THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

[quote="Orlando St.R" post_id=4732 time=1565979347 user_id=141]
My flap has always slowly closed after 30 mins or so, but now does so within 5 mins.

The tank seems hard enough to remove; the nuts are solid; so I don't want to have to remove it unless I really have to! I will report back once diagnosis is complete.

With yours, I guess the non-return valve is the only item you've not been able to test.
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When I switch off my flap closes almost instantly so it has to be the non return valve but a £50 a pop new from SNG I will put up with it closing.


The Tank is held on with two half inch nuts on studs. Even if you snapped the studs it would very easy to either drill out and put a bolt through as you can get to the top or to put a bolt in the hole and weld the head in place to turn it in to a stud.

Not difficult to test the non return valve if you set up the vacuum pump in such away to create a vacuum in the tank via the outlet to the rubber tube to see if it held. I might try this via the back of the three button switch as this is how I checked to see if the tank was holding a vacuum when I found the hole but I did not recheck it when I reassembled it as the flap was now working.

Thanks for the extra info, Rob, (inc C27005 - as usual not easy to find on SNGB). And thanks for thinking about why mine might not be working properly.

My flap has always slowly closed after 30 mins or so, but now does so within 5 mins. I will wait until the vacuum tester arrives and test the various bits of the system. The tank seems hard enough to remove; the nuts are solid; so I don't want to have to remove it unless I really have to! I will report back once diagnosis is complete.

With yours, I guess the non-return valve is the only item you've not been able to test.

[quote="Orlando St.R" post_id=4690 time=1565730318 user_id=141]
I suspect mine is about to go the same way as yours, Rob. The flap closes slowly a while after turning the engine off. I've been trying to ignore it. :) .
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I was thinking about this Orlando and if the flap is holding open with the engine running but closes when the engine goes off it means the tank is not holding the vacuum. This could mean you have a small hole in the tank, a leak in the rubber tube or the non return valve C27005 is not sealing and allowing the vacuum to be filled or the three button switch is not sealing. My flap closes as soon as I turn off the engine and as my tank is now air tight, I have checked the hoses and the three button switch, I can only think my valve is not working as designed.
In my box of many things I have a spare three button switch with all the hoses still connected.

The pipe is a push in fit to the vacuum cylinder from what I remember so a pair of plumbers pliers or monkey wrench should do it but I also seem to think that the top section is screwed in to the pipe. As long as you try and unscrew it you will either loosen the pipe or unscrew the top whichever gives way first.
There is one for sale on EBay with pictures at https://www.ebay.co.uk/itm/JAGUAR-DAIMLER-HEATER-VACUUM-CHECK-VALVE-SERIES-1-XJ6-XJ12-S-TYPE-420-DS420/152631714616?epid=1923853014&hash=item23898f2338:g:5~0AAMXQQANREpLS to give you an idea and the photo is reproduced below.
[attachment=1]s-l1600.jpg[/attachment]
The part number C27005 is being sold on SNG but has a slightly different design in that the tubes are opposite each other rather than sticking out the same side. The picture of theirs is also below and this is why I think the top section is a screw fit. I do not think I have a spare but will go and take a look.
[attachment=0]Vacuum valve.png[/attachment]

I had a bit of a look at this today. There's nothing obviously awry, so I have ordered up one of those vacuum testers and will chase the problem through until I find it.

One quick question, Rob: How does one detach the non-return valve from the tank?

Thanks for the tips, chaps. Several things to look at there. I will get around to it at some point.

I sand blasted mine until spotless & then self etch primed followed by many protective coats.

You obviously have a leak but it is finding where the leak is first. Could be one of the hoses that has become old and perished. Mine were all in good condition. Could be the return valve on the tank that is allowing the vacuum to leak back out or it could be a hole in the tank as I had. There is no shield on this tank like the one on the brake vacuum tank so it might get pitted by rust and stones. My leak was under the fixing bracket where some mud had been caught in the past and had rusted through the side of the tank.
I have a brake vacuum bleeder which I was able to attach to the various tubes to create a vacuum so I could test them all.

I suspect mine is about to go the same way as yours, Rob. The flap closes slowly a while after turning the engine off. I've been trying to ignore it. :) .

I'll bear in mind your fix when the time comes.

All sorted now. The metal is too thin to weld but it all cleaned up well and allowed me to patch up the hole with araldite. As it is a vacuum and not a pressure tank it is trying to pull the araldite into the hole rather than pushing it out so it has sealed very nicely. Followed up with another coat of black paint and some underseal and hopefully it should outlast me.