Purpose of False Valve Seats

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jlakes85
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Purpose of False Valve Seats

Post by jlakes85 » Fri Jul 05, 2019 9:16 am

Hi All,

I've come across a design with this feature on a slide valve. Is this to ensure that the wearing surface is completely replaceable? Thanks again

-jlakes85

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cbrew
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Re: Purpose of False Valve Seats

Post by cbrew » Fri Jul 05, 2019 9:33 am

not sure what you mean by "False Valve Seats"? please add more detail to your question.
Thanks
If it is not live steam. its not worth it.

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rudd
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Re: Purpose of False Valve Seats

Post by rudd » Fri Jul 05, 2019 10:03 am

Not sure about models, but this was often done on prototype slide valve engines when the valve seat became too worn to straighten out and maintain the alignment with the gland/valve rod.
Mill the top off the valve seat down enough to install a "false seat" - a slab-o-arn with the ports cut into it and sealed to the milled down surface of the original seat.
I think I've seen something from Jack Bodeman about doing this on a model.

jlakes85
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Re: Purpose of False Valve Seats

Post by jlakes85 » Fri Jul 05, 2019 10:34 am

From the drawings, it is a separate steel piece that bolts on top of the actual cast iron valve face

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rudd
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Re: Purpose of False Valve Seats

Post by rudd » Fri Jul 05, 2019 10:49 am

yes, that sounds like a false seat.
Why would it be steel with all the associated rust issues? Maybe not a problem on a model, but I'd think cast iron would be a better material for several reasons. Corrosion (CI develops a "skin" that slows further corrosion), wear, and the porosity of the iron to hold on to oil better.
I'd like to hear reasons my logic is faulty.
Is it a bronze casting that gets the seat?

jlakes85
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Re: Purpose of False Valve Seats

Post by jlakes85 » Fri Jul 05, 2019 11:20 am

Hi rudd,

The cylinder is cast iron..I'm assuming the designer meant to make the seat out of 303 or 304 SS. The valve is cast bronze

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cbrew
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Re: Purpose of False Valve Seats

Post by cbrew » Fri Jul 05, 2019 2:53 pm

hmm, with a model, the damage most really be bad to justify the need to add a new seat plate.
and Stainless Steel or Steel are both poor choices.
when it was time to resurface the cylinders on my locomotive, I just mounted them in the mill and used a fly cutter, they cleaned up with in .010. did the same with the valves and lapped them in
If it is not live steam. its not worth it.

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gwrdriver
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Re: Purpose of False Valve Seats

Post by gwrdriver » Fri Jul 05, 2019 8:44 pm

I've used valve face "inserts" (my terminology) on two locomotives. In the first instance it was to save castings with poorly placed steam passage cores. In the second instance it was to enable better design and easier machining of steam passages where there was no coring. In both instances the valve faces were cast iron.
Last edited by gwrdriver on Fri Jul 05, 2019 9:15 pm, edited 1 time in total.
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Bill Shields
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Re: Purpose of False Valve Seats

Post by Bill Shields » Fri Jul 05, 2019 8:56 pm

i'm with cbrew on this.

why in the world would someone make a sliding valve surface from stainless steel?

replaceable inserts in a model (of any material) are tough to make and probably more trouble than they are worth (sealing will be a tough go...)

getting the cylinders into the milling machine after a few decades of being bolted into the frames (which can require removing the boiler) can be a headache.

I have on a couple of occasions resurfaced valve surfaces in place...takes a careful hand and lots of patience but can be done.
Too many things going on to bother listing them.

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