Dianne Best Personal Web Page 2018

Re-Fitting the  American
Page 5


After previous upgrades to the American, I STILL wasn't happy with the performance of the crosshead pumps! There were too many problems:

1 - the pumps couldn't keep up with the demand for water in the boiler.
By calculations, they should have been able to deliver TWICE as much water as needed but they weren't doing that.

2 - The original design used graphite packing to seal the ram to the pump cylinder, which was about the only option in the early 1960s, but the packing nut was impossible to get at to adjust and replacing the packing required stripping the crosshead off.

3 - The pump mounting was flimsy and allowed too much "lost motion"

4 - Although the pump ram was 0.25" in  diameter, many of the passages in the system were substantially  smaller.

So a re-design and rebuild of the crosshead pumps and feedwater system was in order.




The new pumps were machined from 3/8 x 1" brass bar with  stainless steel rams.



With the cylinder bore of 0.266", that left only 0.050" for wall thickness and,  when drilling to a depth of 3.25" that meant great care was required to keep the drill straight. Sometimes being lucky is better than being good and I was. 0.266" diameter was a good fit for a 3mm ID, 2mm cross-section O-ring but the small O-ring size could not be stretched over the 0.250" ram without damage the end of the ram was turned down and threaded #6-32 and a nut was turned down to slightly less than 0.250" to allow the O-ring to be slipped over the end before installing the nut.



The rear crosshead support had to be removed and the opening for the pump enlarged to accommodate the new pumps and a mounting hole for #4-40 was drilled and tapped directly into the main frame of the locomotive. Fortunately a frame stiffener provides a doubler at that location.



With the pump installed it was time to put the crosshead back together and move to the other side.



The second pump was fabricated and installed with little difficulty and it was on to making 4 check valves with minimum resistance to water flow.
The lower bodies were made from 3/8  hexagon brass bar drilled and tapped 3/8-24 and drilled through at 1/4".
The tops were made from  3/8 round brass bar threaded 3/8-24, drilled through at 1/4", and fitted with a brass hex nut from the same bar stock as the body.



The top components were soldered together. The 1/4" tube was allowed to extend through the top to act as a ball stop and was filed with crossed passages to allow the water to flow through when the check valve is open.



With t\he pumps mounted, it was on to installing the delivery plumbing. The rubber tube allows the pumps to move as they require. One T fitting is for the engineer's side pump and the second for the fireman's side pump. (It wasn't practical to increase the size of the delivery tube to the boiler check valve because the boiler check is 1/4" and adding a second one or  replacing the existing check with a larger one would require disassembling the entire locomotive!) The discharge tube going off to the right goes to the bypass valve in the tender.



Under the engine the intake line was changed to 5/16" tube and a T was fabricated with 5/16" inlet and 1/4" outputs to the pump.  Again, rubber tubes allow for some pump movement.



The 5/16" inlet line extends to the rear buffer for connection to the tender.


Next task:
- lake testing
- pressure/delivery test





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