[modeleng] Re: Valve problem

Hi Bede

I sympathise with you re your steaming problem.
Over the years, I've had similar problems - and they're not always  
straightforward to solve.
As it happens, most of mine have been with piston valve locos, so some  
slightly different problems. And please feel free to laugh.

On testing my first loco on air, it struggled to do anything, but  
seemed to be trying - with lots of air going up the chimney.
I then tried air on one cylinder only - it ran freely - so the problem  
must have been on the other side? Air was connected to that side only,  
and it too ran !!!
Then I realised - backwards. One side was trying to run forwards,  
whilst the other was running backwards.  All the construction drawings  
showed the arrangement of the LH side of the loco, and I had assumed  
that the RH was to be a mirror image - not so - as I learnt the hard  
way!

Just this year, I had problems with a 3 1/2 in loco which I completed  
a couple of years ago - it had run apparently OK on air, but, on  
steaming, It had the problem you describe.

I checked the piston packing - seemed ok, but I repacked and re-honed  
the cylinder bores just in case.
I checked the piston valves - no doubt about it, air was passing by  
the valves.  I checked the valve bores and the bore clearance - also  
the dimensions of the valve and the port positions - any tiny error  
here will cause problems.
I made up a dummy valve with O rings - It would never have run, but  
enabled me to check that the internal porting was steamtight.

I did find problems with the timing -Stephenson link gear. I has set  
up the eccentrics at 90 deg to the crankpins, in the lathe with a dial  
gauge. However, the valve gear (by design) did not lye exactly  
horizontally. It took a lot of 'messing about' to get the settings  
spot on.

Also - and I think an important contribution to my leaks - cylinder  
lubrication. Cylinder oil has a very significant effect on sealing the  
valves. I did some experiments running the chassis on both air and  
steam - which of course atomises the cylinder oil and gets it where  
it's needed, and seals the valve faces.
It now seems very much better, but I've still to run it for real.

(Incidentally, I did my live steam tests using a steam iron - the ones  
which have a seperate steam generator (1.3 Kw) and run at 4 Bar - they  
have a proper boiler management system with hi /lo water sensors, and  
a high pressure water pump. It ran my 3 1/2 in Hall reasonably -  
connecting directly to the cylinders - although it clearly never  
achieved 4 Bar at the rate I was using steam. If I can work out how, I  
might upload it to YouTube if anyone's interested.)

Just a thought - could you have a steam leak from anywhere in the  
primary steam circuit - the steam outlet pipe, superheaters and  
cylinder connections. I always check with a paint brush and soapy water.

I think you've got to open up the valve chests though, as its quite  
possible a piece of swarf or grit has got into the valve and will  
quickly damage the valve seats.

I hope my comments arn't too trivial, and you soon get sorted


Cheers

NormanC
normanc@xxxxxxxxxxxxxxxx
http://normanclasper.blogspot.com/




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