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steam engine "hook motion"

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steam engine "hook motion"
Posted by gregc on Sunday, February 24, 2019 9:14 AM

i'm curious about steam engine valve gear and dont' understand what they mean by "hook motion".

i think i understand that there is both a D and V hook used to engage the valve rod to an eccentric(?).   I read that the ability to disconnect the linkage is necessary when a stationary steam engine is used in a mill (e.g. textile) and needs to stop immediately and precisely.

there's also the need in some early (pre Stephenson) valve gear to have independent linkages for forward and reverse.

while separate valve linkage is not needed on Walschaerts valve gear, my understanding is that the Walschaerts gear still produces this "hook motion"

greg - Philadelphia & Reading / Reading

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Posted by BigJim on Monday, February 25, 2019 11:25 AM

Greg,
Simply put, "hook motion" or "hooking up", as is more common, is the act of moving the reverse lever from full forward (or full reverse - depending on direction of travell) back toward center. This changes the amount of time the valve is open to admit steam into the cylinder. 

In starting the train, if the valve gear is in full forward/reverse, a large amount of steam is admited. If kept in this position, the engine will quickly run out of steam.

In order for the loco to be able to accelerate before running out of steam, the engineer will "hook up" the valve gear and less steam is admited (proportional to how far the lever is moved)  allowing for the expansive properties of steam to go to work and being more economical.

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Posted by gregc on Monday, February 25, 2019 1:16 PM

you're describing "cutoff", that the Johnson bar is moved more toward the center so that the valve is not open as long and less steam is allowed into the piston when reaching the desired speed.

i've never read "hooking up" and I don't see it in the literature.  Did you see the link in my OP?

and I thought it also referred to the ability of the valve gear, for example, cutoff was not adjustable on the John Bull.

are you saying it's simply the ability to adjust steam cutoff

greg - Philadelphia & Reading / Reading

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Posted by BigJim on Monday, February 25, 2019 5:53 PM

Greg,
Your link took me nowhere but back here to this thread!
Yes, "hooking up" is simply the ability to adjust steam cutoff by moving the reverse lever.

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Posted by gmpullman on Monday, February 25, 2019 7:58 PM

It was a term related to early Stephenson Valve gear. 

Gab motion in UK and Hook Motion in US:

https://en.wikipedia.org/wiki/Gab_valve_gear

Probably the best, understandable, explanation of the V Hook is here:

http://www.catskillarchive.com/rrextra/chapt18.Html

 

Cheers, Ed

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Posted by OT Dean on Tuesday, February 26, 2019 12:55 AM

BigJim

Greg,
Simply put, "hook motion" or "hooking up", as is more common, is the act of moving the reverse lever from full forward (or full reverse - depending on direction of travell) back toward center. This changes the amount of time the valve is open to admit steam into the cylinder. 

In starting the train, if the valve gear is in full forward/reverse, a large amount of steam is admited. If kept in this position, the engine will quickly run out of steam.

In order for the loco to be able to accelerate before running out of steam, the engineer will "hook up" the valve gear and less steam is admited (proportional to how far the lever is moved)  allowing for the expansive properties of steam to go to work and being more economical.

 

For those of you modeling the steam era, particularly the busy years of the first 30 years of the 20th Century, I highly recommend the novel, "The Big Ivy," by James McCague.  My elder brother and model RR mentor gave me a paperback copy of this treasure when I was just out of my teens--and I wore out that copy.  It is probably the most authentic book of railroad fiction ever written--certainly the best I've ever found.  The hero of the book is a railroad "runner" on the fictional Indiana Valley Railroad and tells of his rise through the ranks from lowly roundhouse wiper to one of the best engineers on his division.  It's full of all the details of the days of Steel Rails and Iron Men.  And, incidentally, describes him "hooking up" the valve gear for better speed and economy!  (Stephenson and Walshearts valve gear accomplishes their forward motion above the centerline so letting the linkage drop lower takes less effort.)

I just looked it up on abe.books, and paperback copies start at around $6.00.  Makes you thirsty for a beer at the local saloon and hungry for a "san'wich" from the Free Lunch!

Deano

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Posted by gregc on Tuesday, February 26, 2019 4:41 AM

thanks for the replies

gmpullman
Probably the best, understandable, explanation of the V Hook is here: http://www.catskillarchive.com/rrextra/chapt18.Html

i believe there is a distinction between "hooking up" and "hook motion". 

in early steam engines, separate linkages were needed for forward and reverse that had to be "hooked up" to make the engine run.   There was both D and V hooks.   The link above seems to refer to the linkage

 

the link in my OP was to a google search for "hook motion".    The various links on the search results are exactly for "hook motion".

chap 17 of the catskill site under Fig-7

When a slide-valve is actuated by an eccentric connected directly with the rocker-arm or valve-stem, the point of cut-off caused by the extent of lap, remains the same till a change is made on the valve, or on the throw of the eccentric, unless an independent cut-off valve be employed. Locomotives having the old hook motion worked under this disadvantage; because the hook could not vary the travel of the valve, which is the method usually resorted to for producing a variable cut-off. The link and other simple expansion gears perform their office of varying the cut-off in this way.

"The Big Ivy" sounds interesting and may be the best source for answering my question

greg - Philadelphia & Reading / Reading

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Posted by gmpullman on Tuesday, February 26, 2019 6:01 AM

gregc
i believe there is a distinction between "hooking up" and "hook motion". 

There certainly is.

 

I don't recall mentioning "hooking up" as in shortening the cutoff?

 

Perhaps I do not understand what you are looking for.

 

I posted a reference to the very early Stephenson valve gear.

This may shed more light on "Gab Motion" ? It is essentially an early method of reversing the locomotive through the engagement of the V hooks.

 

https://railwaywondersoftheworld.com/valves1.html

 

Good Luck,

 

Regards, Ed

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Posted by gregc on Tuesday, February 26, 2019 6:08 AM

gmpullman
Perhaps I do not understand what you are looking for.

what does "hook motion" refer to?

greg - Philadelphia & Reading / Reading

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Posted by gmpullman on Tuesday, February 26, 2019 6:20 AM

gregc
what does "hook motion" refer to?

The Brits are calling it a Gab, over here the term was Hook.

The term "Motion" was used to describe any of the "valve motions (i.e. valve gear) of the widely varying and continually improving designs.

 

The next step was to provide an eccentric for each direction of movement, and fix a single gab on the end of either rod, connecting up by suitable rods to a lever on the footplate, so that the driver could engage either gab at will, with a pin in the valve spindle. There were several variations of the gab motion. Some had the gabs pointing downwards towards the valve spindle; some had them pointing upwards; and some had one above and one below, so that they faced one another, and one engaged directly the other disconnected. The final arrangement was a double gab on the valve spindle itself, the ends of the two eccentric rods being connected by a bar.

Substitute Hook for Gab. I wish I could explain it in simpler terms.

 

gab:

 (ɡæb)

noun
1. (Mechanical Engineering) a hook or open notch in a rod or lever that drops over the spindle of a valve to for a temporary connection for operating the valve

  

Thank You, Ed

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Posted by gregc on Tuesday, February 26, 2019 6:28 AM

correct.   there's a hook that is a mechanical device and there are D and V types.

as previously posted

Locomotives having the old hook motion worked under this disadvantage; because the hook could not vary the travel of the valve, which is the method usually resorted to for producing a variable cut-off.

my current understanding is "hook motion" is an earlier term used to describe "cutoff" that is controllable using the Johnson bar (reverser) on Walschaerts valve gear.

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Posted by Overmod on Wednesday, February 27, 2019 11:52 AM

"Hook motion" always, and only, refers to the pre-link valve gear described as 'gab' gear above. 

"Hooking up" refers to lifting the reach rod relative to the link (whether the link be straight, as in early Allan gear, or curved as in 'Stephenson'.  The further you lift this, the greater the cutoff, until you go across center at 'mid' and start to implement reverse at very short cutoff.  This action has NOTHING to do with hook motion, which is short for 'motionwork' and not for the physical movement of the gear in action.

There is at least one very good essay circa 1845 on the early development of locomotive valve gear that covers the issue of continuous cutoff very well. 

Now, the next development is the riding or 'Cuyahoga' cutoff, starting I believe in the 1850s, which provided fine control without having to physically keep lifting and dropping the moving reach rod with a Johnson-bar lever or wheel.   This relies on relatively short-travel valves with Trick porting and the like, and its advantages did not transfer over either to long-lap long-travel valves or to the heavier components that increasing engine size began demanding as the 'hog' era arrived. 

Walschaerts valve gear is a link gear, and consequently all the components are in 'continuous mesh' and alignment; there is no hook, no engagement shock, no need to worry when going from ahead to reverse as the cutoff-control motion is continuous and essentially at right angles to the direction of actuation.  Yes, you still 'hook up' the reach rod to adjust the degree of cutoff, but no, there are no gabs that have to be engaged to move the valves.

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Posted by gregc on Thursday, February 28, 2019 6:04 AM

when did did the term "valve gear" replace terms involving "hook"?

was it the development of Walschaerts valve gear?

greg - Philadelphia & Reading / Reading

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Posted by BigJim on Thursday, February 28, 2019 8:57 AM

Not being previously educated in the very early valve motions, thank you for the research and enlightenment! It was interesting to find out where the origins of the term "hooking up" came from.

.

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Posted by gregc on Saturday, March 02, 2019 4:39 AM

the following diagram posted previously by Ed suggests the need to hook linkage onto a pin to switch from forward to reverse and possibly to stop the engine.

if "hook motion" refers to the ability to adjust cutoff, it doesn't seem possible with this type linkage that physically hooks linkage onto pins.

Overmod
Walschaerts valve gear is a link gear, and consequently all the components are in 'continuous mesh' and alignment; there is no hook, no engagement shock, no need to worry when going from ahead to reverse as the cutoff-control motion is continuous and essentially at right angles to the direction of actuation.

it looks like the the Stephenson valve gear (1841) combined the two hooks avoiding the need to hook linkage onto pins and allowing cutoff to be continuously adjusted.

 

 

Walschaerts (1844) came along a few years later.  Presumably by that time, cutoff adjustment during operation was common practice.

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Posted by gmpullman on Saturday, March 02, 2019 12:54 PM

They weren't all that concerned with cutoff back in the 1850s with boiler pressures around 100 PSI and speeds around 20 to 25 MPH and saturated steam.

Like any technology, it developed over time with improvements to meet demands of the increasing speeds and tonnage.

Cheers, Ed

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Posted by gregc on Sunday, March 03, 2019 4:51 AM

my understanding of the need for cutoff is that initially, the valve is open during the complete piston cycle to maximize force on the piston.   But this is inefficient because it doesn't take advantage of allowing the steam to expand and has maximum pressure at the end of the cycle which also leads to the problem of the piston having to reverse direction abruptly, fighting against the steam pressure on the back side of the piston.

while the throttle can be decreased to reduce the amount of the steam entering the piston, this is still inefficient.

if not at low pressure and speed, at what pressure and speed does cutoff make a difference?   

I can see cutoff being applied even with scaled live steam engines

 

greg - Philadelphia & Reading / Reading

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Posted by selector on Sunday, March 03, 2019 1:59 PM

The reverser is more efficient than trying to 'play' the throttle, which is often sticky and difficult to pry open, or to widen with slightly discrete steps.  It is far easier to simply widen the throttle, allow full steam pressure to the top of the cylinders, and to let the valves do the 'regulating' with a far finer series of incremental or decremental steps.

The cut-off is most useful in controlling the use of thermal energy, and therefore both water and fuel, at higher speeds where you want to get the 'value', or the calorific content, out of the steam to the fullest extent possible.  When the throttle is wide, about the time the locomotive passes the 20 mph mark, say, that is when you want to start shorting the cut-off and limiting the admission.  You want to get more work out of the steam, so.....LET IT!!  Admit, cut-off, and let what has been admitted continue to thrust the piston ahead of it until the piston valve passes and bares the exhaust port.  

If you just crack the throttle, and then use heavy cut-off, you'll have wisps and cooling steam doing almost nothing by the time the piston has travelled 60-70% of its stroke.  There's no efficiency there, and you're constantly fighting the closing spring on the throttle.  You couldn't lift a train of any tonnage that way.  So, do crack open the throttle, but have almost no cut-off and let the steam passing through the throttle valve work all the length of the stroke.  Later, near four cycles per second, you want an initial blast of pull temp/pressure steam, and to cut if off and let the company get the value out of both your wages and the fuel.

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Posted by richg1998 on Tuesday, March 05, 2019 11:38 AM

"Hooks".

This might have nothing to do with this discission but I did read about hooks many years ago.

Another book I read described the mechanisms in more detail for that era. It might have been by White. I have it somewhere in my collection.

http://www.catskillarchive.com/rrextra/abboc.Html

I did bash this loco in HO quite a few years ago. The short furnace version. There are many prototype photos on the Internet. Well, there use to be. I have quite a few.

Rich

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

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