Questions tagged [pressure]

Questions pertaining to pressurized systems and their applications, from containment to system losses to using as a benchmark for measurement.

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20
votes
1answer
466 views

Sizing a pressure safety valve for two-phase flow

I understand that valves in two-phase vapour / liquid were sometimes sized by considering the required vapour and liquid flow rates separately, and then adding the results together. But this is now ...
15
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2answers
6k views

If aircraft are pressurised, why do our ears pop during liftoff and landing?

Something hit me during my last flight: our ears feel that the pressure around us changes quickly during liftoff and landing, they hurt more and more until we make them pop. However, the cabin must ...
15
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8answers
12k views

Why is air pressure in all directions?

Here is a typical definition of air pressure: Air pressure is caused by the weight of the air molecules above. Even tiny air molecules have some weight, and the huge numbers of air molecules that ...
14
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3answers
244k views

How to calculate flow rate of water through a pipe?

If a water pipe is 15 mm diameter and the water pressure is 3 bar, assuming the pipe is open ended, is it possible to calculate the flow rate or water velocity in the pipe? Most of the calculations I ...
12
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5answers
6k views

What is the difference between pressure and stress?

Since the units are the same ($\frac{N}{m^2}$), what's the difference between pressure and stress?
12
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1answer
2k views

Why was Freon used in spray cans before it was declared a threat to ozone?

I've heard that in the past, spray cans (aerosol cans) contained Freon. I found that the Montreal Protocol made the usage of Freon illegal due to its effect on the ozone layer, but I can't find the ...
12
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4answers
5k views

Would an object at the bottom of the sea still experience buoyancy? [closed]

So I understand that buoyancy happens because the fluid exerts larger amounts of pressure from beneath an object compared to above, like in this picture So my question is, what if the object is ...
10
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1answer
772 views

Are all pressure-volume processes polytropic?

I was searching for information about pressure-volume processes when I read, in a heat engineering book, "The process is polytropic with $PV^n = \text{constant}$." How can I know that a real life ...
9
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4answers
11k views

How does pressure change with depth in earth?

I've learned in school that pressure in water changes like $$p(h) = \rho g h$$ where $h$ is depth in meters, $\rho$ is density (e.g. 1000 $\frac{\text{kg}}{\text{m}^3}$ for water) and $g$ is ...
9
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2answers
8k views

How to calculate the pressure a pipe can withstand?

I was looking at high pressure pipes and their pressure ratings. I'd like to know how these pressure ratings are determined. I assume that pipes are tested until failure, and the failure pressure is ...
9
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3answers
4k views

How to seal a pressure vessel

I'm trying to construct a stainless steel high pressure containment vessel (pressure reactor) (2000 psi or so). Yes I realize that this is a don't try this at home type of thing, and I plan to put ...
8
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4answers
7k views

Would engineering bricks explode if used to build an oven?

I'm building a pizza oven and, to do so, I bought a whole load of engineering bricks (not these but similar). They've got five holes vertically through them, each hole is 2x6x6.5 cm (80 ml) and the ...
8
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1answer
182 views

Water hammer and expansion waves

I was thinking about the relationship between water hammer and expansion waves. Pressure seems to drop across a surge wave travelling at the speed of sound in water hammer (after the fluid has been ...
7
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2answers
2k views

How do suction cups work?

These are suction-mounting hooks. I want to visualize and understand how do they stick on walls. After these hooks stick on wall. Like we compressed them. How? Since gases are compressible up to a ...
7
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1answer
2k views

What is this pressure gauge on the London Underground measuring?

I noticed this pressure gauge on the Piccadilly Line of London Underground yesterday. It was located on the side of a row of seats. Close-up of the gauge at hand: click for larger version of image ...
7
votes
1answer
120 views

Multi-gas barometric height formula in isotope separation devices?

What is the barometric height formula for a mixture of gases? The main problem I can see, the curves describing the minimal energy (kinetic + gravitational/centrifugal) won't be any more a simple ...
7
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0answers
17 views

What types of materials can be tested in a split Hopkinson pressure bar?

A split Hopkinson pressure bar can test different types of specimens, I would like to know what types of materials that are suitable to be tested with this method?
6
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4answers
3k views

Is it useful to stuff my glasses with newspaper to protect them?

(I'm not sure if this question belongs to this stack exchange, but it seems appropriate to me) I have a very practical situation and our knowledge is lacking to be able to solve our debate. The ...
6
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4answers
4k views

Is a circle the strongest 2D shape for containing internal pressure?

I understand how a circle (or sphere if you want 3D) is the best shape for holding a vacuum inside a container, but what if you wanted to have a large positive pressure inside of the container instead ...
6
votes
2answers
7k views

How metal fittings seal connection without rubber gaskets?

I am well familiar with the concept of gasket. From my non-mechanical engineer perspective, I can understand how a standard rubber gasket works in various plumbing ...
6
votes
2answers
2k views

Can I seal the inside of a water well to use it as water reservoir when the well is dry?

We've had unusually dry weather and our well has run so low that we had to call in a water hauling company to refill it a few days ago. The water man told me that even though he dumped in ~ 1000 ...
6
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3answers
2k views

How do I calculate the max flow rate for a pump with no power restrictions?

Let's assume we have a pump and it can draw as much power as it needs. As the pump speeds up, it creates vacuum in the intake. At some point it draws the gas/liquid so fast, the intake pressure is so ...
6
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4answers
1k views

Is it possible to fire a ball of water that holds its shape?

Background I participate every year in a huge water balloon battle. The clash happens between two universities so you can imagine that the commitment, at least for some people, is quite high. To give ...
6
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2answers
118 views

Does negative pressure inside the barrel affect low-powered railguns?

Just something I was wondering about when I've seen this on reddit today. Unlike in firearms where the pressure propels the projectile, in a railgun, wouldn't the pressure ahead/behind of the ...
6
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2answers
1k views

How to equalise the water distribution in a leaky pipe irrigation system?

I have a 200 litre water butt and plenty of 22 mm plumbing pipe and fittings and I want to build an irrigation system for my vegetable patch so that I can open the tap after a few dry days and ensure ...
6
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1answer
1k views

Calculate elasticity of rubber balloon

I am developing a model for the respiratory system of a neonate (newborn child) for a BME project by using pressure/volume data of the lungs. To model these, I plan to use a rubber balloon. However. ...
5
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2answers
186 views

For a small valve in a fluid system, what is the relationship between pressure and flow rate?

The specific example I have in mind is a car tire with a small leak in it. As the pressure increases, does the outflow of air increase linearly, i.e. $v\propto P$, or does it have some more ...
5
votes
1answer
10k views

Why is my Venturi pump much weaker than expected?

I'm trying to make a simple Venturi tee which will have air flow through it while sucking some water from down below (like paint sprayers do). I want the device to pull the water to a height of 1 ...
5
votes
2answers
77 views

Is there a pressure relief mechanism that operates faster than sound in a material?

In the event of an explosion through a high pressure gas pipe, is there a way to vent the pressure wave, in order to protect downstream objects? The mechanism must be faster than sound; pressure ...
5
votes
1answer
949 views

How do gas flow regulators avoid choking?

According to compressible flow theory, a downstream pressure of 0.528 times upstream pressure is sufficient to choke a flow device. So, how do industrial grade pressure regulators throttle a wide ...
5
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2answers
135 views

Recoil of hydraulic lift/elevator

I noticed that when a group of people enter in an hydraulic lift/elevator often when the last person steps in the lift/elevator has a small but noticeable recoil: the lift goes down a few mm then it ...
5
votes
1answer
230 views

Determine elevation from the difference in air pressure

Given: A problem in my thermodynamics text reads as follows... The barometer of a mountain hiker reads $13.8$ $psia$ at the beginning of a hiking trip and $12.6$ $psia$ at the end. Neglecting the ...
5
votes
1answer
516 views

Are there any precedent designs for a mechanically-delayed pressure release valve?

I need to release pressure of around 50psi, after 3-4 seconds of initiating, from a vessel using a mechanical switch. I had considered a pneumatic solenoid, but I want to forgo the inconvenience of ...
5
votes
2answers
888 views

Gigapascal pressures in a small package

How small/compact can a pump or other mechanism be, that would allow compressing gas (or liquid) to pressures of excess of 10GPa, continuously? Throughput may be minuscule, of order of milligrams per ...
5
votes
1answer
212 views

Minimising permeation rate of hydraulic fluid through hydraulic hose

I am designing an experiment where the hydraulic hose is going to be subjected to relatively high internal pressure for prolonged period of time and it is absolutely imperative that the rate of ...
4
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2answers
1k views

How do I calculate the weight needed on a press board to deliver a certain amount of pressure?

I'm building a press for cider. I'm going to be using a 24" x 24" press board. I'm looking to deliver 40 psi to the cider. How can I determine the amount of weight required, in tons? What sort of ...
4
votes
2answers
178 views

Making a radial (only) seal inside a small tube

I'm trying to make a adaptor to fit a nozzle about 5mm wide which only applies pressure radially during insertion. Pushing in a standard O Ring would apply some force axially up or down the inlet due ...
4
votes
2answers
396 views

Turning an engine over with engine compression

When you compress a bicycle pump and seal the opening, the pump will automatically return to it's initial position when you release it. I suppose this is how air suspension works as well? if you have ...
4
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3answers
3k views

How an airfoil works

I have read on many sites that for lift to occur, the pressure below a wing must be higher than the pressure above it. This happens by somehow moving air faster over the top of the air foil so the ...
4
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5answers
5k views

Understanding pressure drop and mass average values

While studying some papers, I didn't understand the following sentences: deltP the pressure drop across the turbine, evaluated using the mass average values at ...
4
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4answers
3k views

Calculating maximum internal pressure from maximum rated external pressure?

Is there a calculation / rule of thumb that can determine a containers rough maximum negative pressure (vacuum) from it's rated internal pressure (assuming a single layer construction so there is no ...
4
votes
2answers
267 views

Ensuring even flow in liquid pumping in distribution circuit under suction

I have a liquid circuit which looks a bit like that: The system is under suction, and the flow rate through each unit should be about 10ml/min. However, we noticed that unit ...
4
votes
4answers
118 views

Understanding Pressure

Ok so what happend is that i started to think about Submarines and why exactly you cannot open the bottom heatch at lets say the Challenger Depth. At least i am pretty sure you cannot do that. Right ? ...
4
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3answers
671 views

At How Many RPMs Would Aluminum HDD Platters Shatter?

I'm using hard drive platters to create a Tesla Turbine. I'd like to get as much efficiency out of it as possible. That being said, for safety concerns, I'd need to know a generic range at which they'...
4
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2answers
4k views

Solenoid valve pressure drop

I'm designing a solenoid valve for an automated irrigation project that I'm working on. After having looked at some designs, I have a question. For most of the designs I've seen, the orifice is ...
4
votes
1answer
1k views

Tankless air compressor for electronics desoldering station

I purchased a Weller WSD161V soldering station (similar to this one, at least with regards to the pneumatic system I'm about to describe -- sorry, I was unable to find a manual for my specific model ...
4
votes
2answers
715 views

Why is high stagnation pressure important for propulsion?

In my propulsion notes I always see mention of the importance of minimizing stagnation pressure loss across the inlet shock of a ramjet/turbojet/turbofan. Could anyone explain further why this is the ...
4
votes
1answer
209 views

How do I find the impact pressure of cavitation due to implosion of a super critical fluid bubble?

I have solved the Rayleigh-Plesset equation for a time varying bubble of a super critical fluid. I am trying to find if the impact pressure caused by SCF bubbles is lesser as compared to that caused ...
4
votes
1answer
158 views

Is Scrooge's giant glass dome feasible in real life?

In an Uncle Scrooge (or Scrooge McDuck, not sure of the translation here) comic named "Treasure Under Glass", Scrooge orders a giant glass dome to be manufactured in order to aid his endeavours ...
4
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0answers
86 views

Part to pierce the valve on a 16g CO2 cartridge and connect to a Solenoid valve

The specific part that I’m after is something that can connect to a solenoid valve and a CO2 cartridge that will break the seal on the end of the CO2 cartridge. The solenoid valve connection is ...

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