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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. T

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    Hey all! 👋 I need to buy one of those yellow tempering valve caps with the triangle inset on top of the lid, so I can adjust the tempering valve on my Saxon 140L hot water service.. it’s only got a crappy blue lid with no triangle inset, and I can’t adjust the valve any other way (difficult...
  2. D

    Dual flush valve for 2" flush pipe?

    Any recommendations for a push-button toilet dual flush valve, please (and must have a cable over 310mm)? Tried a Fluidmaster model but plumber says it won't fit the 2" flush pipe. Thanks.
  3. N

    Can the ballcock valve 'stick' shut due to hot weather?

    Our attic water tank (which is boarded in and not easily accessible) decided to stop filling up today... (we couldn't hear it filling up) and with the temperature outside reaching 32+ I am wondering if this might have caused a problem. The temp this evening outside has gone down to 21 degrees...
  4. T

    Anyone know what flush valve this is please?

    Got to change this flush valve!
  5. P

    Navien 240E Pressure Valve Discharge

    Hey all, Not a plumber - know just enough to be dangerous.. We just changed our water filters out in the house, and ever since our combo Navien 240e is discharging small amounts of water all day out the boiler side pressure valve. Boiler is off with summer (still using hot water side), but...
  6. M

    URGENT My t valve seems to be too thick for my shark bite cylinder

    I cannot get my shark bite fitting to fit over the white supposed to be a half inch copper T valve is it because it’s corroded just seem to be too thk
  7. D

    How do I remove this quarter turn ceramic valve?

    I cannot work out a way to actually remove the cartridge so I can replace it. Trying to fix a dripping tap! Help please….
  8. M

    Changing type of shower flow rate valve

    I have had the following thermostatic shower installed: Moods Round Shower https://www.homesupply.co.uk/Moods-Round-Shower-Pack-2-with-Two-Outlet-Valve-and-Rigid-Riser-Shower-Kit-DICMP0036 The flow rate control on this shower is full on or off. Would it be possible to change this valve to...
  9. M

    Changing flow rate valve

    I have this shower installed: https://www.homesupply.co.uk/Moods-Round-Shower-Pack-2-with-Two-Outlet-Valve-and-Rigid-Riser-Shower-Kit-DICMP0036 The temperature control is variable, but the flow rate control is either full on or off. Would it be possible to replace valve to a variable one? Thanks
  10. Wamus_202

    Which Gate Valve will turn off cold water to the taps?

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  11. B

    Arrow flow of water on valve query

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  12. J

    Air admittance valve below toilet

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  13. R

    Gas Shutoff Valve Okay or not okay

    Hiya, I had someone tell me that the valve in the house was not okay, can someone give me a view ? thanks
  14. J

    3 port zone valve question

    Can a three port zone valve allow circulation through both rad circuit and cylinder coil at same time or does one circuit take priority??
  15. C

    Extender for main shower on/off valve

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  16. M

    How can I remove this flush valve?

    I've got water trickling into the pan of a toilet. The cistern water level is nowhere near the overflow pipe, so I suspect there's a faulty seal at the bottom of the flush valve (a Geberit model). However, I am unable to detach the flush unit to check. There don't seem to be any side clips to...
  17. C

    I have fitted flowmasta bottom fill valve. the water flow

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  18. A

    URGENT Assistance with an issue I have with a toilet float valve?

    I have moved into a property and amongst several other issues, the toilet float valve appears to keep getting stuck and therefore prevented from filling. I am unsure what type of float valve I have. Each time I push the top part of the float (pictured on the left) it then starts to fill. I...
  19. I

    Ballcock valve needing replaced

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  20. N

    Honeywell BS864-2 22mm possible to replace head without draining?

    I may have a faulty motorised valve head on a Honeywell BS864-2 22mm is it possible just to replace the head or must it be the whole fitment? Do you need to drain the tank to fit a new head on the valve? Thanks