Can’t for the life of me remember what the water sensor name is that stops the machine if water is not flowing, but anyway I need one for a k40 machine tried a couple but they do not work, the machine still thinks water is not flowing, so has anyone got a suggestion for one that plugs straight in the original wiring please, at the minute I have to keep checking the flow by looking in the tub, as I have had to disconnect the faulty one and the others do not seem to work. cheers in advance. Ohh by the way the old one connects at the front of the psu board
I think you should be able to use basically any NO (normally open) water flow sensor.
Which ones have you tried that are not working?
Hello, I’ve tried the generic ones from china no name on them I’ll post some pics tomorrow of them, mine has 2 wires on the OEM one, thought if I purchased the same 2 wire one it would work but no I was wrong.
Do you have a meter you can use to test the sensor? If you take it off the PS and do a continuity test across the leads does it show open or closed? Ideally it would only show continuity when water is flowing through.
No sorry I don’t have one or know how to use one either, these are the 2 I have tried so far on this Link
The description in the link isn’t explicit about whether the switch is normally open or closed but based on the function it’s almost certain it’s meant to be normally open. Based on that the switch should be working. It should only complete the circuit and allow electricity to flow when water is passing through the sensor.
You said you had one previously installed that was working?
Make sure there’s nothing on the power supply that’s potentially jumping P and G closed. If you disconnect the sensor entirely does the machine still function? If so, there’s a problem on the power supply side.
Ideally you’d have a meter to check some of this. I suggest you get one as they’re generally quite useful. Continuity test is literally just connecting two probes to two leads to check for a circuit.
If I disconnect the sensor the machine will not work, I use a jumper on the connection to join the pins and the machine works fine, it was the standard one that came with the machine that worked but then packed in working hence why I have been looking for a new one, a friend is coming over tomorrow who is actually an electrician to test things for me.
Thanks for the help 
Interesting situation. That means somehow the sensor is shorting without flow. I’m trying to think of a situation where that would occur but I don’t believe those sensors are that sophisticated.
Let us know what you guys find. Good luck.
So my friend could find no fault with the shut off switches, after a lot of figuring out, on my water pipe I had a smaller pipe used to get it to where it needed to go, this smaller diameter pipe was restricting the flow that much it would not trigger the switch, even though it had water flowing the flow was weak due to the smaller bore pipe, changed it all over to 10mm ID and hey presto all good, just shows even though you have flow with the water it needs that extra Umph.
Thanks for you help
Awesome. Glad you got it sorted. Thanks for the closing the loop on this one.
What’s not making sense to me though is that without sufficient water flow the switch should have been left open. Meaning it should not allow the laser to fire.
If you had been in a situation where you couldn’t get the laser to work with the slow trickle that would make more sense. Have you confirmed that with flow restricted that the laser shuts down?
It was because the water was restricted the laser did not fire, when the smaller reduced tube was on I was having all the problems, even though the water was flowing I presume it could not activate the switch due to poor pressure.
Got you. I realized that I completely misunderstood the original problem. I thought when you said the sensor wasn’t working that it was always firing when it should not. Not that it wasn’t firing when you expected it to.
Apologize as I would have given you different guidance in that case. Either way, glad you sorted it.