User talk:Andy Dingley/Archive 2011 September

← Archive 1 | Archive 2 | Archive 3 →

File:GERMAN TANK DISGUISED AS AN AMERICAN TANK.jpg

Hello!

Your edit was completely wrong. There was no valid source stated. Please get familiar with COM:L, so that such actions won't accur again. User:LX did it correctly. Regards, High Contrast (talk) 12:06, 5 September 2011 (UTC)

Lose the patronising attitude. Andy Dingley (talk) 12:19, 5 September 2011 (UTC)

Rotary piston air compressor

Hi Andy, I've been working on modelling out air compressors/motors and for one design, I was thinking that a rotary piston air engine (basically a radial engine) might be suitable as another air compressor design. The idea is to have an alternative design to the regular piston compressor, which is more efficient and is also better at bleeding off heat. Since piston compressors allow a great deal of compression per stage, they're also quite cost effective. The compressor could be useful for compressing diving cylinders, so I'm also hoping to make the design suitable for this (may require special lubrication system).

I found a rotary piston air engine (SF376 and UTAM4) at http://home.ctlnet.com/~robotguy67/classic_cars/air_engines/V-Twin/air_engines.htm , http://www.fluidlinecomponents.com/images/stories/products/airdrills/products-air%20mot-taiyo.pdf). From the pictures and text alone, however, I don't understand the exact functioning of the valve system for the first design. I understand that there is one tube with 4 holes (each placed at 90° from each other). I also understand that there is a tube with 4 pipes unto it, which directs the air. However, how these (and the other parts) exactly work together with the poppet valves, pushrods, lifters, ... is a bit of a mystery to me. I even don't understand the piping (ie in the Howstuffworks motor animation (http://science.howstuffworks.com/transport/engines-equipment/radial-engine2.htm ), there are 2 valves per piston, but one is the outlet, so I don't get why you have 2 pipes attached to each piston).

I was wondering whether you have some pictures of how the valve system for a regular radial engine works, and/or the workings of poppet valves, ... (I don't get the schematics at http://en.wikipedia.org/wiki/Poppet_valve ); also I think that since there is no spark plug in compressed air motors/compressors, there are actually only 2 strokes, so things can be a little different.

KVDP

"air compressors/motors" The idea of "compressors/motors" is about as misleading as combining electric motors and generators. It doesn't work at anything beyond the hand-waving level. Someone sent me a Youtube link at the w/e for a New Zealand guy who'd built a steam lawnmower by placing an empty propane tank on a barbecue stove and leading the steam to the old two-stroke petrol engine's spark plug hole, through a solenoid valve. You can make all sorts of things this way and give your mates a laugh, you might even mow some grass, but it's never going to be an improved piece of engineering.

"which is more efficient and is also better at bleeding off heat. "

I'm puzzled by this. How does re-arranging the cylinders make it more efficient? Also how does bleeding off heat make it more efficient?

The idea is to capture and reuse the heat using a stirling engine (generating power with this mechanical surplus energy); I'm allready working on a similar system for a regular (line) IC motor, but radial engines seem even better for this (more liquid can be pumped around the cylinders, and probably at a more efficient way (flow of the liquid). User: KVDP 08:42, 7 September 2011 (UTC)

Motors don't work on heat, they work on enthalphy. You need to learn the difference.

Radial engines exist, and really only exist on aircraft, because it was a way to place all of the cylinders in the airstream at the front of an aircraft and so get the cooling advantages. Important for an early petrol engine. Radial air motors are used because it avoids the stopping on "dead centre" problem (see Barring engine). For radial compressors though, why bother? Radials are also awkward to make - bulky, and non-square angles. Of course you can make radial compressors, but I'd want to see a good benefit to it before I re-designed my production line to make this awkward shape.

Compressors put energy into compressed gas by increasing both its pressure and (inevitably) its temperature, by some basic thermodynamics. Cooling this is necessary for engineering reasons, to stop things failing. However cooling the compressed gas doesn't increase efficiency, rather the opposite.

The articles I read made it sound that it does increase efficiency, as cooled air (not a cooled engine/compressor) is more easy to compress (something to do with adiabatic/isothermic law). Isn't the same method btw used in petrol/diesel engines (cooling the air/mixture so the piston can press in the liquid more) ? User: KVDP 08:42, 7 September 2011 (UTC)

I can't imagine pre-cooling the air as being useful. The gains are small, the difficulty of doing so large. Where compressors deliver to a reservoir or long pipe network, they'll cool down anyway so there's no need to do anything particular. Where deliberate cooling certainly is used is for intercooling between multi-stage compressors. The air is heated in the first compression stage, so just a simple finned pipe radiator can dump excess heat to ambient air. This then reduces inlet temp to the second stage, which is, as you say, useful. A similar thing is done for internal combustion engines, but only when turbocharged. An intercooler (an expensive high-flow honeycomb radiator) is used between turbocharger and cylinders. In both of these cases, the compressed air is being used rapidly after it's first compressed, so there's no time for slow cooling in the pipes alone.

Piston compressors are "cost effective" for manufacturing costs, but they're also less efficient than screw compressors, may require lubrication (which means oily air) and are noisy. In industrial use they're getting rarer and rarer, as the cost of casting or machining compressor screws comes down. They're not chosen for efficiency and I don't think their single stage compression is even that much better than a good screw compressor these days - although it is a complex task to make screw compressors.

That's true, I'm working on a rotary screw compressor aswell (this is 3/2 more efficient; see http://www.appropedia.org/Compressed_air_energy_storage_and_use_system ) However, I wanted to have a radial-design aswell, and have a design specific for diving applications.

Lose the vane compressor. Vane compressors are limited by the compression ratios they can achieve. For compression above atmospheric, they become a problem for lubrication. Their only real market these days is in below-atmospheric work. They're very common as simple first-stage vacuum pumps and when used as compressors, this is almost always because the inlet pressure is already below atmospheric (vapour collection systems etc.), where other types of compressor have problems.

Why do you want a radial design? Are you just collecting the set? There needs to be an advantage to choosing designs, not just pokemon.

In regards to the efficiency: offcourse if the compressor would be pretty much useless as a diving cylinder compressor, I won't design it. However, I did saw (commercial) radial compressors before; see http://www.bock.de/en/Product_overview.html?ArticleSizesGroupID=169 Not sure how they attain the efficiency claimed though (I believe trough the use of nitrogen, but then again perhaps they only use this as a liquid for extra cooling, so the design should be viable)

In regards to the oily air; I do remember that they are frequently used in diving applications, although I've indeed seen that the lubrication method isn't fully seperated from the air. They seem to use "oil scrapers" (see http://www.hycompusa.com/news/news-stories/ ,image near "oil insulation". Perhaps other methods too are possible though (ie thinking of a system as http://www.machinerylubrication.com/Read/775/reciprocating-compressor , see image 2A, 2B). User: KVDP 08:42, 7 September 2011 (UTC)

I don't know about diving or SCBA, but oil is really bad in breathing applications and (AFAIK) it's now far simpler to use oil-free compressors than to use oil and have to clean it out later.

The radial compressor you describe is a refrigeration compressor. These are different again, especially as this one is for a transcritical CO₂ system (explained here). These are high-pressure systems where leakage muct be avoided entirely ("hermetic" compressors). In this case, the compact layout and seal-avoiding design of a radial compressor is worth using.

Piston compressors are usually simpler than engines because their valvegear can be automatic. Rather than the camshaft, rockers, pushrods and poppet valves of a car engine, a compressor can use simple spring-loaded valves. These can be poppets or flat spring flaps. They can also (which makes them even cheaper) be placed entirely in the cylinder head of a compressor, without needing any connection to the crankshaft. This avoids gears and also the need to make the head-crankshaft spacing accurate and consistent, so the overall machine gets much simpler.

I really need schematics to understand a system, mostly since I have no experience with these types of engines/mechanical linkages. User: KVDP 08:42, 7 September 2011 (UTC)

There is no linkage, the valves here are just spring loaded and each one works independently.

Looking at the engines you link, the first one [1] is a five-cylinder radial engine. It's hard to see the valves, but it appears to be "crankshaft ported" with a pair of five-way small-diameter rotary valves. The crankshaft is hollow and has a hole in the side. It runs through a bearing block with five hole in it. When holes line up between block and crank, that valve is "open". The holes are probably machine rectangular and very carefully spaced & sized, to give the best timing and valve opening. This technique is well known for small single-cylinder two strokes, but it tends to give very small ports. With five cylinders these would be very short, especially as it's hard to arrange overlap between them. It might work for a high pressure air engine, but it doesn't work for petrol engines as these breathe at quite low pressures, so need long valve open times.

Again, I need schematics, also because I don't see how a single hole can line up with the correct hole on the crankshaft (ie the timing sequence isn't 1-2-3-4-5, it's 1-3-5-2-4) User: KVDP 08:42, 7 September 2011 (UTC)

This is a compressed air engine, so it's effectively a two-stroke and not a four-stroke. The firing order is 1-2-3-4-5.

With four-stroke radials, they use a cam ring (I should write an article on this). This is a two-cam camshaft (inlet & exhaust) that is shared between all the cylinders in one row of a radial engine. Compared to a "normal" inline camshaft, it's very short and fat - the diameter of the crankcase, but only a few cm long. It is transformed from a shaft to a ring. Each cam "track" has two lobes on it, and it rotates at quarter engine speed (not half, as usual for four-strokes). Each cylinder valve thus sees a cam lobe pass by once every two crank revolutions, as for any four-stroke engine. The two lobes/quarter speed difference is to get the "interleaved" firing order, 1-3-5-2-4, of a four-stroke radial engine.

If you compare it to the commercial air motor ([2], third page), you'll see a better developed version of the same basic idea. The ports are notches in the crankshaft, rather than a central hole, so the connection is a fixed one from the side, rather than the length of a rotating shaft. This also allows both inlet & exhaust ports to be on the same side, allowing a much simpler crankshaft with a one-sided overhung crank. The inlet & outlet valves are overlapped, so that each cylinder has just the one port. The long ports from valve to cylinder head can now just be one pipe (or drilling) that goes both ways, not two separate pipes. The exhaust port goes through the crankcase, supplying lubricant from the air.

In the Taiyo document, there aren't any front/back views, just side view crosscuts. I'm not familiar with the design, so I still don't get the valve mechanism. User: KVDP 08:42, 7 September 2011 (UTC)

Look for the single narrow shaft that is the crankshaft, the look at the passages drilled in the block just outboard of this. The long diagonals are the single air passages to and from the cylinders.

You need two ports (or one bidirectional port) because you can't just vent directly to the atmosphere. You need exhaust silencers, oil traps etc. This used to be done for aircraft engines in WWI, but they were filthy things that threw oil everywhere.

Poppet valve isn't a useful article, it's too badly written. There are any number of car explanations though (as I suggested, try to find Setright). Radial engines are a little more complicated because they have large cam rings instead of camshafts. This is just to make better use of space.

I'll search for the Setright articles. User: KVDP 08:42, 7 September 2011 (UTC)

If you go back to 1900 and blowing engines for blast furnaces, you can find huge low-pressure air compressors that used actuated valves (i.e. camshaft or similar) for air compressors. For anything faster or higher pressure though, self-actuated valves with springs are how it's done. Andy Dingley (talk) 10:56, 6 September 2011 (UTC)

I'll see whether I can find more information, if indeed the compressor design is useful to make (as you explained earlier, ie in regards to efficiency)

User: KVDP 08:42, 7 September 2011 (UTC)

Category:Ball bearings into Category:bearings or Category:Rolling element bearings

Hi Andy! Did you (or your bot) undo the changes, revision 59299672, per COMMONNAME Undo as it says? what does it mean? I meant to clean up the Category:Bearings.Ball bearings and roller bearings were grouped up in Rolling element bearings which was included in bearings, so no extra link was necessary, no? Or what about putting ball and roller bearings right in bearing category? Cheers --Carnaubo (talk) 17:15, 12 September 2011 (UTC)

Wikipedia is an encyclopedia, its function is to explain things. Commons is a media repository, categorization exists so that people can find things.

Neither of these goals are to be a defining (and narrowly tree-structured) taxonomy of meanings.

Ball bearings are a major group within bearings, and a likely term that users will both search for, and will wish to find when browsing. It's thus reasonable to keep it in the main category, even if it's also a sub-sub-cat of it, via the not widely-known term of rolling element bearings.

ok thank you, so I guess putting roller bearings there is ok? instead of in the rolling element bearings cat.? I think they belong together (roller and ball bearings). anyway, whats Category:Self-aligning bearings for when we have Category:Spherical bearings? I shouldn merge them? Can I put Category:Spherical roller bearings into Category:Spherical bearings? I better ask this time just to be sure.. Thank you for your answer, --Carnaubo (talk) 19:34, 12 September 2011 (UTC)

Roller bearings are rolling element bearings too (as part of the taxonomic tree). Personally I wouldn't list them under bearings, because the wording is close enough to rolling element that anyone browsing the bearings category would see that already.

Self-aligning bearings are rotating bearings that self-align, no matter how they do it. An obvious type of these are the spherical roller bearings, and also spherical ball bearings (currently bundled along into spherical roller bearings). A further type, not yet illustrated, are the self-aligning pillow blocks that are a simple cylindrical bearing inside a (non-rotating) swivelling housing. For this reason we shouldn't merge self-aligning bearings into spherical roller bearings.

A quite different type are spherical bearings. These are already described (in a vain attempt to avoid having to explain this again and again) on the page for that category. They do not rotate. They do not have rolling elements, of either form. It is a mistake (all too common on Wikipedia and Commons) to pattern-match words and assume meaning, rather than understanding the subject matter. Andy Dingley (talk) 20:14, 12 September 2011 (UTC)

Well I'm glad you mentioned that's a common mistake on Commons! Thanks for taking care. It looked a bit messy to me but it's good to hear there's some intention behind. Good night, Andy! --Carnaubo (talk) 22:42, 12 September 2011 (UTC)