Re-facing Slide Valve & Ports

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Builder01
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Re-facing Slide Valve & Ports

Post by Builder01 »

My slide valves are starting to dig a groove in the port face on my cylinders. Both cylinders and slide valves are made from cast bronze. It is to the point that a bit of steam is blowing by the valves when I open the throttle because they are not seating well. I have done several tests to prove that this is the problem. There may have been some lubrication problem that has caused this. I'm not sure just yet what has caused this, as there is only about 80 hours of running time on the locomotive.

I hope the grooves are not too deep. I would like to lap the cylinder port face and slide valves on a sheet of abrasive glued down to a surface plate. What type of abrasive is recommended so I don't end up embedding abrasive into the bronze?

David
Marty_Knox
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Re: Re-facing Slide Valve & Ports

Post by Marty_Knox »

Timesaver non-embedding lapping compound. You would be much better off using a true lapping plate.
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Builder01
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Re: Re-facing Slide Valve & Ports

Post by Builder01 »

I don't have a true lapping plate. Is there anything I can do that would work as well, or, nearly as well?

Time is a consideration as well. I will be hauling people at the my club's next open house. I will have a week between events to strip the cylinders from the frame and true up the valves and port faces in time for the open house. If I can do this using abrasive sheet on a surface plate, this should not be a problem.



David
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Re: Re-facing Slide Valve & Ports

Post by rkcarguy »

Maybe not enough clearance, and things are getting tight when the heat of the steam expands the valves?
Do you have enough meat on the slide valves to line them with something? Like mill them down a little and attach a layer of Teflon or something?
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Bill Shields
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Re: Re-facing Slide Valve & Ports

Post by Bill Shields »

80 hours is not a lot of time. What materials are used (cylinder / valve)?

If you don't have a lapping plate, you might consider using a fly cutter on the cylinder surface just enough to remove the wear / grooves, then polish the surface as best you can.

If a surface plate and abrasive paper is all you have then work with it...but go slow.
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DianneB
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Re: Re-facing Slide Valve & Ports

Post by DianneB »

Builder01 wrote: Wed Sep 05, 2018 10:24 pmI don't have a true lapping plate. Is there anything I can do that would work as well, or, nearly as well?
I have used plate glass as a surface plate with considerable success. Not "window glass" but the thick glass used for display cases, etc. Plate glass can often be had from any commercial glazier and isn't too expensive if you aren't particular about the dimensions and can take their "left-over".

I have adhered thin abrasive sheets to plate glass and used it for lapping valves - it works well.
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Re: Re-facing Slide Valve & Ports

Post by Soot n' Cinders »

I polished my valves and port faces with abrasive paper on a surface plate, worked just fine for me. I used ultra fine paper though and it did take a while to work up to it. I went up to 1500 grit wet/dry paper and used some WD-40 or Kerosene on it to help clear the particulate. Definitely have to work slow, too much force and youll get a convex surface and have to start all over again.
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Builder01
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Re: Re-facing Slide Valve & Ports

Post by Builder01 »

As I mentioned in my first post, the cylinder and slide valves are cast bronze. The engine has actually run quite well before this recent problem. As such, I'm pretty sure the clearances are fine.

I have a surface plate, but, no lapping plate. If I use abrasive paper, I am interested in what type will not embed particulates into the bronze.

Soot n' Cinders, what type of wet/dry paper did you use, (or, is there only one type?) I am asking about the specific kind of abrasive on the paper. I don't want to get the abrasive embedded into my cast bronze cylinders and valves.

David
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Re: Re-facing Slide Valve & Ports

Post by Soot n' Cinders »

Builder01 wrote: Thu Sep 06, 2018 8:28 am As I mentioned in my first post, the cylinder and slide valves are cast bronze. The engine has actually run quite well before this recent problem. As such, I'm pretty sure the clearances are fine.

I have a surface plate, but, no lapping plate. If I use abrasive paper, I am interested in what type will not embed particulates into the bronze.

Soot n' Cinders, what type of wet/dry paper did you use, (or, is there only one type?) I am asking about the specific kind of abrasive on the paper. I don't want to get the abrasive embedded into my cast bronze cylinders and valves.

David
I used 3M brand paper and had no issues with embedding. I imagine the kero helped prevent embedding too since it acts like a light lubricant
-Tristan

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Fender
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Re: Re-facing Slide Valve & Ports

Post by Fender »

Bronze sliding on bronze is not a good combination. To reduce future wear problems, consider changing the valve to another metal such as cast iron or even glass-filled ptfe. Usually, you want dissimilar metals bearing on each other, such as bronze on steel or bronze on cast iron. An exception is cast iron bearing on cast iron, which works well.
Last edited by Fender on Thu Sep 06, 2018 8:57 am, edited 1 time in total.
Dan Watson
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Builder01
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Re: Re-facing Slide Valve & Ports

Post by Builder01 »

Thanks Tristan, I wonder what the abrasive on the 3M paper is? Are your cylinders and valves cast bronze?

Dan, cast bronze is the material offered by Blackgates in England as a premium material over cast iron. This material has been used successfully for many years by others. I am pretty sure my problem stems from a lubrication problem.

David
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Fender
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Re: Re-facing Slide Valve & Ports

Post by Fender »

David, I’m sure the bronze on bronze will work, but lubrication problems in the valve chest is a frequent problem, especially with mechanical lubricators. Bronze wearing against bronze would never be used in industry.
Dan Watson
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