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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

    Mixer taps and check valves

    Hello, I have a few mixer taps to install in bathrooms and kitchen. The kitchen tap also has a wondering spray arm capability. On researching something else, i stumbled across people saying that a check valve should be placed on the cold mains feed. How can I tell if the mixer taps/spray arm mix...
  2. E

    URGENT thermostatic controller on radiator replacement advice needed

    the thermostatic controller has snapped off the top of one of the radiator valves is the threaded metal collar standard to all valves? Can I fit one fro a different make?
  3. oscarwplumbing

    Changing/fixing a bunch of seized imperial and metric valves

    Hi everyone, I'm new here! I've bought my first house - needs a fair bit of work doing to it, including the plumbing. I'm keen to do stuff myself rather than getting contractors in, wherever possible, not just for cost, but also because I want to learn (a useful life skill surely!) I'll...
  4. T

    What Isolation valves are best

    Hello, Is it ok to use a full bore isolation valve to isolate a hot and cold feed to taps or should I use a service restricted bore. I’m thinking about using a full bore with a handle as my default as I find that most of my customers struggle to muster up a screwdriver to isolate the water when...
  5. Naseemkhan1682

    Stop Valves for LDC 50mm Connection

    Hello, I received an offer from the Water Board for a LDC MDPE 50mm connection. We are currently laying the works required in our boundary. A stop valve is required for the external meter chamber but we are unsure which type to buy? There are many available online with substantially...
  6. S

    Where to sell extra fixtures and parts

    So I have multiple fixtures, valves, PRV's, fittings etc that I am looking to get rid of. Where is the best place to sell these things? Most are brand new some used but in good condition. I started doing CAD for my company and don't really do side work anymore or work in the field really and...
  7. L

    How do i fix this please

    Help. So I’m trying to fit a shower in a bathroom in an old tenement flat in Edinburgh. Unfortunately the thread on the air off valve has broken (thankfully in the off position) and so will need replaced but I can’t switch the water off from the tank. I don’t want to flood downstairs obviously...
  8. A

    How can I turn down this traditional towel radiator with tap valves?

    I have recently had this radiator fitted and currently it gets very hot. I would like to turn the radiator temperature down however I'm unsure which valve I need to turn. I am not sure which is the flow or return. Or does it not make a difference? At the moment, both valves in the picture are...
  9. Hobo128

    Pumped shower valves

    Good morning all So been asked to install 2 power showers at a property recently... The property has a combi boiler which is only about 3 years old which customer doesn't want to change.... The only option I can see is an unvented cylinder and header tank. Can anyone else see any other...
  10. T

    Toilet Water Shut Off Valves Questions

    Hi, I was thinking about replacing the 3 x original Toilet Shut Off values as shown in the photo, in a property in Florida. They are not leaking and still work. I fixed some water weld around the wall cover to make them more rigid. Does anyone know if they are one piece? Or can the hose part be...
  11. G

    Overflow Bath filler and valves

    Hi, I'm really struggling to find out what part I need to use deck valves like this with a overflow bath filler. Most bath fillers seem to only have one connection. This one has 2, one for hot one for cold which looks like it could work. Anything I'm missing? thanks
  12. J

    UFH Thermostatic Mixing Valves

    Are there fundamental differences in some of these TMVs?. The attached one, below, would seem to be the better type where a shuttle moves to balance the hot&cold flows, as it increases one flow it decreases the other to keep the mixed flow constant, necessary say in showers etc. I have seen...
  13. S

    Are my myson power extra valves closing too quickly?

    Hi, we've been having a problem with our motorised valves. Every time the heating turns off there a number of loud bangs as if the water is hitting the valve too quickly which is then sending a shockwave through the pipes. Would this be faulty valves in that they are closing too quickly or is...
  14. N

    How to replace old 3/4 Radiator valves with 15mm TRV

    Hi There, I want to swap out my old valves for TRVs but the threads are different sizes, and I'm unsure how to resolve it. My current existing radiator valve setup is: The current valve has a 3/4" thread going to the radiator. I can't quite work out what's on the radiator side, but the...
  15. A

    Replacing bathroom radiator valves

    Trying to change bathroom radiator valves but I can’t get the old olive/nut off… any advice? Also the small plastic part next to the pipe, will I need to put that back in before fitting new valve? (Complete novice)
  16. R

    Cold Radiator - questions regarding valves

    Hi all, I'm hoping someone here can help. The radiators in my living room aren't heating as well as the radiator in bedroom, hall and bathroom in my flat. I've checked and both seem to be free from trapped air (tried to bleed and water came straight out). Now one radiator gets a lot warmer...
  17. D

    Balancing heating system, does it cost more?

    New to the site and looking for help. Recently, I decided to balance my heating system as some radiators where barely getting warm compared to others and after checking they didn't need bleeding, this seemed like the next step. I have balanced the system and all the radiators get hot at...
  18. S

    Low carbon steel pipes and rad valves

    Hi all hope all is well with everyone. Im a plumbing and heating engineer and I have worked only on domestic systems but am currently crossing over to commercial plumbing. I havent ever really done any steel pipework hence my question to you . . How or what is the procedure to changing a rad...
  19. M

    service valves or not

    Refurbishing a bathroom - cold water is mains fed, hot from combi. There is a main service valve to the whole system where the supply enters the house. Do I need to have service valves on bathroom sink, shower and bath? Normally if I have to repair/replace anything I just shut off the main valve.
  20. P

    Brass "Faringdon" lockshield valves leaking

    I have just tried to balance my heating system (16 cast iron rads, 3 towel rails), all the lockshields were fully open. When I try to close them down, they all leak, from a dribble to a gush. When I say all, I tried 6 and then stopped. The system was installed 9 years ago. Despite extensive...
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