Stuart Triple Expansion Engine

Alec Ryals · Feb 17, 2014

Looks like in drawing the nut and extending stud rod was machined flush with the top of the piston sure not very clear.
Alec

SirJohn · Feb 18, 2014

From the drawing it looks like there should be a lock nut on top of the piston.

rhankey · Feb 18, 2014

Alec Ryals said:
Looks like in drawing the nut and extending stud rod was machined flush with the top of the piston sure not very clear.
Alec

That is not so. Here is a enlargement of the drawing. the top of the rod/nut protrudes 1/16" above the top of the piston.

Alec Ryals · Sep 21, 2014

Not sure if this were im wat to post this but why use rings on a engine that will only see air hence it makes a 90% INCREASE in dag!
Alec Ryals

rhankey · Sep 22, 2014

Alec Ryals said:
Not sure if this were im wat to post this but why use rings on a engine that will only see air hence it makes a 90% INCREASE in dag!
Alec Ryals

A triple expansion engine won't run well on air unless you have a lot of blow by, plumb the air directly to each of the three cylinders, utilize some sort of simpling valve to direct air to all three cylinders, or otherwise. An expansion engine is predicated on steam being able to work multiple times, whereas compressed air only works once. Normally with compressed air, the HP cylinder will do all the work while the IP and LP cylinders do nothing.

That said, piston rings on three cylinders of an engine this size does add a lot of drag. Before I installed the piston rings, my triple turned over with very little effort on the flywheel. With all the piston rings installed, it is quite tight.

Charles Lamont · Sep 23, 2014

rhankey said:
Normally with compressed air, the HP cylinder will do all the work while the IP and LP cylinders do nothing.

The low pressure piston has more than 5 times the area of the high pressure one, so rather than compressed air, it might well be better to run it off a vacuum pump!

rhankey · Sep 23, 2014

Charles Lamont said:
The low pressure piston has more than 5 times the area of the high pressure one, so rather than compressed air, it might well be better to run it off a vacuum pump!

I'm not sure how well the valve timing would work if drawing a vacuum from the exhaust port.

Be it a vacuum pump to the exhaust or compressed air to the inlet of the LP cylinder, you would need to keep the pressures low, as it would be pretty easy to bend a rod or crank. The LP cylinder is intended to receive less then 1/5 the pressure of the HP cylinder.

Alec Ryals · Sep 24, 2014

Im using 2-56 setscrews to get in place then a pin to hold in place.
Alec Ryals

Alec Ryals · Dec 2, 2014

Does any one know the size of screw to use to hold the shroud in place hence 7BA seems a bit large , Any ideas would be of great help.\
Thank You all and have a Safe and Great Holiday
Alec Ryals

Alec Ryals · Dec 2, 2014

That said, piston rings on three cylinders of an engine this size does add a lot of drag. Before I installed the piston rings, my triple turned over with very little effort on the flywheel. With all the piston rings installed, it is quite tight.[/QUOTE]

Why use piston rings if to use air ?
Alec Ryals

rhankey · Dec 2, 2014

Alec,
Stuart specifies 18 Brass Round Head screws that are 7BA x 3/16" long to secure the lagging (or what you refer to as the shroud). That size seemed perfectly to scale on my engine.

An expansion engine like the Stuart triple is not designed to run on air. Unless you have reworked the supply lines or added sampling valves, or have a lot of piston blow by, running a triple expansion on air will result in the engine running on only one cylinder. Compressed air only works once, so once it is expelled from the HP cylinder, it will provide no further work in the IP or LP cylinders. Steam on the other hand will expand again after it has come out of the HP cylinder - just not quite so much as the first time, hence why the IP and LP have correspondingly larger displacement.

Alec Ryals · Dec 15, 2014

I see some folks put valves on top of the cylinder heads besides the ones on the side are these for oil ?
Thank You
Alec Ryals

Alec Ryals · Dec 29, 2014

Has anyone here on this Forum ever run a triple on steam?
Thanks\
Alec

Alec Ryals · Jan 27, 2015

Hello All,
Well I have a lot more pictures to post here when I get some free time but was wondering if any one would know if the 30* degree ectrinic is for the L.P. cylinder?
Thank You
Alec Ryals

Mechanicboy · Jan 28, 2015

Alec Ryals said:
Hello All,
Well I have a lot more pictures to post here when I get some free time but was wondering if any one would know if the 30* degree ectrinic is for the L.P. cylinder?
Thank You
Alec Ryals

L.P and I.P 15 degree and H.P. 30 degree. It is due timing of steam engine calculated for steampressure, expansion, exhaust and compression to make steam engine economical and less water consumption from boiler. Most difficult for new beginners with I.P. excenter sheave. See photo.

Mechanicboy · Jan 28, 2015

And still more photo..

Mechanicboy · Jan 28, 2015

And still more.. And there is not picture: Tap the treads 7BA in the excenter sheave before the half of excenter is cutted of the tap of the excenter sheave who is fastened into the collet.

Mechanicboy · Jan 28, 2015

You need the spesial tool to turn the excenter sheave. The holding pin is made of drill rod to prevent stretching and bending under work. The degree disc has a flat side: Set the mark aligned with other mark and set the excenter sheave and degree disc in vertical. How do: Use machinist square standing on cross slide and set both on excenter sheave and degree disc with the mark aligned with other mark on the tool then fasten the excenter firmly with nut. After the first sheave is ready, then mark up the disc and excenter sheave, loosen the nut and turn to next the mark with the disc and excenter sheave is in right position (do not turn the excenter and degree disc from each other!) then turn the second sheave.