throttle questions from a noob

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first off id like to thank everyone on this site for the bytes of information i have found.

I've got a couple of questions about throttles/ constant speed maintainers(i believe they are called governors for steam engines)

is there some sort of mechanism that will allow you to mechanically( with out adjusting airflow) change the speed(rpm) of a steam engine, and when that desired speed is reached, maintain said speed?

I've seen the governor system on the "hit or miss" engines, but that's not a variable speed system is it?

also another question, does anyone know the location of, or a formula for, how thick the walls of a cylinder (made of aluminum) should be for a certain psi of steam pressure.

thanks for the help

RJ

 

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oops, forgot something

the "throttle" on this engine

if you adjust the pressure or volume of air into the piston chamber, will the linkage arm on the side keep it at a constant speed, or accelerate intill it hasn't enough pressure to accelerate? ( basically, does an engine with this linkage always run at its highest potential?)

 

[steamer]

Hi,
You can throttle the air/steam going into the cylinder

or

You can shorten the duration of valve opening. This is called controlling with cut-off.

Most model steam engines have relatively long cut-offs. Typically 88% of stroke.

If you limit the duration to say 50% of stroke, the engine will run slower.


Dave

 

[Maryak]

RJ,

Cylinder Thickness
T = P x D
------
2t

Pressure
P = 2T x t
------
D

Where:
D = Diameter
t = UTS
T = Thickness
P = Working Pressure

For Aluminium

Safety Factor using air 15
Using steam 25

UTS Aluminium (average) = 15000 psi

Using air = 1000psi
Using steam = 600 psi

For a cylinder of 1" bore and a WP of 100 psi

Air = 0.050" Wall thickness
Steam = 0.083" Wall thickness

Hope this helps ???

Best Regards
Bob

 

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awesome, thanks guys that helps,
a question on Cut off, is that something that is predetermined or variable? or both based on design?

and Bob, on the formulas, what do you mean by safety factor? (the numerical value you stated) how do i work that into the aforementioned formulas?
also what does UTS stand for

thanks for the help guys

RJ

 

[Maryak]

RJ,

Safety factor is the maximum stress considered to be safe for use in particular engineering situations.

UTS is the Ultimate Tensile Strength of the material being used to engineer the part.

Looking up the tables for Aluminium UTS in tension, it can vary from 10000 psi to 48000 psi, dependent on which alloy etc.etc. I settled on the low end at 15000 psi.

This UTS is divided by the safety factor to give the number for use in the formulae.

The differences in safety factors between air and steam are an allowance for the temperature variations encountered using steam, (which stress the cylinder more), than when using air.

Again the numbers were selected from tables which have pre-calculated the individual factors making up the total safety factor.

The tables I used were found in Machinerys Handbook.

I hope this helps. ???

Best Regards
Bob

 

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thats what i needed ;D thanks a ton

RJ