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

    'Loose' ceramic valves

    I've replaced the ceramic valves on my kitchen tap, but the new valves are freer turning than the old, and the levers move down from a partial open position under their own weight. I've not had this before - is it duff new valves?
  2. W

    Ideal standard push Btn flush valve

    Hi all, I am trying to find an alternative flush valve to fit the cradle of a ideal standard push btn flush. It is all tiled in and changing to a Siamp or fluidmaster is not an option anyone have any ideas Thanks
  3. E

    Fitting an air admittance valve to 32mm push fit elbow problem

    In the photo there is a grey 32mm push fit elbow between the sink trap and down pipe. I want to replace the elbow with a "male" push fit tee attached to an air admittance valve to stop gurgling noises. I can't find a tee fitting that description, can anybody offer a solution as you can see space...
  4. T

    Stopcock/valve advice please

    Hi everyone, I've joined the forum today as I've found myself going round in circles with what I think might be a pretty simple problem, hoping someone can help. Our dishwasher is leaking and the manual says this can be fixed by cleaning the water inlet filter. To do this, we need to close the...
  5. M

    Non return valve failure?

    Hi there, All was good until one day the hot water suddenly started running quite a lot cooler. Putting my hand on the output at the boiler it's still hot there so I'm guessing there's a problem with cold water feeding into the hot water somewhere along the line. I have mixer taps on two...
  6. J

    Gas valve on fire?

    Hi everyone, My customer has a gas fire (Gazco Logic HE fire, about 10 years old). It's a slide control fire. The fire has become difficult to light. One has to push a lot more firmly down on the control slide to get it to light. At which point, all is fine. The pilot is good, new battery...
  7. D

    Radiator return valve shutoff issue

    Hi, I need to remove some radiators for redecorating and went to try and shut off the valves either side of my rad. I have TRV on one side and on the other side I noticed a blank top with no valve or peg sticking out that allows you to turn on or off (see pictures). I checked the other rads in...
  8. N

    URGENT Replacing a Radiator Valve on a Boilermate 2000 system.

    My daughter's place has a small water leak on a ground floor radiator valve. The radiator pipework is small diameter.i.e 8 or 10 mm. A plumber is coming back in a day or so to make necessary repairs. I am a little concerned as the house has a Boilermate 2000 on the upper floor and the...
  9. T

    Unused Stopcock Valve Crusty

    Hi Folks, Over the weekend, my wife insisted that I cleared out a junk cupboard in our utility room, in doing so I discovered a stopcock (that we have never used) had a load of crust around it. It looks to me that at some stage it probably leaked and sealed itself. I've never used it as it's...
  10. J

    Old un-pressurised heating system - top up valve

    Hi All, I hope you are doing well. I have old un-pressurised heating system and I need to top up the water but I cannot locate the bloody valve. Where is it? Is it in the attic? I also have this valve with black screw on top. Should this be opened or closed? Thank you
  11. B

    Noise from 8-Bar filling valve (Megaflo)

    In our sealed Megalo system, when hot water tap is used (say in bathroom shower) the megaflo is taking in some fresh water, I guess to compensate for the water used. The incoming water go via a pressure relief valve [most likely its this one: Heatrae Sadia 8 Bar Pressure Relief Valve -...
  12. T

    Can I use push fit type tap connectors on toilet fill valve

    Hello, I have a troublesome fixed 15mm copper pipe with isolation valve going to my toilet fill valve. It's too tight for a Flexi hose. Can I use a push fit tap connector instead which will give me more flexibility in fitting?
  13. L

    Part drain, complete drain or isolate single rad to fix weeping valve extension?

    Hello Plumbers I’ve replaced a 540mm high cast iron rad with 740mm high, like for like but still a 20mm valve extension was required. All was ok until I've spotted a v small leak (like 1 drip per hour) between the valve nut and extension piece. So I suspect I just need more PTFE + compound...
  14. B

    TRV Valve is leaking out of pin

    Rad is leaking from TRV valve, seems to be seeping out of where the pin comes up. I tried tightening up the nut below the pin, but that didn't help. I then looked online and saw that removing the nut and packing with some plumbers tape may help, but whenever I try to remove the nut a load of...
  15. P

    Cant get boiler Viessmann diverter valve out!

    I need to replace the diverter valve - I unscrewed it from the hydraulic block but for the life of me I can't get it out. I even spoke to Viessmann tech and they advised twisting and yanking hard but this tosser is not budging AT ALL. The valve was replaced 2 months ago by someone else. Is there...
  16. T

    Isolation Valve Old Leak

    Hi, Throughout our house there are numerous isolation valves which are on almost every plumbing fixture. Clearly whoever plumbed this had a thing for using them but I have heard elsewhere that they cause problems and are prone to leaking, especially when used after long periods. I noticed a...
  17. D

    Diverter Valve Operation

    Trying to find out exactly what happens when my system boiler is called to supply the radiators and hot water cylinder at the same time. For example today, whilst the boiler was on heating the water, the room stat triggered the boiler to supply the rads. The diverter valve installed in the...
  18. W

    "Fire hydrant" valve - wrong way round?

    Hi, I am going to a job tomorrow where the customar says they have a 1 inch square valve head (what i would call a fire hydrant valve, maybe theres another name) in a manhole that turns the wrong way ie. Anticlockwise is off and clockwise is on. I'm in the Midlands and customer says some...
  19. FRAM777


    I need to replace a 3/4 or 22mm blending valve on a Telford Trident electric hot water boiler. see attached picture of the original part. Telford asked me 100£ for the part and refused to provide the technical details. I am pretty confident this is not a proprietary part and similar parts...
  20. M

    Flush valve with handle

    Has anyone if this flush valve using the handle instead of the button? Are they good?
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