Help with 'Speedy' valve gear and other issues...

[Roger]

Here's a view of the top fittings of the Lubricator, with the Elbow I'm making next.


20180110_110909 by Billy Roberts, on Flickr

So it's the usual setup, with an extension added to the 3D model for it to attach to the collet, and a containment area to make sure it doesn't try to cut it off!

PXL_20240607_211707595 by Billy Roberts, on Flickr

The roughing is done with a 1.5mm Carbide End Mill, with the program flipped in the Y-axis and the 4th axis turned through 180 degrees to do the other side. Obviously you have to clock up the stock to be central to the 4th axis centre of rotation and also set the height to the correct radius, close to the cut. If you don't do this, the two halves won't line up.

PXL_20240607_221155922 by Billy Roberts, on Flickr

The cutter was then swapped for a 1mm Ball Nosed type and the finishing program run with 50 micron overlap (2 thou)

I've made a mistake and didn't allow the cutter to go down far enough to clean up the face where the thread goes...

PXL_20240608_094251678 by Billy Roberts, on Flickr

... so that was cleaned up next...


PXL_20240608_094609392 by Billy Roberts, on Flickr

... and the hole drilled and tapped M1.6

PXL_20240608_095233724 by Billy Roberts, on Flickr

The 3D printed fixture is just a 10mm diameter cylinder x 15mm long with the model subtracted from it. You have to remove any holes in the model else that will leave pieces of the model to remove later. I also added a 1.6mm stalk where the thread goes so that it left a hole for a M1.6 bolt to help with alignment and holding it securely.

I used 7 perimeters to make sure the wall thickness was very strong. The default is 12, and that's a bit too easy to deform.


PXL_20240608_095727777 by Billy Roberts, on Flickr

I left enough of the model sticking out to just be able to get a clock onto it for setting up.


PXL_20240608_101156386 by Billy Roberts, on Flickr

And this is all you get for that effort. I could have made a full sized one in the same time!

PXL_20240608_101500301 by Billy Roberts, on Flickr

I thought I'd have a go at making the Wire type Cool Handle for the Warming Valve. I don't want it to rust, so it's a choice of Stainless Wire or this Phosphor Bronze.

PXL_20240608_192811700 by Billy Roberts, on Flickr



PXL_20240608_194902771 by Billy Roberts, on Flickr

It needs a little more tidying up, but once it's got a little tranished it should look ok.

PXL_20240608_201622034 by Billy Roberts, on Flickr


I cut the heads off four M1.4 screws to make four studs to mount the Dummy Hydrostatic Lubricator. With those in place, I thought I'd have a quick look to see how that looks. Now you can see why I wanted to have it there because it's right in the way of the pipes that need to go down that side.


PXL_20240608_211334331 by Billy Roberts, on Flickr

There are a few more pieces that need to go onto the Lubricator, but I'll do those later. The M1.6 grub screws won't be here for another week or so, but I can now get on with running those pipes and finishing off the parts under the Footplate.

[oldnorton]

Beautiful work Roger. You can rightly take pride in what you are building. I know this loco is going to run, and run well, but I question how much track work you want it to do, or you will destroy so much of its beauty. Yes, run it four times a year, but have another work-horse loco to do the passenger hauling on your home railway?

I only start such thoughts as I face them myself with my reasonably tidy Britannia. I have just replaced the wooden cab floor for the second time as the previous ones could not take the heat. My green steam manifold is turning black as it endures around 40 hours at 160 degC.

I am not wanting to put you off. You have done a superb job. I am only wanting to add some realism to any plans you might have. Put it in a glass box, no. Use it, yes but how much.

Norm.

[Roger]

Jun 9, 2024 17:09:39 GMT oldnorton said:

Beautiful work Roger. You can rightly take pride in what you are building. I know this loco is going to run, and run well, but I question how much track work you want it to do, or you will destroy so much of its beauty. Yes, run it four times a year, but have another work-horse loco to do the passenger hauling on your home railway?

I only start such thoughts as I face them myself with my reasonably tidy Britannia. I have just replaced the wooden cab floor for the second time as the previous ones could not take the heat. My green steam manifold is turning black as it endures around 40 hours at 160 degC.

I am not wanting to put you off. You have done a superb job. I am only wanting to add some realism to any plans you might have. Put it in a glass box, no. Use it, yes but how much.

Norm.

Hi Norm,
I'll run it as much as it interests me. Since we don't have a club track, it won't get used every Sunday. Hopefully I'll get out ten times in a year, but that might be ambitious. It ought to be pretty robust, even though it looks a bit fragile. Everything that has to work is pretty simple, even if the exterior makes it look otherwise. It would drive me nuts to have to keep fixing things and for it to be a nightmare to get apart. I've focused on making maintenance as simple as possible, without compromising too much on asthetics. Time will well whether these ambitions are realised.

In the meantime, I'll keep plugging away on what I find interesting until it's ready to Steam. Hopefully that will be this coming year. I've got the nightmare of painting the Bunker to deal with first!

[chris vine]

Hi Roger,

When you do run it, I think you should used something like distilled water. The salts in ordinary water can make a real mess if there are any weeps. Not that your fittings will dare to leak!!

Also, the lack of muck if you used distilled water will mean there is less to clog up some of your tiny passageways...

Chris.

[Roger]

Jun 9, 2024 18:31:25 GMT chris vine said:

Hi Roger,

When you do run it, I think you should used something like distilled water. The salts in ordinary water can make a real mess if there are any weeps. Not that your fittings will dare to leak!!

Also, the lack of muck if you used distilled water will mean there is less to clog up some of your tiny passageways...

Chris.

Hi Chris,
Weeps! Perish the thought. Seriously though, the sea of 'O' rings ought to make it pretty water tight.

The smallest passageways are in the Whistle Valves and piping. The rest of it is all as large as on any other Locomotive. The insides of all of the functional parts are large, even if the outside might suggest otherwise.

I'll be able to run it on Distilled or RO water on occasion, but realistically it's going to have to run on whatever is provided. I don't want to appear like a Prima Donna and have a pampered and precious Locomotive.

I hear what you're saying though. It would be great if all tracks had an RO system like they have for the Severn Valley Railway.

[92220]

Lovely work Roger!! If you want to use phosphor bronze instead of steel, for any parts, or brass, you can make them look like steel by nickel plating. It is a really easy process. Kits are available on the internet. I bought mine from Chronos, who do 3 different kits. One is a matt finish nickel plate, then there is the Bright finish kit which is highly reflective like EPNS cutlery. The third kit is there Standard finish which is a gloss finish but not as bright as the Bright kit. This one should produce a finish like steel. There is also a company on the 'net, that sells Black Nickel Plating kits, but this process is a bit more complicated. I have a kit but haven't used it yet, so don't know how good it is. Another finish I have just used is a Black Self Etch Primer, made by Paragon Paints, which is part of Stationary Engine Parts Ltd. They also supplied a special thinner for spraying the etch primer. I used it to paint the backhead plate on my loco, which has a load of tiny M0.6 and M0.8 hex head screws. The primer went on so thin, with the Badger 200 airbrush, the screws were all totally visible as if plated rather than painted. It is a really dense Black primer so the coating can be VERY thin and still totally opaque.

Bob.

[Roger]

Jun 10, 2024 10:49:44 GMT 92220 said:

Lovely work Roger!! If you want to use phosphor bronze instead of steel, for any parts, or brass, you can make them look like steel by nickel plating. It is a really easy process. Kits are available on the internet. I bought mine from Chronos, who do 3 different kits. One is a matt finish nickel plate, then there is the Bright finish kit which is highly reflective like EPNS cutlery. The third kit is there Standard finish which is a gloss finish but not as bright as the Bright kit. This one should produce a finish like steel. There is also a company on the 'net, that sells Black Nickel Plating kits, but this process is a bit more complicated. I have a kit but haven't used it yet, so don't know how good it is. Another finish I have just used is a Black Self Etch Primer, made by Paragon Paints, which is part of Stationary Engine Parts Ltd. They also supplied a special thinner for spraying the etch primer. I used it to paint the backhead plate on my loco, which has a load of tiny M0.6 and M0.8 hex head screws. The primer went on so thin, with the Badger 200 airbrush, the screws were all totally visible as if plated rather than painted. It is a really dense Black primer so the coating can be VERY thin and still totally opaque.

Bob.

Hi Bob,
That's a very good point, I hadn't really thought about Nickel Plating.

[Roger]

The dummy whistles are mounted on a little bracket which I'm lucky enough to have the Works Drawing for.

Here I'm machining the holes for the Whistle Elbows and the location for the gusset with a 0.8mm PCB cutter.

The slot goes all the way front to back, but also there's a section where it goes all the way through.

PXL_20240616_131538862 by David Buckland, on Flickr



PXL_20240616_182112604 by David Buckland, on Flickr



PXL_20240616_190302272 by David Buckland, on Flickr



PXL_20240616_200437770 by David Buckland, on Flickr

I decided to make a former and pins to make certain the bend was in exactly the right place...

PXL_20240617_191922907 by David Buckland, on Flickr

... like this.

PXL_20240617_193427091 by David Buckland, on Flickr



PXL_20240617_193540415 by David Buckland, on Flickr

With a little work with needle files, the Gusset fitted...

PXL_20240617_194507007 by David Buckland, on Flickr

... although I should have made the tag stick through a little further. I used the point of a small tap to spread the tag so it held in place.

PXL_20240617_194521251 by David Buckland, on Flickr

Then is was business as usual with a hairpin of 0.5mm Silver Solder wire and Nail varnish.

PXL_20240617_195331812 by David Buckland, on Flickr

I'm resting it at a steep angle to encourage the Silver Solder to create a fillet along the bottom of the gusset too.

PXL_20240617_195743556 by David Buckland, on Flickr



PXL_20240617_200034185 by David Buckland, on Flickr

That seemed to come out ok, so now I can get on with the Whistles themselves. I'm waiting for some other parts to be delivered so I can get back to finishing the Whistle Servo Valve and finish what's under the footplate.

PXL_20240617_203553568 by David Buckland, on Flickr

[Roger]

A bit more progress on the dummy Hydrostatic Lubricator now the M1.6 and M2 Stainless grub screws have arrived from China. I had to buy a 0.7mm and 0.9mm Allen key for those, since they were smaller than any of the ones I've used to date.

The hexagonal caps on the top bar are a slide fit in the threaded portion, held there by a drop of screw lock. The Gland Nuts for the glasses are held on a thread or two of the M1.6 Stainless grub screw, with Screw lock run into the joints. The handles are also held in with Screw lock.

PXL_20240628_210542431 by David Buckland, on Flickr

There are a couple more fittings to make and parts to add to the tall valve on the left, but it's almost finished now.

The 'Glass' tubes are short pieces of 1.5mm diameter Acrylic, turned to length while held in a pin chuck. There's a small error on the bottom bar which I might fix, but it's not obvious unless you know the Lubricator intimately.

PXL_20240628_210641039 by David Buckland, on Flickr

It's quite an eye catching feature on the Backhead, so I wanted it to look plausibly right. It's a lot of work, because there are so many separate parts to make, and they're all pretty small. Making M1 threaded studs and assembling the triangular flange with nuts was very fiddly.

Anyway, I'm pretty happy with it so far.

PXL_20240628_210654721 by David Buckland, on Flickr

[Roger]

This is the Jockey Valve bush and gland. The two separate parts are actually one in this case, with the hexagons turned slightly to make it look like it's a gland that's been screwed in. The hexagons are sufficiently different sizes to be able to machine them both from the end.


PXL_20240704_135921876 by David Buckland, on Flickr

A narrow parting tool then adds the simulated thread.

PXL_20240704_140311189 by David Buckland, on Flickr

The arm was machined from MS rod, first on the end to get the overall profile and the holes...

PXL_20240704_201719744 by David Buckland, on Flickr

Then on its side...

PXL_20240704_204107868 by David Buckland, on Flickr

... so then end...

PXL_20240704_205513366 by David Buckland, on Flickr

... and the inside can be machined.

PXL_20240705_094902019 by David Buckland, on Flickr

I'm using a parallel 0.7mm pin instead of a taper pin. It doesn't need to come off, so it's going to be attached with Loctite.

PXL_20240705_095413478 by David Buckland, on Flickr

The Shaft is Stainless Steel, turned down to 3mm initially so it's rigid enough to set up and cross drill for a Split Pin without deflection.

PXL_20240705_105246549 by David Buckland, on Flickr

That was turned down to about 2.5mm then finished in one cut to 1.4mm to avoid it deflecting too much.

PXL_20240705_110951321 by David Buckland, on Flickr

The connecting link is forked at both ends and joggled, so that's a pain to make. I've used the same method as used for some of the valve linkages. The bar was machined off square on both ends so it was easy to set up in the vice. It was then roughed out at full depth with 0.5mm cuts and then finished with a sharp cutter.

PXL_20240705_202617422 by David Buckland, on Flickr

The end slots are 1mm on one and and 1.2mm on the other, but both were cut with a 1mm Carbide End Mill, not a PCB cutter this time because it would have taken forever.

PXL_20240705_214057523 by David Buckland, on Flickr

The pin holes were then drilled...

PXL_20240706_085927553 by David Buckland, on Flickr

... one end partially cut off...

PXL_20240706_094129950 by David Buckland, on Flickr

... followed by the other...

PXL_20240706_100157857 by David Buckland, on Flickr

... and finally the centre, done very tentatively since it's not held on by much when it broke through.

PXL_20240706_122548110 by David Buckland, on Flickr

The bracket holding the Jockey Valve is joggled, so a forming tool was made for that job. Yes, I know it could have been bent over in a vice, or using the folder, but getting a nice crisp and accurate form isn't easy that way, and it doesn't take zero time.

PXL_20240706_130647936 by David Buckland, on Flickr



PXL_20240707_082759689 by David Buckland, on Flickr



PXL_20240707_082908225 by David Buckland, on Flickr

Anyway, here are those parts, ready for chemical blacking.

PXL_20240707_084145843 by David Buckland, on Flickr



PXL_20240708_193829837 by David Buckland, on Flickr



PXL_20240708_193838482 by David Buckland, on Flickr

Attaching it to the Regulator Flange was almost impossible in situ, so I decided to take that off instead. However, I couldn't pull the bush out of the boiler and had to make a simple puller for that. It uses the studs from the dummy gland to pull it out. It's not a tight fit, but the O-ring makes it sticky. I'll put a smear of Silicone Grease on that when it goes back in.

PXL_20240709_145322051 by David Buckland, on Flickr

So the whole Jockey Valve arrangement looks like this...

PXL_20240709_145649799 by David Buckland, on Flickr

... and this on the Locomotive.

PXL_20240709_152222453 by David Buckland, on Flickr



PXL_20240709_152234411 by David Buckland, on Flickr

[dscott]

Superb as as always Roger.
Just catching up on your progress.

David and Lily.

[Roger]

After much experimentation with the Whistle Servo Valve, I've come to the conclusion that the design won't work. It's fine on air, but on steam it just isn't reliable.

So here's another experiment with a spool valve design instead. Part of the problem with the diaphragm style of valve is that the alignment of the valve element isn't well controlled. The diapragm also has steam on both sides of the diaphragm which reduces the available force to operate the valve.

The design below aims to remove those issues, but will almost certainly introduce other ones. A hybrid design using the best aspects of each might be a better solution. I'll see how this goes first though.

Valve showing connections by David Buckland, on Flickr

The sectioned model below shows one set of innards. The steam for the whistles is introduced at the necked portion of the valve. The O-rings are separated by thin cylinders with cross drilled holes to let the steam through. I copied this idea from a spindle type I used to repair.

The spool is pushed left by pilot air on the 12mm diameter piston which has its other side open to atmosphere.
Once moved, the steam can pass into the LH section where there's another basket type spacer which allows the steam to reach the output fitting.

It's a really simple idea, but it takes a bit of effort to make it into a compact unit for both whistles.

The return spring is shown in its uncompressed length.

A common inlet pocket distributes the steam to both valves.

Sectioned valve by David Buckland, on Flickr

The body is made from SAE660 Leaded Bronze because I've got plenty and it's better than Brass for this. I'm using a 16mm 2 flute indexable milling cutter because I need to machine 30mm long.

PXL_20240817_084726198 by David Buckland, on Flickr

The bores were roughed with a milling cutter, drilled out and then reamed. The covers are held on with M1.6 bolts to keep it small.

PXL_20240817_181010085 by David Buckland, on Flickr

That was parted off...

PXL_20240819_103225541 by David Buckland, on Flickr

... and finished to length with a 62mm facing cutter.

PXL_20240819_160159130 by David Buckland, on Flickr

The port pockets are only 1.5mm deep, just enough to locate the union fittings. The odd shape of the middle pocket is to move the centre line of the port away from the other two.

PXL_20240819_192545774 by David Buckland, on Flickr

A 3D printed fixture allows the 12mm bores to be held centrally for boring in the lathe.

PXL_20240820_111145059 by David Buckland, on Flickr

That's necessary to get them to size and truly round.

PXL_20240820_181244109 by David Buckland, on Flickr

The spool is a piece of Stainless Steel. It's too thin to machine without supporting the end to keep it parallel.

PXL_20240817_204326364 by David Buckland, on Flickr

There's a 2.5mm retaining ring of the O-ring at the end. I've made that with a 5.5mm hex so it's easy to tighten.

PXL_20240821_092007655 by David Buckland, on Flickr

The basket spacers are a simple turning job and a quick job on the 4th axis to add the cross holes.

PXL_20240820_145036115 by David Buckland, on Flickr

This is the large input fitting which ends up being an elogated rectangle.

PXL_20240817_093203825 by David Buckland, on Flickr

The inlet covers for the 12mm pilot piston has an O-ring and M3.5 hole for the fittings I've already made.

PXL_20240817_192317565 by David Buckland, on Flickr

And here all that is, ready for assembly.

PXL_20240821_152122452 by David Buckland, on Flickr

The same techique of masking with nail varnish and thin flux all over was used, although this time I've used chunks of Silver Solder for the joints. It won't need much.

PXL_20240821_182104437 by David Buckland, on Flickr



PXL_20240821_193230375 by David Buckland, on Flickr



PXL_20240822_105545041 by David Buckland, on Flickr

That's now ready for assembling an testing.

I'm fully expecting to have to provide some method of oiling the valve, and also possibly arranging for a needle valve to bleed steam so that it's always hot.

Watch this space!

[simon6200]

I don’t usually comment because I’m stunned into silence. Your ability and desire to work at this scale astonishes me.

[Roger]

Aug 22, 2024 21:19:25 GMT simon6200 said:

I don’t usually comment because I’m stunned into silence. Your ability and desire to work at this scale astonishes me.

That's very generous of you Simon, but it's not as hard as it looks when you have the tools I'm lucky enough to have.

[Roger]

So far so good. The valve works very well on compressed air, even though the return spring is only just strong enough.

Trying this on steam gives different results. The valve opens, but the spring doesn't close the valve. Presumably the Steam increases the friction on the O-rings. I've used Silicone O-rings, but those might prove to be too soft. I think Nitrile ones will be ok, even though they aren't rated to very high temperatures. The temperature they're likely to see is somewhat less than the temperature at the Boiler.

I tried pushing the spool with a piece of welding wire, so simulate a stronger spring. That seems to do the trick, so I'll make some when the new thicker wire arrives from China. I've ordered both 0.5mm and 0.6mm wire which ought to be sufficient.

PXL_20240824_090519522 by David Buckland, on Flickr

I think there are some useful modifications that are worth doing. A rod in the centre of the spool that extends out of the body would allow the valve to be forced closed if it became stuck for some reason. It would also help during the development.

I'll also see if I can add a vent hole top to bottom, at the back of the Pilot Valve piston. That would allow for a pipe to be attached to the top so that Steam oil could be introduced at that point. I'll probably still need some way to oil the inner part of the spool. One thought is to have a one way ball valve that allows oil to enter the Steam feed cavity when the pressure drops.
The main thing is to get the valve to work properly on Steam.

At the moment, the whistle is overblown at full pressure, so that might need a restrictor somewhere to make sure that doesn't happen. However, that can't be too small else it won't work when the pressure is low. I don't think it matters if the whistle doesn't work below say 40psi, because you're not going to be able to drive the locomotive with it that low.

[chris vine]

Hi Roger,

Lovely and elegant too. The servo valve looks a bit like a valve pack on some vintage aero jet engine!

I find that Bongo runs quite well on 40 psi, and gets up quite a speed easily. The brakes and whistle are useless though...

Chris.

[doubletop]

Aug 24, 2024 9:26:44 GMT Roger said:

So far so good. The valve works very well on compressed air, even though the return spring is only just strong enough.

Trying this on steam gives different results. The valve opens, but the spring doesn't close the valve. Presumably the Steam increases the friction on the O-rings. I've used Silicone O-rings, but those might prove to be too soft. I think Nitrile ones will be ok, even though they aren't rated to very high temperatures. The temperature they're likely to see is somewhat less than the temperature at the Boiler.

I tried pushing the spool with a piece of welding wire, so simulate a stronger spring. That seems to do the trick, so I'll make some when the new thicker wire arrives from China. I've ordered both 0.5mm and 0.6mm wire which ought to be sufficient.

PXL_20240824_090519522 by David Buckland, on Flickr

I think there are some useful modifications that are worth doing. A rod in the centre of the spool that extends out of the body would allow the valve to be forced closed if it became stuck for some reason. It would also help during the development.

I'll also see if I can add a vent hole top to bottom, at the back of the Pilot Valve piston. That would allow for a pipe to be attached to the top so that Steam oil could be introduced at that point. I'll probably still need some way to oil the inner part of the spool. One thought is to have a one way ball valve that allows oil to enter the Steam feed cavity when the pressure drops.
The main thing is to get the valve to work properly on Steam.

At the moment, the whistle is overblown at full pressure, so that might need a restrictor somewhere to make sure that doesn't happen. However, that can't be too small else it won't work when the pressure is low. I don't think it matters if the whistle doesn't work below say 40psi, because you're not going to be able to drive the locomotive with it that low.

Roger

Really neat stuff as usual. As you are finding running whistles on steam is a whole lot different to air

A couple of comments; I am assuming that the whistle cluster sits somewhere under the running boards? Surely the mouths should be facing down so that condensed steam can escape easily? Otherwise you will end up with gurgling whistles. (EDIT I have just realised the whistles can be rotated in the carrier frame)

The mouth of the bottom, higher pitch whistle appears too close to the upper whistle and the steam flow could be impacted. It that contributing to the over blowing?

Pete

[Roger]

Aug 24, 2024 21:56:55 GMT doubletop said:

Aug 24, 2024 9:26:44 GMT Roger said:

So far so good. The valve works very well on compressed air, even though the return spring is only just strong enough.

Trying this on steam gives different results. The valve opens, but the spring doesn't close the valve. Presumably the Steam increases the friction on the O-rings. I've used Silicone O-rings, but those might prove to be too soft. I think Nitrile ones will be ok, even though they aren't rated to very high temperatures. The temperature they're likely to see is somewhat less than the temperature at the Boiler.

I tried pushing the spool with a piece of welding wire, so simulate a stronger spring. That seems to do the trick, so I'll make some when the new thicker wire arrives from China. I've ordered both 0.5mm and 0.6mm wire which ought to be sufficient.

PXL_20240824_090519522 by David Buckland, on Flickr

I think there are some useful modifications that are worth doing. A rod in the centre of the spool that extends out of the body would allow the valve to be forced closed if it became stuck for some reason. It would also help during the development.

I'll also see if I can add a vent hole top to bottom, at the back of the Pilot Valve piston. That would allow for a pipe to be attached to the top so that Steam oil could be introduced at that point. I'll probably still need some way to oil the inner part of the spool. One thought is to have a one way ball valve that allows oil to enter the Steam feed cavity when the pressure drops.
The main thing is to get the valve to work properly on Steam.

At the moment, the whistle is overblown at full pressure, so that might need a restrictor somewhere to make sure that doesn't happen. However, that can't be too small else it won't work when the pressure is low. I don't think it matters if the whistle doesn't work below say 40psi, because you're not going to be able to drive the locomotive with it that low.

Roger

Really neat stuff as usual. As you are finding running whistles on steam is a whole lot different to air

A couple of comments; I am assuming that the whistle cluster sits somewhere under the running boards? Surely the mouths should be facing down so that condensed steam can escape easily? Otherwise you will end up with gurgling whistles. (EDIT I have just realised the whistles can be rotated in the carrier frame)

The mouth of the bottom, higher pitch whistle appears too close to the upper whistle and the steam flow could be impacted. It that contributing to the over blowing?

Pete

Hi Pete,
The picture is a little misleading, the whistles do slant down slightly, and the edge of the open mouth is pointing to the bottom. The whistles are actually further apart than they appear, but I hear what you're saying. I'll see how they sound tomorrow in a new Steam test with the modified valve.

[Roger]

I've had another think about the Servo Valve design. It dawned on me that I didn't need to have the third 5mm ID O-ring on the spool if I sealed the spring end and provided a vent hole for the spring cavity to the outlet.

So here's how that looks. I've bored out the end of the body to accommodate a 12mm O-ring in the same way as the Pilot end. I've made a new spring cover that includes the O-ring and is now 1.5mm longer to account for the missing O-ring.

The motivation for these changes is to reduce the friction on the Spool Valve element.

Again, the spring is shown at the unloaded length. It still needs to be slightly stronger in my opinion.

Two ring servo valve by David Buckland, on Flickr

I've also added a new vent hole for the back of the Pilot Piston, this time top to bottom. The hole is 1mm diameter and is offset so that it doesn't break into the Steal Feed pocket. The idea is to add a 1.6mm Copper to this at the top and provide a way to squirt some Steam Oil in there while oiling up.

Drilling this hole is almost impossible in the finished body, because the hole is off centre, and it's not going to enter the opposite side of the bore without deflecting. The solution is to make a 12mm bung that's clamped into the bore so that the drill goes through solid material all of the way through.

So the Oiling hole goes through both Piston bores so that they can be lubricated by a single pipe.

PXL_20240826_183156753 by David Buckland, on Flickr

This is how that looks, ready for testing tomorrow. It works nicely on 40psi using air, but I've learned that this means nothing until it's been tried on Steam. The action does seem very snappy.

PXL_20240826_200129101 by David Buckland, on Flickr

I'm currently running this on Silicone O-rings but they might be a bit soft. I've ordered some FKM O-rings which I think might be a better choice. We'll see. Those are coming from China, so I can't try those yet.

[ianholder]

Hello Roger, I have always found that viton o-rings work for me. But I am interested to know why you are going to China when all types of o-rings are readily available here. I have used Simply Bearings whenever I need them and they usually come by return. They have a vast range of sizes in all materials. Regards Ian ( I am only a customer of Simply Bearings)