SU Fuel Pump Arc supression

[geoberni]

Cutting a long story short, I recently overhauled an SU Pump which I'd brought on ebay as a runner but leaking around the body. For which I brought a full SU Repair Kit.

Having completed that job, including fitting the 'varistor' as they still call it, even though the pump didn't have one (or any other device) fitted.

So the 'varistor' is for Arc suppression, basically reducing the burning of the contact surfaces when they open.

I found this really interesting article on the MGT society website:
https://ttypes.org/extend-the-life-of-y ... a-transil/

Having fitted the overhauled pump to Basil to test it out, I left it there and stripped his pump. It was in a far worse condition, bottom line I then thought if I just get a new diaphragm rather than a whole kit, I can reuse the rest removed from this first pump, the contacts were in a far better condition, almost new.
So I got a new diaphragm and then wondered about a varistor, or Transil as the MGT article called them.... SU don't sell them separately and my enquiry to them went unanswered...

I got one from ebay "1.5KE24CA Stmicroelectronics Diode , Tvs , 24V , 1.5Kw" a bidirectional type TVS diode, basically meaning it's a Diode, but unlike one that is single direction, it is 2-way when the voltage spikes like in an arc.
They really work, when connected the spark of the contacts repeatedly opening and closing practically vanishes.

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The other thing worth sharing is that I used the old gaskets as templates to cut my own from a suitable sheet of gasket paper.
When I was assembling the pump, I had trouble with the mechanism travelling up and down properly. Why wasn't it throwing over when all assembled?
Basically, ensure that the inner line of the gasket does not protrude over the edge of the depression in the middle section of the body. The Diaphragm has to freely move up and down into that section and I had a tiny little overlap in a few spots. I held the gasket in place on the middle body section and ran the scalpel around it again, just to tidy the edge up and all was good.
The operating tolerances on the pumps really are that tight.
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I just thought I'd share this if anyone is considering working on their pump and not planning on buying a whole kit complete with all the weights etc.

Just in case anyone is wondering, I swapped the pumps over again, to test out Basil's original with my DIY gaskets and Diode and it works perfectly.

[rocco]

Thanks for sharing. Reminds me of the time I bought an old Honda Deauville because they used to burn through fuel pump points.

[svenedin]

The "arc suppressor assembly" is available from SU. I am not sure what this actual component is but recently they were using Zener diodes:

https://sucarb.co.uk/supressor-assembly.html

Many other parts are available but the SU website is awkward to navigate. To see the parts list click on "view components" underneath add to basket and scroll down to the parts diagram.

https://sucarb.co.uk/su-fuel-pumps-spar ... c-diagrams


Stephen

[myoldjalopy]

A couple of times in the long distant past I have had failure of the petrol pump due to the points having burnt out. About 23 years ago, an old-time mechanic fitted a condenser to the pump (he also fitted one to the coil) as a kindly gesture. Whether that made any difference or not I don't know, but I suppose the idea is the same as the arc-suppressor gizmo, just like the condenser in the dizzy. In any case, I have had no burnt-out points in the last 23 years.......

[geoberni]

The "arc suppressor assembly" is available from SU. I am not sure what this actual component is but recently they were using Zener diodes:

https://sucarb.co.uk/supressor-assembly.html

Many other parts are available but the SU website is awkward to navigate. To see the parts list click on "view components" underneath add to basket and scroll down to the parts diagram.

https://sucarb.co.uk/su-fuel-pumps-spar ... c-diagrams


Stephen

Thanks for that Stephen.
That new SU site, it was only changed in the past few months, is a nightmare compared to their old one, which looked dated but was at least far easier to navigate. Just a pity their Customer Services never replied to me.
I'm more than happy with my £3 Diode as per the MGT link I gave.

The ''Transil' as described on the MGT pages is a Diode, but they are designed to 'stop being a diode' over a certain voltage in this case 24v, so can be arc/spark suppressors.
The are also available as Bi-Directional so fitting one of that type stops the pump being polarity conscious, like the original 'Zenner' option.

[geoberni]

A couple of times in the long distant past I have had failure of the petrol pump due to the points having burnt out. About 23 years ago, an old-time mechanic fitted a condenser to the pump (he also fitted one to the coil) as a kindly gesture. Whether that made any difference or not I don't know, but I suppose the idea is the same as the arc-suppressor gizmo, just like the condenser in the dizzy. In any case, I have had no burnt-out points in the last 23 years.......

The first version of Arc Suppression that SU tried was a Capacitor, or 'Condenser', that's why some pumps have that huge bulge on the cap, to accommodate the electronics of the era, a huge paper film wrapped device. It worked but not as well as they hoped, then came the Diode that made them Polarity sensitive, then the latest little device,...
I was really surprised at how well they work, both the SU version and the one I fitted. Without it, obvious sparks jumping the contacts, connect it up and they diminish to a tiny spark you can barely see, even is a dimly lit garage.

[svenedin]

I think I will try your eBay arc suppressor in a Victorian doorbell that I have. Mind you, it has platinum points and little sign of any damage after 130 years! Platinum was chosen as it is very unreactive (a Noble Metal) and has a high melting point.