Coal fired Garratt K1

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Trevor Thompson
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Coal fired Garratt K1

Post by Trevor Thompson » Mon Dec 21, 2020 5:42 pm

I have put Linda aside and have got the Garratt out to sort out a number of issues:
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The locomotive almost works. The boiler works the fire works. I can get and maintain steam. Both units work on air but of course there are minor air leaks which prevent it actually running on steam. The radio control works.

There are a number of modifications I want to make:
  • replace the ball joints which transmit the steam to the different units.
    modify one of the valves on the front unit.
    make sure the articulation is sufficient for 4ft 6inch radius curves.
    replace the clack valve the one I have has never worked properly and move the clack valve so it is closer to the water pump.
    change the water level indicator for an electronic one like in Linda.
The biggest problem is the water pump which has stopped working - just when I thought I had it run in and working well on steam - and pumping as well. It is a Weir pump which means that it is a steam driven pump. I went for that because it works when the loco is stationary and it does not need a flexible pipe to get the water from a bogie to the boiler.

This is a short video to give a flavour of the pump operating: https://www.dropbox.com/s/qsoyofz2jut5r ... 1.m4v?dl=0

A Weir pump has two valves one on top of the other. So it is more complicated than a cylinder to drive a locomotive. The upper valve is knocked across when the piston reaches the end of its travel. That makes the lower valve move (its pistons are in the extensions to the valve chamber), and that in turn controls the piston.

I have stripped it down (yet again) to work out what has happened.
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I can see straight away that the valve faces are worn where the valve has been moving back and for.
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I started out honing the faces and valves.
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Then I stopped. I realised that it will just wear again. I need to rethink this.
Perhaps the valve is too small. hence the wear. It shouldn't be lubrication.

So Im giving this some thought!

Trevor

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Mon Dec 21, 2020 11:22 pm

I have thought about a total redesign of the valves. Making the lower valve central on its face, and that valve chamber thicker. Putting the top valve face on the side of the first and modifying the actuation mechanism.

Ive come to a conclusion: There isn't anything fundamentally wrong. It is just that the valves themselves are too small and the area in contact with the face is too small. So perhaps a minor redesign - just to allow the valve to be a bit bigger.

So I had a look at some of the drawings for cylinders I have filed away and noted the circular valves shown are in the order of 10mm OD and 6mm ID. Lets see if I can design valves with this sort of cross section without having to start making too many bits from scratch.

Trevor

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Re: Coal fired Garratt K1

Post by -steves- » Tue Dec 22, 2020 7:55 am

I can see this being a cracking bit of engineering work, following with interest :thumbup:
The buck stops here .......

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Tue Dec 22, 2020 7:39 pm

So I have been working on the valves today. But first for anyone who is interested in how this pump works:
feed pump.jpg
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A diagram showing how it works. follow the steam from the top through the top valve to operate the shuttle valve and then to drive the piston. When I first tried to make this I thought you could use a valve to make the piston move - just like in a locomotive cylinder. What happens ( I tried it of course) is that the piston oscillates with the throw getting shorter each time until it stops mid stroke. by mechanically isolating the top valve (which is operated by the piston connecting rod movement) from the valve controlling the piston, the piston is able to move through its full stroke before reversing direction.

I am making a new cylinder/valve chamber for the shuttle valve to operate in, and setting the valve in the middle of the face so that I can use a bigger valve. It is going to be taller so the top valve is going to go on the side of the shuttle valve chamber. So firstly a false valve face with new valve ports is needed. I have used lock tight to bond a piece of brass underneath the old valve chamber. I have drilled through the holes which hold the valve chest down so that the new face will fit on the studs:
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I have also drilled new valve ports using the dimensions I metioned above. So 1.4mm diameter holes 4 mm apart. I have used the milling machine cross slide to make those measurements.
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I have fitted the valve face to the cylinder, mounted it in the vice and drilled through the 1.4 holes just enough to pop the surface of the cylinder:
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Re: Coal fired Garratt K1

Post by Trevor Thompson » Tue Dec 22, 2020 9:13 pm

The last photo (in the last post) showed the three holes popped into the surface of the cylinder. You can see the original valve ports to the left of the photo. There is also an exhaust drilling sitting on its own at to the right. The new valve face has been taken off and is sitting on the vice.

The original valve face is now modified by milling slots 1.5mm wide in its face . These slots link the new ports with the old ones. a slot in the large exhaust hole to that exhaust drilling mentioned above:
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When i was milling the slot on the left the pump moved in the vice - that is what caused the misshaped slot. Luckily it didn't break through into another slot, so I will try it as it is. My plan is to use some special locktite gasket compound which I have to bond the new valve face to the old. It isn't a permanent bond - but it isn't far off permanent!

Now to make a new shuttle valve chamber. Firstly a blank of 15mm thick brass, cut to length. The new valve face has been temporarily bonded to it with locktite. once it has set the mounting holes can be drilled - and then we need the four jaw chuck in the lathe.
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Re: Coal fired Garratt K1

Post by Trevor Thompson » Wed Dec 23, 2020 7:21 pm

I have now faced both ends of that new valve chamber, drilled and reamed it 7mm diameter for the shuttle valve to run in. Its now in the milling vice and a 10mm diameter hole has been drilled through it:
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I have a milling cutter just under 10mm diameter in the chuck (I now I should get the collets out) and I am going to mill 2mm each way and then just open up the ends so a 10mm diameter valve will slide in it. I want 4mm throw on the valve - but I want to keep the overall length of this chamber as short as I can. The final length can be adjusted later.
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This is the result fitted. Looks OK so far.

Im thinking about where the various drillings will go to connect the ends of the shuttle cylinders to the valve ports on the the next level up - before I start drilling.

I have glued a blank port face on to the side of the valve chamber:
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The face plate is just temporary - it provides the port spacing. You can see I have popped the exhaust passage onto the bottom of the valve chest, and when the glue is hard I will pop the 3 port holes through as well. The central port (exhaust) should line up with the exhaust drilling. Its this drilling which will connect the exhaust from the top valve to the exhaust line. I am keeping this set of drillings fairly high up in the valve chest so that there will be room in the lower part for a steam supply drilling to supply steam from one valve chest to the other. Only one steam inlet connection will then be needed. So todays final photograph:
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Just as a reminder to myself I placed all the bits I want to reuse next to the old valve chamber. I have to be careful with the drillings to keep clear of where the holes for holding these end covers on go. Or at least I have to think through where the cover holes go compared to the steam drillings. Its the steam holes I have decided on.

You can see the shuttle pistons with their O rings. Those slide nicely so I want to reuse them. They are too far apart. With the old chamber I had to assemble the shuttle by fitting one piston fitting it into position and then fitting the other. The hole through is smaller than the cylinder as you can see in the photo. I had lots of trouble getting the pistons to stay put - they kept unscrewing. I am making the new one with a 7mm bore all the way through. Now I will be able to assemble the shuttle with permanent locktite before fitting it. Or maybe make it in one piece and make new pistons? Tempting - it couldn't unscrew then!

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Re: Coal fired Garratt K1

Post by -steves- » Wed Dec 23, 2020 8:38 pm

I am not saying much, but I am following this with a very keen interest :thumbup:
The buck stops here .......

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Fri Dec 25, 2020 9:55 pm

I am going to drill those passages to take steam from the valve ports to the ends of the shuttle cylinders. Its always a bit tricky doing this - one slight error in drilling and it wrecks the component.
I have measured carefully and marked where the holes have to go, there is just room to avoid the fixing holes (as long as the drill goes in true)
The first thing is to clamp the block and ensure it is level - so that the drill goes straight down:
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I have centre punched where I want this hole to go - and measured how deep it can go. I want to drill far enough to intersect the hole which comes from the side, but not far enough to break through. So I just let the drill sit on the surface and zero the dial on the mill head:
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Having drilled to the correct depth - 12.3mm in this case I re-nounted the block and drilled the other hole. This time drilling down through the correct valve port, and to the measured distance. Rather than just drill using the lever to press the drill down I like to use the vernier depth wheel, it is a milling head. Sometimes the drill can snap as it breaks into the other passageway - and this way it doesn't drop and catch as it breaks through.

I have an air line from the compressor in the garage next door, to I can blow air into the drilling to see if it comes out the other end - and it it comes out of anywhere it should not come from!
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So this is the block with the holes down from the valve ports and in from the cylinder ends:
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The next stage is to drill from the end of the cylinder into the passageway. Firstly a 1.5mm mill to create a flat into which I can drill (without breaking a drill). Note that it is offset compared to the cylinder bore - but it is in line to hit the steam passage:
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Now without moving anything centre drill:
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and finally drill into the steam passage. I know when its through when scarf is visible in the passage:
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I usually tap the end of the hole in the face 10BA, and insert a bit of 1.6 brass rod also tapped 10BA, just far enough that it doesn't block the drilling into the end of the cylinder. In this case I might just use the end covers to block them off.

End covers, shuttle and valve next.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Tue Dec 29, 2020 9:28 pm

The end covers, shuttle and valve, are ready:
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It all fits, and the throw is correct, and limited by the hole in the chamber, so an improvement on my last attempt. Test assembly tomorrow and then to make the second valve.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Mon Jan 04, 2021 6:07 pm

Now I have both valve chambers and their valves made.

They are trial assembled while I wait for more 8BA studding to arrive (for the second valve chamber):
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You can see the temporary bolt heads. I did manage to reuse a few components but made far more than I intended from scratch. The valves and faces are lapped, and it is all ready for final assembly.

Of course it needs testing to make sure it actually works, and then I have to modify the mechanism which causes the piston movement to flick the upper valve.

Then I can start to modify the loco!

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Wed Feb 03, 2021 6:56 pm

An update:

I have assembled the water pump and tested it on compressed air. A video of this operating manually in the half complete state can be viewed here:

https://www.dropbox.com/s/ozg7lapmczas7 ... t.mp4?dl=0

As you watch it you will notice the following:

1. the water pump piston moves in the same direction as the valve stem ( I wasn't expecting that - and will take that into account shortly.
2. the piston snaps across firmly - but there are some times when it doesn't move in response to my moving the valve.
3. when it fails to move you can hear a hissing sound

So what is going on?

The valve which is controlled by the valve rod is tilting inside the chamber as I move the valve stem. As it rocks it allows air to go down the exhaust drilling - hence the hissing, and of course when that happens the valve does not operate the shuttle valve and the piston does not move.
If I move the valve rod slowly (and carefully) it doesn't rock - and then the piston moves properly.

So I am going to try to apply a bit of downward pressure onto the valve itself - a thin bit of bent brass perhaps to stop it rocking. I also noticed that when I let go of the valve rod the rod tend to be pushed outwards. That is something I will also have to fix. Perhaps the same bent brass will fix both issues?

So I will fine tune this before making the new feedback mechanism.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Wed Feb 03, 2021 9:19 pm

As a change from thinking about pumps I had a go at some of the other alterations:
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This is the cab removed as far as I can without disconnecting all the servos. I have dismantled the steam manifold which sits on top of the red O ring, and removed the top connection for the water gauge. That is where I am going to fit an electronic water gauge sensor.

It was quite a bit of dismantling - 4 servos to disconnect, and 4 steam valves to be separated from their pipework.

I have modified the boiler fitting, turned a PTFE bush to fit into it and made a brass sensor. To be specific I bored the boiler fitting 3mm, turned down a length of 4mm PTFE to 3mm OD, and pressed the PTFE into the hole in the boiler fitting. then I cut the PTFE so 3mm stuck out from the boiler fitting, and bored the boiler fitting again in the lathe to 1.8mm diameter. Having reduced the end of a brass rod to 1.78mm diameter I was then able to press the brass into the hole in the PTFE. The brass rod had already been cut to length and had its small end tapped 10BA.
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The sensor complete with PTFE washers to insulate an electrical connection to the outer fitting from the inner core. Of course I had worked out where the water level in the boiler should be, and established from that how long the sensor needed to be to just reach the water.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Wed Feb 03, 2021 9:26 pm

So the cab back on and the sensor in position. The cables have also been run around the top edge of the cab. One yellow one pink.
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While the cab was off I removed the old clack valve and replaced it with a plug. It sits below the valve in this photo - and removed a plug which was blanking off the whistle steam supply.
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So tomorrow a whistle valve to fit onto that thread in the middle of the photo. The servo is already fitted and connected.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Thu Feb 04, 2021 6:37 pm

I had made the whistle and valve when I was making these for Linda. It should have been a straight forward job to fit them, but of course it was a bit more complicated than that.

Anyway its fitted:
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I just have to connect it to the servo arm with a bit of bent wire, and reverse the servo throw. The servo is in the top right of the photo.(there are 5 servos in the cab - but there will; still be room for a driver and a foreman)

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Thu Feb 04, 2021 6:44 pm

So back to the pump.

I have removed the cover of the first valve chamber and cut up a bit of brass sheet to make the shaped piece to the left of the pump:
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There is a hole in it because that could line up with the steam supply pipe and I don't want to risk blocking it. The amount of bend is created using trial and error. I just want it to touch the lid and touch the valve without applying too much pressure:

This is it fitted:
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I have replaced the cover and will test it when the gasket compound has had overnight to set.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Wed Mar 03, 2021 8:25 pm

I have just about finished the pump.

I have soft soldered the two new valve faces into position, using PTFE tape inserted into the steam drillings to try to prevent them filling with solder. It worked. In fact I pre-soldered each face carefully and held them together while I just melted the solder. I think the technical term is "sweating".

I have made a few more new components - particularly the tube which connects steam unit to the actual pump. It has a slot in a different place, and the rocking arm which moves the valve. I had to make that a few times to get the motion right.

So here is a short video of the pump running (dry) on air at 12psi:

https://www.dropbox.com/s/5qr4xtcic7cwd ... 1.m4v?dl=0

I might make a better rocking arm - the one in the video obviously does the job but it could be improved. I am after reliability! By the way the pump starts whenever the air valve is opened - no hesitation and it doesn't mater what point in the cycle it had stopped at. So I am happy.

A few final adjustments and it can go back onto the loco. Then on to clack valve and piping.
Last edited by Trevor Thompson on Sun Mar 07, 2021 8:48 pm, edited 1 time in total.

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Re: Coal fired Garratt K1

Post by Keith S » Thu Mar 04, 2021 2:00 am

I am always astonished at what people can make at home when they have the appropriate skills. That little pump is a miniature marvel.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Thu Mar 04, 2021 7:54 pm

Thanks Keith, it does look the part. I have got this far before (twice) but it has taken this third attempt to really get it to work reliably and consistently. The key was the larger sized valves.

I thought it worth testing that it actually still pumped water before fitting it back under the loco. So some video if it moving water and pushing it through a 1mm diameter nozzle (to simulate back pressure):

https://www.dropbox.com/s/y3uobu7ijla2t ... 4.m4v?dl=0

So having established that it is worth fitting - I removed the subframe from the chassis and adjusted the fixings:
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looking from the other side it was clear that the steam inlet arrangement needed modifying (the pump is now wider and fills more of the space under the boiler):
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It is that threaded fitting which takes the steam pipe and the pipe would touch the bracket for the dummy air reservoir - the black tube. So modify that tomorrow, and refit it all, then perhaps the clack valve!

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Fri Mar 05, 2021 10:02 pm

The pump is back in place on the loco.
IMG_1385.jpg
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Many of the features of the prototype are incorporated in my model (and that is part of the issues of getting it to work properly).
The water from the two tanks enters pipework in the ends of the chassis, and then along a pipe on the right hand side of the loco just below the footplate - its the black tube running along the middle of this photo. Here we diverge from the prototype in that the water goes down the brass tube in the centre of the photo and then through a copper tube to the bottom of the water pump. In the prototype the water is taken off further to the rear and goes to injectors. In the photo there is a brass pipe at an angle. This has the Goodall valve in it, and a non return valve. It means that the boiler can be filled using the usual plastic bottle if required, and the pump and pipework can be primed before use. The non return valve stops the water pumped by hand from just feeding back to the water tanks. Looking at the back end of the pump the water feed pipework looks as though it is going to hit the track. It is actually just clear - but there is is no reason why the whole pump cant be raised a bit to solve that is it is a problem in action.

From underneath the loco:
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The clear plastic tube in the centre of this photo is the exhaust from the pump with a copper pipe leading into the smokebox and ending up alongside the blower nozzle. The exhaust from the pump does seem to augment, and perhaps even replace the blower, to keep the fire alight. Behind (and therefor above) the clear tube is a copper pipe which supplies steam to the pump. This supply has its own displacement lubricator and that is just to the top right of the photo, just above where the plastic pipe becomes a copper pipe. The clean brass hexagon, is the drain for the lubricator. The outlet from the pump has yet to be connected (threaded outlet on the left of the photo) and we need a clack valve to connect it to.

The front bogie, which is the low pressure end, is on the right of the photo just on the edge of the photo. You can make out the front cylinders, top and bottom. There is a hose connector visible between them. This is where the intermediate pressure pipe (which takes the exhaust steam from the high pressure unit (rear bogie) to the inlet for the low pressure unit (front bogie) fits. This long pipe under the boiler is a very visible feature of the prototype. The black brass block on the end of that hose connector was my first attempt at a steam operated simpling valve - which of course didn't work!

That is something which will feature here shortly. I think I now know how to make a steam operated valve to allow the loco to start off in simple expansion mode - and then revert to compound mode when moving.

Anyway - the clack valve first.

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Re: Coal fired Garratt K1

Post by Keith S » Sat Mar 06, 2021 5:43 am

"Simpling valve" is a term I'm familiar with from marine compound engines. I had no idea locomotives employed this as well. At the risk of sounding over-enthusiastic, I am really enjoying your efforts to include these "complications" (and I'm deliberately using a watchmaking word here) on your model.

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