Author Topic: Steam port position  (Read 3338 times)

Offline John Rudd

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Steam port position
« on: April 25, 2015, 04:40:39 PM »
I'm looking to build a V twin steam engine for my boat 'River Queen'

Bore is going to be 8mm and stroke 11mm.....

Crank will be around 20mm diameter, shaft...6mm and crank pin 3mm......

So how do I determine where the ports need to be in relation to the centre line of the crank shaft?

I remember summat back in school about the 'Locus of a point P'......
Can any one help me out here please?
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Offline gbritnell

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Re: Steam port position
« Reply #1 on: April 25, 2015, 08:50:09 PM »
Hi John,
I don't quite understand what you're asking. The ports are located on the centerline of the cylinder which is located on the centerline of the standard which is located on the centerline of the base. This would make everything in line but somehow I don't think that's what you're asking.
gbritnell
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Offline gjhelst

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Re: Steam port position
« Reply #2 on: April 25, 2015, 11:15:36 PM »
Hi John,

If we call the inner diameter or bore of the cylinder d, then the depth of the steamport should be 5/8-3/4d, the width of the steamports for steam-in or fresh steam should be 1/10d and the width of the steamport for steam-out or used steam should be 1/4d. The width between the steamports should be 1/10d and if the depth of the valve 1/6d.

This information comes from Handboek Model Stoommachines (Handbook Model Steam Engines) by Rob van Dort and Joop Oegema.

I hope it is of any use for you.

All the best,

GertJan
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Offline Maryak

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Re: Steam port position
« Reply #3 on: April 26, 2015, 01:05:08 AM »

I remember summat back in school about the 'Locus of a point P'......

Can any one help me out here please?

Is this an oscillating engine?

Bob
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Offline John Rudd

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Re: Steam port position
« Reply #4 on: April 26, 2015, 07:53:25 AM »
Thanks guys, yes  this is an oscillator.....

Hoping to start cutting metal today......so far I have gathered there is a relationship between the crank and trunnion distance and the angle that the cylinders move. Somehow this determines the port positions.....

There's some kind of magic involved in getting this right.......
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Offline gbritnell

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Re: Steam port position
« Reply #5 on: April 26, 2015, 12:43:27 PM »
Hi John,
The length of the cylinder will determine the position of the ports at each end. At this point I can't give you the exact diameter of the port but I would say something around 1.5mm would be more than adequate. They will be located on the centerline of the cylinder. The stroke of the engine will then establish the amount of rock-over the cylinder has from the pivot shaft. With the cylinder in the true vertical position the ports in the cylinder and the ports in the standard should not be open to each other. As the crank starts to turn from TDC and the cylinder rocks over the ports should start to overlap thus allowing steam at one end and exhaust at the other. Once this point of overlap is established it will give you the centerlines of the ports on the standard. As the crankshaft continues to turn and the cylinder rocks to it's extreme position the ports will be fully open to each other, cylinder to standard. When the crankshaft reaches the bottom of it's stroke the ports will then start to unlap and steam will be cut off along with the exhaust flow. This in steam terms would provide a little bit of compression cushioning similar to a slide valve engine. When the cylinder rocks over to the other side of center the events will start over and move the piston in the other direction. The more lap you have between the cylinder port and the standard port will determine when the steam is applied to the piston and how long it charges the cylinder.
gbritnell
PS. One other dimension you didn't include would be the distance from the horizontal centerline of the cylinder to the centerline of the crankshaft. This will be determined by the length of stroke of the engine plus the extension of the lower head for piston shaft support, plus the length of the packing nut, plus the size of the crankpin trunnion, plus a little clearance.
« Last Edit: April 26, 2015, 12:50:49 PM by gbritnell »
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Offline ironman123

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Re: Steam port position
« Reply #6 on: April 26, 2015, 01:49:08 PM »
John, can you be more descriptive of your "River Queen" boat please?  Also it's length amd beam.  Thank you
Ray
Central Texas

Offline John Rudd

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Re: Steam port position
« Reply #7 on: April 26, 2015, 02:17:34 PM »
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Offline gbritnell

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Re: Steam port position
« Reply #8 on: April 26, 2015, 05:27:39 PM »
Hi John,
Did I not answer your question sufficiently?
gbritnell
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fcheslop

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Re: Steam port position
« Reply #9 on: April 26, 2015, 06:36:58 PM »
Hi John, Iv made Vic Smeeds River Queen also with a V twin wobbler and she is a good little boat to sail
Make a drill jig to drill the ports in the blocks its far easier
This pic shows a single acting engines frame been drilled

cheers

Offline John Rudd

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Re: Steam port position
« Reply #10 on: April 26, 2015, 06:39:47 PM »
Graham,
After researching a bit more, I have a better understanding,  :happyreader:

My thanks to all contributors... :cheers:

I've started off with my cylinders....brass with an 8mm bore....photos to follow( another hurdle.....)
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Offline Stilldrillin

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Re: Steam port position
« Reply #11 on: April 26, 2015, 09:03:57 PM »
Hi John.

You now know all you need to know. Probably......  ;)

I remember an instruction, to drill the holes in the frame at the 70* position. (Full sweep of the cylinder, being at 90*).
This gave an overlap, for longer cylinder filling/ exhaust.

David D

David.
Still modifying bits of metal... Occasionally, making an improvement!
Still drilling holes... Sometimes, in the right place!

Offline John Rudd

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Re: Steam port position
« Reply #12 on: April 26, 2015, 10:15:30 PM »
Hi John.

You now know all you need to know. Probably......  ;)

David D
Ooh, I doubt that David.... :Jester:

I'm sure my efforts will be rewarded with a running engine.... :whoohoo:
Mebbe see you at Harrogate..... :cheers:

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