Slide valve

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VGC
Posts: 111
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Location: Europe / earth - yet in freedom ;-)

Re: Slide valve

Post by VGC »

Emfinger wrote: Sun Jun 13, 2021 9:14 am Bill if you are not able or interested please don't ask for dimensions.
RussN, he wrote this without Bill having refused anything. So which option would you prefer now?
a) Promise manufacturing first, and then having the choice between being guilty for disfunction -and- iterating and teaching until success, against any possible unreasonable resistance?
b) Asking for dimensions and manufacturing exaxtly one try? This option has already been disabled by Emfinger if I read correctly.

To me, this appears to be unsolvable for people who do not like jumping into black holes ;-)
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milwiron
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Location: Flanagan, IL.

Re: Slide valve

Post by milwiron »

Yeah, I'm with VGC on this. After 4 pages of posts we have one hard dimension to work with- .015 of lap and the supposition that 1/2" throw isn't enough.
I quoted hundreds upon hundreds of machining jobs during my career, there seems to be no hope of a successful ending here.
Denny
Last edited by milwiron on Tue Jun 15, 2021 3:15 pm, edited 1 time in total.
"Measure twice, curse once."
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Harold_V
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Re: Slide valve

Post by Harold_V »

Emfinger wrote: Tue Jun 15, 2021 9:25 am No one has offered to make a valve therefore no specs are needed.
I'd like to intervene here.

First, no one in their right mind would even consider, let alone accept the obligation, to build something about which they know nothing (no reasonable details have been forthcoming).

Secondly, when someone is attempting to be helpful, it seems to me that one should show gratitude, not strike out because they are not hearing what they hope to hear.

A display of appreciation costs nothing. Caustic remarks are damaging. They are unwelcome on this board.

Need I say more?

H (moderator)
Wise people talk because they have something to say. Fools talk because they have to say something.
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baggo
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Location: Derby, UK

Re: Slide valve

Post by baggo »

Ok, still trying to be helpful hopefully :D

Tom has given the dimensions for the ports, the slide valve and the valve travel and we've filled in the missing dimensions? We've deduced that the lap is 0.125" and the 0.5" valve travel should match the travel required in full gear. The size of the exhaust cavity is dubious and I think too big but that won't affect the setting of the valve.

What hasn't been mentioned so far is the peculiarity of Stephenson's valve gear in that the amount of lead it gives varies with the cut off/position of the reverser (Johnson bar as you call it). Stephensons is what is known as a variable lead valve gear as opposed to Walschaert's which is constant lead (lead being the amount that the valve port is open when the piston is at top and bottom dead centres. Lead can be positive and negative. If negative the port opens after top or bottom dead centres)

With the normal locomotive type of Stephensons the lead increases as the cut off is reduced (Johnson bar moved from full gear towards mid gear) and this increase in lead can cause serious problems if it becomes excessive. The amount of increase depends on the design of the valve gear e.g. the length of the eccentric rods etc. To stop this it is usual to design the gear to give zero lead (or only a small amount) in full gear or even negative lead in full gear. Many Great Western locos were designed with negative lead in full gear so that the lead didn't become excessive at the normal cut offs used for running.

This may be Tom's problem and why he cannot get the correct port opening on the rear port when he sets the valve for the front port. Tom's using a figure of 0.015" as the lead in full gear and it probably shouldn't be anything like this. It may well be a negative figure in which case the ports won't open until after top and bottom dead centres (Without the drawings of the valve gear we can only guess though) Basically, the valve won't be centred about the mid point of the valve travel using that amount of lead and you will get different port openings.

So I would suggest trying to set the valves with the Johnson bar halfway between full gear and mid gear and see what happens then. At that position the valve should have some lead at both ends of the cylinder and you should be able to centre it. Note though that the valve gear travel will be reduced and you will only get the ports opening say halfway.

Hope that helps and has not further clouded the issue.

John
Secretary of The National 2½" Gauge Association
Member of North West Liecestershire SME

http://www.modeng.johnbaguley.info
Emfinger
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Location: Yucca Valley, CA

Re: Slide valve

Post by Emfinger »

milwiron wrote: Tue Jun 15, 2021 2:31 pm Yeah, I'm with VGC on this. After 4 pages of posts we have one hard dimension to work with- .015 of lap and the supposition that 1/2" throw isn't enough.
I quoted hundreds upon hundreds of machining jobs during my career, there seems to be no hope of a successful ending here.
Denny
My request was for someone who may be interested in making a pair of slide valves. Until someone offers to build them, no dimensions are needed.
Tom
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milwiron
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Re: Slide valve

Post by milwiron »

Got it, I deleted my fairly long reply.
Good luck, I wish you all the best.
Denny
"Measure twice, curse once."
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Bill Shields
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Re: Slide valve

Post by Bill Shields »

I guess that i am missing something...you want an offer to build something without providing a drawing of what you want built.

Good luck with that.. :P
Too many things going on to bother listing them.
VGC
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Re: Slide valve

Post by VGC »

After all I read here, I would expect a contract with the obligation to execute the work for free before getting the drawing.

But do I really want to find out if I am right?

No ;-)
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Bill Shields
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Re: Slide valve

Post by Bill Shields »

don't really give a hoot at this point - dead issue / seems to be a waste of everyone's time
Too many things going on to bother listing them.
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Harold_V
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Re: Slide valve

Post by Harold_V »

Yes, it is a waste of everyone's time.
I ran my commercial shop for 16 years. At no time in those 16 years did I quote a job without knowing what it entailed. Anyone who would do so is asking for trouble. All readers are advised to ignore this individual.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Emfinger
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Location: Yucca Valley, CA

Re: Slide valve

Post by Emfinger »

I don't know where you people get off making up all of this. I only asked if someone would be interested in making 2 slide valves. If someone said yes then I would send the info. and we could talk about the cost. I never asked anyone to solve my problem or to offer solutions, but several of you wanted to diagnose the problem, that has been done by me.
PS
I found a person who has made the valves for me.
Trust me I won't be asking for help from any of you...
VGC
Posts: 111
Joined: Tue Sep 22, 2009 3:17 am
Location: Europe / earth - yet in freedom ;-)

Re: Slide valve

Post by VGC »

Perhaps you should use the remaining time for training your communication skills rather than to get a steam locomotive running.
You did not even tell us the scale of your loco but expect a decision although you even did not explicitely say that you want to pay for the work.

If you are willing to apply the same discussion style on your meeting with Petrus some day, you perhaps should get used to wearing a parachute on your back soon.
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