What is Valve: Definition and 233 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. D

    Engineering Quantitative Risk Assessment of a Chlorine storage tank

    Storage tank leaks are caused by the failure of the pressure relief valve, tank body, or tank piping. If the pressure relief valve fails, can't it contribute to tank body and/or piping failure from overpressure? But the tank body and tank piping can fail by other mechanisms (mechanical...
  2. H

    Temperature after closing the valve

    I have the following task and I am not getting anywhere: A steel tank with 15 m³ volume, well insulated from the outside, contains air at a temperature of 288 K and a pressure of 1 bar. It is connected to a compressed air line via a valve that is initially blocked. which constantly supplies...
  3. barryj

    B How does a bathtub/shower diverter valve work?

    As we know, when we turn on a tub/shower combo the water initially starts to flow out the tub faucet. When the lever is raised, the water is diverted to the upper shower head. How does this work? I have learned that the tub faucet lever merely blocks off the water from coming out of the...
  4. D

    Full Pressure release valve

    A mechanical pressure release valve opens at pre designed pressure and then automatically closes once pressure drops to a lower point generally around 5 to 10% of the designed release pressure. However I need a mechanical pressure release valve which opens automatically at pre designed pressure...
  5. Cburg

    Looking for Pneumatic control valve information

    I am looking to find out if there is a control valve type that will move a duel port cylinder in both directions but then the current to the valve is turned off the cylinder will NOT be locked up. I thought a 5/2 double coil valve would do this but it holds cylinder when current is removed...
  6. S

    Engineering Calculating valve sizes for a compressible liquid

    I have converted given pressures from bar gauge to bar abs Inlet pressure = 20 - 1.013 = 21.013 bar abs Outlet pressure = 6 + 1.013 = 7.013 bar abs therefore pressure drop (x) x = {p_1 -p_2 \over p_1 } = {21.013 - 7.013 \over 21.013} = 0.6662542236 bar abs Comparing to the chart values for...
  7. C

    How to determine mdot for choked airflow through a valve, given T,P

    Hello, I am working on a project that involves air at high pressure and temperature flowing through an orifice (valve) from one container to another. For each container, the volume, temperatures and pressures are known. The valve diameter is also known, and the fluid is air (which can be...
  8. P

    Pressure change in pipe due to sudden closure of valve

    Water is flowing in the pipe with velocity v0. Upon sudden closure of the valve at T, a pressure wave travels in the -ve x direction with speed c. The task is to find ##\alpha##, where ##\Delta P = \rho_0 c (\Delta v) \alpha##. The 1st step is to set up an equation using conservation of mass...
  9. Nauticale

    Force from Water Entering a Pressurized Tank with No Relief Valve

    Hello all, I am trying to understand how a force at the opposite wall from water entering a pressurized air (atmospheric pressure) tank, and for this discussion it is rigid, with no relief valve to displace the compressed air can be deduced. I have created a simple illustration and believe this...
  10. L

    Help with linear solenoid calculations (engine valve actuators)

    Hello, thanks in advance, I do many many things, jack of all trades but master of none. Would some one be willing to help me with some formulas and calcs for making my own linear solenoid? I can give the final specs I'm after then I could use advice on materials and other variables. I'd like...
  11. MaHo12345

    Relationship between flow and pressure in a valve

    Hi, I have a valve which is connected to a pipe on both sides. I measure the pressure upstream of the valve. Downstream of the valve is a screw pump. I control my valve using an analog voltage input between 0 and 10 volts. According to the datasheet, the relationship between the analog input...
  12. T

    How will a ceiling extract valve affect a radiator?

    An apartment has a radiator, about 1000 W. Nearly right above it is an extract valve for the ventilation system which extracts 35 m3/h. The vertical distance between the two is around two meters. Is there a risk that this will prevent the radiator from functioning properly as the hot air will...
  13. Big Tommy C

    Calculating Valve Size With a Hydraulic Accumulator

    Hello, Hope everyone is doing well. I have a personal project I am working on and am trying to figure out the nature of the hydraulic system. I want to size a valve to the system properly and have been reading a lot about the Cv value. I don't fully understand how to implement this value into...
  14. melmel4546

    5/3-way proportional directional control valve VPWP

    how does a 5/3-way proportional directional control valve VPWP work ? and Information about the 5/3-way proportional directional control valve plss. :cry:
  15. S

    Friction loss in water flowing through a globe valve?

    Imagine water flowing inside this from say left to right. Energy can't be destroyed or created. Pressure can reduce due to the three 90 degree turns. Is the pressure or energy loss due to the heat or deformation or kinetic energy loss of the water to the wall inside? What must be the wall be...
  16. 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...
  17. kunalvanjare

    PWM for controlling liquid flow through a Solenoid Valve

    Hello guys, I am looking to control the flowrate of water through a Solenoid Valve in a continuous closed-loop process. I inquired about Proportional Flow Solenoid Valves and these are a little too expensive and only a handful of manufacturers are supplying those. But I looked online for some...
  18. Z

    B Would a Dyson sphere need a "relief valve?"

    Would a Dyson sphere need a "relief valve?"
  19. F

    How to calculate a pump's operating point for a fully open control valve

    How do you calculate the flow rate and differential pressure (the operating point on the pump curve) for a centrifugal pump if all of the flow is through a single control valve with known ##C_V##, discharging to atmosphere? Clearly the flow rate and differential pressure of the pump will be...
  20. kunalvanjare

    Alternative to a Proportioning Motorized Valve?

    Hey guys, I'm looking for a way to control the opening of a valve as per feedback from an upstream flow meter. I have a motorized proportioning ball valve, but it takes about 10-15 seconds to complete it's rotation (one-way). I need to find a way to expedite this so was wondering if there are...
  21. A

    Understanding the Impact of a Valve on Fluid Properties Upstream and Downstream

    I want to know the relation between the properties upstream of the valve and those downstream. Assume that the throttling device is small that not enough surface area is available for Q to occur. Changes in kinetic and potential energy are negligible. If I define my system to be the fluid...
  22. William123

    Can you help me find the right hydraulic valve?

    Hi I'm a novice when it comes to hydraulics but I want to be able to make use of it in future projects. I thought building a small scale excavator might be a fun project to start with. However I'm a bit confused when it comes to the valves that will control the different motions. From what I've...
  23. S

    Automotive Design of a Valve stem cross section in a Steam turbine emergency valve

    I want to design cross section area required for valve stem when valve is closed under spring force. Valve stem should be designed for buckling load but I am unable to calculate buckling load coming due to impact force coming when valve bangs on valve seat. Valve is having concentric spring. Is...
  24. Benjamin_harsh

    How can we pump air into a bicycle tire without opening the valve?

    How can we pump air into bicycle tire without opening the valve? I mean If valve (dunlop bicycle valve)is closed, then how pumped air going into the tire?
  25. G

    Burst valve obligation on hydraulic lifting cylinder

    Hi everyone, I heard that there is a regulation\obligation that requires burst valve installation on lifting hydraulic cylinders. My questions are: Is this requirement apply to all lifting appliances or just appliances involve with personel lifting ? Is this requirement apply to forklift...
  26. S

    Impact force calculation due to a rotating object in Overspeed Trip Valve Design

    Bolt comes out by distance d=1.58 mm when speed of rotation of shaft reaches its trip value (w_trip). m is mass of trip weight (Bolt assembly) One of the approach which I had considered is work energy theorem. Initial energy = 0.5m*(w_trip*(r+d))^2 Final Energy= 0.5m*(w_trip*r)^2 (Assuming bolt...
  27. J

    How to calculate the time required to open a valve to inflate a balloon?

    Problem Statement: I have a canister (0.15L Volume). This will be filled with compressed air. A solenoid valve attached has a diameter of 2mm, and the air will flow through this into a pipe which leads to a balloon. The pipe diameter is 3mm, with a length of 300mm. The pressure required to...
  28. C

    For a throttling valve, why is it that temperature remains the same?

    For a throttling valve C.V analysis, I am wondering why is it known that temperature remains the same for ideal gases. I understand that using the energy balance equation, I end up with h1=h2. Pretty simple so far. By breaking down enthalpy into its components u1+P1v1 = u2+P2v2 I realized that...
  29. M

    A valve changing area in RELAP5

    Hi, how can I define a time-Area table for a valve? I know the stem-area table but it does not satisfy my purpose. I want to change a valve's area with time
  30. 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...
  31. S

    Pressure differences in a leaking vacuum vessel

    Hello all, I'm new to this forum and I'm mucking about with some self-made physics conundrums, and I need some help! So, What I am aiming for is a roughly cylindrical vessel (it can, and I think probably has to, be tapered to achieve the effect) with the air being pumped out of one end, and a...
  32. M

    What is the difference between nozzle (or a ventury) and flow control valve?

    In both the cases, the flow cross section area of the pipe is reduced.But in case of nozzles the velocity increases,pressure reduces and the flow rate is maintained.But in case of flow control valve, flow rate changes.(Assuming the fluid to be incompressible) Why is there a difference between...
  33. M

    Throttle Valve vs Carburetor: Exploring the Difference

    In carburetors, at the throat or ventury, the area decreases and so velocity of air increases (by continuity equation.).This is reason for suction of fuel from the float chamber.But in case of throttle valve, when the valve closes(area of flow reduced), the quantity of air fuel mixture passing...
  34. chemisthypnos

    Automotive Hydrogen Car Fuel Tank: Preventing Permeation & Valve Check

    How do hydrogen powered cars prevent the permeation of hydrogen through the valve used to fill the car's tank with hydrogen? Is a regular check valve used or is the valve special in some way?
  35. N

    Valve to vent entire volume upon reaching a set pressure

    Greetings, I have an experiment that pressurizes a small volume at variable rates. 1, 2, and 3 psi/sec. I am trying to think of a way to reproducibly drop the pressure of the container by a known amount while it is being pressurized. Are there valves for this type of experiment? What are...
  36. Steven Bolgiano

    The phenomena of Siphons - Directional check valve prevents siponing

    I have in a prototype model, a pipe connected from one tank of liquid to another holding tank (at a lower a lower elevation). Its a biodigester, so the way it works is when liquid is added to tank #1, an equal amount is displaced through the pipe, into the lower level holding tank, #2. The...
  37. 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...
  38. mkematt96

    Force required to dislodge a sphere from pipe (Valve design)

    I'm designing a valve that uses a ball to seal the valve. When the valve is empty there is no force acting on top of the ball. When water flows in, it will push up on the ball to dislodge it, water will flow into the valve and push the ball up until it seats into the top hole/chamfer which then...
  39. R

    Flap Valve Opening - Rope Tension and Anchor Pull Out Force

    Hi everyone, I have attached a sketch which may help understand the question I have. I have a hinged flap which hangs vertically (hinge at top). The flap weight is 10kN and it is 1.8m tall (uniform mass). At the bottom of the flap is a lifting eye. 2.5m away and 0.3m above height of the hinge...
  40. J

    Cheap, suitable one way valve for aspirator vacuum pump?

    I have a glass aspirator vacuum pump that has a built in one way check valve, but after a week of use, it no longer functions and when input water is turned off, there is a sudden backflow of water into the vacuum line. I'd like to add a one way valve inline to allow the vacuum pull but not...
  41. N

    How do you control an Electronic Butterfly Valve with PID

    The butterfly valve I have is controlled by sending voltages to it. It accepts 0-10V and maps a specific voltage to a specific position from completely closed (zero degrees) to completely closed (90 degrees). To clarify/reiterate it is not controlled by a servo motor. I am using this valve to...
  42. M

    Pressure drop across a valve in tank

    Hey I've gotten some good answers here before, so I'm giving it another try: Recently I attended a building-engineering meeting, and trying to learn something new (or refresh old knowledge in some cases..) I had a hydrodynamic question/case. My firm is engineering a concrete tank for a water...
  43. H

    Partially closed pump discharge valve question

    Hi all, I have a question about the effect of partially closing a pump discharge valve on the system curve, wondering if you guys can help me out. Right now I have the yellow pump curve and the orange 2 inch system curve , producing around 120 gpm against around 110 ft of head. If I expand...
  44. J

    Finding Check Valves for Water Droplets

    I'm having trouble finding any valves to use for my certain application. What I'm doing is trying to capture water droplets into a sealed container. What I need is some sort of check valve that needs nearly no pressure to let water through, but keep it contained once it has gone through the...
  45. wolram

    Help with finding vintage valve amplifier circuits (amplifiers for a rock band)

    Can anyone help please, I have been searching for vintage valve amplifier circuit diagrams and components. I need help in finding valves, transformers, and diagrams. I intend to build amplifiers for a rock band so i would like to build one with a 3KW output if that is feasible. Thanks for any...
  46. Anton Zhyzhyn

    Column of water, vacuum pressure and a one-way valve problem

    A conceptual problem related to a design I'm working on: If I use a pump to suck air out of the top of a vertical pipe, with the bottom of the pipe in water, I can only make the water rise around 10 metres inside the pipe, if I produce a perfect vacuum. Now let's say the pipe was 100m long and...
  47. HethensEnd25

    Well insulated tank with valve entropy problem

    Homework Statement A well-insulated tank of volume 6 m3 is divided into two equal volumes. The left part is initially filled with air at 100 C and 2 bar, and right side cell is initially empty. A valve connecting two cells will be opened so that gas will slowly pass from cell 1 to cell 2. The...