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.

More on the 1385 Boiler Delivery and Subsequent Progress

It has been some time since our last C&NW 1385 status update. Upon delivery of the boiler, a few photos were posted with the promise of more to come, but as Mid-Continent entered our busy special event season the sharing of additional photos and videos got put off by more pressing projects. However, that doesn’t mean work halted on the 1385. Now that the busy 2019 season is behind us, we’ve had a chance to put together this mega-update for you.

Boiler Delivery

C&NW 1385’s boiler has represented the single most challenging part of the locomotives rebuild. Planning of the boiler was started early in the rebuild process and in-depth engineering work started in 2015. The construction contract was signed with Continental Fabricators in late 2016. Many design iterations went back and forth as the project volunteers, boiler engineer, and manufacturer exchanged ideas and tweaked components. Finally, by late September 2019 the boiler was ready to ship, arriving on September 26, 2019. The following photos explain the activities.

In addition to still photos, a series of GoPro cameras mounted on the locomotive, a tripod camera, and a drone were all on hand leaving no angle uncovered. The following photos and video are courtesy Jeffrey Lentz and Randy Long. Update text by Peet Deets and Jeffrey Lentz.

After departing the previous day from St. Louis and arriving at SPEC Machine in the middle of the night, 1385’s boiler is prepped for unloading. Although paling in size to some locomotives, the 1385 is hardly small – seen here dwarfing SPEC Machine’s forklift being used to unload spare boiler tubes from the trailer. As hinted at by the photo backgrounds, SPEC Machine is not normally a locomotive heavy repair shop and is actually located on a working farm.

1385’s running gear was pre-positioned outside on temporary track in order to receive the boiler.

LEFT: SPEC Machine owner, Steve R., talks unloading strategy with 1385 Task Force volunteer Pete D. (in hard hat). CENTER: Mid-Continent volunteer Ed R. gets ready to attach the crane’s lifting straps to the 1385 boiler. RIGHT: Brett M., the engineer of the new boiler, is on hand to help with the boiler lift and make sure everything goes smoothly.

The new boiler is gently lifted off the trailer as SPEC Machine’s Steve R. looks on.

In short order, the boiler has been positioned over the locomotive’s running gear and has started being lowered.

SPEC Machine’s Tyler R. keeps hold of a tether attached to the boiler. Wind speeds picked up as the lift was underway, causing the boiler to want to sway and swivel. The tether straps permit control over the lift without risk of getting fingers or hands pinched by the 41,000 lb boiler.

Despite the large size of the equipment involved, it is a game of fractions of an inch when it comes to placing all the pieces together. Here 1385 Task Force member Mike W. is seen taking a tape measure reading as they battle a bit of a breeze while trying to set the boiler on the exact spot needed.

LEFT: Some components couldn’t be fabricated until after the boiler was fitted and tolerances defined. In the meantime, timbers are used to support the boiler on the firebox end. CENTER: Ed R. verifies boiler placement against blueprints from the Chicago & North Western railroad. RIGHT: The increasing wind level made positioning the boiler on the exact centerline of the frame increasingly difficult. A speed square is pulled out to verify the accuracy of the last attempt.

1385’s boiler is Inside SPEC Machine’s shop, waiting on other parts of the locomotive to catch up before the cab can be installed. Since previous updates, the roof has been covered and rain gutters installed. Inside the cab the wiring for various electrical systems have been installed.

Boiler placement continues to be adjusted as friends and family members look on from inside the shop.

One of the boiler supports was discovered to be positioned slightly too high causing the boiler to sit unevenly. Adjustments are quickly made by Mike W. and Steve R.

With the ash pan and grates not yet installed, this view looking up into the firebox was possible, showing the arch tubes which help circulate water around the firebox walls.

After a bit of struggle fighting the wind, the crew was finally able to get the boiler placement just right and the crane was able to set it down.

Key members of the 1385 crew gather for a group photo to celebrate the completion of a major step in the 1385’s journey toward operation. From left to right, Tyler R., Pete D., Steve R., Mike W. Tim K., and Ed R.

After the boiler was placed and a lunch break enjoyed, a tractor was used to tow 1385 inside the shop bay where work will continue.

Progress Since the Boiler Delivery

In the time since the boiler was delivered work has continued on the hundreds of to-do list items that need to be checked off before the locomotive assembly can be completed. These tasks are less attention-getting than a new boiler, but no less important to the locomotive’s rebuild.

In November 2019, a MCRM members work session was held to help organize the thousands of parts and pieces associated with the locomotive. The palette racking set up during the Member’s work session is being put to good use. As seen here, the racking has tripled the amount of usable space for storage in that spot.

Progress has been made on items that will go both inside and outside the new boiler. Here is the air-operated firedoor that is the target of every fireman. The 1385 is a hand-fired coal-burning locomotive so every shovel full of coal passes through this door. The control valve, cylinder and piston have been rebuilt so the door was able to open itself for the first time in over 20 years.

SPEC Machine’s Steve R. is explaining the disassembly of one of the two steam-driven air compressors that supply air for the braking system and other appliances of the 1385.  Both compressors will be torn down for inspection and necessary repair.  After rebuilding they must be tested to Federal Railroad Administration specification in order to prove they can deliver enough compressed air for safe train operation.

Here is a shot of what is actually the bottom of the superheater header.  As you can see the years have not been kind to the header and some pieces have been broken out.  It was found that the header was weldable so the small blocks shown were welded in to replace that material that had been chipped out.  The area to be repaired must be pre-heated to several hundred degrees Fahrenheit and will be covered with insulation afterward so it will cool very slowly to prevent cracking. The second photo shows the bottom of the superheater header after the welded repair.  After a bit more cleanup the sockets seen in the surface will be cleaned up by machining so they will be ready to accept the superheater units and be clamped to a steam tight joint.

This is the throttle body that normally resides inside the steam dome and is used to control the amount of steam getting to the cylinders.  In the first photo it is upside down in the large milling machine so one of the surfaces that connects to the dry pipe can be cleaned up and made steam tight.  A leak at that end of the throttle body would allow a constant flow of steam into the cylinders that could not be controlled.

The second photo shows the throttle body as it will sit in the steam dome.  The throttle spool will fit down into the large opening and when the throttle is shut the top of the spool will rest on the upper edge of the opening where you can see the small beveled edge.  The bottom side of the spool will rest against a similar sealing edge inside the body to create the steam tight seal of a closed throttle.

The first photo above is of the throttle spool sitting upside down on the bench.  The shiny edge just inside the ring of the spool closest to the camera will contact the sealing surface inside the throttle body.  The shiny edge at the table will contact the surface at the top of the throttle body.

The second photo shows the sealing surface at the bottom-most end of the throttle body where the body will connect to the dry pipe.  This is the surface that was getting machined in the picture of the body in the milling machine.

This is the superheater header wrapped in insulation to allow it to slowly cool after the repair welding.  The superheater eventually will be installed inside the smokebox at the front of the boiler. The two large flanges seen in the photo connect to the branch pipes that carry the superheated steam down to the valves and cylinders which then turn the driving wheels.

This is the bracket mounted inside the steam dome at the top of the boiler that will hold the throttle body. The fire tubes and a couple of superheater flues are visible inside the boiler.

This is the throttle body (now attached to the bracket from the previous photo) and looking at the sealing surfaces for the spool.  The shaft of the throttle spool will drop down through the hole in the center of the body.

A different view of the throttle body mounted to the bracket and edge of the steam dome.  The front of the locomotive is to the right and the backhead, cab and crew would be to the left.  Differing from the old boiler, the new boiler has a removable steam dome and the dome ring has been pulled off to accommodate this fitting work.  When re-installed, the ring will extend well above the throttle so the dome lid can be properly installed.

Lastly, we have a before and after picture of the ball ends of the superheater units.  Before cleanup you can see how rough they became through use and storage.  The ends now have a freshly polished sealing surface.ange.

Thank you for your patience with our delays getting this update created. We’re looking forward to a productive 2020!

Please remember that while we appreciate the public’s enthusiasm to see 1385’s progress, the contractor shop where the 1385 work is taking place is a private business, not a museum. They are not open for public tours. Any persons without prior authorization showing up at their shop hoping to see the 1385 will be turned away. If you wish to partake in future 1385 volunteer work sessions, consider joining Mid-Continent as a member.

1385’s Boiler Arrives in Wisconsin

With the C&NW 1385’s new boiler fabrication just completed, Mid-Continent Railway Museum wasted no time getting it on the road to Wisconsin. The boiler has now joined the running gear at SPEC Machine outside Middleton, Wis., where the locomotive will be reassembled.

The boiler left St. Louis on a truck last night and arrived at SPEC Machine around 2 AM today (September 26, 2019). Crews from SPEC Machine, Ideal Crane, and Mid-Continent Railway Museum’s #1385 Task Force volunteers worked together this morning to safely lift the 41,000 lb. boiler from the trailer onto the locomotive frame. Work wrapped up around 2 PM this afternoon.

We took lots of photos and video and will share a more complete account of the day’s activities along with video in the next day or two once we’ve had an opportunity to edit it all together. In the meantime, here are a few quick photos from today’s activities.

C&NW 1385’s boiler is gently lowered onto the locomotive frame. Jeffrey Lentz photo.

We appreciate the public’s enthusiasm to see the 1385’s progress first-hand; however, the contractor shops where the #1385 work is taking place are private property and not open to the public. Anyone requesting to see the locomotive at those locations will be turned away. Please help #1385 return to operation as expeditiously as possible by respecting our contractors’ wishes.

1385’s Boiler Painted, Ready for Delivery

With the hydro test successfully completed, 1385’s boiler has received a shiny coat of paint on the boiler exterior and it looks great! Most of it will be covered later though by lagging (insulation) and boiler jacketing.

C&NW 1385’s new boiler – painted and ready for delivery. Photo courtesy Continental Fabricators.

The smokebox has also been attached for shipment. The smokebox has only been tack welded in place as it will need to be detached later. It will need to be attached to – and become part of – the cylinder saddle first. Then the boiler is attached to it.

Front view of 1385’s boiler with smokebox attached. Photo courtesy Continental Fabricators.

Sharp-eyed viewers will notice in the smokebox door ring has been bolted in place upside down.  It has just been temporarily fastened in place and it too will be removed and re-added probably multiple times before the locomotive is completed.

With this, the work at Continental Fabricators is complete. Now the boiler will join the cab and running gear at SPEC Machine in Middleton, Wis.

PLEASE NOTE: We appreciate the public’s enthusiasm to see the 1385’s progress first-hand; however, the contractor shops where the #1385 work is taking place are private property and not open to the public. Anyone requesting to see the locomotive at those locations will be turned away. Please help #1385 return to operation as expeditiously as possible by respecting our contractors’ wishes.