Repairing a Hydractive Electrovalve...

[CitroJim]

One fatal problem with Hydractive Electrovalves is corrosion to the base of the alloy valve block that results in an LHM leak. They corrode because they're in contact with the steel sphere base and moisture causes electrolytic corrosion. The corrosion continues until the large hexagon at the base is sufficiently corroded to expose the green sealing O ring.

New valves are likely to be NFP soon and anyway, if they are available they are very expensive.

This is a typically corroded one, showing the green O ring just peeping out as pointed to by the arrow.



I have a lot of these and today I set about seeing if they could be recovered and made good again. I may have succeeded...

This is a really bad one where the hexagon has almost completely corroded away. This is the innards of the valve after the coil and shuttle, slug and springs have been removed.



First job was to machine off the corrosion until it was just gone.



Leaving a nice circle of clean metal...



The diameter of this circle was very carefully measured and a replacement ring machined from alloy bar stock. The outer diameter was set to that of the original hexagon (24mm) and the inner bored to just a tad under the diameter of the cleaned-up valve body...



The end result of the machining was a ring 4.5mm thick...



This was carefully fitted over the cleaned-up circle on the valve body...



The valve reassembled...



And installed onto a spare Hydractive Sphere Block...



And there it is, one electrovalve that should be good to go again. I'm looking for a guinea pig locally to try it on but before doing so I shall seal the new ring onto the valve body with some strong bearing retainer adhesive and treat it to some new O rings.

Any I do in future I'll make the new ring a heat-shrunk fit and I think then no adhesive will be needed.

It may not work but as the valve was scrap anyway it is worth a go...

[citroenxm]

Was that the valve I gave you Jim that was completely gone.... If so, it came off a V reg Estate Exclusive!

Nice one... If I was closer, Id certainly stick it on one of my blocks to try out!

[Citroenmad]

That is excellent Jim, if anyone could make a fix it was you

You could have a little sideline going here!

I can guarantee that if I walked into my local Citroen dealer and said "My car is a Xantia, can I order a replacement hydractive electrovalve please?" they would just look puzzled and say "that part is no longer available". They would have made their mind up about this upon hearing the word Xantia ...

Very good job indeed

[CitroJim]

Was that the valve I gave you Jim that was completely gone....

Yes, it was your valve Paul Thanks for that, it was an excellent guinea pig for the repair test. I'd let you have it back but want to trial it on a car locally first for a few weeks to see if it is successful.

From a V reg car? Gosh, it looked like it had been under the sea for several hundred years...

[bxzx16v]

The majority of Citroen dealers now are useless now , it's only those that have been agents for years who have a slight idea about the older stuff .

Mark

[citroenxm]

Was that the valve I gave you Jim that was completely gone....

Yes, it was your valve Paul Thanks for that, it was an excellent guinea pig for the repair test. I'd let you have it back but want to trial it on a car locally first for a few weeks to see if it is successful.

From a V reg car? Gosh, it looked like it had been under the sea for several hundred years...

Jim, Send it to me, Ill fit it to my car and try it!

[CitroJim]

You could have a little sideline going here!

Maybe one day Chris but not right now. That one is a definite one-off until fully tested and then I'll be happy to advise anyone who wants to do the same how to do it in much more detail. You'd be amazed at how much work is involved, not only in the machining - which has to be done carefully and to tight tolerances - but in the disassembly of the valve, cleaning and reassembly. On and off it kept me amused all day today...

[myglaren]

And Jim the resident magician!

[handyman]

Looks like a nifty repair there, Jim.

What was the grade of alloy you used? It might be possible, if this repair works, to use a corrosion resistant grade of alloy to stop the electrolytic reaction or to get the alloy assembly anodized, prior to reassembly. There are also some high grade inhibitor coatings (paint) that might stave off the corrosion. Makes you wonder how much thought PSA give to some of the stuff they design and build. Its not as if cathodic reaction is something new!

I see you put the ML7 to good use. Mine now looks alot sadder than yours. Telling thing though is the most important object in the last photo. Was it still warm?

Handyman

[Chris570]

Telling thing though is the most important object in the last photo. Was it still warm?

Handyman

I was on duty, so yep

[CitroJim]

Was it still warm?

Yes, it was That was a celebration one made by Chris570 following some success or another with his XM

I've no idea what the material was, it was just a scrap of alloy bar I had in in the useful bits of metal box. All I know it is hard and may be of aeronautical provenance... That was my last bit...

That's a tragedy loosing an ML7 I might not use it every day but by golly it's one of the most valuable tools I have. I'd be lost without it. Mine's a 1953 model and been in the family for three generations now. It's an heirloom

The only easy way I can think of corrosion proofing is to cover the base and block in something like Waxoyl but it would be critical to do it when everything is bone-dry and salt free otherwise the agents of corrosion just get trapped under a protective layer and can work unseen and unhindered...

[handyman]

Hi Jim, some of the inhibitors available in the marine industry will offer a solution to this corrosion problem. I#ll dog out some of the data sheets for them and post up. As I stated earlier, the part can be remade using one of the ali-bronze alloys, as used in the marine industry, as these provide excellent corrosion resistamce and are rated even for total immersion.

The replacement part is of a fairly simple form so is easy to recast and machine.

H

[CitroJim]

The original valve body material appears to be coated with something Handyman, not sure if it's anodising though. Certainly the underlying metal as exposed by the lathe was a different colour to the surface...

Yes, be most interested in any data on corrosion inhibitors you can find Anything that can help prolong their lives is only for the good...

[Diabolical]

I'm fairly local to you Jim be happy to try it out.

[RichardW]

That's got to be galvanic corrosion - taking out the aluminium as 'sacraficial' annode. Just need to clag a bit of something more sacraficial onthe side of it to move the corrosion point - something like magnesium (which AFAIK is what they bolt to the bottom of ships - although buying a few kg lump of magnesium and trying to stick it to an electrovalve may be a bit tricky ). Alternatively coat the whole thing in glass flake epoxy which is what they've just painted the Forth Rail Bridge in - good for 20+ years exposure to the elements.