24 votes
Accepted

How do suction cups work?

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 ...
NMech's user avatar
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18 votes
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Why was Freon used in spray cans before it was declared a threat to ozone?

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 ...
Chris Johns's user avatar
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14 votes

Steel expanding in a tight space

The cylinder would expand until constrained by the cylindrical hole. After that it depends on the relative strengths. If the block has thin walls it may be stretched by the expanding cylinder and ...
Transistor's user avatar
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13 votes

How to calculate flow rate of water through a pipe?

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, $D$ ...
Carlton's user avatar
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12 votes
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Is it useful to stuff my glasses with newspaper to protect them?

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. ...
Chris Johns's user avatar
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10 votes

Do I need a pressure relief/safety valve if my pump can't exceed the rated system pressure?

Not a plumbing engineer, but: What about thermal expansion? You reach a dead end, pump stops. Pumps often have a checkvalve that prevents backflow, so you have now created a pressurized container. ...
Thomas's user avatar
  • 109
8 votes

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

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-...
kamran's user avatar
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7 votes
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Why can soda bottles withstand so much pressure?

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 ...
Odano Naotake's user avatar
7 votes
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Units to use in this formula?

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 ...
alephzero's user avatar
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6 votes
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How do gas flow regulators avoid choking?

The short answer is that they don't. Choking is not a bad thing. For a gas flow regulator, it's actually a good thing, because under choking conditions, the mass-flow rate is no longer dependent on ...
Han-Kwang Nienhuys's user avatar
6 votes

Water pump at top floor or bottom?

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 ...
Olin Lathrop's user avatar
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6 votes
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Making a radial (only) seal inside a small tube

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 ...
Jonathan R Swift's user avatar
6 votes
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Fan performance curve

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 ...
SF.'s user avatar
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6 votes
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Steel expanding in a tight space

Assuming your hypotethical question as what it would be for a difference of 200 degrees celsius and assuming the hole as rigid. The volumetric expansion index of steel is $$ \text{ $9*10^{-6}$ - per 1°...
kamran's user avatar
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5 votes

Pipe-network pressure - mass flow relation

Actually the continuity equation means that at steady state, the mass flowrate in a pipe must be constant (as mass cannot be created or destroyed not volume) but the volume can vary. so: ...
CleptoMarcus's user avatar
5 votes
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How do temperature and pressure influence the rate of evaporation of water in a closed vessel?

$\frac{1}{22.4}\frac{\mathrm{mol}}{\mathrm{L}}$ is only valid for standard conditions. Use the ideal gas law to calculate the concentration for your conditions. $s \equiv$ standard conditions $2 \...
idkfa's user avatar
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5 votes
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Small bubbles on a pump discharge

As well as 'proper' cavitation which is a fairly high energy phenomena and certainly a concern in terms of wear on the working surfaces of the pump it is possible that pressure changes are causing ...
Chris Johns's user avatar
  • 15.2k
5 votes

Small bubbles on a pump discharge

I have noticed that on the discharge port of the pump, a short row of bubbles comes out at high flows and low pressures. This does indeed sound like cavitation to me. Cavitation occurs usually in ...
grfrazee's user avatar
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5 votes
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A latch that’s easy to open under lateral pressure

How about a levered latch like this (very rough sketch) showing the catching tooth above the self latching spring and the pivot point.
Solar Mike's user avatar
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5 votes

Is it safe to use a 125PSI rated auxiliary air tank with a 150PSI air compressor?

Don't do it!! Just buy a pressure regulator to put between the two tanks that will decrease the pressure to below 125. You can get these for \$17 at home depot (https://www.homedepot.com/p/Husky-1-4-...
Daniel K's user avatar
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4 votes

Can mercury escape undectectably from a CFL bulb? or does it have to shatter for the mercury to be liberated?

If there were a crack in the glass, then the pressure difference would first cause air to flow into the lamp, which would cause it to stop working (both the mercury and the low pressure are necessary)....
Kevin Reid's user avatar
4 votes
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Is there a pressure relief mechanism that operates faster than sound in a material?

They are called blast valves. You need a delay loop in the pipe so the trigger can get ahead of the shock wave. Our interest was in closing off ventilation air conduits before the nuclear weapon's ...
Phil Sweet's user avatar
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4 votes
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Are pumps used in geothermal systems

They are both correct. There are actually a number of different types of geothermal power plant with the most common being, dry steam, flash steam, and binary cycle. Dry steam plants require pumps ...
loogle1's user avatar
  • 170
4 votes

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

You do this by monitoring the hydraulic pressure rather than the press tonnage. Since force = pressure x area we can rearrange so that pressure = force / area. Using your quaint units of measure, 5 ...
Transistor's user avatar
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4 votes
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What are the design difference of a steel tank that would withstand 136atm inside and 1atm ambient compared to 1atm inside and 136atm ambient?

It's the difference between holding up a weight by by hanging it from a cable vs. putting it on top of a column. A tank that starts out round (ideally, if it starts out spherical) and is pressurized ...
TimWescott's user avatar
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4 votes
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Changing (alternating non linear) screw motion

Cams offer a simple way to make a variable motion profile. Figure 1. A simple cam-operated contraption can be built out of wood. Syringe. Syringe holder. This really needs a slot from one edge to ...
Transistor's user avatar
  • 10.7k
4 votes

Making a radial (only) seal inside a small tube

You could have a barely undersized O-ring around the nozzle, then use a thread around the nozzle to press on the O-ring with a nut. This would require to machining a custom nozzle and nut: The part ...
mart's user avatar
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4 votes
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Difference between pressure suits and anti-g suits

A pressure suit is a protective suit worn by high-altitude pilots who may fly at altitudes where the air pressure is too low for an unprotected person to survive, even breathing pure oxygen at ...
r13's user avatar
  • 8,174
4 votes

Do I need a pressure relief/safety valve if my pump can't exceed the rated system pressure?

Certainly not all piping systems need relief valves. The specifics of the application matter. Relief valves typically protect vessels that can store significant energy and release it violently at ...
Tiger Guy's user avatar
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3 votes
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Method of Calculating pressure of failure in a cylindrical container?

In this answer, I aim to extend the discussion to thicker walled cylinders too. If you want to skip the maths, the pressures are summarised at the bottom. DEFINED TERMS: $\sigma_{rr}$ - radial ...
Involute's user avatar
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