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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. 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...
  2. 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...
  3. 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...
  4. 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)
  5. 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...
  6. 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...
  7. 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...
  8. 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.
  9. 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...
  10. N

    bathroom isolation valves!?!?

    I’m trying to fit new pillar basin taps upstairs. Before I even got to that part I turned off the main stopcock under the kitchen sink but of course it didn’t turn off the water upstairs (who knew!?!) So I tried the isolation valves in the bathroom and only the hot one turns and the cold won’t...
  11. M

    High Flow Double Check Valves

    Hi all, I’ve a customer with a failed double check valve on a water softener, it’s 22mm compression but with a far larger bore than the usual DCV’s you see online. Anyone know if they are called something different or where I can get one? I’ve even been on the water softener website and they...
  12. C

    Corner valves for a radiator

    Hi, I have bought corner valves to use on a new towel radiator. As you can see in the attached pic, one part of the valve has a small circular hole in it, and the other part has a large semicircular hole. Which end - 1 or 2 - should I connect to the water pipe and which end should I connect to...
  13. M

    Sourcing replacement manifold actuator valves

    Hi, we had underfloor heating installed about 15 years ago. Some of the actuator valves are now leaking and we need to replace them. I'm trying to source some that fit. The plastic caps which came with the originals had the 'Watts' brand on. I've tried ordering a couple of the most common valves...
  14. G

    Why 2 double check valves on filling loop

    Hi, I have recently had a water board inspection This is what the report said about the filling loop on our press unit for a biomass boiler…. There is quickfill pipework directly between the mains water supply and heating supply. This type of temporary connection is permitted under the water...
  15. R

    Can motorised valves go under floorboards (legally)?

    Hi guys and gals, I'm looking to try to change from a Y-plan to an S-plan-plus this year to have a heated bathroom. While the house isn't that large, a mixture of south-facing brick and north-facing (and Jerry-built) timber frame construction means no single thermostat will cut the muster...
  16. C

    Isolator valves on basin taps

    Hi I have always had a poor water delivery to my bathroom and en-suit basins. The cold is just about acceptable but the hot is pathetic coming from the tank on the same floor. Both rooms have isolator valves fitted in the correct direction and then to flexi tails that just reduce the flow...
  17. prburkis

    Are there any "Recommended" Smart TRV Valves for large houses?

    Hi All, I thought I'd come to the experts and see if anyone is installing and/or recommending the use of any Smart TRV valves? Particularly in large(ish) solid wall houses. I live in a 1920's arts and crafts house - it's about 2000sqft, not massive, but it's approx 25% larger on the...
  18. B

    Kitchen stop valves result and questions

    Hi everyone, Finally I have figured out what the two stop cocks in the kitchen do as they both had to be replaced due to leaks. The one under the sink stops the cold water from coming into the kitchen tap and the one which is in the wall panel is connected to the incoming mains water and needs...
  19. R

    Valve tips and advice

    Hi all! as I am attempting my first plumbing project and the stakes are high, I would greatly appreciate picking your experienced brains regarding valves. I am building an overland truck/motorhome and since I will be traveling to remote areas and underdeveloped countries I'd like my plumbing...
  20. L

    How do I fit Bosch thermostatic valves to old radiators .

    background: I have 15 radiators 20+ years old with no thermostatic valves and Bosch instructions depend on replacing the actuator part only of old thermostatic valves. Surely there is an option for new complete valve replacing? Tom
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