Boiler fittings

[modeng2000]

I am making water gauge fittings with a blow-down cock. The cock is a tapered valve much like the normal cylinder cock.

How is it ensured that the valve seats properly in the conical hole? I have seen a nut and captive washer used by Stuart Models to hold the valve onto it's seat but wondered if there are any other ideas in use.

John

[SteveW]

Modeng2000,

Again years ago at school.... The idea was to make a tapered 'D' bit at the same time as making the turny bit of the valve. By same time I mean one after the other using exactly the same top slide setting. It's also worth making a spare valve just incase.

Then make the valve body and use the 'D' bit for the final tarting up of the hole.

As for securing, try a wavey spring washer and a nylock type nut.

It occurs to add that the new boiler regs require that the turny bits for taps and cocks etc. are fully captive.

[modeng2000]

Hi SteveW,

I am using stainless taper pins for the turny bit and the appropriate reamer for the hole. This seems to be a painless way to get matching parts. My only concern about nyloc nuts is what happens to the nylon if it gets hot. I suppose a pair of lock nuts and a washer would be a good alternative.

Fine about the boiler regs, I wouldn't want anything coming apart in use.

I have looked for info on making tapered D bits in my collection of books but can only find out about 'normal' ones. I guess they are made the same way but more carefully!

John

[Tel]

modeng2000 said:

I have looked for info on making tapered D bits in my collection of books but can only find out about 'normal' ones. I guess they are made the same way but more carefully!

John

Pretty much. But you need a short parallel section at the small & big ends of the tapered bit to allow you to 'mike' your way down to the half way point. The bit at the small end can be cut away later - but leave the section on the big end

[modeng2000]

Thanks Tel, once you know most things are obvious aren't they.

John

[SteveW]

Modeng200,

It occurs to me that taper pins are of a taper designed to go in and stay in not unlike a Morse taper. A 'turny' thing for a cock will need a much fatter taper and fat enough to get a cross hole in it without cutting it in half. Also cross drilling a piece tapered SS could be tricky unless you use the valve body or similar jig. Any bur on the SS bit could also compromise the hole.

As for using nylocks I'll buy your point but they're a load less messing about than lock nuts. I know the fibre types can go all unnecessary when they get hot and the all metal type can screw up the male thread if use more than once.

[modeng2000]

SteveW,

I picked up the idea of a taper pin for the 'turny thing' from this site mokei-jouki.hp.infoseek.co.jp/eW-drainsystem.htm

I should have said that I am building a G scale Shay loco so that you have some idea of size.

So far two trial cocks have been successful. The initial burr problem was overcome by drilling from both sides of the 'turny bit' using the body as a jig. A pair of locknuts works but is not too convenient. With a steel thread, perhaps a brass captive nut would work without damaging the 'turny bit' thread. One such nut has a slit part way through from the side and the gap is then closed a bit to make the thread tight. Don't know what it is called and I have only seen them in steel.

I have now read Geo. H Thomas's words about plug cocks and I think I will have to use a steeper taper say something like 10 degrees which is I believe what is normally used. Otherwise binding could easily be a problem.

John

[SteveW]

Modeng2000,

So far two trial cocks have been successful.

I bow to your success, that'll teach me

That URL you offered looked interesting but I still worry that when the cocks get hot the taper pins may get pulled in and either lock on or off.

[Nexuas]

My model of RUSSELL has these taper drain cocks which were fitted by the builder, he said they worked for a couple of outings then seized up. In the end he drilled them through and fitted screw fittings below the cab floor to control the flow down the drain pipe...

[Tel]

by far the best method is to get aholt of a Stuart plug cock & emulate that - they work forever.

As far as setting the nut, take a leaf outta the book of some full sized blokes - let the screwed portion of the plug protrude about 1.5 threads beyond the nut & upset the threads (bash 'em wif a 'ammer)

[modeng2000]

This is to say thanks for all the wisdom you have passed on to me.

I can well believe that taper pin cocks can easily seize up and have decided to go for a steeper taper much like the Stuart type which seems to be about 1:6 instead of the 1:48 of the pins.

I was just trying to avoid some machining I guess!

[modeng2000]

My 'T' boiler for a G scale Shay has just passed a static pressure test. This was I am sure, mainly due to the help I have had from this forum. Thanks.

John