How Do You "Hook Up" A Steam Locomotive?

I THINK it means that the engineer has adjusted the engines valve gear/cut off to its most efficient position for the speed and load on the engine.

I could be wrong and if I am we both will find out when Rich or Hot Water finds your topic.

Just my two cents

Bluecometk is correct.

The reverse gear in a steam locomotive can sorta be likened to the manual transmission of a car. In "first gear," the reverse lever will be put full forward, "in the corner." This lets steam be admitted to the cylinder for nearly the full piston stroke--that's a lot of power. As the train picks up speed, you don't need to be putting that much steam in; you "hook up" the gear by pulling the reverse lever back a notch here and there, which "cuts off" the amount of steam going into the cylinder. This is like putting the transmission into second, third, and fourth gear. You don't need as much steam, because the steam that is admitted expands to fill the cylinder. It's this expansion of steam that provides the horsepower.

Just like a car couldn't get moving if you tried to start in fourth gear, a steam engine would be difficult or impossible to start moving if you tried to do so while "hooked up."

When starting a train, the valves must open long enough to admit steam into the cylinder for almost the full stroke of the piston. This is needed when starting in order to get a long, steady push on the piston to get the wheels turning. When the reverse gear is set "down in the corner" at full stroke, steam may be admitted into the cylinders for 80% or more of the piston stroke.

If the reverse gear was left at that very long cutoff, the engine would quickly reach a point where it cannot run any faster because it is fighting itself to run. This will happen at a relatively slow speed - 20-30 mph. Even with the throttle wide open, the engine will not go any faster! This happens because so much steam is being admitted into the cylinder that it cannot all be exhausted before another power stroke starts. There is so much "back pressure" that the engine simply cannot run any faster. The engine makes a tremendous amount of noise when operated like this, but it doesn't develop much horsepower. It is also extremely wasteful of fuel.

As the speed increases the engineer "hooks up" the valve gear by moving the reverse lever back towards center a notch or two at a time. Each movement of the valve gear towards center shortens the cutoff a small amount. When running at 60 mph, the cutoff will be shortened so that steam is admitted for only 20-25% of the stroke. The steam works expansively for the remainder of the stroke.

It is fairly easy to tell when a steam locomotive is hooked up properly. If you can hear individual exhaust "chuffs" at high speed, the engine is hooked up right. If the exhaust has a steady roar like a jet engine, the cutoff is set way too long and the engineer is just making a lot of noise and wasting fuel.

The term "hooking up" actually comes from a very early steam locomotive design (1830s?), which had only two positions on the valve gear, for forward movement, i.e. full stroke and shortened stroke after starting. The "operator" of the locomotive, literally moved the link to a shorter stroke position and placed that link on a "hook", which kept that valve gear like in place. There was one of these links for each side's valve gear arrangement. Thus, upon moving, the speed was gained after the link was placed on its hook, i.e. "hooked up".

Well how about that. Thanks, Jack!

I learned something new today.

Thanks guys and I like hot waters ex of where hookup came from.  Both of you did good.

The reverse gear in a steam locomotive can sorta be likened to the manual transmission of a car.

There is a much more closely related automotive analogy.  While few cars have variable valve timing they all have variable ignition timing, we just don't think about it much since it has been done automatically for about 75 years.

When a gasoline engine starts the spark plug must fire as the piston is near or just past top dead center.  If the spark comes too early the engine will run backwards.  That can cause injury to anyone hand cranking the engine and can cause damage if the engine is not stopped immediately since the oil pump is also running backwards.  But a gasoline engine can not run efficiently at high RPM with the spark occurring near top dead center.  The spark must be advanced so that the fuel air mixture is first ignited well before the piston reaches top dead center.  This allows time for complete combustion to happen between moment the piston reaches TDC and the end of the power stroke.  If the spark remains retarded and the engine is run at high RPM the still burning fuel air mixture can damage the exhaust valves as it is exits the cylinder.

A gasoline engine running at high speed with the ignition timing properly advanced is very similar to a steam locomotive running expansively with the valve timing "hooked up."

Very good analogy, Ted.

In fact, some valve gears were capable of "Variable Lead" which is essentially the same thing you are talking about here with the spark advance in an automobile ignition. If memory serves, the Stephenson Valve gear was capable of variable lead, which opened the steam admission port a little earlier in the stroke when hooked up. This is directly analogous to the centrifugal advance in an old distributor, or the computer-controlled spark advance we have now.

While there were some performance advantages to variable lead gears, especially at high speeds, the difficulty of maintaining the Stephenson Valve Gear was its ultimate downfall. Walschearts and Baker gears were fixed lead gears, but they were almost bulletproof and easy to keep in time and running right. The small performance advantage of variable lead was not enough to compensate for the maintenance problems with the Stephenson Gear, which is why so few locomotives used it.

Even the little Flagg Coal Co. 0-4-0  #75 ran smoother when I "hooked 'er up" in both forward and reverse!

Rich

Thanks, I'm glad to hear that you found that an apt analogy.  Dave and I have had a chance to drive and work on some interesting machines.  It is nice when some of that obsolete knowledge finds a useful application.

If you are even in Seattle in the summer let us know if you would like to go for a ride in something with manual spark advance. 

Interesting. I never knew that about spark timing, but it does make sense. I suppose it's more analogous in terms of what is happening inside the cylinder.

Of course, neither anaology is perfect; with a car, we're dealing with internal combustion and a transmission. With a steam engine, we're dealing with valve setting, and a transmission that really doesn't change (a crosshead and rods).

When I'm trying to simplify and explain steam locomotive operation, or what the valve gear does, to our museum guests, most of whom are not railfans, they definitely understand car analogies. Throttle ("accelerator") and brakes are no-brainers.

The overall function of the Johnson Bar is also easy to understand: Push it forward, we move forward; pull it all the way back, and we move backwards. Middle, obviously, is "neutral."

It's an easy next step, once they understand that the Johnson Bar ultimately functions as a "stick shift," to explain the more subtle function of "hooking up" by using the "car manual transmission" analogy. While gearheads would undoubtably get the spark advance analogy, most folks have an easier time understanding that "hooking up" the valve gear is very much like shifting through the gears on a car.

(Another analogy I use that most men seem to understand: our oil burning engine uses a burner and an atomizer. When I tell them that the atomizer sort of works like lighting the spray from a can of hair spray on fire, the response from guys is ususally "Oh, yeah, of course..."  )

Lol! At least buy it a drink first!

Mike Maurice