Safety valve location

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Mike Walsh
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Location: St. Louis, MO

Safety valve location

Post by Mike Walsh » Tue Jun 22, 2021 7:06 am

Hello

Will be doing some solder repairs on my copper boiler later this summer if all goes well.

I have the opportunity to make some modifications. Currently, the safety valve (1) is located dead center on the steam dome lid. As most know, this is where the dry pipe inlet is located. I am about 75% sure I am relocating the throttle to the smokebox (from the dome), requiring me to make an "Extension" to raise the dry pipe inlet to the appropriate location.

Is a safety valve located within 1/2" of the dry pipe inlet ideal practice? Or will this contribute to pulling water when working the throttle hard while popping?

This is a copper boiler so it will be hot during the repairs - I could add bushings directly to the shell (not on the dome) for some Eccentric Engineer safety valves, of which I have a surplus of...

For reference, this is a 1" scale Little Engines Atlantic.

Constructive feedback appreciated.

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gwrdriver
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Re: Safety valve location

Post by gwrdriver » Tue Jun 22, 2021 7:39 am

If not dictated by prototype or obstructions, I'd locate safeties in the last "course" (or section - if any) in front of the firebox.
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Nashville TN

jscarmozza
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Re: Safety valve location

Post by jscarmozza » Tue Jun 22, 2021 7:48 am

Mike, this is a little off topic, but are you going to make your own smoke box throttle valve? I made a smaller replacement for a 1-1/2" scale railroad supply valve that was in my 1" Atlantic, don't know how they managed to get it in there! So far my home made valve seems to be functioning ok. You'll notice a difference in the amount of throttle lever movement between the steam dome valve and smoke box valve, the smoke box valve will require more movement of the lever to open the valve ports. Please post pictures of your progress, this is an interesting modification. Attached is a photo of my smoke box valve before being smoked. John
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image.jpeg

Mike Walsh
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Re: Safety valve location

Post by Mike Walsh » Tue Jun 22, 2021 9:32 am

Thank you for the photo, John. I am uncertain what I will use. I may use a bronze ball valve with SS stem/seats. I may consider a homemade design. Time will tell. The challenge at present is to make the repairs and possibly the modification for the safety valve. The more I think about it, the modification sounds more feasible since many clubs require two pops. I only have one at present

Glenn Brooks
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Re: Safety valve location

Post by Glenn Brooks » Tue Jun 22, 2021 12:48 pm

Mike, Iam no expert, but I’ve always heard the safety should be located at the highest point in the system- which allows it to gauge highest pressure. Hence the steam dome is the ideal location. Maybe someone expert in boiler design can join in and clarify...

Glenn
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Pontiacguy1
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Re: Safety valve location

Post by Pontiacguy1 » Tue Jun 22, 2021 1:56 pm

A lot of your early locomotive designs had the safety valves coming out of the steam dome either at the top or from the side, sort of like the whistle. Later, as locomotives got larger and overall height and clearance became issues, most locomotives had them directly on the boiler barrel in front of the cab, or somewhere near there. As far as function goes, it doesn't matter where you put it as long as it's at the top of the boiler where there will only be steam, and it has no way to be shut off or isolated during use. Just go with what the prototype did, and if you're not following a prototype, then do what makes the most sense to you esthetically.

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pat1027
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Re: Safety valve location

Post by pat1027 » Tue Jun 22, 2021 2:42 pm

A higher point in the boiler will be less prone to carry over than a lower point. It matters for the take off to the throttle but not so much the safety valves. Height won't affect pressure.

I came across this video after an abrupt problem with severe foaming. Not completely related to the original post but interesting none the less.


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Builder01
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Re: Safety valve location

Post by Builder01 » Tue Jun 22, 2021 3:52 pm

Glenn Brooks wrote:
Tue Jun 22, 2021 12:48 pm
Mike, Iam no expert, but I’ve always heard the safety should be located at the highest point in the system- which allows it to gauge highest pressure. Hence the steam dome is the ideal location. Maybe someone expert in boiler design can join in and clarify...

Glenn
Highest point equals highest pressure? Huh, what?

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gwrdriver
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Re: Safety valve location

Post by gwrdriver » Tue Jun 22, 2021 7:13 pm

In our models the pressure is essentially equal everywhere. The drypipe intake opening should ideally be located at the highest point in the boiler to avoid priming, thus the existence of domes. There is no rule stating such, and for every rule there are exceptions, but I favor the boiler shell location near the firebox end because maximum pressure, and accidental overpressuring, is more likely to occur in that area.
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Bill Shields
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Re: Safety valve location

Post by Bill Shields » Tue Jun 22, 2021 7:45 pm

The pressure inside a loco boiler js the same everywhere...if you discount the weight of water at the mud ring as measured to the waterline.

Put em where you want em and they look good.

On top of the steam dome tends to carry over less water if the boiler is full.
Too many things going on to bother listing them.

Harold_V
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Re: Safety valve location

Post by Harold_V » Wed Jun 23, 2021 1:52 am

Glenn Brooks wrote:
Tue Jun 22, 2021 12:48 pm
Mike, Iam no expert, but I’ve always heard the safety should be located at the highest point in the system- which allows it to gauge highest pressure.
Help me understand that, Glenn. Seems to me that the pressure inside a boiler is not variable by location. Have I missed something?

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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Bill Shields
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Re: Safety valve location

Post by Bill Shields » Wed Jun 23, 2021 6:39 am

No...you have not..

Pressure is the same except for a slight depression caused by velocity directly in the mouth of the dry pipe.

Slamming the throttle closed can cause a pressure wave inside the boiler that can cause intermittent lifting of the safety valves
Too many things going on to bother listing them.

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