What is Compressed air: Definition and 145 Discussions

Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches and others, as well as to atomize paint, to operate air cylinders for automation, and can also be used to propel vehicles. Brakes applied by compressed air made large railway trains safer and more efficient to operate. Compressed air brakes are also found on large highway vehicles.
Compressed air is used as a breathing gas by underwater divers. It may be carried by the diver in a high pressure diving cylinder, or supplied from the surface at lower pressure through an air line or diver's umbilical. Similar arrangements are used in breathing apparatus used by firefighters, mine rescue workers and industrial workers in hazardous atmospheres.
In Europe, 10 percent of all industrial electricity consumption is to produce compressed air—amounting to 80 terawatt hours consumption per year.

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  1. K

    Using compressed air through a venturi pump to suck oil?

    Hello, was wondering if I could pass compressed air through a venturi pump to pull floating oil from a tank? If yes, how do I control the eventual mixing of oil with the air from the outlet end? The requirement is given to me by one of my clients who wants an easy, and low-cost solution to...
  2. E

    I Filling a rigid tire from a pressure regulated compressed air line

    This thought came to me while I was trying to fill my MTB bike tire a while ago as an exercise in laziness to not "check" the tire pressure with a separate gauge! Mostly, my mind just wanders... If I have some very large tank filled with compressed air at gauge pressure Ptank. The hose runs...
  3. P

    I Compressed gas energy storage formula

    Hi, I’m looking for formula to find the energy stored in a compressed gas for non ideal gases, for example, argon. The formula should also include the thermal energy caused by compression. Thank you in advance.
  4. downeast

    Pick the Best Compressed Air Inlet for Loop Pipeline

    Which compressed air inlet to a ring (loop) pipeline would likely be best in terms of least turbulance and best flow (avoiding dead head)? Given: 1) The inlet has to be in the corner of the rectangular loop. 2) Air consumption will be constant and evenly distributed throughout the loop. 3)...
  5. Danimal

    B Object falling through highly compressed air question

    If you had a tube a couple of miles long filled with very compressed air, say 6,000 PSI, would an object you dropped in it fall very slowly? Even a heavy object like an anvil, how long would it take to drop?
  6. F

    Submarines that don't use compressed air to sink and rise?

    I have been wondering about submarines for a while, and especially their ability to sink and rise on command. I understand that they do this through ballast tanks and replacing water with compressed air, which increases the buoyancy force and helps them rise. (I understand that my knowledge is...
  7. Ameen1985

    Design a compressed air energy storage for a PV plant

    Summary:: Design compressed air energy storage for PV plant [Mentor Note -- Thread moved from a technical forum, so no Homework Template is shown] Hi All For a PV project of 5 kW, we will use a CAES. The preliminary design will consist of a compressor - 2 heat exchanger - Air receiver - air...
  8. S

    Compressed air pressure vs hydrostatic pressure

    Hi all, I'm new on here and will start off with what I think is a simple clarification. I'm questioning my workings due to previous work being completed by another engineer and thought this was the best place to ask. Essentially we have compressed air being supplied through a hose, the hose...
  9. bigyabbie

    Plumbing Compressed air powered water pressure

    Hi there, I have a few interesting problems that I have been exploring for a while now, but i quickly get beyond my level of knowledge of physics, so wondered if members of this Forum may be able to assist. One of the projects that we have been trying to solve is how to maintain a decent quality...
  10. T

    Understanding energy losses in a compressed air system

    When measuring pressure drop across a compressed air system shown in the included figure, I get different results depending on the system downstream of the actual component I am measuring pressure drop across. Btw this is a real experiment that has been ran. The numbers below are different but a...
  11. T

    Compressed air problem (pressure and flow rate calculations)

    When dealing with a compressed air system I would like to know how to make some calculations to predict pressure and flow rate throughout a system. e.g. If I have a compressor that can supply 50 cfm @ 100 psi at the source, and the air flows through a system of pipes, filters, turns, etc. which...
  12. M

    How to advoid water condensation in compressed air piping

    Hello all, I'm having problems with my compressed air system. In the factory have some clean rooms with temperature are maintained around 23°C. The outside of clean rooms are normal condition (around 32°C). When i checked some air supply points outside. There were no water in compressed air. But...
  13. Anand Sivaram

    I Liquid Air and Compressed Air Density

    Densities of Normal Air is 1.225 kg/m3 at STP, whereas the density of Liquid Air is 870 kg/m3. That means liquid air is 710x denser that normal air. Then suppose, we compress normal air to more than 710 atmospheric pressure, then it could have a density more than that of liquid air. Is this...
  14. Ismael Jarada

    How to measure the torque of a compressed air engine?

    Summary: The main idea of my graduation project is to convert the motorcycle engine to work on compressed air that come from a 180 L tank (10 bar compressed air inside the tank ) I have some problems to how calculate the required torque to move the cart . The main idea of my graduation project...
  15. K

    Compressed Air Engine Calculations

    Hi, I posted a question a while ago which I have managed to do some more calculations for. I need a bit of help to see if they are correct. I am trying to obtain power and torque values at different rotational speeds of a single cylinder compressed air engine. The inlet pressure into the engine...
  16. R

    Does pressure in a compressed air system increase....

    does pressure in a compressed air system increase when going from a 2" air line to a 1" air line.
  17. K

    Compressed Air Engine Calculations

    Hi,I am designing a compressed air engine for a project. A little stuck with calculations. I need to work out how long the engine will run at its top speed using a air pressure which is supplied from a compressed air tank.Compressed air pushed down a piston which is connected to a camshaft. As...
  18. bob012345

    Maximum Force of Compressed Air

    What's the maximum force that air from a typical garage air compressor tank, the kind that's used to inflate tires assuming the pressure is around 150 psi.? Can the force be changed by nozzle design? Thanks.
  19. Ed Lenarduzzi

    Compressed air, heat and pressure?

    Yes compressing air increase its temperature but does that necessarily increase pressure? In an pellet gun a spring driven piston compresses the air which increases the temperature but wouldn't any increasing pressure simply retard the piston's advance? Because the chamber volume is not fixed...
  20. M

    How long will it take for compressed air to reach 29 psi?

    A large tank filled with air is compressed to 49 PSI. A valve is open and air escapes through the hole (d = 0.04 ft) to the atmosphere. How long will it take for the compressed air to reach 29 PSI. Assume constant temperature. Not exactly sure how to approach this problem since the flow rate...
  21. D

    Compressed air flowrate calculation

    Hi, I have a airbottle of 30bar pressure, 1000lit.From the airbottle I had made a line of 25 nb and fitted a pressure reducing valve in the line with set pressure 5bar.I am interested to know the flowrate in the line. Please help
  22. I

    Compressed Air Energy Storage System

    Homework Statement I have a CAES system that takes air at a pressure of 102.2kPa and temp of 24 degrees C. It is compressed to 85 bar adiabatically at a rate of 168 kg/s. I know that Cp = 1.005 kJ/kgK and Cv = 0.718 kJ/kgK. The question is - determine the amount of work consumed by the...
  23. N

    I Compressed Nitrogen: Calculating Pipe Flow Time

    Hello, first time on this site and wondered if anyone could help me on what the proper equation or equations would be to answer this question. I have a 300 cubic foot tank of nitrogen air that will provide nitrogen to a rectangular pipe at 5 psi with a flow rate of 10 CFM to atmosphere at the...
  24. R

    Velocity of compressed air through pipe

    This started out as a thought experiment and then I realized I was stuck in how to figure it out. If I have an airsoft rifle that uses compressed air in the tank at 3000 psi. It leaves the bottle regulated down to 800 psi. It then goes into a second regulator that reduces the pressure further...
  25. J

    How much energy is stored in compressed air?

    Hi all, My name is Jesse and I love renewable energy and finding ways of beating coal. Right now Solar Photovoltaic energy competes with coal in sunny areas during the day, but at night, you need to store the energy from solar and it's not worth it due to the cost of storage mechanisms (might...
  26. B

    B Internal energy of compressed gas

    Hi, I've been reading about compressed air energy storage and keep coming across that in 300 bar containers the achievable energy is 0.1MJ/L. Is this 0.1MJ/L of the volume of the air it is compressed to or of the total L of air that was initially used? (E.g If 1500L is compressed to 300 bar...
  27. A

    Automotive Air compression firing mechanism

    Hello, I am high school student working on a project to design an air cylinder, which would fire seed pellets from the drone at specific time intervals with sufficient pressure to embed them into the soft soil. I looked up on the Internet about airguns and other stuff but couldn't find...
  28. D

    Calculating the Impact of Compressed Air on Hydrostatic Pressure Testing

    Hello, I have a question regarding the effect of compressed air. I'm working on hydrostatic pressure testing a component. The component will be filled with water and compressed to 1000 psi. I'm concerned about the small amount of air that'll be present inside and worried about the effect in...
  29. A

    Adiabatic compressed air and energy calculations

    Homework Statement . Consider a pump that is required to compress air in a factory. The cylinder in the pump has an inner diameter of 2.00 cm and length 60.0 cm. Air is drawn into the pump at atmospheric pressure and 18 degrees celcius and the pump adiabatically compresses the air to a pressure...
  30. szopaw

    Final velocity of an air rifle pellet from compressed gas

    As in the title, I'm trying to establish the approximate velocity (sans friction and other losses) of a pellet propelled by compressed gas from a tank. Below is what I have came up with myself, I would appreciate if someone could review this as say whether the end values are reasonable. I have...
  31. B

    Dynamic/Static pressure -- High speed railways

    I am currently doing a research project in the attenuation of pressure waves. With an focus on dealing with sonic booms the are generated from high speed train tunnels. my experiments involved pressurizing a cylinder then using a rapid release valve allowing the air to escape along a pipe. I...
  32. A

    Using Isothermally Compressed Air to Cool a Refrigerator

    If I have a steady supply of isothermally compressed air at 7 psi (approximately 148 kPa) at a temperature of 4 degrees C, how would I calculate the amount needed of that air per unit time to maintain the temperature of a 14 cf refrigerator at 3 degrees C? A 18 cf freezer at -18 degrees C?
  33. Shariq Qazi

    Air Compressor Pressure vs CFM vs SCFM

    So my boss hook me up with the Compressed Air Calculations which we never did previously at our workplace. So started researching about the subject and designed a Compressed air system. The only thing i am not sure about now here is the relation between CFM vs SCFM vs Pressure. Let us take an...
  34. G

    Mass flow rate through a regulator

    Hi, We have a canister at a set pressure (4500psi) full of compressed air. A single stage pressure regulator is fitted to the canister that reduces the outlet pressure to 850psi. The flow from the regulator is then used in a divergent nozzle to create a thrust force capable of lifting a small...
  35. S

    Does compressor efficiency account for intercooler energy costs?

    Hi all, I am looking at a air compressor train design which looks like this: I know how to work the compressor work needed for a two stage compressor, and hence how much work I can save using 2 instead of 1 stage. The question I have is: How much energy does it require to operate an...
  36. P

    Compressed Air Turbine: A Sustainable Solution for Power Generation

    I don't know whether this is appropriate for this part or not, but I am now looking for turbine/machinery that can be run by compressed air to produce power/electricity. Is there any manufacturer of such a machine is available?
  37. P

    Low temperature production with compressed air

    Suppose, there are two cylinders of compressed gas, say air. Both are at same temperature and pressure and the amount too is same. Now, contents of both are released but in a different way. One has been released directly and the other has been released through compressed air turbine having a...
  38. S

    Water injection improves or reduces gas turbine power?

    Hello, I am currently working on a storage project which allows me to decouple the compressor from the expander of a gas turbine. (see image link below) The reason I use a gas turbine is to reheat the air which was cooled after being compressed. As you can imagine there is a efficiency loss...
  39. Monsterboy

    Work done by compressed air on the piston

    Homework Statement A closed cylinder of 0.25 m diameter is fitted with a light friction-less piston.The piston is retained in position by a catch in the cylinder wall and the volume on one side of the piston contains air at a pressure of 750 kN/m2. The volume on the other side of the piston is...
  40. CK328

    Equation for spring force for a cylinder on compressed air

    Evening all, I've recently undertaken a project where my roll is to analyse the suspension of a mountain bike. The suspension unit in question is a Rock Shox Monarch RT3. To give a brief summary: The shock uses compressed air as the spring, the pressure is adjustable via an air valve. The shock...
  41. CK328

    Mathematical modeling of a mountain bike rear shock

    Evening all, I've recently undertaken a project where my roll is to analyse the suspension of a mountain bike. The suspension unit in question is a Rock Shox Monarch RT3. To give a brief summary: The shock uses compressed air as the spring, the pressure is adjustable via an air valve. The shock...
  42. A

    Design a Venturi Pump with Compressed Air and Water: Feasibility & Parameters

    I am trying to develop a Ventury https://www.physicsforums.com/javascript: Pump using Compressed Air a d Motive Fluid and Suction Fluid is Water from Shallow Well. Compressed Air parameter is 6CFM Air at 7 bar using 2hp Motor & Compressor set, and required Suction Lift is about 5m. Discharge...
  43. C

    Compressed air under immersion

    Hello everyone, I am designing a machine that will utilize jets of compressed air underwater. Does anyone have information about the physics of gas underwater? I would like to know how far the jet will travel before floating upwards, based on the pressure of the air and diameter of the nozzle. I...
  44. I

    Air Cannon School Project Firing Paper Projectile

    Hey guys building an air cannon for class that shoots a wad of paper from a normal sheet of 8.5/11 paper will be dry. Question is... Is Psi more important or CFM with this light weight projectile? Plan on building from PVC, can do 100psi easy. Plan on using a diaphragm valve with a solenoid for...
  45. AEGIS

    Adiabatic or Isothermal? Compressed air energy storage

    Hi, I'm doing a high school physics project and am trying to figure out if a certain setup that I'm using is adiabatic or isothermal, in order to determine what equation I can use to calculate the work that my setup does-- the threads I've come across so far only explain the difference, but not...
  46. D

    Question about cooling due to expansion of compressed air

    Hi! I'm a teacher in Mechanical Engineering, and I organize a (yearly) student's project where they design and create a cooling machine. The machine works by compressing air, cooling the compressed air, and then rapidly expanding it. This can lead to temperatures of minus 7 degrees Celsius. I...
  47. K

    Need a valve for retention of compressed air in cylinder

    Hello all! I am designing a machine which consists of a horizontally mounted vessel which has a movable lid. The lid is moved up-down with the help of a pneumatic cylinder & is guided on linear bearings. My question is during maintenance, when the lid is UP, and for any reason there is a...
  48. T

    Compressed Air Reverse Thruster

    Hello everyone, I'm attempting to determine the impulse that can be generated by expelling compressed air from a pressure vessel stored aboard a moving craft through nozzles in the nose of the craft. The vessel has a forward momentum of roughly 2,000,000 Ns. EDIT: For semantics sake, consider...
  49. David Gin

    Mixing compressed air with different dew points

    Two compressed air(A, B) at 100 PSIG: Air A - Compressed with -70C dew point. Air B - Compressed without entering an air dryer. If this two compressed air is distributed into a tank together, would the the air mix to form Air C (same pressure with dew point between air A and B)? I have read a...
  50. C

    How to apply Eulers Eq and continuity eq to compressed air

    Can we apply Euler's Equation and continuity equation to compressed air flow from tank or orifice.