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Mechanical Q: Hydr Pressure

BullGator

BullGator

Active Member
Hey everyone. This is my 2nd post, I have been looking at the site for a month now, and I tried the search funtion...


For HYDROLIC PRESSURE Questions: In the study books they use the larger diameter divided by the smaller diameter to find the mechanical advantage. It seems to work(?) in the Barrons and Arco books, but it just doesn't seem right since you are supposed to divide the areas.
[Area2/Area1 = Distance1/Distance2]

What is the correct way to find the MA in these problems? Is it ok, for the purposes of the exam, to just use the diameter/small diameter to get the MA?
Thank you.

PS I take the test on the 21st.
 
donmagicjuan

donmagicjuan

Don't. Bite. Your friends!
pilot
If you square the ratio of the diameters you get the same result as dividing the areas. Simply dividing the diameters should not give you the correct answer, unless the ratio is 1.

EDIT: Wait, you didn't mean displacement instead of diameter, did you?
 
BullGator

BullGator

Active Member
donmagicjuan said:
If you square the ratio of the diameters you get the same result as dividing the areas. Simply dividing the diameters should not give you the correct answer, unless the ratio is 1.

EDIT: Wait, you didn't mean displacement instead of diameter, did you?
Click to expand...

I meant diameter.

In the texts, they don't square the diameter ratio. Foreinstance, in the diameters are 2inch and 8 inch, they would say the MA=4. (If the small area moves down 4inches, the big area moves up 1inch...)

[(Using radius sqr instead of diameter:) In that example I would think the MA= 16/1 =16; so if the small area moves up 16inches, the big area moves down 1inch?]
 
donmagicjuan

donmagicjuan

Don't. Bite. Your friends!
pilot
Diameter ratio squared gives the same result as radii-- the 2s cancel. But regardless, the answer should be 16 as you stated in the above example.
 
BullGator

BullGator

Active Member
Thank you. That is a relief. I thought I was going crazy looking for extra examples of hydrolic questions.


Also, to anyone who has taken the ASTB: Are there really questions (more than 1 that is) about "the principles of gases and liquids (with respect to pressure, volume, and velocity)"? I hated those questions in chemistry/physics, and would like to avoid studying them until after taking the ASTB (while waiting for selection then OCS). I know the basic stuff when it comes to these principles (eg pressure and volume), but when it comes to more complex issues and equations I am pretty slow.
 
BullGator

BullGator

Active Member
Anyone who has taken the ASTB:

Are there questions about "the principles of gases and liquids (with respect to pressure, volume, and velocity)"?


I hated those questions in chemistry/physics, and would like to avoid studying them until after taking the ASTB (while waiting for selection then OCS). I know the basic stuff when it comes to these principles (eg pressure concepts and basic understanding of volume), but when it comes to more complex issues and equations I am pretty slow for now.
 
PropAddict

PropAddict

Now with even more awesome!
pilot
Contributor
AllYouCanEat said:
Are there questions about "the principles of gases and liquids (with respect to pressure, volume, and velocity)"?


I hated those questions in chemistry/physics, and would like to avoid studying them until after taking the ASTB (while waiting for selection then OCS). I know the basic stuff when it comes to these principles (eg pressure concepts and basic understanding of volume), but when it comes to more complex issues and equations I am pretty slow for now.
Click to expand...

I remember a few questions about gasses in theoretical pressure vessels separated by a petcock, what happens when you open the valve. There were also Bernoulli questions. As I recall, they were more of the type "What happens: Higher P or Higher V?" than the "Calculate the pressure differential between A and B." With any kind of physics or engineering background, they are cake.
 
BullGator

BullGator

Active Member
Thank you PropAddict. I studied the Bernoulli principle part just recently, but the rest is helpful.
-edit: I read this back and it sounded pretty sorry for a thank you. I truely appreciate the help man, thank you. Knowing that well help me be more calm/confident and relaxed before the test since I have a better understanding.-

FlyTPay, does this mean I won't get jets? Heh.
I have the confidence for sure, for anything but spelling a select range of words (my down fall :icon_rage, luckily I usually know which ones).
-Did I mention I, like Muhammad Ali, am the greatest :) That's what she said.-
 
BigIron

BigIron

Remotely piloted
pilot
Super Moderator
Contributor
AllYouCanEat said:
Thank you PropAddict. I studied the Bernoulli principle part just recently, but the rest is helpful.
-edit: I read this back and it sounded pretty sorry for a thank you. I truely appreciate the help man, thank you. Knowing that well help me be more calm/confident and relaxed before the test since I have a better understanding.-

FlyTPay, does this mean I won't get jets? Heh.
I have the confidence for sure, for anything but spelling a select range of words (my down fall :icon_rage, luckily I usually know which ones).
-Did I mention I, like Muhammad Ali, am the greatest :) That's what she said.-
Click to expand...

If you use firefox, it spell checks for you.
 
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