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Old Nov 16, 2010, 07:22 PM
Grumpa Tom
Kmot's Avatar
United States, CA, Los Angeles
Joined Sep 2003
23,614 Posts
Question
Question about running on compressed air, maybe steam also

When a specification calls for an engine to be run at 10 PSI, does that mean 10PSI set first with all the valves closed? Or 10 PSI with the valves full open and the engine running?

Reason I ask is because I am confused about it. I noticed when running my engine that my pressure gauge reads near zero yet the engine runs. If I dial up to 10 PSI the engine races at 2000 rpm.

I closed the valves and set the gauge to 10 PSI. Then I opened the valve and let the engine start. The gauge needle fell to near zero, but the engine was running at 1120 RPM.

So for example, when a manufacturer says MAX PSI 30, does that mean with the valves closed first?
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Old Nov 17, 2010, 08:38 AM
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Toronto, Canada
Joined Nov 2004
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Hi Tom,
I always figured that it was boiler/compressor pressure with the engine running and valves open, but I may be wrong (it won't be the first time). One thing to watch when bench running is you are usually running without a load on the engine, and it is quite easy to over speed the engine. I wish manufactures would list max rpm.
Regards,
Gerald.
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Old Nov 17, 2010, 10:56 AM
Grumpa Tom
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United States, CA, Los Angeles
Joined Sep 2003
23,614 Posts
Thanks Gerald. Graham does mention in the manual that the engine would be running up to 4000 RPM at 30 PSI. It must be a scary thing to run it that fast, lol. Just 2000 RPM seemed extreme to me!

DISPLAY OPERATION
When using the VRLA as an operating display model, it is an advantage to mount a flywheel on the
engine. This will assist the engine in running at a lower speed so the works can be seen. A good size
is from 2 to 3 inch diameter and 4 to 6 ounces in weight. Of course the youngsters will want to see
how fast it will go, and in such cases the engine can be operated with out a flywheel or with only a
light flywheel. In such cases, the maximum RPM will be about 3800 to 4000 RPM at 30 PSI of air
pressure.
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Old Nov 18, 2010, 08:02 PM
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Toronto, Canada
Joined Nov 2004
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I always found that one you reach 1000 rpm everything is a blur, I like them running slow enough that you can see the parts moving.
Regards,
Gerald.
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Old Nov 19, 2010, 07:51 AM
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Bradford West Yorkshire, UK
Joined Apr 2010
1,668 Posts
Quote:
Of course the youngsters will want to see
how fast it will go,
Yea, send them to an I/C display stand. At 1K the prop will leave a nasty mark on Anything it touches.

Regards Ian.
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Old Nov 20, 2010, 02:05 AM
I SEE NO SHIPS
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Somerset England
Joined Feb 2007
1,229 Posts
Try a Novarossi 1/8 scale on road race engine at 38,000 rpm on for size !
I had one explode while "running in " when the conrod let go.
That is why I now like nice slow steam engines better .
Well that and the fact that my reaction times are slowing down (hate getting beaten by young whelps !)
Anyone want to buy a couple of full race carbon and alloy Piccos in mint condition ?
Dunc2504
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Old Nov 27, 2010, 03:54 AM
Model Engineer, sometimes
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Old Nov 27, 2010, 05:36 AM
I SEE NO SHIPS
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Somerset England
Joined Feb 2007
1,229 Posts
Hi Bogs .
You obviously have much more experience of steam than me , but I do not agree that running an engine on air is worth "NAFF ALL".
I use air to set up my engines (especially valve setup and timing) and to bed in the crankshaft, rods and other bits that are remote from the cylinders.
Obviously I never use more air pressure than is available from the intended boiler , as you say , you could make just about anything run with enough pressure.
I find it much more convenient to remove any high spots by running on air than steam .
But of cource the acid test for any steam engine is running the thing on steam .
Dunc2504
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Old Nov 28, 2010, 03:07 AM
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Old Nov 30, 2010, 01:40 AM
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Bathurst District, NSW, Australia
Joined Nov 2010
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Couldn't agree more Bogster - running on air is useful in the early stages, but doesn't tell you much about the real condition of the engine. This thing, for example, runs a treat on air - in both directions - but has thus far resisted all my attempts to get it to go on steam

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