Off the cuff Tech Talk with John Wilson from Ravenheat
Guys, a few of you have asked about a natter about diverter valves. Sorry if this is a bit basic for some of you guys, but obviously we’re not all on a par when it comes to knowledge. One thing I will say guys, as gas engineers, there’s one thing that we can’t believe in, and that’s ghosts. If we believe in ghosts, then it can knock us off track. There’s things that is right and things that is wrong, and when you’re in front of a boiler you’ve got to look at everything in sequence, okay?
We’ll just address three different types of diverter valves this morning. Obviously I don’t want to bore you to death with too long a video, so I’ll go through … and just remember guys, I’m doing this off the cuff. There’s no editing goes on here, this is off the cuff, so if there’s little bits and pieces that I say which is just not quite correct, then I apologise.
Right, we’ll start of in the old days, shall we? here we’ve got the old Giannoni diverter valve, okay? On the end of the diverter valve we have a plunger. The plunger, here we have a microswitch, okay? This could be a double microswitch or a single microswitch, depending on the type of boiler it’s fitted to. How does this work? Here we’ve got the coal mains, and here we’ve got the coal mains into the plate; or going even further back in time, down to the double-pass … going up to the double-pass heat exchanger. Here we’ve got the rubber diaphragm.
As we move on to the body of the valve, here we’ve got the central heating flow. Here we’ve got the central heating return, and here we’ve got the bypass, and the bypass is the bypass that supplies the plate heat exchanger. So basically when Mrs Smith opens the tap, the plunger moves, the diaphragm moves, the plunger moves, it hits the microswitch. When it hits the microswitch, all that’s doing, guys, is moving it from a lower burner pressure … cental heating … to a higher burner pressure … domestic hot water.
But as it does that … what it does at this part of the valve, it closes down the heating section on domestic hot water there, and opens up the bypass here to supply the plate, okay? Failures on this valve, as we know … one, we could have a pinprick in the rubber diaphragm, so the customer says they have to open the hot tap maximum for it to fire. That’s a pinprick. We can have a situation where the plunger’s not moving at all.
Then there’s a tear in that diaphragm, okay? We could have a situation where the water’s not performing. As I say, there’s no ghosts. If you’ve got the correct flow rate through the hot tap as matched with MI, and you’ve got the correct burner pressures, then the hot water’s got to get warm. If it’s not, then you need to investigate why. So if we grab this central heating flow underneath the boiler, if that starts to get warm, then this valve is passing, and basically all it is is some debris stuck in there. I’ve seen it on brand new boilers many many years where there’s a big blob of salt had just stuck in that disc there, so it were allowing 50% of the water to go to the plate, and the other 50% to beetle off around the heating. So as I say, it’s simple.
You can also have a situation where you’ve set the flow rate, you’ve set the burner pressures, you’ve grabbed the central heating flow, and it’s still not getting warm. In that case guys, if the burner’s staying on, then simple, isolate the coal main underneath the boiler, make sure the hot tap stops running. If the hot tap continues to dribble, then something is passing. It could be a shower valve, it could be the hot and cold washing machine, it could be a mixer tap that’s passing. Simple, okay. so, that’s basically the old Giannoni diverter valve.
Now, there’s one thing before I move on from this. You think this is old hat. I’m sorry guys, I disagree, because with modern valves which we’re going to look at shortly, especially when you’ve got a plastic block, you guys are fitting mini expansion vessels and you’re fitting antishock valves on the coal main. There is an argument to say we’re going backwards, not forwards, because this valve, okay, there’s your antishock and there’s your mini expansion vessel, so it was built into this valve. So it wasn’t necessary. The power of marketing is a very clever thing, but there we go.
Right, let’s move on to … this is a more up to date block that we’re used to working on. Here we’ve got the electromotor for the diverter valve, and here on the coal main we have the cartridge, and on that cartridge we have a flow sensor. So when the hot tap is open, this flow sensor illuminates, okay? That tells you that basically there is power to the electromotor and it’s energised. Now, how does that come about?