Author Topic: Greene Automatic Cutoff Steam Engine  (Read 56470 times)

Offline crueby

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Re: Greene Automatic Cutoff Steam Engine
« Reply #405 on: August 08, 2020, 12:47:40 AM »
Is it possible that the inlet valves aren't opening much? I like to back off yhe screws on an end cap to check that.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #406 on: August 08, 2020, 01:08:01 AM »
With the transparent steam chest covers I can see the valves directly.

Offline crueby

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Re: Greene Automatic Cutoff Steam Engine
« Reply #407 on: August 08, 2020, 01:18:16 AM »
With the transparent steam chest covers I can see the valves directly.
Thats handy!


Just had a flashback to an engine build where I thought I had all timed right but it wouldn't run. Finally traced it to a gasket where I forgot to punch the center steam hole.   :wallbang:

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #408 on: August 08, 2020, 09:35:04 PM »
My push fitting for 1/4" tube showed up from McMaster (next day delivery!), so I hooked it up for some leak detection.  The major culprit thus far are the transparent covers.  Seems they don't provide a good seal to the block as they're thin (1/8") and flexible, plus there are only the 4 screws at the corners holding them down.  Given this, I don't see teflon gaskets working, and I don't want to try either of the two gasket liquids I have.

So I decided to machine a couple of brass covers and skip the see-through for now.  Once I can seal the steam chest I can check the exhaust valves.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #409 on: August 08, 2020, 11:27:02 PM »
Covers milled from 3/16 brass.  I used the trick of securing using Scotch painters tape back to back with loctite adhesive between them.  Makes for a very secure hold on thin stock.



With the covers in place, the steam chest no longer leaks.  Now I'm seeing some oil being blown past the exhaust covers.  Still no resistance on the piston.  More investigation to come.


Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #410 on: August 09, 2020, 09:34:11 PM »
Tested the exhaust valves today and they not valving whatsoever.   :'( 

I suspected I'd have issues but went ahead with full assembly given hope over experience.   :hammerbash:  I removed the outer covers to show part of the problem.



The valve passage has chipout on the bottom at the ends.  Sealing the passage relies on the covers.



If the semi-circular boss doesn't meet the fixed grate securely there will be leakage.  Too short and air escaped between, and too long the cover won't seal to the block.  Even with the valve closed there is air in the interior since there needs to be some space to allow the moving grid to slide.

The fix I contemplate at the moment is to make the fixed grid's length the same as the width of the block so that its ends are flush with the sides.  The bosses on the covers  and brackets would be removed.  That should remove any airpath around the end of the grid.


Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #411 on: August 10, 2020, 08:34:18 PM »
Disassembled parts needed to separate the cylinder block preparatory to being able to assure air tightness in the exhaust valves.





Block has input valves and cylinder head still attached.  For the test I'll add the piston and frame-side head.  However, examination of my stock shows no remaining 5/8" brass rod to remake the stationary grids, so pending delivery of my order I'll start on other fixes.  Today I milled off the bosses on the exhaust covers.

I need to finish the flywheel and drill holes for direct lubrication and oil cups eventually, so now is a good time for that.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #412 on: August 14, 2020, 03:37:00 AM »
I think I'm on a good path toward eliminating air leakage with the exhaust valve mechanism.  As a reminder, here is the assembly as designed:



Like hobbits, all between the faces of the cover (blue) and brown bracket live in a hole. If the mate between the half circular bosses on these two isn't precise with the fixed grate (yellow), air can leak past even when the sliding grate supposedly closes the valve.

My solution is to do away with the semicircular bosses and make the fixed grate long enough to be machined flush to the sides of the cylinder block.  With the cover and bracket then screwed flush to the block, a good seal is  more assured.

So I remade both fixed grates somewhat long but did not cut through the grid openings, attached them in the hole, and carefully machined them flush taking about 1 thou off the block.  I added the piston and crank side head and screwed the covers tight on the side away from the crank.  When I applied air and moved the input valve open, I found that the exhaust opening was not emitting any air flow and the piston rod was driven outward.  So no leaks around the ends!

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #413 on: August 23, 2020, 12:56:19 AM »
After doing all the exhaust valve rework I hooked the cyl block up to air.  Still seems leaky  but in manipulating the valves manually I got the piston to move.  So with enough pressure the engine "ought" to operate despite leaks.

So this afternoon I reassembled all the bits but one.  The coupler for the exhaust actuator rod seems to have gone walkabout.  I hunted around the shop for longer than it would take to make a new one, which I finally did.  Too late to to try to do all the myriad adjustments, so I called it a day and will see if I can get movement next time in the shop.

Offline crueby

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Re: Greene Automatic Cutoff Steam Engine
« Reply #414 on: August 23, 2020, 01:17:00 AM »
First movement, great! 




As for the missing part, put out some cookies and shiny ball bearings as bribes for the shop gnomes, maybe they will return it...

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #415 on: August 24, 2020, 01:00:59 PM »
No go Sunday.   >:(

After assembly and adjusting, two major problems.  First, too much resistance in the exhaust valves that I have now initially traced to the new bracket being 25 thou longer than the other, thus causing some binding in the rod connecting them.  This should be easy to fix.

The second problem is that the dashpot pistons are not heavy enough to close the inlet valves.  On the real engines there was vacuum created in the pots that applied force, and in the model a spring that's compressed when the valve opens helps to pull the piston down.  The spring is attached to a rod screwed into the piston that passes through the pot and through the base (which is elevated).  So I will make a temporary baseplate for the cylinder and raise it and the base of the bearing standards on 123 blocks to make room underneath for the springs.

I ordered a piece of 12x24" aluminum plate for the eventual baseplate on eBay, but I don't plan on using it until everything else is finished.  The design of the engine makes it almost impossible to remove the flywheel for transport.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #416 on: August 25, 2020, 05:05:57 PM »
To provide a mounting surface for the cylinder block and dashpots, I cut out some 4.5x5" aluminum plate and drilled all the holes needed for a temporary baseplate.  But instead of the measure twice and cut once advice, I did the opposite.  So that plate got dumped and a second one made.  Wasted half the afternoon.  With the baseplates lifted 2", here's the result.



The dashpot assembly looks like this.



As the piston is pulled upward by opening the valve, the spring is compressed.  The spring force pulls the piston back down once the valve is tripped or released.  The rod around which the spring is located is threaded, and the round disk at the bottom can be turned to compress the spring and add additional force if required.

I ordered the springs from McMaster for delivery tomorrow.

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #417 on: August 28, 2020, 03:30:53 PM »
My springs arrived but all the following day was occupied visiting apartments where my daughter is shopping for her first home.  Back at it yesterday.  Here's a dashpot piston and rod with the spring loading.



With both installed and the tension knob needing only a couple of turns, both dashpots are closing the input  valves as they are supposed to when the trips loose contact with the catch.

Unfortunately the exhaust valves refuse to operate smoothly or at all.  The fact that they are connected to two long rods passing through 4 bearings and fastened together only by pairs of 3-48 grub screws means that any resistance is likely fatal.  I unfastened the center bearing from the governor, which allows an easier meetup of the rods at their coupler.  That bearing looks like some fettling will get it closer to the needed line, but for the time being I'll ignore it.

Each valve assembly when bench-operated singly is smooth.  Similarly, each sliding valve when inserted by itself into the valve hole is very smooth.  So the next days will be locating where parts get out of alignment when screwed down.


Offline Dennis

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Re: Greene Automatic Cutoff Steam Engine
« Reply #418 on: August 28, 2020, 10:00:03 PM »
Hi Kirk,
The valves and assemblies look very good. 
I remember encountering some binding in the exhaust valve operation when building the prototype.  Your valves work free when standing alone like ours did.  For what it's worth, we found the length of the adjustable link between the rotating levers and the valve crosshead was too long and our assembly was trying to move the valve too far.  This is a very busy area and will need a lot of fiddling with the linkage and the working angle of the two oscillating levers to get the exhaust valves to move correctly.  If the long shaft from the eccentric is rotating through too large of an angle, reducing the amount of rotation would require a longer lever arm where the shaft connects to the eccentric and vice versa.

I really like the progress you have made and am looking forward to seeing the engine run.
Dennis

Offline kvom

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Re: Greene Automatic Cutoff Steam Engine
« Reply #419 on: August 28, 2020, 11:45:05 PM »
Dennis, I figured that the adjustable link at the crosshead adjusted the valve travel.  At my last test though it doesn't look like the shaft is rotating over the same angle as the arm, and the valves barely move at all.  I drilled the mounting holes large (.104 to .116) to give some adjustment wiggle when attaching so as to line up the valve stem.  That helped some.

I believe the main issue now is not transmitting enough torque along the shafts and having slippage around the grub screws.  I think I'll pin the shaft to the eccentric lever arm next and the screws for holding it are difficult to access.  Some larger screws for the coupler might be an improvement as well.

 

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