70036 Boadicea

[92220]

Hi Joan.

Interesting check valve designs. However, the ball valve design looks a bit strange, and maybe unfinished. There is nothing holding the o-ring in place. The spring loaded ball can lift the o-ring and the valve won't seal. The ring need holding in place, mechanically, and unless the sealing is actually done by the ball in the tapered bore then it won't seal as drawn. Maybe there should have beeen a short piece of tube, that has been omitted from the drawing, on the left hand side of the valve, to trap the o-ring.

Bob.

[92220]

Hi Jim.

Another point that has just come to mind.... Roger, a while back, in his Speedy thread, suggested that silicone carbide balls would be a better bet than stainless balls. They are harder and also much more accurately spherical. They are also available cheaply on Ebay.

Bob.

[Jim]

Thanks Bob, As things stand the SS 3/16" ball is sealing nicely so I'll leave it as is. As an alternative I have some 3/16" Nitrile balls on stand by but I've not had any problems in the past with the stainless balls on a bronze seat.

Jim

[Roger]

May 7, 2018 8:06:43 GMT 92220 said:

Hi Jim.

Another point that has just come to mind.... Roger, a while back, in his Speedy thread, suggested that silicone carbide balls would be a better bet than stainless balls. They are harder and also much more accurately spherical. They are also available cheaply on Ebay.

Bob.

Just a correction, they are 'Silicon Nitride' balls, the same as used in High Speed Precision ball races. These are much lighter and harder than equivalent Hardened Steel balls and many times harder than Stainless Steel ones. As Bob points out they are almost certainly ground to better tolerances so they have a better chance of seating regardless of which way they happen to come to rest on the seat. You can also press them firmly into the seat to form the shape without fear of distorting the ball. If there's a down side to them, I've not heard of it yet.

[92220]

OOoops!! Sorry Roger, and Jim, for the mistake. It was only just gone 9am and I hadn't yet had my morning coffee to wake me up!! Yes there is a world of difference between silicon carbide and silicon nitride!!

Bob.

[92220]

Hi Roger and Jim.

I've just done some investigation into my mistake, to see just what the difference is. Actually I find that silicon carbide is used for making high precision ball bearings, as well as silicon nitride, though the silicone nitride balls appear to be the ultimate in hardness and accuracy. So it would seem that either is better than stainless balls.

Bob.

[JonL]

What a fantastic thread. I'll never get those hours of my life back but what a great read. I hope I can get close to that standard of engineering some day.

[Jim]

Aug 1, 2018 20:01:17 GMT JonL said:

What a fantastic thread. I'll never get those hours of my life back but what a great read. I hope I can get close to that standard of engineering some day.

Thanks for the very nice comment.

It's been great journey I must say and with more yet to come as I do a couple more steam ups here at home on my Heath Robinson test track, I haven't posted photos of it, I'd be drummed out of the Brownies if I did

I want to be certain everything is working as it should and that the airflow through the rosebud grate along with the adjustments to the petticoat pipe have improved the overall steam raising abilities. I've also taken delivery of a bag Welsh Beans as the fuel I had was a bit on the iffy side given it was a combination of coal from an unknown source and some left over char from 'somewhere'.

Given it's a fair drive to the club and back I don't want to get there only to be told 'Not good enough go home and do it again!' In truth they wouldn't say that, they're a great group of modellers and very supportive too.

Jim.

[terrier060]

May 5, 2018 8:45:50 GMT joanlluch said:

May 4, 2018 23:00:57 GMT Jim said:

I'm remaking the valve seats in the top feeds as I'm not happy with the PTFE ones supplied.

...

I follow Everett Clem's data sheet on ball/hole dimensions when making clack valves. I've always used stainless steel balls and have never had a problem however this case seems different due I suspect to the valve seat material plus the fact that the valve seat is a separate component secured with a screw down ring and resting on a ledge in the valve body so raising the possibility of steam leaking past the actual seat.

Jim

Hi Jim,

It's good to have the valve seats as a separate component as you have, but of course they must be properly statically sealed. I'm sure you are aware of what I used for the water valve seats in my pump. This is the link to the photo in Flickr flic.kr/p/HtYNEQ and this is a quick 3D rendering of the design flic.kr/p/26LSZk5. There's an upper o-ring sealing radially against the body of the valve, and a lower o-ring sealing axially against the bottom part. Of course in reality the o-rings shown in the drawing get compressed rather than interfering the rigid part, but you get the idea. Maybe you can adapt something of it to prevent leaks around your seat component.

Using PTFE as the seats material does not seem a good idea because it's too soft. PTFE is an excellent material for both static and dynamic seals, but it must be understood. Despite it is relatively rigid and we may be tempted to use it as such, we must think of it as a deformable material which ultimately keeps rubber like properties for the last bit of its deformation. In practice, all properly designed applications with PTFE sealing components must set a physical mechanical limit to the PTFE deformation in order to take advantage of that last bit of elasticity that remains after the bulk of the permanent deformation has taken place. From a mere design point of view it's not that different than using rubber o-rings except that the range of elastic deformation in rubber is much extended and allows for more permissive designs. The case of PTFE being used as a seat of a ball check valve does not meet that criteria and thus I'm not surprised that it is causing problems.

Just as a matter of general information, check valves using rubber o-rings as the sealing material for the seats are standard in the industry and are the ones that offer the best performance. Again, they are designed to have a mechanical limit to the (elastic) deformation of the o-ring. This is an example of what I mean that I just found on the internet Check Valve Drawing . The o-ring can not be unlimitedly pressed by the back pressure, but just up to a certain extent set by the geometry of the valve. This is another example I found using a ball in this case Ball Check Valve . Again, the o-ring on the seat can only be pressed up to some extent until the ball reaches a stronger mechanical constraint.  

I hope this is informative.

Joan




It is interesting that Joan mentions the use of rubber 'O' rings in check valves, as I have just taken apart two check valves on the steam launch that I am helping my friend with.  The new boiler is rated at 200psi and all the check valves have 'O' ring seals!

Ed

[Jim]

Thanks Ed, Joan's comments are informative and helpful.

I suspect the use of PTFE valve seats was a quick and cheap option, especially when the valves arrived with a caution 'that the valves would leak for a while until they bedded in.' With the benefit of hindsight the valve should not have been sold unless it was working properly.

Jim

[Jim]

Just an update after taking a break to attend to grandfather duties.

I've been working making a container for transporting 'Boadicea' on the journey to the club. As you can see it's nothing more than a box utilising the steel transfer ramp to double as a lid. Once in the back of the X-Trail it will secured by straps to ensure it doesn't move.

A trial fit was called for to make sure I hadn't miscalculated anything. Fortunately I hadn't plus it was good to have a trial run at transfering what is a very heavy locomotive, from the hydraulic lifting table to the new transport box/

Now the box is finished I'll start making the securing/locking points for the loco to ensure it can't move in transit or accidentally when being unloaded.

Once completed there will be a final steam up to ensure all is working properly before making an appointment with our boiler inspector followed hopefully with a trial run on the club track.

Slowly getting there,

Jim

[simplyloco]

Hi Jim
I must be making progress and anticipating completion as I've made exactly the same thing already!
John

[stevep]

Jim,

On all the transport boxes I have made for my locos, I have had one end fixed, and attached a piece of wood across the end (on the inside), just above the height of the buffer heads. When the engine is in the box, it is prevented from bouncing up and down, and potentially hitting the lid of the box.

I have made the other end fold down for a loading ramp. So I had a separate piece of board that fitted inside this end, again with the cross bar just above the tops of the buffers.

Hope that might help...Steve

[Jim]

Thanks Steve that is just what I had in mind for the front with a stop at the rear with a bar to lock into the loco's rear coupler pocket.

Jim

[racinjason]

Jim when are you planning on coming over I would like to come and see it in the flesh
Jason.

[steamer5]

Hi Jim,
I’ve got an open frame that then has a PVC cover that zips up on 2 corners & has a bunch of clips that go thru eyelits, no idea what they are actually called, that keeps the rain off.. The fixed end has a lump of wood with holes drilled so the buffers fit in, the open end has the same idea for the tender. A trimmed blocks that fit under the loco rear buffer, a bolt then pulls down on the top of the beam & to lock the loco down onto the block. Holds it all nice & firm.
The frame is bolted down to the trailer. Held it nice & firm when the wheel came off the trailer when dad was towing it!

PLEASE make sure that what / how ever you tie her down to your XTrail it’s very well held.....don’t want all that hard work getting bent!

Cheers Kerrin

[Donald G]

Hi Jim
On my loco boxes, I have added an extra piece of plywood in the closed end at buffer level with two holes, these are at buffer spacing which allows the buffers to locate in the sockets and therefore stop both vertical and sideways movement of the engine.
Keep up the good work, it will be great to see it running and you enjoying all the years of work you have done

Donald

[Jim]

Aug 17, 2018 8:59:19 GMT racinjason said:

Jim when are you planning on coming over I would like to come and see it in the flesh
Jason.

Hi Jason,

I have a couple of jobs and a trip away so no exact date yet but will give you a heads up when the big trip is on. Be good to meet up too.

Jim

[Jim]

Aug 17, 2018 9:17:52 GMT steamer5 said:

Hi Jim,
I’ve got an open frame that then has a PVC cover that zips up on 2 corners & has a bunch of clips that go thru eyelits, no idea what they are actually called, that keeps the rain off.. The fixed end has a lump of wood with holes drilled so the buffers fit in, the open end has the same idea for the tender. A trimmed blocks that fit under the loco rear buffer, a bolt then pulls down on the top of the beam & to lock the loco down onto the block. Holds it all nice & firm.
The frame is bolted down to the trailer. Held it nice & firm when the wheel came off the trailer when dad was towing it!

PLEASE make sure that what / how ever you tie her down to your XTrail it’s very well held.....don’t want all that hard work getting bent!

Cheers Kerrin

Hi Kerrin,

Thanks for sharing your ideas re securing the loco during transit. I like the idea of the buffer locking device. Because of the loco's length I will be transporting the tender as a separate item in its own box.

I'll certainly make sure the whole set up is securely tied down and unable to shift. Apart from not wanting to have the loco join me in front seat after braking for a roo the wheat trucks have created some pot holes that tend to rattle the teeth.

Cheers

Jim

[Jim]

Since the last post a bit more progress has been made with the Britannia's transport box in that the rear securing point has now been brazed up and fitted.

As the photo shows the securing post is in place in the box so that as the loco is rolled backwards into the box the long tongue slides into the draw-bar pocket under the cab preventing the rear of the loco from lifting in transit and with the coupling pin in place, preventing it from moving forward.

The next job will be to fit the rear panel to the end of the box and then start work on securing the front end of the loco. Even then it won't be over as I still have the box for the tender to make.

When I started on this project no one mentioned all the extra bits and pieces you needed to get the pride and joy safely from A to B while avoiding kangaroos, wombats, pot holes and other daft drivers.

Jim