Simplex Valvegear Simulation

[Kleenaxe]

Simplex Valvegear simulation.

I have been reading Don Ashton’s magazine articles and website so decided to have a look at a Simplex to see if I could increase my understanding of valvegear design.
There have been a lot of Simplex’s built and they seem to run ok but what is the performance really like and is there room for improvement? I wanted to check this using the simulators now available before I finish my valve gear.

I have entered the dimensions for Simplex valve gear into both Charlie Dockstader’s and Alan Wallace’s simulators but in both cases the values given on the drawings result in a jumble of lines rather than the smooth curves expected. By modifying two of the dimensions I can get a reasonable result but when I apply these dimensions to my Simplex they will not allow the motion to work, i.e. the expansion link is tipped forward due to the eccentric rod being too short and will not allow the motion to rotate fully, I have to go back to the drawing’s dimension to get it to work. So at the moment I cannot use a simulator to examine the calculated performance.

I know there’s more to it than just these two parameters but I using this as an example to show the disparate results I obtain.

Using Alan wallace's Simulator:

With one modification I can get closer to what I expected:
EX Eccentric Rod length: change from 3.9375 to 3.688

and this one evens up the front and rear ends:
DU Union Link: change from 1.250 to 1.1875

I have to go back to 3.9375 and 1.250 respectively to get the motion to work on my Simplex.
My construction is accurate to the drawings and the data entered in the simulators matches this but the above results are obtained so what’s wrong here?

Similar results are returned using Charlie Dockstader’s simulator.

Has anybody already done this and if so what results did you get and also what am I doing wrong with my data entry?

[baggo]

I looked at the Simplex valve gear some time ago but normally use the Bill Hall simulator as I find it easier. However, I've put the Simplex into the Wallace one to have a look, with the following results:





The original design is not bad but can benefit by a bit of 'tweaking' here and there.

Here's the Hall data if you want to have a play with that:



John

[donashton]

Hello,

Simplex owners will report performances to be anything between fine and poor and this probably reflects different perceptions and variable qualities of build. Hardwicke wisely tries to discover the truth via computer as this may aid in any necessary modifications.

Martin Evans used Henry Greenly's over-simplistic formulae resulting, especially in cases of outside admission, in too great angular swings of both combination lever and expansion link, with valves attempting to clout the steam chest ends. He misunderstood the nature of combining two harmonic motions at 90 degrees.

The clues are in John's input figures: 35 degrees of lifting arm for full gear compares poorly with the full size norm of around 28 and the pitch circle is oversize. Other defects are not so obvious until one views the diagrams of the file.

Some years ago I sought a solution which did not involve too much remaking of parts but found this too restrictive. I therefore opted for a redesign to make the valve do as Martin intended. Anyone interested is welcome to email me for my Wallace file (see members' profiles) or to discuss in detail.

Don

[Kleenaxe]

Thanks Baggo for looking at this but I'm not sure it answers the question as
reducing the expansion link backset from 0.53125 to 0.2853 to allow an
eccentric rod length of 3.9375 still leaves me with a missing 0.24X
or there abouts as this has effectively moved the pivot point, regardless
of what this does to the valve timing I still have a significant gap.

Backset change 0.53125 - 0.2853 = 0.24595
Eccentric rod change 3.9375 - 3.688 = 0.2495


I have not been able to get Bill Hall's simulator to run so am using
both Wallace and Dockstader simulators but from what I see the data is the
same as I am using apart from specifiying the backset angle, am I correct to
assume (assumtions run from precarious to dangerous in my experience) that this
is where you got the backset dimension of 0.2853 from?

I'v got something wrong but can't at the moment see what it is.



Another problem with Simplex.

There is an interferance between the coupling rod and the weighshaft of 0.0625 when
the wheels are fully depressed in the frames.

Weighshaft centre to axle centre 1.5
Subtract the following:
throw of crank 1.0625
half the depth of the coupling rod 0.1875
half the dia of the weighshaft 0.1875
------
leaves a gap of 0.0625

Axle movement 0.125 up and down
0.0625
for movement up subract 0.1250
------
-0.0625

Moving the weighshaft up would add further problems for the valve gear.

Yet there are many Simplexes running.

[baggo]

I think you may be getting confused with what the backset figure actually is? It's the horizontal distance between a vertical line through the expansion link trunnion and a vertical line through the driving pin:



The figure of 0.53125 is the distance of the driving pin centre from the centreline of the curved slot in the link, not the same thing. Thus although the driving pin centre is offset from the centreline of the slot by 0.53125, the actual backset is 0.2853.

I haven't got that far with my 0-6-2 version so hadn't noticed the limited clearance between the weighshaft and the coupling rods. To be honest, I doubt if you will get any more than 1/16" upwards displacement of the axle during normal running unless the springing is very soft. If necessary, you could always mill or file a flat on the underside of the weighshaft to give a bit more clearance. It shouldn't be too conspicuous.
John

[Kleenaxe]

Thanks John (Baggo)

You're right, I have been using the wrong value for the backset parameter.
Hopefully the fog should clear a little now.
I knew I had something wrong, I wonder what else.......

Hardwicke

[donashton]

Hello,

Baggo's measuring of backset is correct, always assuming that the 'vertical' line through the trunnion is at 90 degrees to the radius rod when in midgear and not the railhead. It is a pity that so many drawings use ambiguous markings for an important item.

Since this angle often does not relate to the other parts of the mechanism the backset's 'horizontal' set cannot be added mathematically to the centres of the eccentric rod, which has its own horizontal and vertical planes.

I also notice that Simplex's return crank ought to be a little thicker, as many builders will want to check running before finally pinning, and often suffer a shift before fitting a pin.

Don

[KennLindeman]

Had anybody put in the Supers Simplex details into the Wallace Sim

[jma1009]

I set the valve gear on the IWMES Super Simplex some 25 plus years ago and found it ok. After a bit of work. Extensively tested on air.

I also altered the boiler design before it was professionally made for us.

I also asked Don Young to look at the draughting in the smokebox.

I have since reviewed what Don Young recommended, and it is ok in the light of subsequent research/thoughts.

However, Super Simplex is a conundrum; and I never got the IWMES example to steam as it should. Never quite understood why it never didn’t “sparkle”. Our Chairman Reg Wrenn accused me of (when setting up the smokebox draughting) of the smokebox and chimney that didn’t line up leaving saddle to smokebox holes open for connecting bolts. And loss of smokebox vacuum. As many forum members will know, I am very particular and careful with smokebox draughting and the suggestion that I had exposed 10 BA bolt holes to air whilst setting right the chimney made by Reg and the smokebox was utter nonsense.

I simply think Super Simplex has cylinders that are too big for the boiler.

I really don’t recall any valve gear issues other than the excessive expansion link swing and limiting the “over run” of the valves in full gear.

But it is a long time ago and I have only the Don Young amendments to the draughting and boiler mods drawings.

[simon6200]

I put Simplex in the Wallace simulator years ago and I seem to remember that the events were very good. I did the same with Super and it was less good. I can’t remember any specifics.
My Simplex, which I bought to drive while making my Springbok, has never steamed as well as I think it should. I have run it on many a running day and I have to use blower much of the time. It doesn’t notch up beyond two turns (about 7 to mid gear). It is one thing to have a good design and another to translate it very accurately to metal.

[andrewtoplis]

Nov 13, 2024 8:52:10 GMT simon6200 said:

It doesn’t notch up beyond two turns (about 7 to mid gear). It is one thing to have a good design and another to translate it very accurately to metal

My unfinished simplex barely notches up as well, I've got two notches on the lever, full forward and slightly-less-than-full forward, pull it up beyond there and it isn't happy! Perhaps once run it it'll allow for another notch in due course