Plumbing Part IV - Axel
Nelson Riedel Nelson@NelsonsLocomotive.com
Initial: 8/01/03 Last
The axel pump is the primary
source of feed water to the boiler when the locomotive is moving. It
is mounted on the middle truck and driven by an eccentric on the rear axel
of that truck. The eccentric was installed on the
axel when the axel was fabricated months ago. The pump itself and
the rod connecting the eccentric to the mump must be fabricated to
complete the axel pump system. I'm following Kenneth's
design for the axel pump.
Tolerances: The tolerances were checked before
staring on the pump. The cylinder bore is 1.12" long.
The eccentric throw is 5/8" so the piston stroke is also
5/8". The piston height is 3/8" so the piston height plus
stoke is 1.0" This means there is a total margin of
0.12". I don't think the position of the axel were the eccentric
is mounted and the position of the lower spring plank where pump mounts were controlled that well. Besides, these dimensions can change
as the truck flexes and parts move when the springs compress and
expand. I decided to modify the design by making the cylinder
1/8" longer. Since the water is essentially non compressible, the pump operation
won't be affected by the longer cylinder. Also, the stem on the
piston was made extra long. The end of the stem will be finished to
the required length measured after the pump has been mounted in the spring
|Pump: The next step was to do the lathe work for the four
pieces shown here. Nothing unusual except 1/2" square stock rather than 5/8" round stock
was used for the
plug ---- figured it would be easier to mark off the location of
the four screw holes.
Even though clearances of 0.002 were provided between
the piston and cylinder, the fit was pretty tight.
To smooth it out, the bore was lubricated, the piston
inserted, the small end of the piston chucked in the lathe,
and the cylinder grasped with the hand and slid back and forth as the piston
rotated. Worked out the rough spots in a few minutes. Now
is very smooth.
|Cutting the 5 degree slope on the wedge was easy since the
milling head can be tilted. First thought was to leave the
mill straight and shim the one side the wedge up 5 degrees by
slipping the correct size drill under one side. However, the
calculator and computer were both upstairs and I wasn't about to
try to compute the shim height using an old slide rule.
|These are all the pump parts (except the balls) ready for
assembly. Note the O rings are installed on the piston and
plug. The pin on the lower right that blocks the small ball
from going up into the upper chamber is different than
Kenneth's design. He used a 3/32 brass pin and a 1/8" MTP plug.
didn't have a 1/8" plug so I turned the pin shown from
3/16" stainless steel hex stock. The threads are
|The next step was to silver solder the wedge to the pump
body. It was decided to drill the hole in the spring plank first
and test fit everything before doing the
soldering. The drill press feature of the mill was
used to drill the hole at 5 degrees. However, before drilling
the hole, the surface was faced with an end mill to get a surface
perpendicular to the drill so it wouldn't wander when
starting. After the hole was drilled the
pump was assembled in the hole and everything fit fine. The
wedge was then silver soldered to the pump body. The pump
body and wedge were then used as a pattern to drill and tap the
holes that hold the pump to the spring plank.
The final task was to inset the piston and determine where to
put the the hole to connect the rod. The longer
cylinder gave a little more margin so a point midway
between the possible extremes was picked for the hole. Turns out it was within a few
thousands of the point Ken specified on the drawing ---- right on!
Finished Pump: The next photo shows the finished pump
mounted on the truck. The top spring plank is off giving a better
view of the pump. The only thing remaining is to connect 1/4" ID hoses to the nipples on the side of the
pump --- and of course, reassemble the truck.
A neat thing about the pump that was suspected and now
confirmed is that the pump can be removed without disassembling the
truck. Maintenance on the check valves can be performed merely
by removing the screws holding the valve body and then lifting the valve
body off. The piston will slide out after the valve body
and pin to connecting the piston to the rod have been removed.
The body will also slide out if the valve body and pin between the rod and
piston have been removed. A neat design!
|Update - Test: The pump was tested before finishing the project.
The locomotive was run on the test stand with the engine powered by
compressed air. The first test was at low pressure with the output
hose emptying back into the tender tank. Next, the steam pressure
gauge was connected to the output and the engine turned by hand.
The hose connections leaked some that limited the
pressure. Was able to run the engine at very low speed and run a
pressure of well over 100 psi. The pump should work fine.
Some work is needed on the hose connections. Also, need stronger
hose --- the hose used for the test got much fatter as the pressure