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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9
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4answers
10k 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 ...
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1answer
165 views

Is it possible to store leftover pressure from burning a propellant in a pressure vessel?

Say, in a firearm, after giving off a shot, if the barrel were to be closed off, does there exist a way to store some of it in an external pressure vessel, without requiring a mainly-external source ...
2
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1answer
294 views

Is this pressure vessel feasible?

I am intending to construct a small pressure vessel. It needs to be around 7 centimeters in length and width and around 1-2 centimeters in depth. It must be capable of being pressurised to 300 psi ...
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
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 ...
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2answers
1k views

Water pressure in a filled sphere

If I were to fully fill a sphere with water without any air trapped inside, how to find the pressure of the water at, say, the center of the sphere?
3
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1answer
193 views

Pressure sensors with best precision

Measuring pressures have many different applications which require proper encapsulating of the sensors, but at the core there is a limited amount of techniques. To my understanding, the two leading ...
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 ...
8
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1answer
176 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 ...
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2answers
726 views

Pressure drop across column in gas phase: what changes?

If you force high-pressure gas through a packed-bed, the gas pressure drops. However, the ideal gas law states: $$P = \frac{RT}{v}$$ so for an ideal gas, the pressure drop must be associated with a ...
3
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1answer
724 views

Controlling the flow of powder from a container

I was wondering how you would control the flow of powder from a container (with a small cylindrical dispenser at the bottom). The container is filled with powder. As the container drains, less ...
3
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1answer
9k views

Vacuum Pump Power Calculation

This may be a silly question, but I'm not a mechanical engineering. What's the best way to calculate the energy required to reduce the pressure of a gas stream below atmospheric pressure? Obviously ...
2
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2answers
214 views

Can pressure rise due to heat flux in a pipe?

I'm talking about a: smooth circular pipe without any valve at inlet or outlet without pressure losses due to friction subjected to a constant heat flux from outside on the entire pipe ...
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. ...
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0answers
58 views

How to attach a shell covering to a flat piece with clay as adhesive? [closed]

I have a ceramic nozzle type structure sort of like this: The outer casing is joined with clay material with the inner ceramic nozzle. What we do is, we attach the clay in the casing, put the nozzle ...
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 ...
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0answers
503 views

Calculating engine pressure from measureable quantities

How can I calculate the engine pressure in units of Bars by using torque, the cylinder volume, motor efficiency, and the gear reduction ratio? My values are as follows: ...
3
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3answers
548 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....
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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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 ...
3
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2answers
729 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
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2answers
496 views

How to verify results from a manometer/venturimeter?

I'm designing a system to determine pressure drops across thin samples while simultaneously measuring velocity (and through multiplying by area, volumetric flowrate). I need a way of determining how ...
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 ...
3
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2answers
217 views

Water pressure divider

Let's suppose I have a water jet as source, and this jet goes through a tube and is equally divided into 4 tubes. Is there a way to control the flow/pressure at each of those tubes separately by ...
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 ...
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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 ...
5
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1answer
203 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 ...
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 ...
3
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1answer
149 views

Hydrocyclone effectiveness vs. absolute pressure

Some sources say that higher pressure in hydrocyclones implies better performance it leads to a finer filtration. But why? Is it because water is almost incompressible and the particles can be ...
5
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1answer
459 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
129 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 ...
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 ...
5
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2answers
796 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 ...
3
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2answers
315 views

How to design a hemispheric flexible pressure vessel?

Consider a balloon, it is a flexible, expanding pressure vessel made of synthetic rubber. I am trying to design a system that will use hemispheric pockets of neoprene to grip an object, much like 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 ...
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 ...
3
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3answers
8k views

CFM in relation to Static Pressure

My background is more Chemistry and Biology, not Physics, or specifically engineering with fluid dynamics, so bear with me! Also, this is a little long, so I will do my best to make it easy to follow. ...
5
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1answer
200 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 ...
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1answer
151 views

Determine abs pressure in a tank where the atm and vac pressures are given

Given: A problem in my thermodynamics text reads as follows... A vacuum gauge connected to a tank reads $5.4\cdot psi$ at a location where the barometric reading $P_{Hg}= 28.5\cdot in$. Determine ...
2
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1answer
3k views

Mass and weight of air in a room

Given: A problem in my thermodynamics text is stated as follows... Determine the mass and the weight of the air contained in a room whose dimensions are $V=$ $15ft$ x $20ft$ x $20ft$. Assume the ...
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1answer
191 views

Px26-015 pressure sensors output

I had a PC Mountable Wet/Wet Differential Pressure Sensor I used it to measure a pressure difference , I don't know how to convert its output to pressure !
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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 ...
2
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1answer
377 views

Dead weight pressure tester for very low positive pressures

Does the dead weight tester technology provide capability for an accurate, low pressure calibration standard in the range of zero to 150 cm H2O, and if so is there a manufacturer that provides such an ...
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 ...
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
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2answers
261 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 ...
5
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2answers
184 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 ...
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 ...
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?
20
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1answer
453 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 ...

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