Testing 1385’s Steam-Powered Air Compressors

Chicago & North Western #1385’s two air compressors underwent testing on October 16, 2020 with the help of the Roudebush family’s steam traction engine. The steam-driven air compressors supply the air pressure needed to operate the braking system for the 1385 and its train.

This was the first time the compressors have operated in over 20 years. As the video shows, both air compressors passed the Federal Railroad Administration’s requirements for service although further tweaking will be done to improve performance.

Video clips provided by M.L. Deets, Steve Roudebush, and MCRM archival video recorded by Dorthy Lane Streck

Superheater Header Finish and Installation

In our last update, we discussed how the Chicago & North Western #1385 had been converted in 1926 to become a superheated locomotive. One of the components added as part of that 1926 conversion was the superheater header. The superheater header’s job is to take steam from the dry pipe and direct it to the superheater tubes for a second round of heating before the steam is sent to the branch pipes and down to the cylinders.

We now pick up on the repair of the superheater header and its installation.  After the gas weld repairs were finished to mend the broken “T”-slots the header was mounted in SPEC’s large CNC milling machine.  A skin cut on the superheater unit face was made to give an even working surface and then the sealing surface for each of the superheater ball ends was machined. 

Superheater unit face after machining.

The T-slots were also machined to a minimum clearance to accept the new T-bars that will be used to clamp the superheater units into the header for a steam tight seal. 

The original design was to have an individual T-headed bolt for each unit but that concentrates all the clamping stress in the small area of the shoulders of the bolt.  It is believed that is why the sections of the header broke out and had to be repaired in the first place.  The T-bars will distribute the stress along the length of the slot and hopefully preclude any more breaks in the slots. The nuts are extra long so that while the engine is on service the threads of the clamping bolts will be protected from the abrasive blast of cinders flying past and the corrosive nature of the cinders and ash that will collect.

Picture of all the T-bars and clamping bolts in place on the header with a reminder that the header is lying on the palette upside down. 

The header and superheater units await installation.

After that operation (and many other tasks) the header was placed in the smokebox prior to mounting it for a test fit.  

The superheater header sits in the smokebox as it is readied for installation.

Finally, the header is moved into its working position. Looking through a branch pipe hole in the side of the smokebox we can see the freshly machined surface that will seal against the dry pipe as it seats in the flange in the front tubesheet.

The header is gently slid over the studs and when the nuts are tightened it is finally in its home position for the first time on our new boiler. 

A little closer look and a bit of imagination and you can see how the superheater units will be drawn up into the header with the ball ends straddling the T-slots. 

The header is tested for fit inside the smokebox.

One side of the slot will deliver the steam from the throttle to the superheater unit and the other side will collect the superheated steam for delivery down the branch pipes to the valves and cylinders. 

With the fit-up and sealing proven, tabs are welded to the inside of the smokebox to support the weight of the header while in service.  The sealing surfaces of the branch pipe flanges also get dressed and lapped to seal against the donuts used in the branch pipes.

With the test fitting completed and everything checking out, the header and superheaters have all been installed and are now mated to the header.

Superheaters and header fully installed and mated.

A sharp eye will catch a ring of different color between the superheater units and the header.  Due to a discrepancy between the C&NW drawings and how the boiler was actually built we’ve been given an opportunity to improve the sealing surface by adding a heavy brass gasket. 

These collars not only take up the needed space but also give us a brass-on-steel sealing surface rather than steel-on-steel and provides us a replaceable sealing seat for easier maintenance down the line.

All photos provided by M. L. Deets.

 

Dry Pipe Work

Today’s steam status update looks at work taking place on the 1385’s dry pipe. Before jumping into a description of the work being done, it is helpful to first understand a little bit more about how boilers work and some of the terminology of steam.

The Science of Steam: Dry Steam Versus Wet Steam

The job of a dry pipe in the locomotive is that when the throttle is opened it will deliver the driest available steam out of the boiler proper and deliver it for the next stage of use by the locomotive. What that next stage is will depend on the type of boiler.

The idea of “dry steam” seems counterintuitive since steam is made from water and we generally think of water as being wet. However, in scientific terms, wetness is defined as “the ability of a liquid to adhere to the surface of a solid.” Pure steam is not liquid and does not adhere to a solid and is therefore not wet. If you place your hand over a boiling pot of water, the steam will make your hand wet only because the steam coming into contact with your hand is rapidly cooling off to the point at which it is able to recondense into liquid water again.

Converting and maintaining all of the water molecules into steam is not easily accomplished. The liquid water sloshing around inside the boiler and the extensive system of piping through which the steam must travel means there is plenty of opportunities for the tiny droplets of liquid water to get mixed in with the steam or recondense into liquid. Some of those tiny droplets fall back down into the liquid water lower in the boiler, but other droplets will become suspended in the steam. When a substance exists as a mixture of both gas and liquid such as this it is called vapor.

The ratio of gas molecules to liquid molecules is called vapor quality. For example, if a vapor contains 95% steam and 5% liquid, it is said to have a quality of 0.95 or 95%. Water vapor that contains very few suspended droplets is referred to as dry steam. Water vapor with a higher ratio of suspended droplets is referred to as wet steam. Dry steam, because it is less dense, rises above wet steam, which means the driest steam is always found at the top of the boiler.

How the Throttle and Dry Pipe Work

With the terminology and science of steam and its varying degrees of quality out of the way, let’s get back to the subject of the dry pipe. As was stated, the purpose of the dry pipe is to transport the driest available steam from inside the boiler to where it can be put to use by the locomotive. Since dry steam rises, a dome is added to the top of boilers so the driest steam can gather at a single location to make it easier to collect. This dome-shaped reservoir for dry steam is unimaginatively called the steam dome.

It is within the steam dome that 1385’s throttle is located. When the throttle is placed inside the steam dome, it is called dome throttle. Later locomotive designs which included superheaters (more on that in a moment) would often instead have the throttle at the front of the boiler next to the smokebox rather than inside the steam dome. Those are referred to as front-end throttles.

When the engineer pulls the lever on the 1385 to open the throttle, it permits the steam in the steam dome to enter the dry pipe where it is then directed to the next phase of use. C&NW #1385 was originally built as a saturated boiler, which meant that from the throttle the steam was sent directly to the cylinders for use in turning the wheels.

In 1898, the first superheated locomotive, a Prussian State Railways S4 series, was introduced to the world. In a superheated boiler, after the water has been heated to form saturated steam, that steam is then sent for another round of heating in the superheater. This accomplishes two things. First, it further dries the steam by converting the remaining liquid water droplets into steam, improving its vapor quality. Secondly, it introduces additional heat energy to the steam molecules. Greater heat energy means more work can be accomplished using the same amount of steam. This translates into better fuel and water efficiency and more tonnage that can be pulled by the locomotive. 

Energy efficiency was taken very seriously by railroads even at the opening of the last century. To take advantage of the advancement of superheater technology, #1385 was modified by the Chicago & North Western in April 1926 to convert it from a saturated boiler to a superheated boiler. Many of its fellow R-1 class locomotives also underwent the conversion.

locomotive schematic

IMAGE 1: Simplified illustration of the throttle, dry pipe, and related components within the C&NW #1385 steam locomotive boiler.

 

Progress on C&NW #1385’s Dry Pipe

At the throttle end of the dry pipe there is an elbow that must seal to the bottom of the throttle so steam cannot leak in while the throttle is closed. The throttle end elbow has a machined sealing surface much the same as the bottom of the throttle (seen in Image 3) and a bronze ring or donut of the opposite shape is clamped between the two pieces as a metallic gasket. The bronze ring can be seen between the throttle and the elbow as Steve R. of SPEC Machine is fitting the pieces together (Image 4).  A large U-bolt will cradle the dry pipe elbow and come up through the holes shown in the ears on the throttle body to clamp the pieces together and form a steam-tight seal.

IMAGE 4: SPEC Machine’s Steve R. works to install the throttle. The access hole in which Steve is working will eventually be covered by the steam dome. Brett Morley photo.

The smokebox end of the dry pipe requires a double seal. The back side must seal tightly against the flange in the smokebox (circled in Image 5) to keep the steam inside the boiler.  The front side has to seal tightly against the input flange of the superheater header (circle in Image 6) so the steam to be applied to the cylinders doesn’t leak out to the atmosphere. 

front view of 1385's smokebox with front tube sheet exposed

IMAGE 5: The red circle indicates where the dry pipe will pass through the front tube sheet.

 

Superheater header

IMAGE 6: This is the superheater header. The input flange that connects to the dry pipe is circled in red.

Below is a better look at the superheater header’s sealing surface prior to machining (Image 7) and again just prior to installation (Image 8). The double sealing ring was machined as a separate piece. Below photos show it before being welded to the dry pipe (Image 9) and after (Image 10).  

During installation, the dry pipe is slid through the flange in the smokebox toward the steam dome and throttle and can be seen almost in its home position (Image 11).  The superheater header will be installed on the studs shown and will clamp down the dry pipe in order to achieve the necessary steam tight seal on both surfaces.

Dry pipe partially sticking out into smokebox

IMAGE 11: Viewed from inside the smokebox, the dry pipe is in the process of being inserted into the boiler. The studs surrounding it will support the superheater header.

The fitting work shown in this post was carried out in early July 2020. Be sure to keep an eye out for upcoming updates in which we’ll be detailing work on the throttle rod and superheater.

All photos in this update are by ML Deets unless otherwise noted.

Catching Up with 1385

In the shadow of the COVID-19 pandemic and its resulting shutdowns over the past few months, we have been fortunate SPEC Machine has been able to work on the Chicago & North Western #1385 at all. Many of the things done during this time period has been measuring, fitting and design work that provides little to no visual change to the locomotive which makes progress reporting a bit more difficult. 

That said, the boiler and smoke box have been positioned which allows for the furnace bearers to be made. The boiler is fixed solidly to the smokebox and cylinders but like so many other things, steel expands as it gets hotter.  When the 1385 is fired up it will start at ambient temperature but when it reaches a full head of steam of 200 PSI the boiler will be about 388° F.  This will cause the boiler to grow in length.

To accommodate this, the rest of the boiler and the front corners of the firebox rest on a pair of bronze shoes called furnace bearers. The shoes bolt to tabs welded to the front-bottom of the mudring. These shoes allow the boiler to freely expand and contract as needed while still being supported by the locomotive frame.

Animated illustration of boiler movement

The below photos show the tab as well as the top part of the shoe holder that will support the weight of the boiler.

On the fundraising front, the 1385 project was recently the recipient of a $7,000 donation from the Bluewater Michigan Chapter of the National Railway Historical Society. While this is good news for the 1385, it sadly was donated as part of the Chapter’s dissolution and distribution of assets. The Bluewater Chapter was established in 1982 and was well known in railroad circles for operating many successful mainline passenger excursions around the Midwest, helping to bring railroading to the public. The Chapter faced tough times in recent years as mainline excursions became more challenging to operate for a variety of reasons, ultimately leading the group to dissolve the Chapter last year. We salute the Bluewater Chapter members for their amazing work over the years and are appreciative of this final act of generosity toward Mid-Continent’s 1385 program.

You Can Help Get C&NW 1385 Back in Service

Ever since the C&NW No. 1385 restoration was resumed in 2011 work has progressed steadily thanks in large part the financial support of the 1385 project’s enthusiastic followers. That financial backing has allowed hired professional machinists to work on the project 5-days-a-week and allowed progress to occur exponentially faster than could be accomplished by volunteers alone.

As we head in the home stretch we’re asking for your continued support so that the 1385 restoration can continue moving forward without delay. Please consider joining the growing list of nearly 1,000 project contributors by donating today. You can do so by visiting our Donation Page and specifying in the donation form that you want your contribution to support C&NW #1385.

Donating is easy thanks to our online donation form which accepts all major credit cards and Paypal, or you can use our printable donation form to send with your mailed contribution. Thank you for helping us get this far!

With your help this will soon be a common scene at Mid-Continent Railway Museum.