Re: Why is quartering a necessity?

I cancelled this message which went out incomplete. I resent the complete one a few minutes later.

The only reason for the analogy was because you seemed to have difficulty thinking about it in degrees. The result is the same - at the crank.

No. It is irrelevent what the angle of the cylinders is. It is a property of using a crank shaft or axle to convert reciprocating motion into rotation.

The pistons must be at their extremes when the crank is at to dead centre.

And the explosion, steam admission/exhaust, etc happens (simplistically) when the piston is at top dead centre. Which means when the crank is at TDC.

So if one of the three cranks is not symmetric with the other two, the beat cannot be symmetric.

piston, even though it

Mechanically it has to.

No, you didn't. You used the clock analogy which only works at the crank axle. A clock is a continuous rotation, not reciprocating.

And how does that allow it to fire at 4 o'clock when the crank is at

4.30?

that cylinder would have

difference of the center

That still does not permit a beat at 4 o'clock with the crank at 4.30.

in the Gresley system

timing you can derive

times. If the valve timing

with one cylinder

valve got later and

direction, so that 7

become steadily worse!

And I'll leave you to work out what happens when you move the valves further along the valve spindle with respect to the steam ports to compensate for the angle.

Reply to
Christopher A. Lee
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As I always say: I've learned something new; I can go home now.

Reply to
Brian Paul Ehni

The crank doesn't care if we talk degrees or clock faces.

OK, try it with one cylinder pointing straight up at 90 degrees to the others.

Sure, I have no problem with that point.

Exactly, in a very simplistic and not too useful simplification. :-)

There is no logical link (mentioned) between your first comment and your conclusion.

center piston, even though it

It can't, because at 120 degrees after the first beat, a 120 degree crank is 7 degrees past TDC of the center cylinder which is inclined or advanced by 7 degrees. With those settings of cylinders and crank you are going to hear an asymetric beat.

OK, we've forgotten all about the clock.

We've forgotten all about the clock! Let's count the cylinders in order of action 1,2 and 3. The action:

- Cylinder 1 reaches TDC and the inlet port opens.

- 120 degrees of rotation of the Gresley crank axle later, the middle crank set at 113 degrees from crank 1 pushes the center piston to the TDC of the center cylinder which is set 7 degrees higher or 7 degrees in advance of cylinder no1.

- 120 degrees of rotation later, the no3 crank, set at 127 degrees from no2 crank, pushes the no3 piston to TDC of cylinder no3. See, every 120 degrees a piston begins it's decent from TDC and at the half way intervals a piston begins it's movement from BDC. - 6 absolutely evenly spaced strokes and 6 evenly timed exhausts from the cylinders.

center line.

therefore that cylinder would have

difference of the center

in the Gresley system

only timing you can derive

times. If the valve timing

cut-offs with one cylinder

the valve got later and

direction, so that 7

become steadily worse!

Well, I can see how you could do that in one direction of travel, but in doing so you've doubled the angular error on the opposite stroke. It's now 14 degrees out of time given absolutely perfect valve gear.

Reply to
Gregory Procter

Turning over the leaf on your desktop 'page per day' calender to see the new date apparently doesn't count as learning something new! 8^(

Reply to
Gregory Procter

On Wed, 17 Nov 2004 20:31:47 UTC, Mark Newton wrote: 2000

The ones I was referring to were the 900 class 2-10-2s. The low pressure cylinder was directly behind the high pressure. The valves appear to have been driven by the same valve rod. The valve gear was between the frames.

Reply to
Ernie Fisch

The problem with deriving the low pressure valve timing and cut-off from the adjoining high pressure valve is that you can't adjust the low pressure cut-off to the most advantagous settings.

Reply to
Gregory Procter

Some days, even that's a victory!

Reply to
Brian Paul Ehni

Depends - you could look on it as the loss of yesterday! :-(

Reply to
Gregory Procter

This not really complicated topic has generated 16 follow up posts so far. Could you guys maybe draw some pictures so we can understand what's going on?

Reply to
<wkaiser

Christopher, there are no explosions in the cylinders of a steam engine. In fact, there is a pressure loss when the steam is admitted to the cylinder and the start of the admission usually isn't right at the end of the stroke of the piston but rather a little bit later as the full pressure at the top of the stroke does no good except to strain the whole engine. Go look at pressure diagrams for steam engines to see where the actual timing is for a real steam engine. Also note that the valve timing is a variable with steam engines (that is what the Johnson bar is for) with longer timings when the loco is putting out max power and shorter when speed is attained and the requirement for power is less. It is interesting that it is better to control speed by the valve timing rather than by closing the throttle as this method produces better economy with the engine, using less water in this fashion.

-- Why isn't there an Ozone Hole at the NORTH Pole?

Reply to
Bob May

Outlook number one: the fact that the center cylinder crank on Gresley 3 cylinder locomotives is 7 degrees off equidistant accounts for the uneven exhaust beat.

Outlook number two: the 7 degrees off equidistantly spaced crank is a correction for the 7 degree raised center cylinder of the Gresley 3 cylinder locos so the exhaust beat should be even. The unevenness occurs because the valve timing of the center cylinder is achieved by deriving the timing through a collection of cranks and levers from the other two. In time all the bearings wear and the valve moves late after all the clearances are taken up, both on inlet and exhaust strokes and on TDC and BDC strokes.

This takes something better than an ASCII drawing to get across.

I think Christopher is trolling me but I'm giving him the benefit of the doubt.

Regards, Greg.P.

Reply to
Gregory Procter

I know that. It was shorthand. And why do you think I qualified it by talking about the lead so many times until I felt it wasn't necessary to do so any more.

Reply to
Christopher A. Lee

If you try to control speed purely with the regulator you're in big trouble! At zero speed, at the first opening of the regulator, you get full steam pressure on the piston(s) and therefore maximum torque. The regulator can only control the _amount_ of steam that passes it so it's effect is speed dependant. (The faster you go on any throttle setting, the lower the steam pressure becomes on the piston)

Reply to
Gregory Procter

No. And I had thought you were trolling me.

I had asked you for a mechanical explanation several times, and it was only when you finally gave one that it made sense.

So I hunted through my library looking for Holcroft's own explanation. I couldn't find a detailed one although he himself confirmed that it gave six even beats.

However I don't remember ever hearing an even beat on a Gresley

3-cylinder engine in BR days, even when they looked recently ex-works.

So I drew diagrams of the rotation at each stage of both your and his descriptions.

It seems you're right and I was wrong.

If everything is set up correctly, and there is no wear and no whiplash from the levers then the beats should be even.

Holcroft was aware that the outside valve spindles would expand with the heat, but Gresley said he would take that into account.

Holcroft's own engines were better in this last regard.

It's a pity his original 1917 4-4-0 proposal was never built, because that would have had the "ideal" conjugated motion - a compact setup with short 1:1 levers taking the motion just forward of the combination lever and driving the valve from the rear.

There's a diagram of this in volume 1, page 85 of his memoires.

Reply to
Christopher A. Lee

Indeed, no. Hence the French practice of providing a separate reverser/valve gear for the HP & LP engines.

But from what I've read of the ATSF tandem compounds, lack of separate cut-off for the LP side was the least of their problems.

Reply to
Mark Newton

Oh, tandem compounds! Sorry, Ernie, I see now that we're all at cross purposes with each other.

Greg's NZ A class engines were arranged with the LP cylinders outermost, and the HP cylinders inboard but in a common casting. On reflection, as they were De Glehn system engines, they may well have had separate valve gear for the HP valves between the frames. I wish I hadn't packed all my books away just yet! :-)

Were the 900 class engines the ones originally used as helpers at places like Cajon Pass?

Reply to
Mark Newton

Actually the boiler WAS flexible ... well sort of.

The rear portion was a more or less conventional boiler.

The front section was sort of a big preheater, or feedwater heater, but it WAS under pressure like the rest of the boiler In front of that was a conventional smokebox.

The middle was what's interesting. Between the two water filled portions was a chamber that amounts to an intermediate smokebox. This is where the joint was located. This portion was NOT under pressure. The joints were of two types (on different classes of loco). One was bellows, the other a sort-of ball and socket. Both had big problems in practice. The ball and socket obtained excessive wear from the abrasive cinders, and the cinders packed into the gaps in the bellows and rendered it inflexible. Both types of locos were failures.

Note that both AT&SF and GN (perhaps among others) had rigid-boiler articulateds with similar intermediate smokeboxes. These were more successful, in that they worked, but were still poor performers, excessively complicated, and soon retired.

Dan Mitchell =========

Reply to
Daniel A. Mitchell

OK, then my continued efforts are justified, even though I'm forced to give up my dream of ever becoming a teacher. ;-)

No, those little bearings in the rocking arms wore very quickly, and the valve itself would have to be set correctly.

That factor in itself would ensure that the inner valves were only centralized as the valve stem expansion passed through the correct setting.

The Germans built many thousands of three cylinder locos between about 1910 and

1956. Most just used a third set of Heusinger valve gear, mostly situated on the left side of the loco and using a cross shaft to get between the frames. It was a relatively simple, effective and trouble-free setup with none of the uneven beats of Gresley's locos.

Reply to
Gregory Procter

On Thu, 18 Nov 2004 20:12:20 UTC, Mark Newton wrote: 2000

Not being a Santa Fe fan I don't know. The reference I have is for Tehachapi. They were probably used on Cajon as well.

Reply to
Ernie Fisch

What do you mean by the "regulator"? If it is the British word for the throttle, you have to remember that when you first open the throttle, the pistons do indeed fill with steam, causing max torque but how do you limit that torque??? You can't do it by the valve motion as that doesn't limit the amount of steam but rather when that steam is admitted to the cylinders. If you consider that the valve timing is either at the limit or at the center, you lose the ability to control the amount of expansion of the steam as you go down the track. From this is where you gain the efficiency to run a certain distance.

-- Why isn't there an Ozone Hole at the NORTH Pole?

Reply to
Bob May

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