Wednesday, October 25, 2006
I’ll start things off with stationary engines.
The concept behind a stationary steam engine is fairly simple. Steam is generated in a boiler and then piped to an engine where it is used to push a piston down a cylinder. The piston is attached to a push-rod, which turns a crank attached to a flywheel and pulley. Just like that, you have a nice smooth power source to power your machinery.
The problem is, if you just pipe steam into a cylinder, it will push the piston to one end and stop. If you want to push the piston back, you can seal off the other end of the cylinder and pipe steam in on the opposite side of the piston. That’s still not going to help though because if you pipe the same steam pressure to both ends of the cylinder, the pressures cancel each other out and the piston doesn’t move.
What’s really necessary is to make the system work is a set of valves that allow steam to enter one side of the cylinder while allowing it to escape from the other. Unless you want a worker next to the engine all day opening and closing valves, you need a valve gear mechanism.
In its simplest form, a valve gear mechanism is just an eccentric on the crankshaft connected to a pushrod that moves a plate or piston back and forth, that directs the flow of steam and exhaust. This would work for some things, but doesn’t allow the engine to be run efficiently in reverse without stopping to modify the engine setup. After you’ve figured out how to reverse the valve operation there’s another problem.
If you want an engine to run efficiently, you need the ability to adjust the length of time the steam valve is open. Simply leaving the steam valve open for the entire length of a piston’s stroke will give you tremendous power, but it also uses plenty of steam. To reduce the steam consumption, you open the valve briefly at the beginning of the stroke, then shut it again, using the expansion of the steam to move the piston, rather than just the raw pressure supplied from the boiler. Of course the amount of power you need can vary considerably, so it’s necessary to make adjustments to the valve timing while the machine is still running. There are multiple versions of valve gears that deal with this, which were adapted to various applications like steam locomotives and tractors.
After you’ve solved those problems, there’s one more little detail, how do you keep the engine running at the same speed all the time when the load on the machine is being varied constantly? This is where a device called a governor comes into play. It’s a device that creates a feedback loop so that the speed of the engine has an impact on the power applied to each stroke.
In the picture above you will notice a tan belt running from behind the flywheel to a small pulley on the left hand side of the engine. This pulley is geared to something that looks a little like what you’ll see in the next picture.
This is a simple theoretical design. It’s not perfectly accurate to any one device, but it at least similar to what you will see on most steam engines. There are two weights on the end of link arms, and as the assembly rotates, these two weights move further outward until they balance they reach equilibrium with the force supplied by the counterweight. The rod traveling through the middle of the assembly is free to move up and down as the weights and counterbalance push it, and it is this movement that controls the application of power. There are many versions of this type of governor with seemingly endless variations of springs, weights, and linkages, but they all come back to the utilization of centrifugal force on a counterweight.
Even the simplest little engines, like this one, have some sort of governor to control their speed. On this one, you’ll see it located right on top of a valve on the steam supply line.
As always, there are a few more unusual versions of this centrifugal governor design. Here’s an example of an un-restored skinner engine which actually mounts the governor assembly inside the flywheel.
As before, 2 counterweights are spun around and pulled outward from the center of rotation. In this case, they are opposing a force supplied by a large set of leaf springs which are also mounted inside the flywheel. It is also worth noting, that while the previous two examples we’ve seen controlled the engine’s speed by controlling the steam supply, this governor actually changes the motion of the eccentric which controls the amount of travel of the slide valve.
As time went by, the steam engine was refined to get more power for less energy. Valve designs evolved so that valves opened very quickly and precisely in order to get a quick burst of steam into the cylinder, allowing for considerable power at high speeds. As this video shows, there are plenty of moving parts used in some of the more complicated valve systems.
In this case, there two intake valves (located on the top of the cylinder) and two exhaust valves (on the bottom) being driven off of a complex cam system. Two dashpots (seen in the floor) are employed to control the valves as they open and close so that they can be moved quickly with minimal shock.
Another advance in steam engine efficiency was the introduction of double (possibly even triple) expansion steam cylinders.
If you look at this picture you’ll notice that this corliss engine, the ‘Marshall’ manufactured by Allis Chalmers, happens to have two cylinders, one of which is much larger than the other. The reason for this is that even after a quantity of steam is used once, it usually has some remaining potential for expansion. The problem is, this ‘used steam’ occupies a much greater volume than it did originally and it provides much lower pressure than before, so in order to get similar amounts of force, you need to have a larger surface area for it to push against. With this in mind, you can understand how it is appropriate to first send steam to the small cylinder and then send the exhaust from that cylinder to the larger cylinder.
This increases efficiency by getting more energy out of a given quantity of steam, but it also adds considerably to the complexity of the machine. I think this is best illustrated by this next picture.
I really love that view of the engine because most of the parts you see in the picture are moving, so watching it run is quite impressive.
Eventually these beautiful behemoths would be replaced by other power sources, but that doesn’t mean they become any less interesting.
Friday, October 20, 2006
Tuesday, October 17, 2006
Monday, October 16, 2006
As usual, I spent most of my time in the small town of Ballarat. I've already posted several pictures from there. I could post a few more pictures from there, but it would only be more of the same. I ended up catching a train from Ballarat to Melbourne.
It was a nice chance to relax and watch the Australian countryside.
I ended up in a Hotel in Melbourne near the Flinders Street Station
This area is apparently the place to meet in Melbourne. It has considerable train traffic as well as a couple of tram stops right outside. In the evening the entryway to this place was absolutely packed with people. Chances are, most of them are intent upon going to the river walk area.
Along the river in Melbourne there's a long stretch that's filled with cafes, restaurants, pubs and shops. It's a bit quiet in the morning, but it's swarming with people in the evening. As is usually the case in Melbourne, there's also a considerable amount of green space left open so that the area doesn't seem exceedingly crowded.
Of course if you want to get a tour of Melbourne without having to walk, you can hop one of their 'City Circle' trolleys. These old style trolley cars can take you around to see the attractions of Melbourne.
I have to say, I'm not too crazy about crowded cities, but Melbourne is really pretty nice.
Friday, October 13, 2006
Tuesday, October 10, 2006
Monday, October 02, 2006
I left off in Nikko, Japan where I was visiting some of the beatiful shrines that have made the region famous. After a quick lunch, my companions and I proceeded on to nearby Lake Chuzenji.
It may be a little difficult to believe, but this picture really was taken on the same day as the rest of the pictures I posted from this trip. The difference is, that by this point in the day, we had climbed up high enough into the mountains that we were above the clouds. That's right, Lake Chuzenji is actually up in the mountains. It was created as the result of a volcanic eruption which led to the formation of a natural dam, trapping a large mass of water.
This area is also home to a large number of waterfalls. I stopped by Yudaki falls, which is fed by water from nearby Lake Yunoko. Though not listed as one of the best waterfalls in Japan, it is certainly impressive.
Proceeding up a little higher into the mountains we come to Lake Yunoko. Though much smaller than Lake Chuzenji, this area still draws quite a crowd but for a different reason.
This area is home to a number of hot-springs, which actually provide much of the water for the lake. Multiple spas have sprung up in the area, making this a popular destination for Japanese tourists looking for a place to take a relaxing vacation. The town even has public bath where anyone can dip their feet into the steaming hot water from the springs.
Of course all of this water has to go somewhere, which brings me back to where the previous picture was taken, almost. This was taken above the Yudaki falls, which apparently offers and impressive view from above and below.
That's all from Japan. After this I traveled on to Singapore and Thailand, but I'm afraid there aren't any pictures from there, at least not from this trip.
Stay tuned though, I have a few photos from Australia to share!