The Steamboating Forum

There appears to be two usages of the term "wire drawing". On an indicator patern the steam admission line should parallel the atmospheric line from asmission to cut off. If the line starts to drop before cut off as a result for throttling as the vale closes, this is refered to as wire drawing of the steam in all the older steam mannuals I've examined. This is problem gets worse the slower the engine is running.

Some where along the line wire drawing has become a commonly used to describe steam cutting and valve seat erosion.

In the UK it appears that wire drawing is use as a term that describes throttling. Since a throttled valve can cause errosion to a valve seat it's not hard to see how the term has made that leap.

But a wire drawn valve seat, and wire drawing of steam are very differant things.

Now where should the calorimeter be connected?

Dave

Interesting… Now I have questions.

So it would be better to vary the speed/torque of a steam engine the same way one would vary the speed/torque of DC electric traction motor, by essentially using the mechanical equivalent of an electronic pulse width control.

Ok now the funky valve linkage of a Corliss steam engine makes sense!

Mike said something about Fred having a weird linkage? So… Fred, show me your linkage! I am interested in going with something unique as far as a steam engine goes and that includes the linkages.

Cheers,
Scott

Poppet valves like the Skinner Marine Unaflow virtually eliminates any wire draw since the valves have very crisp opening and closing. The skinner also used a double cam system to vary the cut off and control forward and reverse. In the Skinner literature, one of the stated advantages was that the speed of the engine can be controled by the cut off with the throttle fully open, eliminating "wire draw".

Dave

You are all leading Scott into madness from which there is no escape. Valve gear madness. A fatal disease if you are lucky! (laughing my face off)

Mike

"Wire drawing, as I was talking to Scott about it, is shown on an indicator card as a place where a port is closing rather slowly and thus the energy considerations in the previous posts shows up on the card. When the same situation occured with a throttle or a governor, it became called Wire Drawing even though it doesn't show on an indicator card."

The term "Wire Drawing" has come to mean simply,"throttling steam with a significant pressure drop" in that definition either term has the same meaning, "wire drawing" or "throttling". As steam engines started to use cutoff for economy, the throttling of steam flow as the steam admission valve closed was recognized as a loss, and it was named (way back then) with the term "wiredrawing", although it did not involve any cutting of valve seats. Almost all of us know the term "throttling", it is very commonly used in IC engine practice, automobiles, etc. Perhaps our predecessors of 150 years ago did not know this term so well, but those who were around steam engines probably knew the process by the term of the past, "wiredrawing".

fredrosse wrote:The term "Wire Drawing" has come to mean simply,"throttling steam with a significant pressure drop"

How the steam car folk use it, if I understand them correctly. It's when the demand exceeds the boiler generating capabilities - so much so that boiler water is drawn in to the steam line. Looks like all the definitions fall under one common or related meaning "throttling steam with a significant pressure drop"

-Ron

I've never heard that use. I've always called that Priming. Bad juju all around to let liquid get that far up the system.

Fred, Mike

I have a couple of times tried to increase the overall economy by linking up, which with a Stephenson link is the only possible way to control the cutoff. However, the engine was not feeling very comfortable, and I couldn't accertain a significant improvement in economy.

It seems to me that the Stephenson link - though a simple and effective way to reverse the engine - is not very suitable to control the cutoff. I did an analytical study of the piston valve movement. The resulting diagrams show that, when linking up, both steam admission and exhaust are advanced considerably. While the advanced admission causes the engine to run uneasily, the advanced exhaust neutralizes the gain obtained through the modified cutoff. In view of the large number of boats equipped with a Stephenwon link, where linking-up is usual, I can imagine that some other causes or design differences negate this cutoff possibility on my engine.

As the hard wood consumption is bearable (consistently 1 kg per km - 4 pounds per nautical mile), I stick to the way mentioned above (boiler pressure 6-8 bar and throttling).

Albert

Albert,
Yes, as several of us have mentioned on here in the past, the valve events on many gears are not the best when hooking up a long ways. I do get a significant reduction in steam consumption from back off about 15-20 degrees from full motion.
That's an interesting fuel consumption number. What sort of wood are you burning?

Mike

Mike,

I'm burning well seasoned beech. At the end of this past steaming season I made a good experience with rather short pieces (half the length I had used so far). They cover the fire grate more evenly, which improves economy. They are thick chunks, thus reducing the reloading frequency.

Albert