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Specifications for 20hp 16" high boiler.

The boiler shell is assembled from five separate pieces, consisting of a cylinder, top and bottom tube sheets, and top and bottom bands.

The cylinder is ¼” thick and consists of rolled plate with a vertical seam. Material consists of carbon steel (pressure vessel quality – ASTM A515, grade 70). Minimum tensile strength of this material is 70-90 KSI. A515 is a recognized material grade for boilers and pressure vessels. The inside diameter of the cylinder is 23-1/4” by 15-7/8” high. The vertical seam on the cylinder is welded from the outside, following bevel grinding. A steel bar (ASTM A36) 1” wide by ¼” thick is first clamped and centered over the joint on the inside of the cylinder extending its full length enabling full root penetration of the outside weld of the beveled butt joint and to the backing plate. Following this operation, a single fillet weld is placed on each side of the backing plate on the inside. 7018 electrode rod is used for the above processes. The outside weld to the seam is ground flat, enabling placement of .050” diameter cadmium coated spring wire (tensile strength 309,000 pounds) between the bands. The wire is uniformly applied to the cylinder between the bands in three separate layers under tension (60 pounds). The spring wire is secured to the cylinder by screws placed into the bottom band and 1/16” holes drilled through the top bands. Breaking strength of a single wire strand is approximately 900 pounds.

The bottom tube sheet is 5/16” thick, the top sheet ¼” thick. The tube sheets are perforated with 33/64” diameter holes. The holes are spaced from the center of the sheets in rows with a triangular pattern. Hole spacing is 13/16” on center between and within each row. Tube web at the narrowest point is approximately 5/16”. The diameter of the sheets is 23-1/4” Each sheet is welded into the cylinder flush with the ends. The tube sheets and cylinder are beveled approximately 30 degrees in preparation for welding. The sheets welded into the cylinder such that the holes in the top sheet are in line with the holes on the bottom sheet. The bottom sheet is secured with multiple passes, including an internal fillet weld and two external welds. 7018 electrode rod is used. Following this operation, the top and bottom bands are placed on each end of the cylinders and welded using 7024 rod. This is a low profile weld which extends from the tube sheet, over the cylinder end, and onto the band, serving to bind the entire weldment. The material used for the tube sheets is ASTM A515.

The boiler bands consist of a 1” by 3/8”” rolled bar 22.5” outside diameter, and a 1.5” by 3/8” rolled bar 21.5” outside diameter. The 1.5” wide band projects below the bottom tube sheet ¼”, enabling the boiler to rest in the boiler frame without the tubes contacting it. Material used for the bands is ASTM A36. The main purpose of the bands is to provide stability and strength to the shell and providing a track for the spring wire to be applied to the cylinder.

All welding on the boiler is performed by a pressure vessel certified welder recognized and tested by the American Welding Society (AWS).

Following welding and prior to tubing the shell, the boiler is stress relieved in a temperature controlled oven using the standard protocol for this type of operation. The purpose of this operation is to promote stability of the pressure vessel when subjected to heat.

The boiler tubes are hard drawn copper and are ½” O.D. with a .049” wall. Tube length is 16”. The boiler consists of 680 tubes. Inserted in each end of the tubes is a steel ferrule which projects slightly below the tube sheets. The purpose of the ferrules is to provide additional strength to the tubes and help secure the tubes to the sheet. All tubes and ferrules are taper expanded into the tube sheets. The boiler is tapped with a 3/8” NPT in the top center. This opening feeds saturated steam to the throttle valve which is placed on top of the boiler.

Following tubing and ferruling the shell, the boiler cylinder is tension wound with spring wire. This wire is cadmium plated to resist surface rust.

The last step in this manufacture of this boiler consist of a cold water hydraulic test. The boiler is tested to 1000 PSI and checked for leaks. This is a 10 minute test using a calibrated test gauge. A Certificate of Testing accompanies this report. This boiler is intended to be operated between 400 and 575 PSI.


Bourdon Boiler Works constructs replacement boilers for Stanley automobiles. The design and construction of replacement boilers is substantially the same as the original units. The primary exception is that the entire unit is made of heavier gauge materials (tubes sheets and cylinder) and tube wall thickness. Additionally, the spring wire placed on the cylinder is 30% larger in diameter.

Bourdon Boiler Works commenced construction of Stanley style boilers in 1973 and has built approximately 400 units since this date.

P.O. BOX55
PH: 802-457-3787

Click here for information about layout and tapping boilers.

Click here for information about Keeping Your Stanley Boiler Clean.


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