Hydro-static test

Locomotive 924 circa 1908

Northern Pacific Railway steam locomotive 924 has been undergoing restoration in the Conservation and Restoration Center.  This 1899-built Rogers locomotive served the Northern Pacific Railway until 1924. It is a King County and City of Snoqualmie Landmark, with project support from many individuals, foundations and public agencies including 4Culture, Washington Heritage Capital Projects, the Northern Pacific Railway Historical Association, the Emery Rail Heritage Trust and more.

Fire in the 924 firebox

For the last several years a variety of project work has been underway, but the most important division of work has been on the boiler.  The boiler is where water is heated and converted to steam, usually with an oil, coal or wood fire.  The boiler must withstand high temperatures and considerable pressure.  

Locomotive 924 is filled with water, 

and then the water is lightly heated so

as to reduce the strain on the boiler 

when it is pressurized.

For the general public, a little known fact about locomotive boilers is that they must be designed to withstand four times their operating pressure.  So an operating pressure of 180 psi requires the boiler be designed to withstand 720 psi.  This is called the factor of safety, and must consider any wasting or other deterioration of the boiler that occurred since it was built.

FRA inspector Brandon King witnessed
the 924's official hydro-static test.  He
found no exceptions, which is the best
possible outcome.  This means the
inspection found that the Museum
is complying with the regulations.

After measurement, analysis and calculations demonstrate that the boiler construction is capable of withstanding 720 PSI, a non-destructive test called a hydrostatic test is performed.  This test is performed by the locomotive owner, but is witnessed by an inspector from the Federal Railroad Administration.  During the test, the boiler is filled with water, lightly heated, and pressurized to 125% of its stated operating pressure.  

Kyle I. operated the hand
pump.

It was a beautiful morning on Thursday, September 5th when Museum volunteers and staff arrived to "fire" the boiler on locomotive 924.  Recycled wood logs and waste wood were used as fuel, and the temperature was brought up to 100 degrees.  At that point, the fire was dropped and a hand pump was used to bring the pressure up to 225 psi. Visual and aural inspections were all positive - just some light weeping from a handful of rivets.  Most impressive to the Museum volunteers and staff was how tight the boiler was.  One stroke from the hand pump every 15 or so seconds was sufficient to maintain 225 psi.

Kyle and David remove the steam dome
lid and throttle to allow an internal
inspection.

Upon completion of the hydro-static test, the boiler was drained.  After this 125% test, an interior inspection of the boiler and hammer testing of the stay bolts was required.  For the interior inspection, the steam dome lid and throttle was removed so an inspector could enter and crawl along the top course of tubes.

The Northern Pacific Railway steam locomotive 924 rehabilitation and restoration project continues to progress.  The hydro-static test brought great news so now the next phase - steam plumbing - can begin.  Donor support remains critical to the ultimate success of the project; your support really makes a difference.  Please consider a making a donation on the Museum's web site: Donate Now

Thank you for your support!