Numatic George pump lead open circuit

Aha. Seems it's a diode. Anyone have any more info?

Probably cheaper than finding a suitable replacement from Maplin, if you can wait a day or two ...

Yes, that's how I found out. I have ordered one from somewhere.

Meanwhile, it's a 1N4007. Which isn't a 'thermal' diode in that sense, so not quite sure how this works.

I probably have one somewhere. Off to check.

What do you mean by a thermal diode? The forward voltage of any diode has a temperature coefficient -0.002V per degree C for silicon)but that is the only thermal connection to a diode I can think of.

I presume the pump in question is run from half wave AC to control the speed or power dissipation for some reason.

Some cheap electric drills have a switchable diode to provide two speeds/power levels rather than doing it properly with a gearbox.

The Gotek pump in those works on the same principle as an electric door bell. Would that be anything to do with it?

Are you sure it's a diode? If it's the size of a typical diode and bullet shaped with a full metal jacket (as it were) then it's a thermal fuse.

I'm just repeating what the spares list says on one website! Which I think is wrong. It's just a diode, probably for the reasons you give.

Since it has a plastic casing and has '1N4007' written on it...

The pump clearly works on AC as there are no contacts. But it may be half wave AC as described.

Anyway, I'll replace the diode and see what happens.

If the pump manufacturers recomendations are followed then one "bump" is a fuse and the other a diode.

The fuse is easy to check and the diode normally fails short, i.e it will read low ohms both ways round on an Ohmeter.

Numatics parts list makes interesting reading. A Numatic George built from manufacturers spares must approach the cost of a small mansion in Belgravia.

AB.

Sorry, forgot the link!!

AB.

Turns out two of the 'bumps' are crimps and the third is the diode.

I agree!

_Technical_data.pdf

Thanks...interesting.

Sounds like one I've had turn up at a repair event. IIRC, one of the crimps was a bad connection, and the diode had overheated as a result. I think the motor was a DC (permanent magnet) motor. I don't think a 50Hz AC motor that small can be made which is powerful enough - not even enough space for having universal motor field windings.

The pump is a strange device. Basically a winding surrounding a spring loaded metal slug in a cylinder, with a non return valve and a channel connecting the two ends of the cylinder (can't see the channel but it must be there).

No chance to work on it, probably until the weekend. Need to find some crimps.

The work on the same principle as an old fashioned door bell. Made by Gotek if that's any help.

Yes, someone posted a link. Except doorbells don't need diodes, and only AC doorbells!