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Steam line pressure
Posted by: Mike Clark (---.glfd.dial.virgin.net)
Date: July 19, 2005 04:41PM

I just fitted a pressure gauge to the main steam pipe to the engine of my H (tee fitting to oil feed pipe). Very interesting and remarkable how little steam pressure is actually needed to move the car.

Typically when running with a light throttle on the flat at 35-40mph the gauge shows no more than 100psi, even 50 psi keeps it moving well. Accelerating or a modest hill takes it up to 200psi and it needs a stiff hill (10%) to bring it up to 300psi. The highest seen has been 400 psi when pulling with plenty of throttle on a 25% hill. This is with 600psi boiler pressure.

It is also very obvious how the driver can ease the load on the engine as only a very small closure of the throttle which has little effect on performance can bring the pressure down by 50 psi or more. Moving slowly up a steep hill which gives the impression of being hard work is not necessarily so if the pressure is only 200psi. and it is probably better to let the car find its own speed rather than be tempted to give it more throttle to get going.

Interestingly, but obvious when you think about it, the pressure rises by 50psi or so when hook up is engaged because less steam is being used by the engine but the same amount is coming through throttle thus building up more pressure in the steam pipe.


Mike

Re: Steam line pressure
Posted by: (---.cache.pol.co.uk)
Date: July 21, 2005 07:07PM

Yes, steam chest pressure gauge watching is a fascinating pastime. I have mine directly on the steam chest and like you I find 100 to 150psi sufficient for most needs. Have you fitted a snubber to your gauge? I found that the gauge needle tended to jump around quite a lot, probably indicating that the steam pipe/chest volumes are too low, but then this is one of the Stanley arrangements reasons for success---the demand on that tiny boiler is limited by restrictions of steam supply to relatively large cylinders, except when needed at starting and low speed pulling. It is the opposite of railway locomotive practice.

Jack....

Re: Steam line pressure
Posted by: Mike Clark (---.glfd.dial.virgin.net)
Date: July 22, 2005 04:02PM

No it doesn't jump around but remains rock steady which did surprise me. The connection is by a 1/8th pipe to the oil feed pipe at the front of the steam pipe. There is no indication of pump pulses but a very useful side effect is that if the oil pump pipe became blocked or if it broke away I would immediately know. The winker is not much help in those situations.

Mike



Edited 1 times. Last edit at 07/22/05 05:35PM by Mike Clark.

Re: Steam line pressure
Posted by: (---.cache.pol.co.uk)
Date: July 22, 2005 06:32PM

Maybe the oil is acting as a kind of damper on the pressure fluctuations in the small bore pipe, or perhaps you are connected far enough from the engine so that the port openings are not detected by your gauge. If only we could hook up far enough to maintain boiler pressure in the steam chest.....this was arguably considered best practice for maximum efficiency with a steam locomotive.

Jack...

Re: Steam line pressure
Posted by: Mike Clark (---.glfd.dial.virgin.net)
Date: July 23, 2005 05:55PM

Yes it could be the length of the pipe - there is about 600mm of 1/8 pipe to the gauge.

Stanley's thinking was quite different to that of the locomotive designer who used a massive steam pipe with the aim of getting up to 90% of the boiler pressure through to the steam chest. He could afford to this because the boiler was sized so that it could produce enough steam to run in this way.

Stanley used a very high pressure but throttled the boiler with the small steam pipe to give a reserve so the car could for a short time use much more power than the burner could produce continuously. Just a different way of thinking and one which did not seek the highest efficiency, just the nicest "drive".

Mike


Re: Steam line pressure
Posted by: (---.cache.pol.co.uk)
Date: July 24, 2005 05:07PM

Yes, that sums it up. Clever thinking wasn't it ! More to the point- it works !!
Having been brought up in the railway locomotive world I was astounded when I first witnessed the Stanley system at one of the sccgb tours at Tiverton.
....now if something can just be done about that efficiency.....

Jack...

Re: Steam line pressure
Posted by: Mike Clark (---.winn.dial.virgin.net)
Date: July 24, 2005 05:56PM

Another issue re efficiency which is rarely mentioned is that superheating on the Stanley is only part time becuase the burner goes on and off. This is in contrast to the situation in Whites and others with monotube steam generators.

Even when the Stanley burner is firing full superheat is only achieved when the steam pressure drops low enough to fully open the steam automatic which means dropping by at least 25psi below the set boiler pressure.

In cruising conditions the steam automatic modulates and with a light throttle the burner never gets to full power because part power is enough to hold boiler pressure. I suspect part power is bad for gas/air ratio and makes for a smokey exhaust.


If we had a steam automatic which only gave full flame or no flame the burner would be more efficient because it would be burning more of the time with the correct air/gas ratio but the superheat would become even more intermittant. Rock and hard place come to mind.

Mike



Edited 1 times. Last edit at 07/25/05 03:12AM by Mike Clark.

Re: Steam line pressure
Posted by: Jeff Theobald (Moderator)
Date: July 25, 2005 05:01AM

Hi Mike,
Don't forget that your experiences are different to most, as you have a car that gives excellent performance, with a burner that modulates, whereas, most other Stanley owners are constantly watching the steam pressure etc and adjusting their speed to keep the steam pressure in a good working area.
When I am out and about in the Brooks the burner is on non stop, only shutting down at coffee stops etc, except for those occasions when for some unexplained reason everything seems to come right and we will spend a few hours with a full boiler, full pressure, modulating burner and getting along as good as a 735, this happened on the last afternoon of the recent Midlands tour.

Jeff.

Re: Steam line pressure
Posted by: Mike Clark (---.glfd.dial.virgin.net)
Date: July 26, 2005 07:03AM

Quite true Jeff - donít generally think about boiler pressure - itís just there - certainly no juggling! Going at a good clip (say 45ish) gets the burner going full time and brings the boiler pressure down to 550-575 which is a sufficient drop to fully open the steam auto and then it just holds that pressure. Iíve not been brave enough or found enough road space to find out what speed it can maintain continuously without the pressure falling. My local hill, which averages 10% for 1.5 miles with a couple of stretches of 20-25%, brings the boiler back to 400psi but the car still goes well at that as you would expect from the steam line pressures I mentioned at the start of this thread.

I put a thermocouple on the steam pipe just after the superheater but it reads a bit high because of direct conduction in the wall of the pipe so I will have to move it nearer the valve chest. Iím relining the brakes this week (lasted less than 3000 miles - itís the hill that does it!) but will try the steam pipe temperature again next time weíre out.

I also put a thermocouple into the main burner just below the superheater to get an idea of what the burner is doing (it can show over 1000 deg C at full burner but is often a lot less, in the 6-800s when modulating). In a way the superheater and burner modulating probably have a limiting effect on the maximum superheat - when the throttle is wide open and the burner on full burn lots of steam is going through and diluting the heat uptake. When less throttle is used and the boiler pressure approaches the set level the steam auto partly closes, cutting the burner back to a level appropriate to the smaller steam flow. I put this thermocouple on as I thought it might be a useful way of deciding what size jets to use on the basis that the hottest flame would indicate the right air/fuel mix but as it makes all the steam I need with number 61 jets I have not tried the idea yet.

Mike

Re: Steam line pressure
Posted by: Mike Clark (---.manc.adsl.virgin.net)
Date: October 9, 2006 04:00PM

Wake up of old thread!

I've been watching the steam temperature of my Model H with a thermocouple on the steam pipe just before it enters the valve chest. First thing to be noted it's mainly a measure of temperature of the pipe rather than of the steam passing through and is quite slow to respond to what is going on.

I expected to see changes in steam temperature as the burner goes on and off but really this is not at all noticeable. There must be a very significant "heat sink" effect in the burner. What I do see is a variation of steam pipe temperature with the level of work being done by the burner. On a flat road with the burner going on and off the steam pipe temperature is about 280 centigrade (530F) whereas after climbing a good hill with an average grade of 8.5% for a mile and a half the temperature gets up to 330 centigrade (625F). The pressure in the steam pipe is around 100psi on the flat road and up to 250psi on the steeper parts of the hill with the boiler at just under 600 psi on the flat and falling to 400psi as we get to the top of the hill.

It is difficult to relate these steam pipe temperatures and pressures to determine exactly how many degrees of superheat are achieved. - The general observation is that there is superheat all the time no matter whether the burner is on or off at the time.

Mike



Edited 1 times. Last edit at 10/09/06 05:23PM by Mike Clark.



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