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"Notes from the Unit Shop"

Kevin O'Connor's advice for the beginning small scale live steamer

 

Getting Started with Frank S. 

Part Two of a series on tapping the maximum potential of a Gauge 1 locomotive

"Getting steamed up with a minimum of fuss"

 

 

In Part 1 we got Frank S. ready for steaming.  This essay will focus on steaming up with a minimum of lost motion and anxiety. 

 

Place the locomotive on the track.  Make sure that the wheel flanges are inside the rails.  On outside framed locomotives like Frank S. this alignment is tough to see until sufficient skill is acquired.  Place the tender on the track with the same caution, but do not hook up the drawbar.  Roll the tender up to the locomotive so that the fuel line and nozzle assembly easily reaches the locomotive’s burner assembly. 

 

At this point, lift up both ends of the locomotive and the front of the tender and insert the steam up support blocks described in the sketch at the bottom of this article. The locomotive steamup blocks elevate the drive wheels out of contact with the rails so that they can rotate in place and warm up the mechanism while clearing the piston valves and cylinders of condensate and excess steam oil. 

 

The single tender block cants the fuel tank up at an angle so that the ullage (gas bubble) in the tank is forced forward and there is no chance of passing liquid fuel through the delivery hose and nozzle.  If drops of liquid fuel are passed over to the nozzle through the supply line they will either plug up the nozzle, or more likely, richen the fuel to air ratio beyond the limits of combustible mixture and thus extinguish the fire. 

 

This phenomenon is the reason that Frank S. equipped with single channel R/C; perform so erratically.  The single channel control of the reversing block as an attempt to control both direction and speed is flawed because the reversing block does not have enough modulation designed into it.  As a result the locomotive jerks through starts and stops.  Each time it jerks the ullage in the fuel tank is disturbed by the liquid fuel sloshing (free surface effect) from one end of the tank to the other.   As the slosh (wave) reaches the discharge end of the tank, a slug of liquid fuel finds its way into the fuel line thus to the burner assembly where the fire is extinguished due to a too rich a mixture to combust.  

 

At this point we have the locomotive up on its steam up blocks and the tender is rest on a similar block at its front end and the rear wheel set is resting on the track.  We are now ready to light the fire, but before we do let us review parts of the combustion space and revisit their function. 

 

At the end of the locomotive we have the burner assembly which consists of the fuel nozzle, fuel / air mixing chamber, and burner basket assembled into one unit held in place by two pan head screws and attached to the rear boiler mounting bracket.  This unit meters and accelerates the gaseous fuel through the nozzle, draws in the proper amount of air to provide the correct flammable mixture for efficient combustion at the mixing chamber and directs the flammable mixture into the burner basket where it is burned. 

 

The flammable mixture that we need resides in the order of three to seven percent gaseous fuel mixed with ninety something percent air.  Ideally this mixture ration will only exist in the burner basket, but sometimes not, and sometimes in more than one place, and this is what causes stack and smoke box fires.  If the fuel / air mixture is too rich at the burner basket the flame will not flash (travel) back from the ignition source to the burner basket, but will light somewhere between the igniter and the fuel sources.  

Since the smoke stack is surrounded by an unlimited supply of air a too rich a mixture will tend to burn very happily there until the fuel is cut off or the stack looses all its paint.  If the stack is cast from pot metal such as pewter or Zamack it will melt.  The second, and not so obvious, place that an errant flame will propagate is in the smokebox.  I personally know of smokebox fires that went unnoticed until the locomotive exhibited the forward rake. 

 

Usually this is seen on “funny cars” at an auto race track, that indicated a most abject surrender of the front frame / pilot assembly due to the generation of liquid metal and carbonized nylon.  The nuclear engineers call this state “meltdown” and it is an apt term and a condition to be avoided at all costs.  Both of these errant fires can be avoided by canting the tender’s front end up on steaming blocks and opening the fuel supply valve only the smallest amount. 

 

Ideally the fuel supply / metering valve should be machined as per my previous article (Steam in the Garden. No. 30, Sept-Oct. 95) in order to improve attenuation of the fuel flow, but if not just do the best job of it that you can in getting a really small flow of fuel to the burner assembly.  Hopefully you are lighting off in a quiet place, but if not put your ear to the smokestack while fiddling with the fuel flow control valve.  Listen carefully to the hissing sound that the fuel makes as it exits the gas jet and do your best to get it as low as you can; you can always turn it up later if required. 

 

While you are doing all of this have your ignition source handy to light off.  I alternately use what ever is handiest, either a butane fueled barbeque lighter or an oxyacetylene striker.  I don’t smoke tobacco so I am unwieldy in “flicking my Bic.”  The moment that you are satisfied with the hissing sound that the nozzle is producing, light off the locomotive at the top of the stack.  Make sure that the smokebox door is tightly closed.  Be alert that if the burner lights with a “pop” that the smokebox door may partially, or fully, open due to the momentary high pressure developed by the pop. 

 

I do not recommend lighting off in the smokebox with the smokebox door open.  Usually the door open approach is tried when the fuel supply valve is open too much for the burner to light properly and so it does light in the smokebox where there is a more abundant supply of air.  I suspect that there are Frank S. engineers that have mastered the smokebox approach and I think that they can be recognized by their hairless right hands.  There are probably equestrians that mount on the right as well, but I think that I’ll pass in the interest of longevity. 

 

Peter Jones has called our small-scale live steamers “dragons” in a least one of his articles and I think that “the smokebox lightemup crowd” have taken him too literally as evidenced by the flaming maws that are seen at steamups. 

 

Hopefully all is well and we are rewarded with a light or non-existent “pop” and a gentile “burbling” sound from the burner.  The burble indicates partial and incomplete combustion of the gaseous fuel in the burner basket.  It is caused because the stainless steel burner basket is much colder than the burning fuel mixture and, in its heating up to operating temperatures it is stealing heat from the burning fuel and so, locally and intermittently, combustion is interrupted in one portion of the burner basket only to resume in another.  In practice the flame is jumping around from one set of perforations to another.  The flame will stabilize and the burbling will stop when the burner basket reaches operating temperature.  Only when this point is reached should the fuel supply be increased to the level needed to raise steam. 

 

I recommend that the fuel supply to the burner slowly be increased as the boiler comes up to heat.  If one would go directly to high fire in a cold boiler, the cold boiler will steal heat from the burning flame much in the same way that the burner basket did on the first lighting off.  The result will be incomplete combustion of the gaseous fuel and the production of carbon monoxide, a normally odorless gas, but in this case a bad smelling complex product, and excess water vapor.   This practice will waste fuel in steaming up that otherwise could be used to pull the load.  I use a setting that results in a very dull roar. 

 

Once steam pressure starts to build, pull up on the safety valve stem to test for free operation and freedom of steam flow.  Let the steam pressure come up to 2kg/cm2 (28psig) and put the motion control lever in either the forward or reverse position and slowly open the throttle valve to admit live steam and condensate to the cylinders. 

 

Pay close attention to the cylinder / motion / drive wheels assembly.  With the admission of stream pressure to the cylinders some rotating motion should be observed at the wheels (remember, they are suspended above the track by the steamup blocks) and you may, in fact probably will, see some relative motion between the cylinder blocks and the chassis.  This relative motion is an indication that the cylinder bores are bound up with condensed water that is slowly being squeezed out via the piston rod gland seal, the clearance in the piston valve bore, and the reversing block / cylinder O-ring seals.  It pays not to rush the process, as it will only put undue strain on the valve gear and connecting rod motion. 

 

One advantage of the steaming blocks is that the direction control level can now be pushed alternately forward and reverse causing the drive wheels to try to rotate in either direction.  This cycling of the direction control level helps the cylinders to free themselves of condensate and is far more gentle on the motion of the seals that the oft repeated mantra of “bearing down on the locomotive and forcibly rolling it in one direction or the other” to clear the mechanisms of the condensate.  If you observe the cylinder blocks moving relative to the chassis during the condensate clearing process don’t be unduly alarmed.  

 

Once the condensate has cleared and the cylinders have come up to temperature their relative motion with regard to the chassis will stop and the locomotive will perform normally. 

 

It will pay to check the tightness of the two screws securing the cylinder blocks to the chassis at the end of the run, but as was pointed out in part 1 of this series, their tightness should have already been documented in the pre-steamup preparation.  All four of these cylinder block securing screws are of the Phillips flathead (+) variety and don’t tighten up readily, as the American type Phillips head screwdriver appears to have slightly different angle of attack than the metric type.  Eventually the Phillips slots in the flathead screws becomes routed out and useless.  The answer is to obtain four M5x.05x16 flat head socket machine screws and use them to replace the originals. 

 

I will recommend against two things at this point: do not use the regular, and more common, socket head cap screws in lieu of the flathead head variety, and do not use Loctite™ to secure them in place.  Reasons?  The flathead screw, because of the angle under the head, act as a locator of the cylinder block in reference to the screw’s tapped hole, reversing block, and piston motion.  Cap screws would let the cylinder block “float” with regard to alignment.  

 

Loctite™ is a wonderful tool and I have been using it since 1962, but it has become much abused.  Kind of like a screwdriver being used as a pry bar or as a chisel: it works, but not well.  If the flathead socket Allen screws are tightened to the max using the short lever arm of the Allen key in the bare hand, the correct amount of tightening torque will be applied to the cylinder block screws. 

 

Some Frank S. engineers may say that this concern is overkill, but my practice dictates that one can’t be too careful about little things because they have a habit of becoming progressive errors; I speak from painful experience. 

 

While you are cycling the reversing block control level to clear the cylinders of condensate keep an eye on the pressure gauge.  There is no need to let the boiler steam pressure rise above 2kg/cm2 as the locomotive is not pulling a load and we want to conserve fuel.  At some point the locomotive will clear its throat and run easily in either direction. 

 

For those Frank S. engineers who have replaced the smokebox mounted “gunk” tank with an exhaust tube that discharges out of the stock, I recommend that they fabricate a “U” shaped copper tube that will slip over the discharge tube and so direct the spurting condensate and steam oil onto the track’s ballast, and not all over the locomotive.  Remember to remove it prior to leaving the station. 

 

During the lighting off process and steamup we are consuming gaseous fuel that has been evaporated from the liquid fuel in the tender tank.  As a result, the tank has started to cool and soon fuel pressure will drop due to this cooling effect.  (For a comprehensive explanation, see "What is the Best Fuel for my Gas Fire Gauge One Locomotive).

 

In order to offset this heat loss and temperature and pressure drop, warm water (90ºF to 100ºF) must be added to the tender fuel tank water bath.  In order not to raise the pressure in the fuel tank too much at one time, thus taking a chance on blowing out the burner’s flame, add only enough warm water from a small Thermos™ bottle to the water bath container to restore the dull roar of the burner.   Add more warm water as necessary. 

 

Check the boiler water level and top up through the Goodall type valve if necessary.  To come off of steamup blocks, first lift the locomotive up slightly by the rear of the cab roof and remove the rear steamup block as you place the rear driving wheels on the track.  This area rarely gets hot so bare hands are OK.

  

Next, gently push down on the rear of the cab roof, pivoting the locomotive upward on the rear driving wheels, until the weight of the front of the locomotive comes off of the front steamup block; remove this block too. 

 

Now with the locomotive properly located on the track, carefully remove the steamup block that is canting the tender and the fuel tank upward and properly locate the tender on the track.  Now push the tender up to the locomotive and connect the drawbar.  At this point you are ready to shunt, pick up the consist and enter the mainline. 

 

Part 3 of this series examines the proper and efficient operation of Frank S.

 

This series of articles were originally published in Steam in the Garden.  Appreciation is expressed to both the author, Kevin O’Connor, and Ron Brown, Publisher/Editor, for permission to post to the SouthernSteamTrains.com web site.

 

 

 

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