What is Valves: Definition and 57 Discussions

A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.
The simplest, and very ancient, valve is simply a freely hinged flap which swings down to obstruct fluid (gas or liquid) flow in one direction, but is pushed up by the flow itself when the flow is moving in the opposite direction. This is called a check valve, as it prevents or "checks" the flow in one direction. Modern control valves may regulate pressure or flow downstream and operate on sophisticated automation systems.
Valves have many uses, including controlling water for irrigation, industrial uses for controlling processes, residential uses such as on/off and pressure control to dish and clothes washers and taps in the home. Even aerosol spray cans have a tiny valve built in. Valves are also used in the military and transport sectors. In HVAC ductwork and other near-atmospheric air flows, valves are instead called dampers. In compressed air systems, however, valves are used with the most common type being ball valves.

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  1. S

    Plumbing Question about Pressure Reducing Valves

    I’ve asked this question in a Plumbing Forum and got no answer. So I thought maybe the Physics Forum might be able to help. My home has a high water supply pressure (>5bar) so I’m considering using a pressure reducing valve (PRV). This is basically to help protect the plumbing, as the house...
  2. eleanorwest83

    Pressure relief valves & pressure regulators - What's the difference?

    What is the difference between a pressure reducing valve and a pressure relief valve? pressure-reducing/regulating/ relief/release - There are so many different options available! I read this article on Fluid Controls that did a really good job of explaining pressure regulators, but I am a bit...
  3. C

    Engineering Calculate valve sizing to regulate the flow of natural gas

    Working out as follows x= (20-6)/20 = 0.7 Fk = k / air specific heat ratio Fk = 1.31/1.4 Fk = 0.94 xT = Fk * x 0.94 x 0.7 = 0.658 because xT < x = 0.658<0.7 flow through the valve is choked Expansion factor Y Y = 1 - x/( 3 x Fk x xT ) Y= 1- 0.7/( 3 x 0.94 x 0.658) Y = 0.623...
  4. kunalvanjare

    Controlling two valves with different flow-rates to achieve mixing

    Guys, I hope you guys are keeping well. I have been working on developing a Compact Dispensing Station for my CNC Machine & Parts Washer where coolant is mixed with water in different concentrations & volumes as per the requirement which will vary on a day-to-day basis (not the concentration...
  5. F

    Need Advice: Passing a Ball Bearing from Air to Water

    Hi all, I'm new to this but joined in the hope someone with more experience could provide some advice. In a personal project, I have a particular design dilemma where I am trying to pass a metal ball bearing (or any other spherical shaped solid) from a column of air into a column of water...
  6. amare

    How to model the opening and closing of valves?

    ok guys ! i need to edit this question ! I have an iris type of valve that is installed between the throttle valve and the intake manifold to restrict flow. the valve is to be fully closed and fully opende based on need. there is no partial opening something like that. what i need is the...
  7. amare

    How to calculate the flow rate?

    A valve is installed between the throttle body and intake manifold and decrease its area to restrict the flow. How do I analyze the mass flow rate of air in the decreasing area to know the engine working condition at a minimum valve area?
  8. SAG93

    Valve/Material for Siphoning Air & Blocking Water

    Hello, I wonder if anyone knows of a valve or material that would allow air to pass both ways but prevent water to pass one way. It will be on the end of a tube used for siphoning so that air can be blown in and suctioned out but if water is collected it is diverted away from the end of the...
  9. A

    Using an IR Thermal Gun to check for steam passing valves

    Greetings I am asking about the reliability of using a thermal gun to check if there is passing downstream the valve. The fluid is either steam or air. Wouldn’t the pressure and temperature drop sharply downstream the valve if it is closed but passing ? again I am talking about air or steam...
  10. HDG

    Emergency stop for a machine with valves and cylinders

    a)Design and draw a circuit using the cascade system to operate 2 cylinders (A&B) which, on the operation of the start valve produces the sequence A- B+ B- A+. The cylinders should park in the positions B- A+ when the start switch is in the off position b)Modify the circuit designed for part...
  11. A

    Single spool directional control valves

    I need to source a two-way single spool valve for an on/off application that can be manually operated. Need to get an idea of rated flow rates. struggling to find a decent catalogue, so if anyone knows or can send me anything, please let me know Thanks
  12. M

    B Choke Station in Fluid Pipelines: Pressure, Valves, & More

    Hello What is 'Choke Station' in fluid pipelines? Is it a station in which pressure of fluid is decreasing? Is it a kind of Pressure Reduced Valve?
  13. H

    Question about pressure drops due to friction and valves

    If I'm designing an injector for a rocket engine, I have a specific mean flow rate (m/s) that must be met due to the pipe diameter and the required mass flow rate. I've calculated all the pressure drops due to lost work from friction, valves, and orifice geometries (not from change in area, but...
  14. M

    Two Types of Valves: Conic & Radial Jets

    Hi What are 'Conic (Rotovalve)' and 'Multi-jets, radial jets valve'? These are must be two kind of valves like Butterfly or globe or ... valves. Thanx
  15. Patrick23

    Robot Arms -- which pneumatic cylinders and valves to use?

    Hi, Im trying to make robotic arms actuated by pneumatic valve which I found here http://www.e-pneumatic.com/valves/pneumatic-valves.html And also cylinders here http://www.e-pneumatic.com/pneumatic-cylinders.html and I wanted to ask if one of these cylinder types would work as a robotic arm...
  16. S

    Setting Pressure on Relief valves on Water Cooled Panels

    Gentlemen, I work in the steel industry, specifically in the melt shop department which operates electric arc furnaces. My question is that those electric arc furnaces have water cooled panels around the furnace, and I am trying to install relief valves on the panels. the molten metal and slag...
  17. J

    Where can I find tech specs for prosthetic heart valves

    So I am doing a project for an advanced fluids class where I plan to do a CFD analysis of two different prosthetic heart valves, the bi-leaflet valve and the ball and cage (star-edwards). I cannot seem to find the technical specifications or drawings that I need in order to make a good cad...
  18. A

    Confused about Volumetric Flow Rate & Valves?

    I'm new here, and I have a question that might be easy but really confuses me. Does the volumetric flow rate of incompressible fluid change across a valve?. Based on my analysis, no it can not change since the mass is conserved, and since it's incompressible fluid. I know that the velocity will...
  19. K

    Sizing Needle Valves for Air Flow | 0.025 m^3/s

    I am trying to size a needle valve to make sure that it can allow the required flow rate at the fully open position (0.025 m^3/s). For a given Cv you should be able to calculate the maximum flow rate through the needle valve provided that you know the temperature of the gas and the pressure drop...
  20. T

    Double Regulating Valves & 2-Way Valves: Why Install for Chilled Water Systems?

    In working with chilled water system, why do we install "double regulating valve" and "2 way valve" when connecting the pipe to the AHU ?
  21. M

    Physics of Water Pressure Regulators/Reducing Valves

    My brother is a professional plumber and I'm a physics major, so he often comes to me for explanations of some of the physics underlying his job. I'm familiar with the basics of fluid mechanics, e.g. hydrostatic principles, continuity equation, Bernoulli's law, Poiseuille's law. But often I...
  22. R

    Interstate natural gas pipelines & valves

    Often there's these stories on TV about someone accidentally damaging a large diameter natural gas pipeline while digging a ditch etc. and then a huge raging fire. What I'm wondering about is how frequently are shutoff valves installed on these lines. My intuition says ~30 miles apart at most...
  23. R

    Opening/closing valves and shock types caused

    Hi, I`ve had past experiences with pressure switches giving "strange" (pulsed) signals due to nearby discharge valves closing or opening. Looking a little into it I run into reading about compressibility theory and "shock tubes". Just for info, a "shock tube" is a tube with 2 zones...
  24. G

    Mixing different pressures of air using valves

    Hey guys! I've always been curious what would happen if I used air valves and regulators to mix different pressures of air together? For reference I spliced a few diagrams into one here: And I made a picture of the setup I'm imagining with some nice labels so we all know what...
  25. B

    Safety Relief Valves: Advantages & Disadvantages in Agro-Chemical Plants

    Hello, I work in an agro-chemical plant and we are now installing safety relief valves on all our reactors. Ours is a multi-purpose plant and there are constant change overs in the lines . Our avg. reactor size is 16KL , largest and most of them being 20 KL. Our design manager says that the...
  26. A

    Flow Rate & Valves: Increase or Constant?

    For a fixed pressure differential will the flow rate remain constant or will it increase as the restriction decreases. So imagine certain volumetric flow rate through partially opened valve, will the flow rate increase or will it remain constant as the valves is opened further? Assume density...
  27. D

    How to Conduct Simple Flow and Pressure Drop Tests on Valves?

    Anybody know of some simple tests that are used on valves for flow and pressure drop experiments? is there anythign published online that ye could send me a link to if possible?? thanks in advance regards dave
  28. N

    What is the purpose by putting 2 ball valves together? And there is a

    What is the purpose by putting 2 ball valves together? And there is a gate valve for sampling in between these 2 ball valves. any1 please provide me an explanation thxxx
  29. B

    Maxwell's Demon via molecular reed valves can produce work?

    Well not literally The Maxwell's Demon... If a one-way reed valve can be brought down to size of only a few molecules, don't you think it could allow passage of a gas molecule across a barrier in one direction only? How I think it could work: -The small size (molecular) of the valve is...
  30. Z

    Pressure Safety Valves Calculator - Fire Case Gas Filled Vessel

    Hi Im happy to find the forum, I hope you can help with my questions. I have found this calculator and would like to understand how it works - can anyone help with this? The webpage is -...
  31. M

    Pressure drop across butterfly valves

    Hi, I'll make a valve open and close for some degrees that I have to calculate, the valve motion will produce a pressure wave in the pipeline. I have to know how many degraus I must open the valve to produce a pressure drop that I want. Someone know how I can calculate it? Is there an equation...
  32. M

    Nuclear Plant - Active Component (Valves)

    This is for all you System guys. What are the classifications for a valve to be considered an Active Component? Also, if the valve is classified as an Active Component does it automatically mean that the valve is a Safety Related Valve? I have several valves in my system (Check, Control...
  33. DaTario

    Diodes, transistors and valves

    Hi All Given that one has a basic understanding of the working mechanism behind the diode, how can one develop a comparison between diodes, transistors and the valve. Best wishes, DaTario
  34. A

    Pressure drop in pipe due to bends and/or pressure reducing valves ?

    I am currently doing my final year project and have a few queries. I would be really grateful if someone could answer the following questions for me as soon as possible. • The requirement is to drop the pressure from 140-150 bars at the inlet of a pipe to 2 bars at the outlet of the pipe. •...
  35. J

    Flow through pipes and throttling valves .NEED HELP

    Flow through pipes and throttling valves...NEED HELP! I need some help with a real-life problem I have an open topped water collection tank at elevation. The water is distributed by gravity flow from the tank via a pipe to a lower elevation. At the point of delivery, the pressure head is...
  36. B

    Replacing Expansion Valve with Small Diameter Tube for Efficient Home AC Cooling

    For example in typical window-type home air conditioning: -If I remove the expansion valve and replace the valve with a small diameter tube to constrict the flow of gas so that the average gas pressure difference between the condenser and evaporator coils are the same as when you had...
  37. D

    Reactor scram due to inadvertent opening of multiple safety relief valves

    I'm an engineering physics student writing a mock proposal for a class. I've based the proposal on a specific company that builds reactors and trains personnel for navy vessels and off of this article: http://www.world-nuclear-news.org/nerliste.aspx?id=11724 Essentially it says that during...
  38. C

    Quick Electric On/Off Water Valves

    Hey all, I've been trying for a while to create some electronically controlled water fountains and I've run into a problem. I don't know what kind of electronic valves I should be getting! When I originally started this project I had hoped that I could just use sprinkler valves but I've...
  39. D

    Valves, seals, and latches

    Hello folks. I'm a physics major, but have recently become more interested in engineering. I've been playing around with emachineshop and SolidWorks and tinkering with designs, but I am finding that I have a pretty poor working knowledge of basic mechanisms - in particular, I am having trouble...
  40. A

    Do Fleming valves fail at high frequencies?

    So I've been reading up on optical rectennas, and the sources I read say that the reason such devices are not yet efficient enough to be practical isn't the antenna, it's the rectifier, since solid-state Schottky diodes of the types normally used don't work in the THz range of AC frequencies...
  41. M

    Solenoid Valves, fluid through Nozzle - not closing

    Hello I have a problem that I can't understand... I am putting kerosene pressurised to 160psi through a 1/4" BSP solenoid with 13mm orifice. On the out port of the solenoid is a 1/4" BSP to 2mm ID nozzle. The idea is it sprays out a stream of kerosene. The kerosene is provided by...
  42. C

    Pressure drop expansion valves

    I'm having trouble understanding expansion valves. Gas leaving a diffuser increases its pressure as the cross-section increases (i.e as the gas expands), like in a compressor. We convert kinetic energy in potential energy. That I understand. But in a expansion valve, pressure drops as the...
  43. S

    How do valves in the heart and blood vessels work?

    Hello everyone, How do valves in the body basically work. I can understand how blood flowing on either direction can close or open valves depending on the type of valve. But someone told me it is the elastic recoil of the veins that closes the valve. I thought it would blood that was going...
  44. A

    Pressure drop across valves

    Hi guys, i want to ask why is there pressure drop across valves? Because if you look at bernoulli's equation, the head will be the same in 3 points, before the valve, at the valve and after the valve. The only thing changes when a fluid flow through a valve is its pressure and velocity at the...
  45. wolram

    Checking Valves: An Hour of Coaxing Could Save You!

    The ones that can never be turned off as shown in many films on TV, the hero is shown struggling drenched to skin some times with some lever and the valve will still not turn, well i checked my mains valve and it took an hour with plenty of coaxing to get it to turn free, have you checked yours?
  46. C

    Flow Rates through multiple Valves

    Lets say I have a pump with infinite input. The pump is connected to a valve (V) that has a maximum flow rate capacity of 10 units per second (i.e. 0 to 10 units). This Valve is now connected to two valves in parallel (VA and VB), each identical to the first valve(i.e. max flow rate of 10 units...
  47. A

    Do most solenoid valves work for high acceleration loads?

    hey guys, i'm currently designing a fuel system for a ramjet to be tested onbaord a sounding rocket but it's going to pull around 100g's of acceleration. i can't get a hold of the manufacturer (still waiting for an email) and the supplier here in aus hasn't got a clue if it will survive the...
  48. S

    Valves: Principles & Operation of Heart & Reed Valves

    Hello to everybody! I would like to find out how valves work but I can`t find detailed information through Google. Could you tell me on what physical principles their work is based on? Most of all, I`m interested in heart valves or their analogs - reed valves. Thank you in advance.
  49. M

    Equivalent Lengths (Le/D) for Valves and Fittings

    Can anyone recommend any good references for equivalent length data for valves and fittings? All of my fluid mechanics books only have data for fully opened vales, but I'm currently working on a project where I need to know the values for partially closed valves. I tried to do a Google...
  50. A

    Choosing the Best Valve: Ball vs Solenoid for Reliable Flow Control

    Hi, I want to know the difference between an actuated ball valve and a solenoid valve. Which one is more reliable? I want to program the valve so that it allows flow for 10 seconds to one outlet and after that direct the flow to the second outlet. I know I'll probably need a 3-way valve...