I have a few 1963-1968 S type Heater taps
(p/n C19704) that I have collected and today I purchased a hand-held vacuum pump kit to test them.

I got lucky with the first one I cleaned and tested, since it is holding a vacuum at 23 InHG VAC or 525 mmHG VAC per the gauge. ( Sorry I do not know what that means). It has held the vacuum for over 30 minutes so far.

the questions I have are:

at what vacuum pressure should I test them?
and, is holding the vacuum definite proof that it is good?

Thanks.

 

I think you are spot on with the test vacuum. Most engines produce around 20 in Hg at idle so that would be the vacuum that the valve is likely to see. The fact that it is holding the vacuum tells me that the diaphragm inside is intact but I'm not familiar with that particular part to know if it operates in some other way. I'm inclined to call it good!!

 

A typical XK engine will produce 18 to 22 inch Hg of vacuum when running at a constant speed/constant part throttle or idle.

Jose that should open the water tap properly. So you are testing in the right range.

All it can't guarantee is how long the rubber diaphragm will last.

If you ever find a NOS unit I'm interested in a spare.

 

cdg66mk2, that is great news. The S type Heater tap is a Normally Closed, Opens with Vacuum tap. A very pretty part design made in 2 halves, aluminium and steel, used only in the S type, 420, MK-X and maybe the 420-G.

Daimler limos used a similar looking tap but different port design, does not work in the above models.

I kept the one being tested over 1 hour in the open position at 23Hg to see if the diaphragm failed, I have 3 more to test.

In the OPEN position, (vacuum applied), I poured hot water through the IN PORT and the water came out through the opposite OUT port.
Prior to applying vacuum, I poured hot water through the IN PORT and nothing came out through the opposite OUT port. (CLOSED). So the inner spring and diaphragm are working, I think the WD40 did the trick. Nothing came out through the weep vent. Whether it will last in situ, that is another story.

Glyn, I purchased a NOS tap in original box through eBay UK and sold it to the S type Register who was looking for a tap for a member. It was awfully expensive with shipping to the US, I needed to recover the cost. Haven't seen another since.

Thanks both for the info. Here's the cleaned and tested one. Jaguar numbered these taps. This one is 011766.

 

Jose from what I have found with these valves, it is not the rubber diaphragm that leaks but the centre washer in the diaphragm that rusts out allowing water to get to the other side of the diaphragm and then leak out of the vent hole. This is one that was leaking that I split in half to look at the inners. You can see the amount of rust in the valve caused by running the car on pure water rather than having an inhibitor mix in the system. In the second photo of all the parts laid out you can clearly see the rubber diaphragm on the right is in good condition. Rather than clean these inside with WD40 which is not a lubricant but a water dispenserment agent I have sprayed mine with a silicone grease which is a lot better for the rubber component and will also coat the metal to stop further rusting.




I have one good one I found in my box of many things but on the car I am actually running the SNG Barrett replacement part which is similar to the XJ6 valve but works the same way as the S Type valve ie standard closed / vacuum open. Unlike the S Type valve the new valve does not have water coming in to contact with the internals of the vacuum valve or the diaphragm as the diaphragm on this valve operates a lever which opens the tap. The new Barretts valve is on the left and the XJ6 valve is on the right.

 

Cass. Thanks for the info. I think there are multiple failure modes on these valves. For cars that have had owners that are good about maintaining coolant concentration it is the diaphragm that perishes & for others corrosion. I spoke to an Aussie company that rebuilds them if not corroded. They will neatly un-seam. Fit a new diaphragm & reseal. They won't touch corroded units. Their name escapes me but I have it somewhere.

 

Glyn, find the name of the company if you would? I have 5 unrusted taps.
Cass, you seem to have studied these taps in depth. I have too. Yes I opened one of these valves to understand what the problem was. There are two rubber diaphragms, A large bell-shaped diaphragm and a coin-sized diaphragm.

What Barratt must be supplying must be a modified Series 1 XJ heater tap. Series 1 XJ was the last Jaguar to use a NORMALLY CLOSED - OPENS WITH VACUUM TAP. (1968-1973).

then Series 2 and Series 3 XJ came with NORMALLY OPEN - CLOSES WITH VACUUM taps. (1974-1992).
(1972-1974 were mixed years in which both Series 1 and 2 XJ were built, as I understand).

In my S type I fitted a plastic tap made for a 1965 Ford Galaxy which has the same specs as the factory tap including 5/8" ports and the only difference is the vacuum hose port which is 1/8" as opposed to 1/4" in the factory tap.

The parts guy at AutoZone store found me a reducer adapter to use the original 1/4" vacuum hose with a piece of 1/8" Hose. This was in 2005. Worked perfectly if not more efficiently, and a cheap solution. The Ford tap was $8.00 dollars and the adapter $1.00. Made in China of course. Plus 7% tax for the boys in the State Senate. Today the same tap is over $25.00 thanks to donny's tariffs against China.

 

I'll take a look Jose. I thought I had got their details from you on the Register. I phoned them. Did not take it any further because my present one is OK.

 

Sorry. It was Dave Reilly that listed them.

www.advancediaphragmoptions.com

In the process I also found the typical failure mode of the newer vacuum valve.

 

Thanks Glyn, I now have 3 good valves, all are holding vacuum at 23 Hg.

Would 22-23 Hg also be good for the Scuttle Vent actuator valve ? It is very similar to the heater taps. I have a spare but don't want to damage it applying too much vacuum.

 

Both valves work from the same vacuum reservoir under the left wing so I would say if its good for the heater valve it will be the same for the scuttle valve.

 

Thanks Cass. I will test it at 22 Hg.

how did you remove or opened the crimp seal on the outside edge of the heater tap?
You said it was easy but mine wasn't easy, I had to slice and raise the seal.

I am starting to suspect there are two generations of these taps because the one I opened does not have the rounded center bulge on the aluminium half of the tap. Mine has a flat surface.

 

As I knew it was broken I did not stand on ceremony and try to lever the lip back I just took the lip off with a grind stone and it fell in two.
There could have been a couple of designs but without putting two broken apart side by side you are not going to know if there are differences.

 

As Rob says it will be adequate/suitable for all the vacuum devices on the vehicle & most importantly the brakes.

 

here's part of the collection !

 

Is that a crack on the inlet of top left valve or just a mark?

 

it's a surface scratch on the aluminium caused by the screwdriver when pushing the stuck hose back. No cracks anywhere.
I haven't finished cleaning and polishing them, All three tested and all three hold vacuum indefinitely. Amazing!
The one I opened is the one that was leaking in my S type when I bought the car. I have two more but I don't remember where I put them. Still looking.

I found out that one failure is an accumulation of crud at the vertical tube by the inlet. The opposite (outlet) side of the tube is clean.

 

Ah! That is good news!