# Tag Info

24

TL;DR: Its not the air that's enclosed inside that creates the force, but the lack of air - or more precisely pressure. First of all some nomenclature (this is for the closed type, there is also the open type): When you press a suction cup on a surface what happens is that the air inside it is pushed out. During the compression phase of the cup the air ...

18

Spray cans work by containing a propellant which has a boiling point a small amount below room temperature. When the can is sealed the liquid and vapour reach equilibrium at a relatively modest pressure. When the spray valve is opened this pressure forces out the contents as an aerosol and more of the propellant evaporates as the internal pressure drops. ...

17

Because the cabin isn't pressurized to sea level pressure instead it to about 8k ft equivalent. (while the plane is 4.5 times higher) This means there is less differential pressure than if the cabin was pressurized to sea level pressure. But it's still within the limit of what passengers feel comfortable with. This answer on aviation.SE contains a plot of ...

15

Despite being difficult to manufacture, a sphere is the best shape for a pressure vessel, but due to the manufacturing difficulties are more costly to make. From the American Society of Mechanical Engineers website: Theoretically, a spherical pressure vessel has approximately twice the strength of a cylindrical pressure vessel with the same wall ...

14

While some of these answers are close, they are (at the time this answer is written) all incorrect to some degree. Pressure and stress are very closely related -- in fact, one could argue that pressure is, in a sense, a subset of stress. To be specific, the pressure in a material is the isotropic part of the total stress in a material. Pressure is a ...

13

According to the ASME Process Piping Code (B31.3) $$p = \frac{2 * t * S * E}{D - 2 * t * Y}$$ where $p$ = internal pressure $t$ = wall thickness $S$ = material's tensile strength $D$ = outer diameter $Y$ = wall thickness coefficient (B31.3-1999, Table 304.1.1) $E$ = material and pipe construction quality factor (B31.3-1999, Table A-1A) Note that this ...

13

Laminar Flow: If the flow in the pipe is laminar, you can use the Poiseuille Equation to calculate the flow rate: $$Q=\frac{\pi D^4 \Delta P}{128 \mu \Delta x}$$ Where $Q$ is the flow rate, $D$ is the pipe diameter, $\Delta P$ is the pressure difference between the two ends of the pipe, $\mu$ is dynamic viscosity, and $\Delta x$ is the length of the ...

11

In itself putting paper inside a glass will make very little difference. Glass is a brittle material and tends to fail by shock and point loading. Its static tensile strength is actually pretty good. What will help is packing paper between the glasses as it will help prevent them coming into contact with each other and dampen vibration and impact forces. ...

10

The obvious place to start is "what does psi mean?" It's an abbreviation for "pounds per square inch". If we have a 24" x 24" board, then we have $$24~in\times24~in=576~in²$$ To get 40psi, i.e. 40 pounds for each square inch, we would need $$40~\frac{lbs}{in²}*576~in² = 23040 ~lbs$$. You've asked for an answer in tons, so we need to convert 23040 ...

10

I'd be less worried about the shards and more about the structural integrity of the oven. When the bricks crack they lose most of their structural integrity. This may lead to the oven collapsing. It's much safer to line the inside with firebricks. They are solid and more expensive but you can be sure they won't crack under the heat. They will also protect ...

10

I guess there is no similar law for pressure in earth as it is to different, depending on where you are. But is there a rule of thumb? What do engineers who build tunnels / underground stations do? I approach this question as an engineer who does a lot of work on buried pipes and occasionally has to qualify buried structures for nuclear power plants. Also, ...

9

I have done this before so would like to share some of what I know. Super critical CO2 has some unique properties, for one it is extremely difficult to keep in a closed container since it has near zero surface tension. As such, if a standard threaded fitting is used and the fluid comes into contact with it you can be fairly certain it will leak (and usually ...

9

The pressure rise is easy enough to calculate from the ideal gas law $$PV=nRT.$$ In your case $V$, $n$, and $R$ are fixed so you can convert this to a simple ratio $$P_2=P_1\frac{T_2}{T_1}.$$ Be careful here to use an absolute temperature scale (usually measured in Kelvin). From the numbers you give, the pressure will rise to about 2.6 atm assuming that ...

8

As someone who has been involved with underground infrastructure to depths of at least 1400 metres, there are no rules of thumb. It all comes down to geology and the local conditions. Soils behave differently to rock and sedimentary rock behave differently to igneous and metamorphised rock. Brittle rock behave differently to ductile rock. Brittle rock in ...

8

Filling inside the cup with paper is just to lock in the wrapping of the same paper around the glass. It also offers coverage and protection of the rim of the glass. Because of the integrated, all-around coverage the whole package remains intact in the box with no chance of clinking against each other and it renders strength to the box as well. It is even ...

7

The problem is that the airspeed drops as soon as the airflow leaves the nozzle. It is not the same as a water-jet expelling into air (in that case the density of the water is much greater than that of air so the water holds its velocity much better). The low-pressure air will suck in air from around it in the wider pipe and thus become turbulent around the ...

7

Well liners are generally made to order. One of your issues will be to find a company that can make what you want. You will need to ensure the liner is the correct size and that it does not tear when inserted into the well, while being filled with water, or when it is being removed from the well. You mention your wells are cased with concrete pipes. They ...

7

This phenomenon is known as cavitation for pumping liquids - i.e. for anything that can change phase. If you are pumping gas, then the scenario really does come from choked flow. Let's say you've got a compressor and you're running it as a vacuum pump to evacuate a tank - at some point the tank's pressure on the inside is so low, you can't pump any more ...

7

$$p = p_0 + \rho g \frac{d_{sphere}}{2}$$ $p_0$ would be 1 Bar I assume, you are not specific under what conditions you fill the sphere and I assume the spheres border are made from a solid material. The rest is just that the pressure is not dependent on the shape of the container. You just calculate the height of the water column for you desired point, ...

7

The common pipe threads that are used in buildings for water and gas are tapered threads. The thread is cut on the cone rather than cylinder. In the US, these threads are called National Pipe Thread Tapered (or NPTT1, or simply NPT). They don't seal metal-to-metal. Thread seal tape is wound onto the male thread before it's screwed in. When the tapered ...

7

Is it due to the PET material that it is made of or is it more the shape and structure of the bottle? Short answer: Partially because of both. With that I mean it would be possible to produce weaker bottles changing the material or changing the usual design of the bottles. If it is due to the shape/structure of the container, is it possible to achieve ...

7

You can use any consistent set of units. That includes SI. But if you try to use a pressure in ATM, a sphere radius in feet, a wall thickness in mils, and want the stress in tons per square inch, you will probably get the wrong answer that you deserve!

6

I think the best (and simplest) way to describe something like this is Bernoulli's equation. $$P+\rho gh+\frac12 \rho v^2=constant$$ To use this, we're looking only at instantaneous velocity, because as the air leaks, the pressure will go down. We also should assume that the "valve" is really more of a small hole than anything that fluctuates too much ...

6

This appears to be the pressure gauge measuring the brake pressure of the brake cylinders. According to Transport For London, The gauges that the requestor is describing are the Brake Cylinder Pressure Gauges that we have on every car. These indicate the air pressure in the brake cylinders in real-time and are used by operational and ...

6

It is true that the air on the "top" (suction side) is faster than on the "bottom" (pressure side). The interesting thing is that the air on the suction side is so fast, it overtakes the air on the pressure side (see illustration from Wikipedia: The key to understand the velocity distribution around an air foil is not to look at it independent from the ...

6

There is another reason for this in multi-cylinder engines. While one cylinder is compressing the air, another is decompressing it. The net result is that the torque as a function of position gets smoother as the number of cylinders is increased.

6

Think about the pressures. With the pump above the supply line, the pressure at the input of the pump will be lower than the supply. At roughly 2 PSI per foot, you're down about 18 PSI. Since air pressure is about 15 PSI, the system will at least work as long as the supply pressure is over 3 PSI, but that's still not a good situation. If the "supply" is ...

6

The idea that I was describing in the comments earlier is pretty similar to that described by Mart - I imagined the tube (red) flaring out underneath the O ring, and the opposing taper being either pushed down by hand or driven by a standard nut (black) depending on the sealing forces required. The key difference is that instead of relying on the squashing ...

6

The yellow curve corresponds to a fan that will provide mostly a set pressure differential, say, keeping fumes from escaping a tank through elsewhere than dedicated vents. If there is a circumstance that reduces the pressure differential, it will speed up and increase the flow, to compensate. The blue curve is a fan that doesn't expect any significant ...

5

I'm glad we got rid of that obsolete system of obscure units decades ago. The metric system is so much easier. From the definition of the Slug, ${1 Slug = 1 {lb}_f.{s}^2/ft}$. Substituting that into the units you got, the ${slugs}$, ${lb}_f$ & ${s}^2$ go & ${ft}$ comes in. The only mistake you made was to exclude ${in}^2$ in your final ...

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