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A valve is a device 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 drops to obstruct fluid (gas or liquid) flow in one direction, but is pushed open by flow 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 aerosols have a tiny valve built in. Valves are also used in the military and transport sectors.

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  1. Christopher buzzard

    Uponor underfloor heating valve.

    Can some please identify the valve on this underfloor manifold ( with the black wire coming out of the top). Have an issue where the system is turning off every 10-20 minutes and staying off for a while then coming back on again. The room can’t get up to temperature because of this. Power was...
  2. P

    Stuck shower thermostatic valve

    Help! The shower thermostatic valve has snapped with half of it stuck inside (the front and centre of the valve are out). Long nosed pliers and WD40 have had no success, and the whole fitting is moving when trying to pull. I was thinking it might be possible to get something in, attach to the...
  3. N

    New bleed valve or new radiator?

    Our radiator is leaking from around the bleed valve. Not sure if the damage around the valve is superficial and it could be fixed by replacing the bleed valve or if we need a new radiator. Would appreciate any advice!
  4. woof woof

    Tap tails and isolation valve roblem.

    Hi all. I'm after some help... I hope I can be clear enough... After being in 9 years our bathroom basin tap started dripping. It's a single mixer tap, one with a lever that you move left or right for hot or cold water. I realised it wasn't like the ones we had in the old days where you took...
  5. Bogart

    Honeywell EA122 automatic bleed valve

    Am going to fit an automatic bleed valve to replace the knackered manual one. Reading the Honeywell blurb it says it should be fitted on the positive side. Is there any reason for this? and could I not fit it on the negative side?
  6. A

    Danfoss zone valve wiring

    hi All, i am blocked on an issue: connecting Danfoss AMZ 112 (230VAC) ball zone valve to Heatmiser UH4 wiring center,seems wiring center turns ON the valve (open) when room stat calls for heat, which is fine, but when room stat stops calling for heat, wiring center does not close the valve...
  7. A

    Mansfeild flush valve seal wont seal

    SO, I have done about 30 of these and they all have the same problem... the old seal had become so conformed and imbedded in the base that the seal was so great that you would break the handle trying to flush. So its time to replace, the new seal is straight and flat and not conformed at all and...
  8. M

    54mm zone valve and auto bypass

    I need to fit a zone valve to some 54mm copper heating pipework, I also need to fit an auto bypass. Can anyone recommend a brand to use? Also the best place to buy for the cheapest price etc. I dont do a great deal of commercial work.
  9. B

    Potterton HE Store - Can't repressurise - Valve stuck?

    Hello, I have a Potterton Promax HE Store boiler, and in the past a few times I have had to repressurise the system after getting an E119 error. Usually I take off the bottom cover and turn one valve, hear the water coming in, and watch the pressure increase. However I've got the error today...
  10. G

    2 port valve on manual

    is it ok to leave a 2 port valve on manual and turn boiler on and off as needed until valve replaced
  11. R

    What is this, a drain off valve

    Hi, I'm looking for my drain off valve and the only thing I can see code to one is is value. Is it a drain off point?
  12. A

    Air Release valve size for infra network.

    Hi all, I have more than 500meter potable water network line connecting to buildings, tanks say 25 branches which installed underground-main line starting from 125mm HDPE SDR11 to 40mm HDPE SDR11. What size of ARV to be used at ground level inside 600X600 ManHole.
  13. H

    Bye-Directional Electronic Rad/Stat Valve Installation

    Is there an optimum position for them on a radiator - meaning position them on the Flow or Return side. I mean by this - is there a technical argument - If you have a choice (new installation) to say that mounting an Electronic TRV ( more sensitive) on the return side is better due to the...
  14. A

    Mixing group conflict with Zone valve?

    hi All, can someone help me clarify following issue? is there possibility when room stat calls for heat (UFH system), it opens the zone valve, runs the manifold pump and turns on the boiler but the mixing group does not start mixing the incoming hot water and does not allow the incoming hot...
  15. D

    Noisy automatic bypass valve or pump?

    Hi I have a vaillant ecotec plus condensing boiler which is in the kitchen with an indirect unvented centerstore cylinder in the airing cupboard. All has been well for 18 months (the cylinder was installed in April 2018.) The last few months there has been noise in the airing cupboard which...
  16. R

    Franke tap valve replacement

    I'm trying to change a dripping cartridge in a Franke Panto tap. I have a new cartridge and after a fight involving a decent hammer I've managed to remove the relevant lever. Inside, there is no hex head, double flat or anything else recognisable on the valve - there is what seems to be a...
  17. S

    Shower valve problem???

    Happy new year I have two showers in the house but this only affects one of them and no impact on any taps either. the showers are the type where there’s just a small control showing through the wall (mixer?) with hot/cold and pressure controls on the same unit. the pressure is good but the...
  18. C

    Baxi 105he leaking after servicing with diverter valve kit

    Hi all. After experiencing issues with luke warm hot water and reading about the relative simplicity of refurbishing the diverter valve in the Baxi 105 he I went ahead and did the job (with some trepidation) To my relief the boiler is now working much better, however it is also leaking a fair...
  19. B

    Orkli VZ-2V valve.I can't find info. on this.(normally closed?-Wiring?)

    Fault seems to be an Orkli VZ-2V in a log burner/buffer tank system.The valve is difficult to access & I can't find info.Is this a 'normally closed'valve(open when powered)?Does switch send 230v from grey wire to orange at end of run?
  20. M

    By-pass valve for reducing heating loop

    Good day, I have question regarding by-pass valve for my combi compackt Hreco 36 primary loop. My primary loop is going from 3rd floor to the first floor ( floor heating) , at underfloor heating manifold I have by-pass valve. Recently I have installed Honeywell evohome system and every room is...