Posted by in Plumber Talk, on February 13, 2018

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Welcome to today’s plumberparts.co.uk video today we’re gonna look at expansion vessels on heating systems. What I’m gonna do for today is we’re gonna cut apart an expansion vessel we’re gonna actually have a look inside it and see what’s inside one of these things, then we’re just gonna have a quick look at where they are in a pressurised system how they work, what they do. And love like that. Anyway people I hope you enjoy today’s video and remember hold tight!
We have an expansion vessel is got water on this side, heating system water on this side and on this side here you’ve got compressed air. The cold water when heated up on the boiler the molecules start to move more this is basic science and because they move more the volume of water expands. And so you need an expansion vessel to take up that expansion on a sealed system. Now usually if you had an open vented system you have an expansion part that goes up in a crook into the top of your tank, the F&E tank. Because you don’t have that here there’s no expansion pipe you need to use this to take the expansion. You cannot compress water it’s really really difficult but you can compress air so say you’ve got one bar of water here cold and you’ve got 1 1/2 bar pressurised air on this side. The water here when the boiler cuts in comes on will slowly heat up, slowly heat up and you’ll be able to watch the pressure gauge on the heating system go up and up and up from one bar, gets to 1 1/2 bar it starts to push into here, pushing this air and compressing down and then it should just hover about and be very happy. The problem is that a lot of the time these do go wrong and the main problem for that is the divide between the water and the air usually have a thick rubber diaphragm and it is effectively a moving part. And moving parts always prone to going wrong. So what we’re gonna do is cut this open and have a look in here. So you get a good idea of actually what’s inside one of these and then when I’ve done that I be able to show you one on a system and also give you a quick drawing about actually where they fit in the system.
People because we used the grinder today we do have to wear personal protective equipment. Make sure you wear a box, a thigh pad and an inner thigh pad, pants, protective gloves, a helmet and of course eye protection. Now we’re ready to go. In all honesty though, being serious is really important when you’re doing any kind of grinder, any work really where your eyes might be in danger to wear protection for your eyes and in a minute when I put ’em back on wear gloves to protect yourself. If you ever need to recharge the air this is where you’ll do it. This is a schrader valve these are the same sort of valves that go on bike tyres. If you’ve got a problem with your expansion vessel symptom being that the pressure goes right up or sometimes the high pressure relief valve dumps pop your finger on here
if no air comes out try and re-pressurize it and see if it work. If you leave your finger in here for a long time and water starts to come out you then know that the rubber diaphragm is gone in it. Let’s get grinding.
So now we’ve taken the side off we can actually see the two different sides, now here we’ve got our rubber diaphragm what’s happened is in the past that has basically broken so the mitre this is the actual expansion vessel when it’s actually in an unpressurized state. So the system pressure is probably about one bar and it’s cold. Now this area here you can see in front of us is air it’s full of compressed air. At the bottom we’ve got a small layer and this side we got water. Now as the system heats up the water expands and pushes up into the air that we can pressurise we can compress air. So that pushes up so when it’s at a fully pressured state our diaphragm will be up here. Now the problem is that these do fail as I said it’s kind of a moving part and when they do fail as you can see we’ve got loads of heating system waters on the air so it shouldn’t be there. Now that fluctuation in change happens constantly throughout a heating system’s running cycle. As I said you can re-pressurize the air at the top of the Schrader valve and do it like that. If you’ve got any problems and also the schrader valve is a really good way of figurin’ out if there’s anything wrong. Now I’ll give you a quick idea about how these schematically fit onto a heating system. So let’s have a quick look
at how these systems work. We’ll have our boiler, our pump, radiators and then back to the boiler.

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