Coal fired Garratt K1

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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:
IMG_1379.jpg
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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:
IMG_1383.jpg
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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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Re: Coal fired Garratt K1

Post by Trevor Thompson » Sun Mar 07, 2021 8:48 pm

Keith S wrote: 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.
There have been a few locomotives which have been compounds. The LNWR had one designed by Webb, in the 1870's (if I remember correctly) and of course K1 in 1914. There must have been others - but certainly in the UK they were never very successful. The Webb one seemed to refuse to start after it had been backed onto its train.

Perhaps it was more successful on the continent.

Certainly the concept of K1 was sound enough. For example the 1914 Fowler steam lorry had 2 cylinders, was a compound, and a simpling valve for starting, and that seems to have been a success.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Sat Aug 14, 2021 8:50 pm

Now that Linda is working I have come back to K1 and that clack valve.

So my sketch and the components placed on the book in an appropriate place:
IMG_1687.jpg
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The top component is the ring for the banjo bolt to pass through, the second down is the banjo bolt. The third is the body of the clack valve with its "lid" below it. You might notice that I have made grooves in the faces to locate O rings. 5mm OD and 1mm CSA for the banjo and 5mm OD and 1.5mm CSA for the lid. The black thing in the fold of the book is a 3mm diameter nylon ball. I hope to avoid the pitfalls of leaking stainless balls. The assembly didn't quite go to plan as a straight pipe joining the two main components together fouled the boiler. So I rotated the banjo ring so that the 3mm hole in its side was at the bottom, used a bent copper pipe and fitted it into the side of the clack valve. I kept the pipe joints tight in the fittings so that they would stay still while soldering them. Needless to say I assembled it all and positioned all the components at the right angles before taking them off the loco for soldering.

The components assembled and silver soldered together:
IMG_1689.jpg
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The pipework was not too difficult to make up - it just needed annealing a few times and careful application of a bender. Just needs fitting and testing.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Sat Aug 14, 2021 8:54 pm

And to fit it onto K1:
IMG_1691.jpg
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Connection to the boiler, with the clack valve widen partly inside the frame:

and from the bottom showing the pipework connected to the pump:
IMG_1690.jpg
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Will it work? Not just the clack valve but the pump as well!

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Tue Aug 17, 2021 12:59 pm

So to test the pump actually puts water into the boiler (against boiler pressure) I have set it up on the bench.

I had a few problems with what I had already done - firstly the sensor wasn't registering water level and that was a combination of two things. Firstly I had used lock tight on the fitting into the boiler - and that was insulating the sensor body from the boiler. Should have known that might happen. But it is remarkable that lock tight will actually insulate that well! Secondly I wasn't connecting the wires accurately into the socket to the circuit board through the holes in the black box. Of course the cab had to come off to sort the first issue.

So after establishing that it worked when I poured water into the boiler I then took water out until the red light was lit and connected to the air line:
IMG_1694.jpg
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This is it pumping water into the boiler, you can just see the light on the box is green - and it certainly isn't red - the pump is actually running on the 50psi fed into the boiler through a fitting in place of the safety valve.

The cab is back in place and most of the servos reconnected to their controls. The whistle servo and the blower servo both need their operation reversing. I have lived with the blower operating in reverse but the whistle has to be reversed before I connect it. I have had a prog 3 sitting in the cupboard for a while and have never dared to try to reprogram the Rx 102 - really struggling to understand channels and pins and the method of programming it. That video which Rik created was really useful and gave me the confidence to have a go.

Well I got there! Its a bit convoluted, transfer the function to channel one, reverse it, reconfigure it to the original pin, twice of course. then reprogram channel 1 to control the regulator again.
IMG_1696.jpg
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I couldn't help connecting the controller and giving the servos a final twirl when I had it assembled again, and of course the unexpected happened. As I changed from forward to reverse the green light changed to red - and vice versa. Most odd! Certainly not water level causing that.

I have worked it out - I used a servo plug and wire attached from the spares box to take power from the only spare set of pins on the receiver for the water circuit. I think it must have been wired up for an LED - and it is getting its positive from the top pin, not the middle pin. Solve that easily enough by taking the pin out of the plug and putting it into the correct hole.

I don't suppose I can put off a steam test for much longer?

Trevor
Last edited by Trevor Thompson on Wed Aug 18, 2021 9:22 am, edited 1 time in total.

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Re: Coal fired Garratt K1

Post by philipy » Tue Aug 17, 2021 1:16 pm

Glad you sorted your tribulations.:D
Trevor Thompson wrote: Tue Aug 17, 2021 12:59 pm
I don't suppose I can put off a steam test for much longer?
Garn...you know you want to!!!
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Re: Coal fired Garratt K1

Post by Trevor Thompson » Mon Feb 21, 2022 10:41 am

Having put this locomotive to the side for some months - I have picked it up again. I HAVE to get it to work!

So I left this with the water pump ready to steam test. That test ended up with the pump full of condensate and unable to move. So I made automatic drain valves and fitted them to the cylinder and tried again. I couldn't understand why it had locked solid, but eventually (after a lot of head scratching) worked out that in clamping the pump up under the chassis I had distorted the shaft line so that the pump ram couldn't move. It just needed the fixing screws to be loosened slightly for it to work.

Lots of adjustment of servos, valves and got me to a point where everything was fine - except for the valve gear. I couldn't quite get the settings right for it to work properly - the motion was jerky.

So it was time to dismantle it and sort that out properly:
IMG_2116.JPG
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There are really three issues.

Firstly my early attempts to make piston valves had ended with valves which were so tight in the valve cylinders that the motion had all been subjected to huge forces - and repeated attempts to stop them leaking, running on air, had basically worn out all of the bushes.

Secondly when I built the motion I was copying the full size drawings, as published in "the anatomy of a Garratt", rather than actually understanding how to design Walschaerts valve gear. I have to say that the valve timing seemed to be correct for the piston valves - so that approach probably worked. I just couldn't get the valves to stop leaking steam, so I made the huge decision to remake the valves into slide valves. However changing to slide valves which were constrained to fit inside the outline of the existing cylinder profile has made the design of the valve gear plain wrong!

I have spent more time studying "design procedures for Walschaerts and Stevensons valve gears" by Don Ashton. So I think I now understand what I need to do to get the valve gear to work! More of that in due course.

So I have the high pressure (rear) unit on its own on the bench:
IMG_2121.JPG
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I have spent about a week replacing the bushes in the valve gear to eliminate backlash in the valve timing. That has improved things. However yesterday I realised that there was so much play in the wheel bearings that I was wasting my time. The play was greater than the measurement I was trying to make.

So I have stripped it down and re-bushed all of the wheel bearings. Bear in mind that when I started this project I really didn't know what I was doing, and I didn't have all the reamers, drills and taps etc that I have collected in the last 6 years, so I think the wheel bearings were too loose and lacked the smoothness required to begin with. This is partly why the bearings are now so loose!

So the bushes are remade and are a good fit - and they are reamed. Three of them are reassembled, onto the axles. So that is one axle with the cranks quartered and fixed in place, and the other axle with one crank fixed and one loose. The last crank to be fixed when the coupling rods are fitted.

So I am now re-bushing the connecting and coupling rods - which were also extremely loose.

I am not convinced that the original lengths of the coupling rods were correct (for smooth running), so I am working on getting that right at the moment.

Then I can go back to the valve gear.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Mon Feb 21, 2022 12:30 pm

Each wheel set was made as a copy of the real thing - so the crank acts as the bearing shaft itself and there is a separate bearing with the square housing which runs in the chassis horn blocks:
IMG_2122.JPG
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The wheel set is held in place by bolting it to the spring. The central hole for the bolt is visible.

So this is the one crank which is yet to be secured to the axle. The crank pins have been replaced with new ones made from 3mm rod - which is actually 2.97 mm diameter rather than the odd 2.76mm ones which were in there.

I have made repeated measurements of the inside and outside distance between the crank pins on the right hand side of the unit, and averaged them. I have done the same with the coupling rod journals which have their bushes bored out:
IMG_2123.JPG
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So I can now make the bushes. The ones on the coupling rods will be bored out later when they are in the coupling rods. That way I can use the milling machine cross slide to actually make the holes the 63.9mm apart as per my measurements. The bushes for the connecting rods can be bored in the lathe and just reamed after assembly.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Mon Feb 21, 2022 8:16 pm

I made the bushes for the rods and fitted them. Those in the coupling rods were undrilled, and those in the connecting rods drilled, and reamed. Oh and 0.8mm diameter holes for oil drilled from above:
IMG_2124.JPG
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Looking back at those measurements the obvious anomaly became too obvious to ignore. Why were the readings made with the cranks at top dead centre so different from the readings made at bottom dead centre?

I did the same measurements on the left side of the loco and the measurements were within 0.03mm - which is probably the limit of the accuracy of the measurements. So there is definitely something wrong on the right hand side. Perhaps the crank pins are not perpendicular? That would explain the different measurements. So I have removed the pins, tapped the holes 4BA and fixed brass studding into the holes with locktite. I will file it all flush when it is set and tomorrow I will mount the wheel sets in the milling machine and re-drill the crank pin holes:
IMG_2126.JPG
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Re: Coal fired Garratt K1

Post by Trevor Thompson » Tue Feb 22, 2022 8:55 pm

The cranks have been re-drilled, and the holes reamed. I did it in the mill and rotary table so that I could set the crank throw to the correct measurement and drill both with the same settings. When I didn't get the second one aligned correctly I was able to just rotate the table until the drill was over the centre of the crank, without changing any other settings which could alter the crank throw.

I have now refitted the crank pins by replacing the drill with the pin and pressing it in with the milling head. I think that should make sure it is perpendicular, as shown in the photo:
IMG_2127.JPG
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Having refitted the wheel sets into the frames I repeated the measurements and this time the results were the same at top and bottom dead centres, and the measurements were repeatable and consistent. I have also remeasured the distance between the bush centres in the coupling rod. The end result is that its no good just fitting bushes with centres ready drilled (which confirms my earlier suspicions) - they will be 0.25mm too far apart.

So tomorrows task is to drill the bushes at the correct spacing - and see if they rotate freely.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Wed Feb 23, 2022 11:46 am

The coupling rods fit!

I drilled the right hand coupling rod bushes in the mill, setting them the distance apart suggested by the measurements and they fitted first time:
IMG_2129.JPG
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The left hand one fitted as it was (with new bushes) and the wheels went around without any tight spots. So I set the wheels at 45 degrees and fixed the remaining crank in place where the coupling rods had located it.



It all goes round, with slight resistance - but consistently free. I think the bushes all have around 0.05 - 0.08 mm tolerance - so they are a fairly close running fit.
IMG_2130.JPG
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So now all that play is eliminated I can get back to the valve gear.

Trevor

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Re: Coal fired Garratt K1

Post by ge_rik » Wed Feb 23, 2022 12:32 pm

Absolutely astonishing what you've been able to achieve! As someone who struggles to get a neat fold in a piece of brass sheet (and a double fold is a wild dream), I take my hat off to you ..... :salute: (just imagine the hat)

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Wed Feb 23, 2022 12:37 pm

ge_rik wrote: Wed Feb 23, 2022 12:32 pm Absolutely astonishing what you've been able to achieve! As someone who struggles to get a neat fold in a piece of brass sheet (and a double fold is a wild dream), I take my hat off to you ..... :salute: (just imagine the hat)

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Wed Feb 23, 2022 1:06 pm

Im starting to work on the valve gear. To get it to work correctly I have been studying the book!

So I need to work out how long the return crank should be - and that involves some calculation. I have checked them a few times and corrected some mistakes. So to explain what I'm up to:
IMG_2131.JPG
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This sketch shows the valve gear and the valve and its port face. If you look carefully at the valve itself you will see that the ports which let the steam into the cylinders are connected to the "wrong" end of the cylinders. This is part of the conversion from piston valves to slide valves. It is called "cross porting" - and I did that so that the valve gear could be a true copy of the real thing. This high pressure unit had "inside admission" - which you cant do with slide valves. The steam would push the valve away from the port face.

So to start the calculations I need to measure the actual valve and ports:
IMG_2132.JPG
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The important information here is that the valve is 9.85 diameter, and the outside edges of the steam ports are 9.05mm apart. "Lap" is half the difference between those dimensions. 1/2(9.85-9.05) = 0.4mm. Also note that the valve chamber is only 3.36mm wide - so that is the maximum that the valve can move without hitting the ends.

If I take the lap and add it to the width of the steam port - that is the distance the valve has to travel each way from the centre to fully expose each steam port. That is 1.5 + 0.4 = 1.9mm. That would involve the valve moving a total of 1.9 x 2 mm = 3.8mm - too much it hits the ends. It is normal ( according to the book ) to not fully uncover each steam port - so I will go for it opening it 80%. So 80/100 of 3.8 = 3mm.

To be continued shortly.

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Re: Coal fired Garratt K1

Post by Trevor Thompson » Wed Feb 23, 2022 2:48 pm

The next step is to work out how the valve gear is going to deliver this.

Let me take you back to the picture with the parts named. This type of valve mechanism uses the return crank to provide motion 90 degrees out of phase with the movement of the piston, and the combining lever to provide motion in phase with the motion of the piston. The first part means that the valve is fully open when the piston is half way between the ends of the cylinder , and the second part is opening the valve when it is at the end of its travel.

The diagram has the calculations:
IMG_2133.JPG
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The triangle relates the movement of the valve to the effects of these two motions. The full travel I want for the valve is on the hypotenuse of the triangle 1.5mm - and we are working in the movement of the valve from central to its extent here - half the total. The top side is the amount of movement to come from the combining lever. That is the "lap" of 0.4mm. I will come back to this combining lever and its effect later. I need to concentrate on the return crank first.

X is half the travel to be given by the return crank. 1.445mm.

The lower half of the diagram takes into account that the valve rod travel is less than the travel of the return crank rod. So the measurements are of the actual return crank. So to move the valve rod 1.445mm the return crank rod needs to move 3.356mm.

The next diagram:
IMG_2134.JPG
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This tries to show the main crank rod in the circle. The bigger circle represents the crank pin as it goes round and round. The inner circle it the motion of the return crank pin as it goes round and round. On the left is the expansion link. the dotted line between the centre of the axle (and therefor the centre of the cranks) and the pin on the expansion link defines the position on the small circle which are important. The two points where this dotted line crosses the small circle (marked A) are the points where the expansion link will be central - the neutral position - The dotted nine at 90 degrees to this first dotted line defines the points where the valve will be fully open in each direction - marked B and C.

I have already calculated that the crank needs to move the valve a total of 2 x 3.356mm - and that is the diameter of the small circle 6.712mm. Note that since the line joining the pivot point on the expansion link and the crank centre is not horizontal, the line joining the points marked A is not vertical. That effects the length of the return crank.

Having drawn that out to scale in sketchup I can read off that the distance between the holes in the return crank needs to be 13.136mm.

So I can now make the new return cranks.

I will come back to calculate the length of the return crank rod, and where the pivot point in the bottom of the expansion link need to be after the return cranks are fitted.

Trevor
Last edited by Trevor Thompson on Fri Feb 25, 2022 3:07 pm, edited 2 times in total.

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Re: Coal fired Garratt K1

Post by SimonWood » Thu Feb 24, 2022 8:46 am

This is exciting. I'm looking forward to seeing this running.

The valve gear detail is going over my head right now, but I'm bookmarking this to return to in the future once my own understanding has developed!

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