Talk:Roots blower/Archives/2013

Removed citation

There is no need for a citation on the connection of a Supercharger a.k.a 'Blower' because that is how it works. It is one of the reasons that a Supercharger and a Turbocharger differ. The pressures involved in a Supercharger versus a Turbocharger are much different, the Superchargers pressure being much greater.. Any other form of drive mechanism simply would not work. A Turbocharger also works on an on/off type of service and is only effective while the engine is under load. While at idle, or if the pressure becomes too great it is bypassed via the waste gate. A 'Blower' however due to its design is always 'on' if the Blower is bypassed or not spinning by direct drive no air will reach the combustion chamber due to the sealed chambers created by the rotating vanes in which it must pass, therefore the engine will not run. It is purely a 'Mad Max" Hollywood myth that a blower can be turned on and off as needed. Any other form of design simply would not be an effective Supercharger. That in a nut shell is how a blower works, anyone can prove me wrong feel free to add the information to the article rather than simply taking the lazy mans approach and spamming the article with cite tags.

--DP67 (^talk/_contribs) 20:08, 14 November 2007 (UTC)

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A true supercharger compresses internally, axial or radial superchargers (including turbochargers) all compress the charge air going through. Roots blowers do not compress, they simply pump. To an engineer the difference is very significant - Roots blowers were designed to be scavanger blowers for 2-stroke engines and not compressors for 4-stroke engines, although this has been their main application. The Roots blower is equally effective at all speeds, as designed, but true superchargers are ineffective at low speeds.

The difference between a supercharger and turbocharger is how they are driven, not how they charge the air. A supercharger does not suffer from turbo lag because it is mechanically driven and even at engine idle is spinning rapidly at many times engine speed (and absorbing power). Roots blowers are always mechanically driven at relatively low speed.

It is a common mistake to confuse the drive type (mechanical / turbo) with the blower or compressor type (blower / axial compressor / radial compressor). Theoretically either drive type may drive any blower or compressor but the high speed turbo is really only suited to drive relatively small radial compressors and low speed Roots blowers are easily driven by drive belts. Roots blowers used as compressors (such as by drag racers) are quite effective but inefficient.

The famous 1930s "Blower Bently" was so called because it used a Roots blower and not a true supercharger (W O Bently knew exactly what the difference was, he had worked on supercharged aero engines)

DesmondW (talk) —Preceding comment was added at 23:46, 4 December 2007 (UTC)

Actually, the blowers used on most dragsters are compressors, even though externally the most common versions such as Weiand and B&M type blowers may look like an old Roots, but due to their internal design they aren't really Roots blowers. Yes, they are based on the traditional Roots design but they are modified to provide much higher output pressures. My point for removal of the needless 'citation-needed' was that I have yet to see a blower or supercharger of any design that is not belt or gear driven. It's the nature of the beast. Due to sealed the chambers, if the vanes aren't turning, there won't be enough air getting by, not enough air, the engine won't run. The pressure created by the supercharger would create too much back pressure to be driven by exhaust gases like a turbo. Too much back pressure and the engine will drown. There are such things as centrifugal superchargers and due to their design they will allow some air to slip by while the vanes are not turning, or not under full load but they are a different animal. Yet, they are still powered by belts or gears. Since turbochargers do not have sealed chambers that the air must pass through it really doesn't matter if it's turning or not. You could stop a turbos impeller completely without preventing the engine from running. Might run with decreased performance, but it will run.

Superchargers do have low end power boost. That's why drag racers use them and in some configurations they can get fire out of the hole as well as the virtually unlimited boost. As the engines RPM increases, the amount of drawn air and output pressure increases rapidly. Whereas with a turbo charger there is a limit to the amount of boost it can provide before performance actually degrades. One disadvantage of using a supercharger is that if the engine backfires it's backfiring through the supercharger. And when you are talking about the pressures behind a supercharger as used on a top fuel dragster, well.. Essentially you've got a bomb under the hood! That's why top fueler's tie down the blower with steel braided straps. If the engine backfires, the super charger is gonna try to reach the moon! Unfortunately it looses steam before it reaches orbit and takes out a few spectators when it falls back to earth and lands in the grandstands! If it backfires through a turbocharger there is no where near the chance of such a violent reaction.

Also; a Roots-type blower does create some positive pressure, it might not be as much as its successors or when compared to a turbocharger, but none the less it's still a positive pressure. Being as 2-cycle diesel engines produce little to no vacuum of their own, every little bit of positive pressure forcing the air down it's throat helps. More air you squeeze in, the more fuel you can squirt in, getting as much of the two together as you can, the more power the engine will produce.

As for the differences between 'Effective' and 'Efficient' that depends on which definition of efficient you choose to use. If you are talking about fuel efficiency as in mpg, well, one must make sacrifices for higher performance. The higher the performance the less fuel efficiency. At least in the good old days we used to cram as much air/fuel mix we could into the combustion chamber burn it as efficiently as possible, make it go, and hopefully it go's really fast! :) After all, isn't that the name of the game? As for reliability, with high performance you have to sacrifice that too.. When you are squeezing out every bit of horsepower that an engine can produce it's life span is limited so more routine maintenance is required, and even that only goes so far before a complete rebuild is needed..

Folks today want a 500hp muscle car like we had in the 70's that gets 50 mpg, and a 500,000 mile warranty, sorry, folks you've got to sacrifice something, unfortunately in order to gain performance one of those sacrifices must be fuel efficiency when calculating miles per gallon, the other is reliability.

--DP67 (^talk/_contribs) 05:44, 5 December 2007 (UTC)

Ok, there are several different things here and some confusion between them. You still appear to be confusing compressor drive (mechanical / turbo) with compressor type. Read the following excellent articles for really good explanations:

http://en.wikipedia.org/wiki/Supercharger

http://en.wikipedia.org/wiki/Turbocharger

Both articles point out that turbocharger is short for turbo supercharger and any pump used to force feed an engine can be called a supercharger. You will also see the Eaton developed spiral Roots supercharger, still the same principle but more efficient and one of the most commonly used car superchargers today (Jaguar supercharged engines use these).

The wartime RR Merlin engine used a gear driven radial (centrifugal) compressor which ran many times engine speed, 10,000 - 12,000 rpm I think. Allison engines used in the Lockheed Lightning used turbo driven radial compressors and running I believe at around 15,000 rpm. The two different radial compressors were quite similar in size and specification, only the drive differed greatly.

The Republic Thunderbolt also used a turbo supercharged engine, the same one used in the B 29

I am also guilty of over simplifying. There are two types of pump: positive displacement (Roots & similar) and impeller (axial & radial). Positive displacement pumps will work from standstill but impeller types must be spinning at a few hundred rpm at least before they deliver at all. Positive displacement pumps deliver air volume exactly proportional to their speed, impeller pumps once they start delivering will increase volume considerably more than the increase in rpm and often deliver excess air. A characteristic of any impeller compressor is that air may flow through with the impeller at standstill.

DesmondW (talk)

Correction

I would like to correct the diagram, step b reads "compression" which is incorrect as the chamber size remains constant, it should read "pumping" or something similar. Any compression will only take place as the air is forced into the intake manifold, as step c states.

DesmondW (talk)

Nonsense

< Additionally, the operation of the compressor itself requires energy input, which is converted to heat and can be transferred to the gas through the compressor housing, heating it more. >

This is back-to-front. The hot gas heats the housing.

86.182.42.110 (talk) 12:26, 7 December 2010 (UTC)

Correction

Superchargers increase the output of an engine, not the efficiency. Cooling the inlet charge also does the same: it increases the output, but reduces the efficiency.

A Roots-type supercharger works by pumping at a rate faster than the engine uses the air supplied: if it pumps twice as fast as the engine requires, this will give about one atmosphere of "boost" (less leakage through the engine during valve overlap, etc.). The effect is equivalent to increasing the engine size.

Turbochargers recover heat energy from the exhaust by expansion and cooling and return it to the inlet in the form of a hot, dense inlet charge: this increases the efficiency overall. This is why turbodiesel engines reach such high thermodynamic efficiency levels.

The problem is that most engines cannot sustain an increase of the combustion pressure beyond a limit determined by the materials used: aluminium and iron can only handle so much! Also, petrol engines suffer detonation when the inlet temperature and pressure get too high. — Preceding unsigned comment added by 82.153.154.4 (talk) 14:02, 30 May 2011 (UTC)

Vacuum pump

Roots blowers are commonly used as vacuum pumps, I think there should be a section about that. — Preceding unsigned comment added by 204.8.224.210 (talk) 21:41, 14 January 2012 (UTC)

23 Jul 2012 Applications reword

In "Dragsters", Detroit Diesel also made 8V71 and 12V71 truck engines. Although maybe about the same length as straight 4 and 6 cylinders, they must have a greater capacity, for twice as many cylinders, right? Larger diameter, or do you gear them twice as fast?Sammy D III (talk) 20:32, 23 July 2013 (UTC)

24 Oct 2013 Correction

Mention of ideal gas law is wrong. An ideal gas does not heat up when compressed, but real gases do. No need to get into discussion of deviations from ideal or Joule-Thompson coefficients; just delete the mention of the ideal gas law. -D.A. — Preceding unsigned comment added by 142.90.112.22 (talk) 04:45, 25 October 2013 (UTC)

Naming

Roots, not Rootes. Rootes was a car maker. The Roots brothers started the Roots Blower Company in Connersville, Indiana (sometimes encountered in 1950s UK practice as "Connersville" blowers, or as licence-built Holmes-Connersville blowers).

• Modern GE webbage: Roots [1]
• Connersville tourist board [2]

Also we don't do copy-paste page moves, certainly not to edit-war over such things. Andy Dingley (talk) 16:48, 27 October 2013 (UTC)