I think I broke it!!!

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I think I broke it!!!

Post  highpressure on Sat 04 Aug 2012, 11:49 am

Well today I attended Lingfield Steam Show at Blindley Heath in Surrey with Andy2. Despite what looked like a poor start the weather was quite well behaved and there were 44 miniatures!! 4 half size, 2 showmans a SC agri and a Foden SWB, and the usual array of engines representing most makes.

Recieved lots of compliments about the engine and by 1pm we lit up as now I have the tickets, thats the point!! Very Happy

Julia was very interested to see the engine and we spent about 1 1/2 hours running, and I learnt where the reverser should be set for the best running which is about 5mm or so back from full forward, it has a real sweet spot and speeds up and has a much better exhaust note. I don't think ideally it should be right full forward as it seems to put quite a strain on the valve rods and "stretches" the mechanisms. Pump worked quite well but still leaks through the actual casting and the elbow to the feed pipe leaks in the corner??

We tried to run in reverse which it did for a short while before there was a rather nasty noise and it locked up. We tried to turn it by hand and found that it seemed to lock up in gear but not in mid. Took the HP chest off as it looked like it might be there but nothing untoward and then went to the LP chest.

This is what we found...... affraid





The screws holding the valve plate in have worked loose releasing the plate and then the valve has trapped it. There was the ususal influx of comments from all around about how it "should be done" and "proper engineering" comments, most of which I tried to take with good humour. Sadly when people find out that you didnt machine any of the components, have no interest in making any of the components and don't know one end of the lathe to the other and don't really care, you start to loose a bit of credence. The general concensus of opinion seemed to be however that the screws were certainly too short and ideally could do with being studs with small nuts on, then the plate can't fall off even if it undoes.

Clearly anyone else who has run needs to drop the valve covers off and check these for tightness, it would seem that locktite or thread lock won't help due to the heat, I am considering longer stainless screws perhaps socket heads??

I will speak to STW on Monday to report and see what comes back. Despite this minor set back at the end of the day it was really enjoyable and this is nothing too serious that can't be quite easily fixed, there was some speculation that it may have been a piston ring which would have been much worse in my eyes to sort out and Julia said that it was a well made engine and would be a good powerful machine when bedded in. Certainly enjoyed being in steam at an actual event and had a number of comments about beign on the forum despite never having seen them before, lots of people read this and attend do's.

This is a selection of some of the other engines in the ring.






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Re: I think I broke it!!!

Post  Robfishman on Sat 04 Aug 2012, 2:09 pm

Ooouch. But it looks like it could have been much worse.

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Re: I think I broke it!!!

Post  Dan on Sat 04 Aug 2012, 4:17 pm

On a lighter note it looks like your lubricator is working well!

Hope she's back on the road soon.

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Re: I think I broke it!!!

Post  Tony King on Sun 05 Aug 2012, 12:56 am

Hi Kev,
Nice to see pics, a good collection of engines there.
Sorry you've got bent bits to sort out, but it should be an easy fix with a little help from STW spares department.
It's valuable information for those of us following on behind. I wonder if there is a thread lock that would work at higher temperatures, as that would solve the problem easily?
Regards,
Tony

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Double nuts

Post  Steve Traill on Sun 05 Aug 2012, 1:20 am

I'm not aware of any high temperature thread lock so I would try & double nut anything critical so fixing studs onto the valve plate & then double nutting it would be my solution. If short of space two half nuts can work fine.

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Re: I think I broke it!!!

Post  highpressure on Sun 05 Aug 2012, 3:50 am

Yes, Steve that suggestion came up yesterday along with a few others, I'm going to try slightly longer stainless cap head screws as there is only a very tiny bit of thread to hold in. Alternatively remove tham altogether as they are only really holding the valve in place as before pressure takes over.
Don't know what the concensus of opinion is on that though. But not worried as it has only taken 20 mins to dismantle this morning and shouldn't take too long to reassemble, you could almost straighten the rod out now its out.

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Re: I think I broke it!!!

Post  Tony King on Sun 05 Aug 2012, 5:11 am

I've just taken out all the bits screwed to the slide valves & run the engine on compressed air & it worked fine. That was on fairly low pressure, ie less than 50 psi, so should be no problem when in steam at over a 100 psi.
I reckon "take the bits out", then there ain't nothing to "drop off" & spoil the fun Laughing
Regards,
Tony

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Re: I think I broke it!!!

Post  highpressure on Sun 05 Aug 2012, 6:53 am

Yes, I did think that.

Also an interesting thought, yesterday when we were trying to get the engine to start without the flywheel Julia was initally concerned about the tightness as it seemed worse as it got hot but after we remarked that the clock was at 150psi she said that if the HP valve had a surface area of about 3 square inches that equates to 450 psi pushing it onto the face, hence the amount of force needed to try and move the valve rod!! Even at 50 psi it is still 150 on the face.

Once the rod is fixed I will leave out the bits and run again this weekend at Northchapel and see how it fares, they can always be put back in in about 10 mins anyway.

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Re: I think I broke it!!!

Post  the coleman on Sun 05 Aug 2012, 8:24 am

Hi Kev
iv'e been looking in my selection of loctite and found .Hopes this helps


Loctite 278 High Strength, high temperature Threadlocker

Datasheets Manual Dispensing

Technical Data:
■Maximum thread size: Up to M36
■Strength: High
■Breakaway torque M10 bolts: 42Nm
■Fixture time steel: 20 min.
■Fixture time brass: 20 min.
■Fixture time stainless steel: 60 min.
■Service temperature range: -55C - +200C
■Pack sizes: 50ml, 250ml

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Re: I think I broke it!!!

Post  Tony King on Sun 05 Aug 2012, 8:33 am

Yeah, I noticed that as the pressure went up, it quickly effected the operation of the reversing lever, it became very stiff to move with only 50 psi on the guage. I had to make sure the throttle (regulator!! sorry!!) was shut & open the drain cocks to allow it to be moved with ease.
The " frictional clamping force" holding the slide valves onto their seats must be "colossal"............ Which is why I don't think the springs & bits to keep the valves on their seats will be required!!
Regards,
Tony

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Re: I think I broke it!!!

Post  highpressure on Sun 05 Aug 2012, 9:46 am

Tony,

That description sounds like you have the leaking start valve sydrome as the drains on the LP side make virtually no steam or water condesate at all, as per yesterday, in fact I couldn't remember how we set the cocks up and didn't know which way was opened or closed and it was difficult to tell. If the Pressure is going into both LP and HP and through the exhaust passage it locks the thing up a real treat.

The way to tell is to open the LP cocks if you get any hissing at all as in pressure coming out of them then its getting into the valve chest via the start valve. Trust me, I have been there and seen it more than once with this build during the test steamings and once the valve is blocked ( or sealing correctly ) there is nothing from the drains at all.

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Boiling point

Post  Steve Traill on Sun 05 Aug 2012, 11:00 am

Hi Andy

The boiling point of water at 180psi is 190 degrees C which doesn't leave much of a safety margin if the loctite is only good for 200 degrees.

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Re: I think I broke it!!!

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