Can anyone explain why the Stanley system is so relatively inefficient? (we need a Philip Hopes). All literature I have seen puts the Stanley system at around 25lb steam./hp.hr. My experience is that it is somewhat worse than that. Having read with great interest the article in the current issue of "The Steam Car" mag.by Doug Leeming concerning the pros. and cons. of poppet valves (part 1) and having had some experience of this type of valve I can only conclude that the inefficiency with a slide or piston valve revolves around three parameters:
1. Leakage
2. Short cut-off limitations.
3. Seperate inlet and exhaust valves not possible.

I think that it is not possible to maintain a leak proof piston or slide valve for long compared to a poppet valve which is inherently leak proof for long periods.
Short cut-off only comes at a price (small port opening) with sliding valves.
Exhaust period is always related to cut -off with sliding valves and the expanded cooled exhaust steam uses the same path as inlet steam.

Having said all that it is difficult to explain such a big difference. Doug says that the Duke achieved 12lb steam/hphr. and this with no economiser (which Stanleys have) and only 250lb/sq.in.boiler pressure.

So do points 1.2.3 above explain the factor of 2 or maybe 3 in efficiency between a Stanley and a modern loco.?

A. Small cylinders are always less efficient than large ones. The major heat losses in a steam engine are surface related, and large cylinders have less surface for a given volume.
B. Any single valve engine uses the same port for both inlet and exhaust steam, which maximizes the "initial condensation loss". Any attempt to run in very short cutoff make this loss worse, thus cancelling any gain from better expansion.
C. Common valve gears do not give reasonable events in short cutoff with a single valve engine.
Query; was the Duke a compounded engine? I have never heard of a single expansion locomotive using much less than 18 lb/hp hr.
If by economiser, you mean feed water heater, it has no effect on the steam rate of the engine. It does affect the amount of fuel needed to make the steam.

Thank you David for your reply. No, the Duke of Gloucester was not compounded. It recorded the lowest steam consumption per hp of any railway locomotive. Even the piston valved loco's designed by british rail in the late 50's achieved 13-14lb/hphr. I understand that the surface area increases out of proportion to the volume but I can't believe that this explains such a big difference. The Stanley type engine is working at a much higher pressure (if hooked up) and although the slide valves absorb more power than piston type, they give the same events and probably leak less and can have less clearance volume.
I take your point about economiser not assisting steam consumption, of course this only improves steam production efficiency. It is worth perhaps saying that the Duke had a exhaust steam injector which is effectively an exhaust feed water heater and so increases the overall efficiency for free.
In your experience (which I know is considerable) is 25lb/hphr. all that is possible with the Stanley engine arrangement?

Regards, Jack.

I know nothing about locomotives or thermodynamics and little enough about Stanleys but one difference which may be of significance is that the Stanley boiler is at a very high pressure and feeds throttled steam through a steam pipe which is much smaller relative to the cylinder volume than the steam pipe in a locomotive.

Stanley used a high pressure so as to produce a large volume of steam from a small boiler, throttling the steam and using it in the cylinders at much less than boiler pressure. David has commented on this in another place where he said that in normal running on flat roads his car needs only 150 psi and that steam chest pressure only goes up to anywhere near boiler pressure when climbing a very steep hill.

Clearly having an engine which is much too big for the boiler’s continuous output is what gives the Stanley its magnificent torque and acceleration but is it an efficient way of using steam? Does the steam waste a lot of its energy being expanded through the throttle and inlet system down to 25 percent of boiler pressure before it even gets to the piston? It would be interesting to know what percentage of boiler pressure was found in the steam chest of locomotives under average running conditions.

Mike

Frankly, I am suspicious of the very low steam rates given for the Duke of Gloucester. Are they based on analysis of data using the traditional steam engine indicator? If so, they may miss a large percentage of the actual steam flow through the cylinders, that which condenses on entry and re-evaporates on leaving. When Barrus tested an Ames uniflow engine in 1924, the steam flow accounted for by the indicator was 88 % of that measured by weighing the condensate, which was considered exceptionally good.
The fact that exhaust injectors were used means that measuring water drawn from the tender does not measure steam used by the engine, a significant amount will be condensed from the exhaust by the injector. Perhaps as much as a fourth.
The lowest steam rate I have heard of for the Stanley type 7 (20 hp.) engine is 17 lb/hp hr, with no other data to back it up. Steam rates of 20 lb/hp hr were measured in some reasonably documented tests by Prof. Mason, these were printed in their entirety in the latest SACA Bulletin.
The White compound engine gave rates of 12 lb/hp hr in very good tests by Prof Carpenter, 1906. Other tests by Pro. Benjamin in 1904 and 1909 gave similar results.
Yes, throttling is inefficient. But much less so in steam than Otto cycle engines.

I don't have the test report for the "Duke" to hand ,but the other loco's tested used a steam flow rate meter as well as "the incremental method" to back it up. The piston valved Loco's tests (which I have in front of me) show results as low as 14lb/hphr. But to be fair we must consider the norm. rather than the best and it would seem that 16-18lb is what was achieved under variable conditions which is the condition a car is under.
Mike I agree with your comments on the Stanley system using relatively low pressure at the steam chest from a high pressure boiler with a small diameter steam pipe combined with throttling. This is the secret of the Stanleys success.
Full torque when needed at starting and limited steam flow when running by throttling. But unlike locomotive drivers Stanley drivers don't seem to put so much emphasis on really short cut-off. Typically a loco. would be run at full throttle and minimal cut off---maybe 15% or even less when steam chest pressure would be near to boiler pressure. David mentioned the White as having got as low as 12lb/hphr with a compound engine. Short cut-off in a simple should achieve a similar effect as compounding if valve travel is long enough to allow long lap valves .Here I think is one of the problems. I suspect that Stanley engines have relatively small lap valves so that port openings at anything shorter than 30% are restrictive.

It’s easy for us to criticise Stanleys for using too much steam per horsepower. I am sure they knew this but being very down to earth in these matters they were more interested in getting the nice driving characteristics and reserve power which their system offers. They were the ultimate exponents of the K.I.S.S. principle.

Fuel was cheap (and in any case the mileage they were getting was just as good as any equivalent size i.c. car of the time) and their boiler, which seems large and heavy to us, was small by the standards of 1908. They weren’t trying to go long distances between filling with water and on the roads of the day were spending a lot of time accelerating and slowing down with not much chance of steadily cruising at 50 or 60mph. It is only in present day conditions that we see deficiencies in cruising speed and range - in its day the Stanley did just what was asked of it.

I don’t suppose Stanley worried about getting enough valve opening at shorter cut-off - it worked well enough at 25% cut-off with the valve opening they had. Locomotive drivers on the other hand could adjust cut-off and I have read that skill with this and a “feel” for what was going on was the secret of economical running. A Stanley was not supposed to require huge skill from the driver so he was given no adjustment to confuse him.

Having said all that it is still interesting to discuss and understand these things!

Mike

Point taken Mike. I shouldn't mix two different concepts. Perhaps it would be interesting if someone could build a 'modern Stanley' with all the same attributes but with poppet valves and (therefore?) reduced steam consumption!!
I know that you people with genuine Staneys like 'em just the way they are and they do the job---I am just pipe dreaming.
Regards,
Jack.

Jack,

Don't let me discourage you from chewing cud - it's interesting anyway. carry on dreaming we all do it.

Mike

re Poppet Valves
Driving my Whites(1902 twin simple with slide valves and 1908 twin compound with HP piston valve and LP slide valve) over the last 10 years and can report that the cut-off is quite critical to the driving of the cars. I sometimes forget to shorten the cut-off and the lack of performance soon makes itself known with the limited reserve that the White has.
I was quite surprised when I purchased the Nelson and was unable to alter the cut-off. I was for-ever running out of steam and not having it hot enough when I wanted it probably due to my heavy throttle hand. I fitted a temperature gauge and an adjustable cut-off on this car. The latter pushed the top constant cruising speed up about 10mph. Because you use less steam,it is in the superheater longer and gets hotter so you need less steam to maintain the power.
It seems to me from reading articles that the poppet valve can offer a finer adjustment of cut-off.
I have yet to witness a poppet valve engine in a car. Les Nelson may soon be running the Pearson-Cox with its tiny 3 cylinder engine. The performance of this engine will be interesting to see.

Bob