This looks very interesting:
I wonder where they got their water valve/actuator from...
Reading around the website, it's a 9v MOMO valve (ie needs power only when changing state) - I suspect therefore it's a motorised ball valve rather than a solenoid.
I could see a use for the valve alone. If the whole thing costs 42 quid, the valve must be in the region of 30 quid.
Any ideas?
Cheers
Tim
Tim S coughed up some electrons that declared:
To answer my own question:
Just had a call back from the designer (who I guess is also the owner). Very interesting... They use a custom design latching solenoid valve, driveable by pulse in the range of 6-24v. And he seems happy to sell the valves on their own.
So I'd need a little interface timer that can apply the pulses based on a general demand input (sounds like either a job for a 555 or an AVR/PIC depending on your bent).
Low power (obviously), can handle low pressure at high temps too so good for rads and the price indication I had is lower than my original guess.
0.5bar to 10bar, WRAS, 40l/min max flow - I can see a lot of applications for this...Like a PIR in the bathroom to operate the extract fan, but at teh sam etime cut off the water to prevent flooding.
Or to stop the kids spending 20 hours in the shower :)
Cheers
Tim
just wondering why a 555. All ac solenoids will run off dc, at IIRC about half or 2/3 the voltage.
NT
NT coughed up some electrons that declared:
Because it's a pulse driven latching jobbie.
The bloke said any attempt to continuously feed it will burn the coil out.
OK, 555 may be overkill, could probably do it by dumping a charged capacitor into it using transistors to pump the charge through it.
I think this may be how the company use it - he mentioned using a 6.8mF capacitor.
Anyway, with these valves, you bang a charge pulse through them one way to turn on and the same charge through the opposite way to turn off. Do nothing and they maintain their current state.
Me - it'd probably use a little 14 pin AVR microcontroller and as few transistors as possible. They're like a quid, I'm setup to program them, I can add a few failsafes (like if "call for water" is held high, periodically send a refresher pulse to the valve every 10 minutes, just in case it got stuck the first time (don't know if that ever happens), make the valve "network" addressable too - RS485 being an easy choice) and any other random funky stuff - probably all for a fiver, a bit of veroboard and a little box all running off the 12V SELV supply that I need for other things anyway.
Probably take a day or two to bang up a prototype that works. And energy efficient to boot.
The only thing lacking is positive feedback that the valve is open or closed,which is something you can of course have with a motorised zone valve (mains operated at more cost too). Cheers
Tim
Nifty. It's probably worth checking what testing's been done in terms of estimating the number of cycles it'll stand before failing, as that'll dictate what applications it can be used for.
Stuff like that makes me nervous in case the valve fails - it doesn't look like it has any feedback as to current state, so you really need extra gubbins 'downstream' to check that the valve has actually done what you've asked it to.
cheers
Jules
Simplest way is to dump a big cap into them via a relay. Exact capacitance will depend on the mechanics, I cant really remember what I used for another solenoid + small load app, it was long ago. But I do remember it never missed a beat, which I wasnt sure about when I designed it.
A whole day is a significant cost. The relay cap arrangement may be primitive but its very quick and I had no failures. For best result use a 2 pole relay and parallel the contacts, and of course check the relay life ratings before purchase. The solenoid coil itself will act to limit peak i, so no contact side suppression needed.
BTW this method works fine on voltages significantly above coil rating.
Something must move when the valve opens and closes. Get one and see if you can position the arm of a microswitch in a suitable place or attach a linkage to operate a microswitch.
Jules coughed up some electrons that declared:
Apparently, 200,000 operating cycles as required to get WRAS certification, so he said.
I've ordered a sample of one to play with - I'll let you know what I think.
Cheers
Tim
That was my thought, too - there must either be a sliding or rotating part which acts as the actual valve, and this must have *something* going to the outside of the valve body so that it can be driven by the solenoid actuator mechanism.
Hopefully there's a spot where either a mechanical switch or some sort of optical switch can be attached in order to sense the position of the valve itself (regardless of whatever the drive mechanism is doing).
Of course the sense switch could also fail - but I suspect this doesn't matter as it can still be detected as a fault condition and a real human being can be alterted.
cheers
Jules
Why should anything moving outside the valve body? Normal solenoid valves don't; they use magnetic coupling to operate the valve.
Bob
... and today I learnt something new :-)
Seriously, I didn't know that. Many years ago in early teens (I think whilst futzing with solenoids in school science lessons) I remember thinking 'wouldn't it be nice if valves were magnetically operated', but I'd always assumed that a large enough field would just use too much power to be sensible except for only a few applications.
cheers
Jules
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