tristars have a similar suction control. In addition to the row of little holes going across the front of the sole plate, it has that sliding button on the top to relieve the airflow. I always use mine on normal. I understand it opens or closes a port to adjust the suction in case there's too much clamping due to the nap.

I'm glad I didn't botch the mod by making the holes bigger on the inner surface. Is there a reason 1/8" was recommended? Would 1/16" give any benefit? I'd imagine there's a size you wouldn't want to go bigger than.

I also think the 8 position height adjustment knob is a great idea. Where to get one?


Post# 176117 , Reply# 5   4/6/2012 at 15:06 (2,923 days old) by twocvbloke ()        
"I also think the 8 position height adjustment knob is a

Hesco, parts no. E-268331 (the 8-pos. knob that screws to the base) and either E-380532, E-143021 or E-143022 (the cap that fits over the knob, comes in White or black, not sure about the other one though, call or email Hesco for more details)... :)

The link below shows all the parts and has an order form at the bottom:


Post# 176119 , Reply# 6   4/6/2012 at 15:25 (2,923 days old) by twocvbloke ()        

Quick pic, the S663 and the ZC-880 with the 8-position Dial-a-naps fitted...

(and don't believe the 840 Watts, the S663 now has a 120v 5.5A plastic-topped motor in it, so it's only 660 Watts, though I do have a for-parts 7A motor, I just don't think it's necessary... :P )

Post# 176121 , Reply# 7   4/6/2012 at 15:32 (2,923 days old) by Trebor ()        
1/8" gives the best bang for the buck...

and is easiest to do. Two 1/16" holes have almost the same surface area as one 1/8" hole. So theoretically it should make little to no difference. However, now I am wondering about the airflow vs. suction curve. The two 1/16" holes have an infinitesimally greater surface area than the single 1/8" but the wider dispersion should also increase the suction. More than two 1/16" or 1 single 1/8" holes per side will begin to negatively affect cleaning performance.

The modification works well, and saves the customer from excessive belt replacement. I just wish I could have patented it :)!

Post# 176152 , Reply# 8   4/6/2012 at 19:07 (2,923 days old) by Sanifan ()        

I'm going for the 8 position switch. But I am now interested in experimenting with 1/16" holes on one of my other 3 Sanitiares, all blue line.

I imagine two 1/16" holes evenly spaced on each of the left and right sides of the rear intake nozzle walls would be correct. It seems that angling the holes so that the incoming air gets directed towards the center of the nozzle would help, though I don't know by how much.

I will let you know how it works out.

Post# 176153 , Reply# 9   4/6/2012 at 19:09 (2,923 days old) by sanitairered (Michigan)        

sanitairered's profile picture
I find this topic facinating, would it be possible for you to post pictures of your modification?


Post# 176167 , Reply# 10   4/6/2012 at 21:51 (2,923 days old) by sanifan ()        

Sure, I'll post pics when I get the chance.

Trebor, we got our math slightly wrong. If you think about it, two 1/16" holes will match the diameter of one 1/8" hole, but the surface area is not the same. The two 1/16" holes represent a smaller opening.

It might be that you may need something like three 1/16" to get an opening the same size as one 1/8" hole. The math to figure it out is simple enough, but I'm too lazy at the moment. :)

Post# 176173 , Reply# 11   4/6/2012 at 23:31 (2,923 days old) by Trebor ()        
Oops... Mea Culpa!

I forgot to square the radius... DUH!
1/16" hole = .0031 sq in

1/8" hole = .0123 sq in

SO, it would take approximately FOUR 1/16" diameter holes to equal the surface area of ONE 1/8" diameter hole.

As the place guard said to Judy Garland in the Wizard of Oz, "Now that's a horse of a different color!" My apologies to all, especially you, Sanifan for having led you down the primrose path of mathematical mayhem.

Post# 176178 , Reply# 12   4/7/2012 at 01:02 (2,923 days old) by dialanap (Woodstock, IL)        

dialanap's profile picture
Sounds VERY interesting! I think I may try it on one of my Sanitaires.
If anyone is wondering the thread where this modification was originally discussed is Thread Number: 15921 "Sanitaire SC886 Vs. Kirby Sentra". Trebor gave very good instructions in this thread on how to do this modification.

Post# 176180 , Reply# 13   4/7/2012 at 01:29 (2,923 days old) by sanifan ()        

No problem, Trebor. Glad we caught that before anyone started drilling!

It seems that four 1/16" holes per side will allow for wider, more even spacing across the back of the nozzle. Might be a good thing.

It's been a while since I've taken physics, but I think there's significantly more drag through those four small holes than through the single larger one. Anyone knowledgeable in fluid dynamics? Even so, I think the four smaller holes will offer a benefit.

I'm sure figuring out all the calculations is a rudimentary exercise for a physicist. When I get the chance I'll try four 1/16" holes per side. I'm sure the added drag will call for another aperture of indeterminate size to equal the airflow going through the bigger hole.

Post# 176196 , Reply# 14   4/7/2012 at 06:43 (2,923 days old) by Trebor ()        
I am wondering...

Perhaps three 1/16" holes per side would be sufficient. You are right about the drag factor (no comments, please)

circumference of a 1/16" diameter hole = 0.196" x 2 = 0.392

circumference of a 1/8" diameter hole = 0.393"

This is the perfect example to illustrate the relationship between suction and airflow! TWO 1/16" inch holes have the same circumference and 1/2 of the surface area of ONE 1/8" hole. Eureka! (Sorry couldn't resist :)

Post# 176204 , Reply# 15   4/7/2012 at 08:38 (2,923 days old) by Trebor ()        
Further musings and...

a bit more math. The 1/16" holes will be quite small, and perhaps prone to clogging?

What about 3/32" holes? These would have a circumference of .296" and a surface area of .0069 sq. in. So the circle with a 1/2 again as large a diameter than 1/16" has a surface over TWICE as large. Incredible, but true.

pi x diameter = circumference, r squared x pi = surface. fractions converted to decimals

Post# 176216 , Reply# 16   4/7/2012 at 10:43 (2,923 days old) by sanifan ()        

Yes, very interesting. So maybe three 3/32" holes per side?

I like the idea of spacing them out across the back of the nozzle. I imagine that would be beneficial though, again, I'm just surmising there.

Post# 176220 , Reply# 17   4/7/2012 at 12:04 (2,923 days old) by Trebor ()        

1/16" hole = .0031 sq in, circumference of 0.196"
3/32" hole = .0069 sq in, circumference of 0.296"
1/8" hole = .0123 sq in, circumference of 0.393"

Divide the area by the circumference and the ratio increases, divide the other way and the ratio decreases.

3) 1/16" holes yield a total surface area of.0093 sq in, total circumference 0.588"
4) 1/16" holes yield a total surface area of.0124 sq in, total circumference 0.784"
2) 3/32" holes yield a total surface area of.0138 sq in, total circumference 0.592"
3) 3/32" holes yield a total surface area of.0207 sq in, total circumference 0.888"

As circumference of each hole increases drag will decrease until the fan is pulling at its maximum rate of airflow. If the total length of circumference is increased by increasing the number of holes while decreasing the size of each hole, drag (suction) will increase, while airflow will drop as per the calculations shown in the second and third lines.

I am wondering if the effect would be increased by not equally spacing the holes across or vertically, and what the optimum arrangement would be. I am at my limits here, unless my mathematical muse decides to come out of the closet and come to my aid:)

Post# 176225 , Reply# 18   4/7/2012 at 12:45 (2,923 days old) by Sanifan ()        

Yeah, it's interesting. At this point I'm at the limits of what I can figure out, too. I would think it's much easier for an engineer or physicist.

As for the effects of hole spacing, I don't know. In an R&D situation I expect there would be paper calculations and modeling first, and then 3d and real world modelling. Maybe with dyes to see the effect the holes on the airflow? There's some expense and time involved there that's out of reach for most of us.

As it's just a end-user modification, I the best we can do give an educated guess. Base our actions on experience and word-of-mouth about what works or not.

I'm inclined try three 3/32" holes per side, evenly spaced, to see how that works. Again, it's a question mark if that's the optimal arrangement.

Don't forget, the thickness of the wall also figures into the drag calculation (essentially, the length of the "tube"). Though at that scale the effect may or may not be a major factor.

I'll mull it over. Intersting discussion.

Post# 176228 , Reply# 19   4/7/2012 at 14:10 (2,922 days old) by Trebor ()        
More musings from the engineering muse...

...drilling the hole at an angle lengthens the 'tube' as well.

What about little teeny-tiny trumpet like things that would direct the airflow down into the carpet? Something like a hollow golf tee?

Wouldn't it be great fun to have an engineering brainstorming session at convention?

Post# 176231 , Reply# 20   4/7/2012 at 15:03 (2,922 days old) by twocvbloke ()        

How about just drilling a series of holes at the front of the vac as close to the rug nozzle as possible? :\

That way the air is directed under the brushroll where the roll is sweeping & beating, just like on Tristar power nozzles, so the air is assisting in the sweeping of dirt up towards the fan, rather than blowing on the back of the brushroll creating unwanted turbulence which would disrupt the airflow carrying the dirt into the channel towards the fan causing it to not pick up dirt and debris as well as it should be doing...

Either that or replacing the height adjuster, 1 screw to remove and refit, no drilling required... :)

Post# 176235 , Reply# 21   4/7/2012 at 15:51 (2,922 days old) by Trebor ()        
The holes in the front...

are unattractive to the customer, and potentially weaken the plastic where it can be rammed into obstacles.

Post# 176244 , Reply# 22   4/7/2012 at 16:38 (2,922 days old) by twocvbloke ()        

Erm, have you actually looked at the tiny little gap between the bumper and the rug plate where the holes would go? Do you honestly think that anyone would see small holes in such a narrow gap? And have you looked at a Tristar PN with those very holes in them (at the front of the rugplate no less) in comparison?

Take a look at this pic of my ZC-880, note how narrow the gap between bumper and rugplate is, a series of holes in that gap of up to about 2 Millimetres in diameter would not be visible without actually taking the vac and looking at it like that in my picture, and would be no more of a structural weakness as your idea would be as ABS plastic is pretty damned tough stuff, even with holes driled into it so it looks like swiss cheese, so, on both counts, your logic is flawed...

Post# 176246 , Reply# 23   4/7/2012 at 16:46 (2,922 days old) by Trebor ()        

I was not visualizing the holes there.

Post# 176266 , Reply# 24   4/7/2012 at 21:12 (2,922 days old) by Sanifan ()        

Yes, I initially was of the same mind - that holes towards the front bottom would be better. Like on the Tristar, as per your example. As long as the holes are slightly above the level of the nap they won't get choked by it, as is the origial problem with the nozzle.

When I have time I will look more closely at the plastic there. If sturdy enough, I'd imagine the location would be ideal. It seems to make sense.

The 8 position switch is a great idea, too.

Post# 176271 , Reply# 25   4/7/2012 at 22:36 (2,922 days old) by Trebor ()        
The question is...

would the holes in front actually serve the same purpose? I am not certain one way or the other. I do know that interference patterns can sometimes improve certain outcomes. The holes in the bottom front would sweep the air under the agitator, not over it, I would think. The holes in back would seem to cause a pull from behind the agitator, possibly creating a stronger seal across the front because of the airflow from the rear feeding the fan.

We do know the basic modification works, the rest is just tweaking.

Post# 176683 , Reply# 26   4/10/2012 at 19:26 (2,919 days old) by Trebor ()        
After a lengthy and technical conversation...

with Cliff Brady at Lindhaus,(who agrees wholeheartedly with this mod, by the way) I think the holes in the back might do more good because the airflow will help cool the belt, reduce stretching under friction, and keep the agitator turning as the fan is fed more air, as mentioned before. Not sure the holes in front would have as great an effect in that regard. (This is much more fun than discussing how many angels can dance on the head of a pin)

Post# 177020 , Reply# 27   4/13/2012 at 21:12 (2,916 days old) by Sanifan ()        

I've had the chance to use the modified Sanitaire further and I can't say it lacks for performance. It still cleans very, very well. The one thing I do like a lot is that the suction feels a lot more consistent. There's really no feeling of sucking down onto the carpet.

I want to install the 8 position switch as well.

I think I'll drill six 3/32" holes across that narrow gap under the front bumper on on of my other machines just to experiment. I'd think that guiding the extra airflow under the brushroll would be a good thing. It helps suck in the dirt and the holes are situated to give suction clamping relief, as was the original intention.

I'll let you know how it goes. Probably won't be until next week.

Post# 177021 , Reply# 28   4/13/2012 at 21:15 (2,916 days old) by Sanifan ()        

Am I right in thinking that putting the holes across the front would interfere with using the magnet bar?

Post# 177268 , Reply# 29   4/16/2012 at 08:46 (2,914 days old) by Trebor ()        
Magnet bar...?

I have seen them both on vacuums, and in their plastic bubble packaging. I don't know how many versions might have been manufactured. If it has to fit in that narrow groove, then yes, it would cover the space where the holes would be.

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