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
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1answer
443 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 ...
14
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7answers
10k 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 ...
12
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5answers
5k 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
4k 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
535 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
9k 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
7k 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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2answers
208k 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 ...
9
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3answers
3k 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
6k 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
169 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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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
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1answer
116 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 ...
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
3k 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
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2answers
5k 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
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2answers
1k 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
1k 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
971 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
115 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
928 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
180 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
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1answer
9k 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
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2answers
72 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
809 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
126 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
191 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
410 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
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2answers
679 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
189 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
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2answers
377 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
2k 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
4k 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
255 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
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2answers
3k 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
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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
1answer
204 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
146 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
729 views

Estimating Maximum Speed for a Pneumatic Cylinder

I am designing an machine that is going to use a pneumatic cylinder to accelerate a projectile. I have a tentative cylinder specified, and am working on the control and supply side. I have verified ...
3
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2answers
699 views

Why is minimum pressure specified on a PSU water cooling circuit?

I work in consultancy and I am designing a product for a customer. The customer has requested a specific PSU. I have contacted this PSU manufacturer and they request 6 L/min of coolant flow and ...
3
votes
2answers
55 views

What kind of pressure switch can I use for pressures up to 5-10 tons/cm^2?

I need a pressure switch for an electric circuit that has to be closed once a piston is compressing at a pressure of (approximately as we haven't specified how much force we have to use, and maybe it ...
3
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4answers
11k views

Water pump at top floor or bottom?

Which position of the water pump in the below diagram provide maximum water output to the overhead tank? Each floor is 12 feet in height. I already have the pump (Centrifugal Regenerative Self ...
3
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5answers
1k views

Do flexible water hose cause pressure drop with constant flow?

My dad has a tub by a lake. He has a water pump in the lake to pump up water into a tub. He claims that if he use a flexible hose, the pressure in the hose at the top will be lower than if he use a ...
3
votes
1answer
632 views

How do temperature and pressure influence the rate of evaporation of water in a closed vessel?

I am trying to solve a fairly simple question but I'm kind of stuck on the technicalities: Imagine that water is evaporating into initially dry air in the closed vessel shown schematically in Fig....
3
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3answers
538 views

Would a structurally sound pressure cooker be able to withstand an internal vacuum?

Would the body of a normal round pot shaped pressure cooker (built to cook foods at 15 psi) be able to withstand being evacuated down to high-vacuum pressures? Apparently it has been done before: i.e....

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