Oh for a simple life !

What could be simpler than a half inch copper washer ?

Well - in today's world such a thing is a rare best indeed.

Now - one is going to say well 1/4 bsp is half inch, but its not its 0.530 major thread size.

Most 'imperial' listed copper washers only cover 1/4 bsp as half inch - with a main ID of about 13.5 mm.

Which is really too big for a Cav plug fitting.

Actually - 1/8 bsp is much much closer to 3/8 th - the little bleed screw on the top of 1/2 unf filter heads is 3/8 unf - so at least that one is addressed ok.

Its the 1/2 inch bore ID that is the bug here.

Strange that these old filter heads are 1/2 unf ? The only other things that use 1/2 unf as standard are - of all things - silencers on guns ! - and dive bottles ! Also, classic brake parts use 3/8 or 7/16 but never 1/2 ?

I thought at one time I had found dowty seals in true imperial - ie half inch bore - but I cannot for the life of me find it again ! An imperial dowty - at 14 bsp is main ID of 13.5

Alliance seals have some good info and range - and have good info on sizes.


They list Imperial, German Metric and French Metric ( ie under German there are three 10mm dowtys - one at 10.37mmm ID as opposed to 10.7 mm ID. ( I mean, come on - french and german metric ! )

Anyway - after much searching and I must say, in the process, finding things I never knew existed on this planet of ours, I stumbled on a Minature Steam engine makers site, Macc Models - and hey presto - they sell 1/2 bore copper washers and, to boot, they are 'proper' three layer folded washers. At 17 p each I decided to invest in 20 at 1/2 and 10 at 3/8.

Of course - there is 'no' market for this stuff - it takes wierd specialist suppliers to actually care to make these things available - and good for them.

Most folks are chucking the old cav for newer Racor etc filter bodies - and having all their headaches around 1/4 nptf ! ( again - a crazy rare USA thread - national pipe thread fuel ! )

But - even in swapping out the old cav to a new spin on head - I have still opted to stick with a unf version as my remote primer is unf and they are not cheap.

I see the Racor turbine use 3/4 or 7/16 unf but fit them with o rings. I'm ot sure if a 1/2 unf cav type fitting could be fitted with a suitable nitrile O ring - maybe.

I digress - I shall be interested to see these folded washers. They seem the real mackoy really - I mean steam trains are fussy about washers aren't they !

I've also just recieved my replacement 1/2 unf filter head, spin on M16 x 1.5mm - to pair with the Fleetguard filters FS19599.

I buy with it a 1/2 unf fitting kit of 8mm hosetail, banjo and bolt - to suit my piping arrangement. The bolt is too long for the 1/2 unf housing ! - how do these poeple stay in business ( SSL diesel parts )

Even a standard banjo bolt at 24mm under the head would have been tight - the one supplied was 27mm. I'm so fed up with this - I now have to cut and file the end of the new bolt to make it fit.

To source a new 1/2 unf banjo bolt in 24 mm is not easy - and more postage costs - nobody local stocks them - maybe Western Hose in Weston s Mare might have one.

Its not just the extra length - the shorter bolt has the hole closer to the head - so it lines up better with the banjo housing recess. Its just a cheap crap packed item thats not right that nobody has bothered to see if they actually fit ! It pisses me off - I'm fed up with it.

So - thinking it might actually be a good idea if the mating surface of the spin on filter ring was not just rough casting ! - I removed the centre stub 16mm allen key spigot. I could then get a good look at the porting under it - which was nice and open - I must say.

Under it also was various bits of swarf etc from when they cut the thread !

This is past the filter !

At least the 1/2 unf ports were nicely finished and ground - and generally it a nicely cast unit ( smooth casting ) For £8.99 one cannot complain.

I still cannot for the life of me understand why they put a bleed screw in the head at 'not' the highest point of the housing ! So I have to pivot the head sideways and open the blank screws to fully bleed it out - yawn !

Now the base was clear, I lapped the lower ring on a glass plate I have loaded with wet and dry in a couple of grades either side. Its a very useful thing for flatting things up ! At least now I know the base face is flat !

I sealed the spigot back in with Threebond 1104 - but it hardly needed it as it tightens down to a base boss.

Washed it all through with meths. All sorts of crap came out. Why can't they bother to clean out a filter head after machining it - sort of might be good idea - hey ?

I am told by Western Hose that 1/2 unf is actaully the same as JIC - but Jic has a taper seat. I do note that all cav flter ports at 1/2 unf have a taper seat internally - which is why one can use fitting with either a built in taper seat ( as are my original spigot hosetials ) or utilise an olive type unf fitting.

Any plain screw in fitting has to be under 10mm working length from the washer to the housing - as are the blank plugs - or they bind to the taper seat before compressing the washers. Or don't compress the washers properly - then leak.

There are reasons why I go on about this stuff - if its right it does not leak !

Actually - for a 90 bend out of my primer I could have used a steel olive type fitting cheaper than I paid for the banjo - and its a cleaner run ! One still has the 1/2 washer problem though.

Once over these issues - I do have a nice spin on filter head for £8.99, which takes my old primer unit and accepts Fleetguard water separator filter FS19599 @ £6

My primer pumps into the filter head - so all the filter and lines upstream of it are positive pressure and its a dream to bleed things out.

The first head unit - that went back - was 14mm ports ( which would have eased the washer problem ) but the primer was sucking out of the filter - so the non return was basically at the exit ports - and all the filter body and head was on the suction side of it. That meant you could not use the bulb to bleed out the filter head - it would have sucked air in ! No good to me.

I coud have bought a plain 14mm head ( £10 from biofuel site ) but my primer is 1/2 unf. Add to that it uses a very odd Goodrich style recessed banjo bolt - and the 14mm bolts seem to have dried up ( asap do not have any - I've have not tried Norris ) So I could not even get a remote primer to suit 14mm.

I could have managed to fit my primer 'in line' - using a 1/4 bsp banjo bolt to a 1/4 bsp sleeve - then to pipe - but you cannot get that type of bolt in bsp !

So - the only way I could do a remote primer pumping in to the head - spin on, was as I have done - staying with the plain unf head.

If my 1/2 washer are really nice - I shall brag all round the boatyard - 'my washers are what thy use on steam trains' - 3 fold soft copper - the buisiness !

Right now i'm just thinking - does it have to be this problematic !
Just for a damn 1/2 inch bore copper washer !

Geoff - April 2014

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