Test question!

[BIG DOG]

Had a test today wasn't sure of the answer for these two questions so I skipped them and forgot to go back **(*)failed by two points What's the proper technical term for them? And it's not a lock nut or a lock washer.

[BIG DOG]

Here is another if the same amount of air pressure is put in each inlet will the piston stay the same, move in slowly,move out slowly or I forget what the other option was. I said stay the same but after thinking about it I believe that it would move out slowly as the stem of the piston would take away some of the surface area that the air is pushing on.

By the way I guess I need to brush up on my basic pneumatics anyone know where I can find the info on the net?

[Pedalkisses]

how bout a bearing retainer nut and lock?     and i think it would stay the same

[73swinger]

it's called a "castlleated (SP?) nut" or sometimes called a crown nut or castle nut, and the piston rod will retract faster than extend because of the area of the rod (that cavity will fill faster), BUT the cylinder will make more power in the extend mode because of the extra area on the piston


Sounds like you're doing a millwright test to me

[Bill_Reilly]

Not sure on the nut - on a shock we just call them locking collars. The washer looks different than the external tooth lock washers I buy - not sure what it is. Come to think of it, I was just working with some that looked similar - they had the internal tooth that matched a groove on the shaft, and then you bend one tab over to keep the nut from backing off.
  ...the piston would move out.

[BIG DOG]

[quoteSounds like you're doing a millwright test to me

"castlleated (SP?) nut"  Must have been the (SP?) nut and washer as the answer was only a couple of letters I believe.
    I'm trying to get into the maintenance department at work .....or at least pass the test .They say the test to get in is almost as hard as the tests to get to different levels .I had to pass a math test then a aptitude test There were 3 out of 12 of us left after that .I challenged the test so as I wouldn't have to go take the course .I got 66 out of 100 .So I had to go take the course that the company pays for at the local college 12 weeks 1 day a week fo 5hrs. So after that I'm thinking that I shouldn't have any problem passing .But there is one catch the company doesn't let the instructor see the test so he is kinda guessing at what he should be teaching.We spent a whole day on conveyors and such and there was nothing on the test .Spent no time on pneumatics and there was a bunch of questions on it . You would think that the company would give the instructor some info on what he should be teaching .My mark this time 68 I guess that I didn't learn much from the course that I got a 88 on the final exam .
Feel pretty dejected right now can't believe that I got 32 questions wrong ........Guess I'm not as smart as I thought I was!!
 
 I can only write the test one more time only allowed 3 times then they won't let you write it any more .Oh and after the test you have to put together the pneumatic clutch that you have to answer questions about in the test.( blueprint)Do that wrong.....FAIL So I have to pass the test and assemble the clutch with no mistakes next time! So any good sites to learn from or good info places I can go to help me learn would be appreciated!
 Thanks! I will post a few more questions if I can remember later ......but I don't know the answers ...they won't give them to you.

[BIG DOG]

Here are a couple of more first one which way must you crank the handle to make the weight raise clockwise ,counter clockwise, or not at all?

The next which way must the weight move left or right to make the valve open easier?

[GTS225]

Pic 1 is a "Spanner nut"

The pneumatics cylinder thing is "move out slowly".  Your second-guess hunch is correct, the piston shaft reduces the square area of the piston, thereby allowing the cylinder to extend. Air pressure is measured in PSI, (pounds per square inch), and an identical pressure placed on both sides of the piston would apply more force, (pounds), onto the non-shaft side of the piston.  (Note: There would be some frictional forces to overcome due to the shaft and piston seals.)

The valve/pivot/weight question:  The weight would have to be moved to the left.  Pivot on left side, weight on right; as the weight is moved to the right, the torque, or applied force gets greater on the valve/seat.  Think in terms of a wrench....the shorter the wrench, the less force or torque you can apply. (The weight represents your arm pulling on the wrench.)

Hmmmm.....cranking the handle to raise the weight.......Not enough info.  Is the drawing not oriented correctly?  What does the horizontal shaft represent......a threaded shaft?   What does the rectangle in the middle represent?  If it's some type of gear arrangement, it could be either direction, if it's just an internally threaded block, that's different, too.

BTW....FWIW, I am an industrial maintenance tech for a local cabinet manufacturer.

Roger

[guzzimike]

Pic 1 is a "Spanner nut"

The pneumatics cylinder thing is "move out slowly".  Your second-guess hunch is correct, the piston shaft reduces the square area of the piston, thereby allowing the cylinder to extend. Air pressure is measured in PSI, (pounds per square inch), and an identical pressure placed on both sides of the piston would apply more force, (pounds), onto the non-shaft side of the piston.  (Note: There would be some frictional forces to overcome due to the shaft and piston seals.) 
Roger

Wait a minute...I have a few questions..

Would not the side with the piston shaft in fact have a reduced total cubic area..(this being the volume of this chamber minus the volume of the shaft), as compared to the other (non-shaft) side..?

And if the air pressure input coming in through both ports is the same, would not the area with reduced cubic area have more internal pressure build up..? and if so, would this higher internal pressure in the chamber with the shaft not overcome the pressure on the non-shaft side..?

[GTS225]

Sorry Mike, hydraulics and pneumatics doesn't work that way.  I understand what you're thinking process is, and I think you're comparing it with engine cylinder volume calculations, but you're missing a little something.  Pressure in an enclosed environment is equal on all surfaces, regardless of volume.  What a cylinder does is to convert pneumatic energy into linear motion and/or work.  In so doing, the mathematical equation gets broken down into it's elements.  PSI becomes only P, or force in pounds applied by the cylinder shaft.  The volume has little effect, except to determine how fast the cylinder extends or retracts, depending on the available air flow delivery.
In the case of a cylinder, the shaft is not a part of the "working" surface, and detracts from the square area of that side of the piston, thus you have a greater square area on the non-shaft side.

Roger

[guzzimike]

Hiya, Roger.... I still have a bit of problem with that..

According to Boyle's Law (Pressure and Gasses)

http://en.wikipedia.org/wiki/Boyle's_law

“ For a fixed amount of gas kept at a fixed temperature, P and V are inversely proportional (while one increases, the other decreases)"
 
PV = k

Where:

P: Pressure

V: Volume

k: Constant of pressure and volume in the system...

What Boyle's Law tells us is that Pressure and Volume are inversely proportional..IOW, in a closed system, If you increase one, the other decreases..

In the test example, everything else being equal, the side with the piston rod has in effect been reduced in Volume, hence (by Boyle's Law) the Pressure inside that particular chamber increases compared to that of the other side, in effect pushing harder against the non-piston rod side..

Remember, you can compress Gases, but you cannot compress liquids...




Anyhow, I may be wrong about this...what do I know..


 

[Shorty Thompson]

Here is another if the same amount of air pressure is put in each inlet will the piston stay the same, move in slowly,move out slowly or I forget what the other option was. I said stay the same but after thinking about it I believe that it would move out slowly as the stem of the piston would take away some of the surface area that the air is pushing on.

By the way I guess I need to brush up on my basic pneumatics anyone know where I can find the info on the net?

It'll move to the right until an equalized amout of pressure is obtained

[guzzimike]

Hi Shorty...I think it will move to the Left till equalized pressure is attained..

[BIG DOG]

Pic 1 is a "Spanner nut"
Hmmmm.....cranking the handle to raise the weight.......Not enough info.  Is the drawing not oriented correctly?  What does the horizontal shaft represent......a threaded shaft?   What does the rectangle in the middle represent?  If it's some type of gear arrangement, it could be either direction, if it's just an internally threaded block, that's different, too.

BTW....FWIW, I am an industrial maintenance tech for a local cabinet manufacturer.

Roger

No spanner nut or washer wasn't one of my options though that's what it looks like to me!
The block is a threaded block with crank on the end of the threaded rod I said it wouldn't raise the weight turning it either way.
Guzzi do you think I could use that argument to get the correct answer to the question?
I'm still in shock I can't believe I got 32 questions wrong thats every 3rd one 

[BIG DOG]

So what if you look at it this way  force =pressure xArea

4"dia piston area =3.14x2sq which = 12.56 "sq
pressure =50 psi
force =12.56 X 50psi 628 lbs of pressure
take away any amount of area from the piston (like the piston rod/stem) and that side will have less pressure on it and the piston will move in that direction .

[guzzimike]

So what if you look at it this way  force =pressure xArea

4"dia piston area =3.14x2sq which = 12.56 "sq
pressure =50 psi
force =12.56 X 50psi 628 lbs of pressure
take away any amount of area from the piston (like the piston rod/stem) and that side will have less pressure on it and the piston will move in that direction .

I understand what you are saying, but the problem with that is that you are looking at it on a two dimesional model view..(IE: the frontal area of the piston)...but in reality, it is a 3-dimensional model...with Volume (Cubic inches), no just frontal Areas (square inches) in play...

Look at it this way. Forget the rod /piston setup. Lets say that you have a hollow cylinder laying on its side with a wall bisecting it. You have two ports pushing in an equal amount of air or whatever gas in either side of the wall, like your drawing.. At this point they are in perfect balance..

But now let's say that we introduce a metal cube on one side of the Cylinder (let's say the right side). The other side remains empty.

Everything else being equal, when filled with an equal amount of gas, say 100 CuFt of air,  the side with the cube will be at a higher pressure than the other side, because part of the available space for the gas is taken up by the cube.

Now if the wall in the middle is able to slide one way or the other, it will slide toward the side of less pressure until pressure equalizes on both sides...

Again, look at Boyle's Law..

PV = k

Pressure and volume are inversely proportional.

At least, that's the way I understand this experiment...

The one flaw in this process I can see is if the air supply into the system is a variable....IOW, is the air pressure into the right side of the system varied to make up for the cube's volume.. If that's the case, then presumably you have stasis. Nothing moves.


Here's another example for you:

Let's say that you and I are standing inside equal sized elevators, side by side.

Then 4 people get on your elevator  and their 4 twin brothers get on mine...

Suddenly I cut a massive Fart. 

I can guarantee you that the 4 people in my elevator will be pushing as hard as they can against the door to get into Your elevator...


So there: A Perfect example of Boyle's Laws of Gases at work.

I hope this helps.

[GTS225]

Mike, your understanding of Boyle's law is correct, for a closed system, but....in this case, it's not a closed system as applied by Boyle's.  This has an unlimited volume of air available at each port, but pressure is equal at both ports, so no variable there.  The only "variable" is the square surface of the piston face, (on both sides in this case).  We circle around to altering the energy of the compressed gas, (work available in all directions), to work available in only a linear fashion. The side of the piston with lesser surface area will get overcome by the side with the greater surface area.
I do see what you're saying as to pressure equalizing, but pressure is the result of resistance to flow, and here we have unlimited flow, and the shaft side's air will get pushed back toward it's source due to the greater force (in pounds) of the non-shaft side.

Roger

[nothingbutdarts]

The washer is a locking washer or sometimes refered to as a tab washer for locking the wheel bearing nut in the first picture.

[NYFDFF]

As stated above spanner nut and retaining ring or lock

[fourspeed]

Mike, your understanding of Boyle's law is correct, for a closed system, but....in this case, it's not a closed system as applied by Boyle's.  This has an unlimited volume of air available at each port, but pressure is equal at both ports, so no variable there.  The only "variable" is the square surface of the piston face, (on both sides in this case).  We circle around to altering the energy of the compressed gas, (work available in all directions), to work available in only a linear fashion. The side of the piston with lesser surface area will get overcome by the side with the greater surface area.
I do see what you're saying as to pressure equalizing, but pressure is the result of resistance to flow, and here we have unlimited flow, and the shaft side's air will get pushed back toward it's source due to the greater force (in pounds) of the non-shaft side.

Roger

 

The volume of air is not important in this case. Assume there is an air line attached to each port supplying an unlimited VOLUME of air, but at a certain pressure.

[guzzimike]

Yeah, I was thinking of it as a closed system...


OK, Let's assume that the air (gas) is supplied from a common cylinder through a manifold with two hoses....one each going to each port on the Test rig...

In such a case (ie Closed System), Boyle's Law still applies...

So, if we use a common air feed, Piston moves LEFT.

OTOH, If we use an unlimited Air Feed to the test rig, the Piston moves RIGHT.


SO, my friends, I propose in conclusion that the original test question did not give enough information with which one can provide a proper, correct answer. 

[b569rr]

Total Force =  Area times pressure (expressed in PSI). Nothing to due with volume in this case because the volume is not fixed.

Surface area measured in units squared is greater on the non shaft side x PSI available. Piston theoretically moves left to right (not including frictional losses of the seal as stated above).

[guzzimike]

Total Force =  Area times pressure (expressed in PSI). Nothing to due with volume in this case because the volume is not fixed.

This "volume"  being fixed or not was not specified in the original question...

Therefore there is no correct answer possible for the problem as asked originaly.


But if you guys really want to get testy...(no pun intended)  I would retort that in the REAL WORLD, it is much easier to feed the air into the test rig from a common manifold with dual air hoses (closed sytem) than some 'ethereal', Limitless air pressure source...unless you line up a compressor with two equal air lines and a maniflod, basically the "Closed System" that I called for..... 

Or, two separate, yet parallel air compressors whose output would have to be phased in to within microbars of Pressure of each other so as not to discriminate for one side of the test rig to the other....very hard to do in a real world situation, what with differential heat losses in the compressor's motors and all that...

No sireee...a closed system loop with a common, static air cyclinder feed would be much easier to rig up on a test bench, and under the confines of such a closed system, Boyle's Laws rule...

So, with a "real world" test rig, I would submit that the piston moves Left...as per PV = k

 

Or maybe not, depending on the actual quality of the seal on both the piston AND the rod....



Next question; which came first: The chicken or the egg..?

[b569rr]

Excellent points Mike. Being a proctor for Steamfitter exams, it happens alot. The author of the test question leaves items "open to interpretation". Then the test taker asks the proctor for clarity, which cannot be given.

Tom

[BIG DOG]

1.What are these the answer they wanted was a  KM4 Nut  and a MB4 washer (metric) to me they are just a lock nut and washer.

[GTS225]

WTH !?!?   That sounds suspiciously like a manufacturer's part number for those items.  How in hell are you supposed to know that part number without knowing a thread dia/pitch, and not having the mfgr's catalog?  It makes me wonder if the whole thing wasn't rigged to a certain extent just to keep certain people out, (or make sure certain others got in).

Roger

[motorhead446]

You guys are killing me!, grab a cylinder, put some air in it and see what happens. thats a spanner nut and lock/tab washer. Somebody writing tests is a bit anal. Hands on skills test, break it, and let the student figure out how to fix it. nuff said.

as a side note, I have learned alot on this thread! Thanks guys.