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Post by drjohn on Feb 10, 2009 4:48:02 GMT
Ok - I eventually got the pump out by drilling and cutting the pump stretcher then shearing the two remaining screws holding it in place. Dismantled the pump and the piston slid out perfectly with firm finger pressure. No sign of seizure in the bore, all the clacks were free etc. So the only conclusion I can draw is that for whatever reason, the eccentric grabbed and caused the bending moment.  But there are no signs of damage to the bearing surface of the eccentric or strap.   All the more mystifying as the loco has been run for several hours on air over a considerable period of time, and everything was well lubricated. Dunno  DJ |
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Post by modeng2000 on Feb 10, 2009 7:03:25 GMT
Hydraulic lock?
John
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Post by drjohn on Feb 10, 2009 7:22:19 GMT
Could well have been John, the only thing that makes me doubt that is the pump seized with the piston right at the beginning of the stroke. With the longish run of pipe to the clack on the boiler, I would have expected the piston to have moved at least a fraction because with the amount of force to bend a short bit of 1/4" stainless, the pressure should have caused micro expansion of the copper pipes as it's only pumping about 1/2 a cc in either direction.
The other thing is the output from the pump was "T"ed into the bypass which was open. The boiler feed clack is also quite free and there are no blockages in any of the clacks or feeds in the pump itself - as I said, a bit of a mystery.
DJ
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Post by gilesengineer on Feb 10, 2009 8:46:42 GMT
Dr John, just a thought.
You were running the loco up on blocks - had you packed the axle-boxes up to running height, or were they bottomed out on the keep plates?
The reason I ask is that the pump / eccentric unit being so short may be somewhat susceptible to locking up when the drive is at an angle away from its designed straight line (between the centre line of the pump and the centre of the axle) thereby 'breaking its back'.
Giles
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Post by drjohn on Feb 10, 2009 8:54:49 GMT
Hi Giles - yes I had the axleboxes packed to about half spring compression, and as I said, it's done a couple of hours or more in the exact same configuration running on air.
When I ground through the pump shaft to dismantle it when it had cooled sufficiently for holding onto bits, the eccentric rotated totally freely under it's own weight, and the joint to the pump shaft was also completely free both with plenty of oil.
The only thing I can now think of is perhaps the PTFE long ring expanded with the heat and got stuck, which of course wouldn't leave any marks of violence in the pump bore - when it was cool today, it slid out freely. Perhaps tomorrow I will immerse the pump with the piston in boiling water and see what happens.
DJ
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Post by drjohn on Feb 10, 2009 9:12:22 GMT
Well it's not that - just tried, and boiling it for 5 minutes makes no difference. The piston still slides freely.
DJ
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Post by drjohn on Feb 11, 2009 5:00:39 GMT
Anyway, I have now a fully functional axle-pump-less Simplex - runs like a sewing machine -  I will put something on the side of the tanks - maybe a brass nameplate as it looks a bit slab-sided. DJ |
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Post by dickdastardly40 on Feb 11, 2009 8:48:27 GMT
Congratulations on your efforts DJ!
The difficulties you have faced during your build would have had me throwing in the towel but you have the finished article to show you overcame them.
Onto the Black 5 then, or maybe as the simplex runs like a sewing machine, a steam powered sewing machine for your good lady? ;D
Al
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Post by Deleted on Feb 11, 2009 9:59:46 GMT
You may not know it Al, but he's got a computer driven sewing machine already!
Yes, it's true!
JB
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Post by drjohn on Feb 11, 2009 10:38:57 GMT
OK JB, what brings you here? Just because there's not a thread for "nearly there" Britannias - ;D  And of course, I jest - thanks for looking and the comments from dastardly. DJ |
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Post by drjohn on Feb 13, 2009 1:51:00 GMT
Going back to the pump episode as it might be of use to others - I've studied the video I took and it seems that after I closed the drain cocks, the loco picked up speed very dramatically and then seized up. I don't think that this is a problem which would occur had I been test steaming on a track, but because there was no resistance to the wheels (and it had been sooo well engineered ;D  ) it went exceedingly fast, and that might explain the effect of a hydraulic lock becuase of the amount the pump was trying to deliver through a single bit of 3/16 pipe up to the "T" for the bypass. DJ |
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Post by mutley on Feb 13, 2009 7:47:36 GMT
I think that unlikley DJ. Having had a simplex and driven it 'very enthusiastically' the only problem I had with with the pump was down to my own fault as a I mentioned in the injector thread.
Andy
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Post by drjohn on Feb 16, 2009 10:11:21 GMT
Hi Andy You can spin the wheels much faster totally off load than you can ever do on a track, and I seriously think that was the problem. Now stripped the paint from the smokebox/chimney, without damaging the rest of the paint job (crafty old Scotsman! ;D) and will shortly be doing a repaint with "proper" smokebox paint.  Incidentally, when I asked Precision Paints (Phoenix now) for high temperature paint for the smokebox, I might as well have been puffing smoke from my nether region as they didn't seem to know what I was on about DJ |
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Post by drjohn on Feb 17, 2009 11:05:17 GMT
Addendum Just talked to a "sensible" bloke from precision paints who tells me the paint they sold me is ideal for smokeboxes -- why didn't I think of that ? Respray tomorrow. DJ |
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Post by drjohn on Feb 18, 2009 10:41:46 GMT
Final comment - smokebox now repainted and looks pretty fair, using the "dull black" from Phoenix paints. Once it gets the brass plaques along the tanks and one at the front, I'll post one final picture then I'll be out of your hair for a bit while I set to on the Black 5.  DJ |
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