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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. RedYellowLorry

    Worcester Keyless Filling Lever Not Moving

    Hello, I'm trying to top up the pressure on my Greenstar 30i ERP but the blue keyless filling lever won't move. It doesn't feel stiff, it feels as if it has been locked some how. Do I have to do something to get it to move? If anyone has any suggestions I would be very grateful. Thanks...
  2. M

    Concealed cistern fill valve.

    Has anyone got an idea what make concealed cistern this maybe? I need a new full valve for it. Thanks
  3. B

    Recommendation for Radiator Bleed Valve

    I bought the a bleed valve from S****fix about a year ago: s****fix.com/p/radiator-vent-blanking-plug-nickel-2-pack/40972 It worked fine initially, but I noticed that the little bleed screw needed to be turned a little tighter each time I bled that radiator to seal it up again. Having bled it...
  4. SamTylersJacket

    Is this a isolation valve?

    Is this a isolation valve?
  5. N

    3 way valve not working got hot water no heating help

    I have an old Potterton suprima boiler with a hot water tank and pump. We have hot water but no heating, the light on the boiler is showing amber (no call to heat) I have been told that this is likely due to the 3 way valve or motor on it (Myson Power Extra). I am wondering whether to try and...
  6. M

    Please identify divertor valve

    Can anybody identify the make of this divertor valve. Actuator is missing!! Cheers.
  7. Peadar

    Water flow won't stop after long flush

    My toilet flushes ok when the long flush button is pressed - but water continues to flow into the toilet bowl. No problems with the short flush. I have a Siamp Optima 50, the overflow funnel doesn’t seem to drop back down on the long flush. The short flush does all purposes but family members...
  8. B

    How to fit McAlpine ARB-1 anti rodent valve?

    I am trying to fit an anti-rodent valve ARB-1 to a MacFit MAC-1 WC pan connector. Instructions for the valve say"remove ..... ribbed seal" from WC connector and discard. But as far as I can see the seal is bonded to the WC connector and is not removable. Would be grateful for advice if someone...
  9. N

    Zurn PRV what is the torque of bell housing screwed to valve body.

    Hi, I am not a plumber but want some help finding at what torque at which the PRV's bell housing screwed to the valve body. can the plastic bell housing pop off the main valve body due to pressure or unscrew itself due to prolonged water hammer effect? PRV: Wilkins Zurn NR30 40mm 500kpa
  10. C

    Leaking Isolation valve

    Hi Just had a new bathroom installed with a toilet bowl that reaches the back wall. Its has a bottom entry cold feed to the cistern. The fitter put an isolation valve on the pipe work for this :-(, the copper pipe comes up from a plastic pipe push fit. See photo. I did a tissue paper test and...
  11. E

    Sealing off isolation valve

    Hi, The isolation valve feeding my toilet cistern was leaking. After considerable effort, I was able to lift up the cistern to put an O-ring washer around the top of the inner circle referred to with an arrow in the attached image. Unfortunately, when I let the water through, there was a burst...
  12. M

    is it possible to change shower cartridge rather than the whole valve

    i currently have a valve/cartridge that controls only temperature is you turn it one way or the other. is it possible to remove the cartridge to replace it with one that can control both volume and flow rate? it may be about 30 years old/original to home. everything is accessible as i am...
  13. R

    Where can I buy this exact isolation/service valve?

    The isolation valve connected directly to our toilet fill valve has started to leak (I assume the washer has deteriorated). I'd like to get a like-for-like replacement so that I can just do a straight swap of the entire isolation valve without having to worry about resizing pipes, but my google...
  14. J

    Thermostatic mixer valve

    I will be taking out my bath and putting a shower tray in. Under the bath there is a thermostatic mixer valve, I can't see ATM but pretty sure it's going to the bath taps, it is about 6 to 8 inches out of the floor boards so will be in the way, is it ok to cut it to floor board level'ish and...
  15. Stuartpm

    Straight valve to turn shower on & off (you'd think this would exist)

    Hi - recognise this a bit of an odd one. We have an old failed mixer valve which we need to replace. This valve actually predates a temperature controlled boiler, so the mixing functionality is irrelevant, since the cold water pipe is isolated/off. I'd ideally like to replace the shower valve...
  16. I

    Thermostatic rad valve

    I'm in Canada, where the standard is NPT. I just put in a heat pump and shut off the hand valves but I want the rads in the room to warm up if the heat pump can't keep up. NPT thermostatic rad valves are available but are hellish expensive. The sizes I have are 3/4" and 1". The system used to be...
  17. SteveRobert5a

    Megaflo temperature/pressure valve won't open

    Good morning! I have a dripping tundish, so decided it's time to replenish the air gap in my Megaflo - something I've done from time to time in the past. So I've turned off the water, opened a hot tap, and then tried to open the pressure relief valve on the Megaflo. But it's stuck: the plastic...
  18. B

    Weak flush - pneumatic button mech or flush valve?

    I have a wall hung pan with a concealed cistern. The flush is the "old style" Grohe Eau2 dual flush pneumatic button. When pressed the flush valve lifts lightly and closes giving a very short weak flush. You can manually lift the flush valve in the cistern and it moves freely, flushes fine and...
  19. T

    Thermostatic shower valve

    I am redoing my bathroom and not sure what the best way of doing my shower is which is in my bath, I want a rain shower and so I was thinking of using a thermostatic shower valve as I have removed the plasterboard to re tile (new build) and thought this is a good opportunity to do it, my...
  20. A

    Radiator Bleed Valve - 1/8-27: Thread Type

    Morning all. I hope this is the correct place for this post. If not i'll happily move it to another forum area. I am renovating a property and the old cast iron radiators need a refresh, and i'm going to fit some new bleed valves amongst other things. The female thread in most of the rads...
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