Burner & Fire Pan Design
The burner and fire pan on the Shay has been redone several times to get to satisfactory performance. The designs here incorporate that experience plus data from full size Heisler and Garratt oil burners. The following links contain the reference data:
The Shay uses a single burner. The Heisler is somewhat larger so two burners will be provided. The two burners will share an atomizer steam regulator and atomizer pressure gauge. There will be valves between the regulator and the burners to permit each burner atomizer feed to be shut off. Each burner will have a fuel valve. The blower will also have a regulator and a pressure gauge. The blower and atomizers will be arranged to connect to air for startup and then switch to steam after pressure has built. The regulators have given a little trouble on the Shay so they should be accessible for maintenance. The fuel line to each burner will have a fuel filter that is easily removed for cleaning/replacement.
The prototype oil burner fire pan was usually lined with fire bricks and/or a refractory material. I assume this was done to protect the fire pan from damage from the intense heat. (The boiler firebox is protected by the water jacket. The fire pan has no water jacket) The most recent fire pan on the Shay was fabricated of 1/8" channel and 1/8" plate and it seems to be holding up without a coating of refractory material so the plan for the Heisler is to use channel, heavy plate and no messy refractory material.
The fire pan should be easy to remove for maintenance. The drive shaft between the engine and the middle truck runs under the fire pan and must be removed before the fire pan can be dropped. The universal behind the engine can be disconnected by removing a retaining ring and the associated pin. Once that end is disconnected, the rear end of the shaft will slide out of the slip joint.
The fire pan will be attached to the bottom of the boiler with four 10-32 screws, two on each side.
The fire pan should be removable as a unit with the burner nozzles, the baffle, the rear support for the super heater tubes and the igniter sparkplug. The fuel lines and atomizer steam lines should be equipped with standard compression fittings for easy disconnection.
The fire pan on the Shay uses 2" channels for the sides and 1/8" plate for the bottom. The drive shaft under the middle of the Heisler fire pan limits the pan height to a little less than 1.5". The drawing above shows the fire pan which is constructed from 1.25" X 1/8" channels for the sides and 1/8" plate for the bottom. The part numbers link this drawing to individual part drawings further down.
The bottom is attached to the channels with 6-32 screws. Once everything is assembled and known to fit, the inside corners of the channel will be welded.
The atomizer steam line was run through the fire pan on the latest shay modifications. There isn't enough room between the burner units and the side of the fire pan to do that here and still have an easy way to use standard compression fittings to disconnect the atomizer pipe to remove the burner for maintenance. (The burners might need to be cleaned so it is a requirement that each burner be easily removed without removing the fire pan.) The plan is to run the atomizer steam line and fuel line for each burner down the side of the fire pan. There will be no fittings next to the burners. The lines will be fitted with compression fittings just beyond the rear of the fire pan. There will be brackets for the lines along the side of the fire pan. The bracket will hold the steam line against the side of the fire pan for heating of the steam and hold the fuel line about 1/4" away from the side of the fire pan to provide some heating but not too much. Each tube bracket will be secured with one screw and the burner bracket (HM654) is secured with two screws so the burner can be removed by taking out four screws and disconnecting two compression fittings.
The baffle and superheater tube support were left off this drawing for clarity. They are included near the end.
The drawing above shows the fire pan and burners (blue) in relation to the frame, engine, middle shaft and universals. Note that there is a slight interference with the universal under the front of the fire pan. The front channel and bottom plate will be notched back 3/8" in the middle to provide clearance. There appears be be ample clearance for the rear universal. However, that universal will move up and down some as the truck flexes so the rear channel might also require a small notch. There appears to be some interference between the burner and the universal on the drawing. However, the burners are toward the sides of the fire pan and the universal is under the middle of the fire pan so there is ample clearance.
Parts HM650, HM651 & HM625 are all made of 1.25" X 1/2" X 1`/8" channel. The large hole in the HM651 rear channel is for the igniter spark plug. The adjacent smaller tapped 6-32 hole is for a screw through the HM659 igniter plug retaining plate. Additional holes in the front channel are required to hold the baffle described later.
The bottom shown above is straight forward. As mentioned previously, the bottom and possibly the channels above may need to be notched in the front and rear to provide clearance for the universals.
The baffle shown above is similar in size to the baffle the boiler maker put in my shay boiler. That baffle was supported by square bar stock welded to the side of the fire box. The baffle here is attached to the front channel of the fire pan. There will be a ~ 1/4" gap between the side of the baffle and the firebox side. The baffle support will give additional support and also support the end of the superheater tubes. The baffle support is attached to the fire pan and the baffle with short pieces of 1" X 1" X 1/8" angle. All these pieces are made from mild steel bar and plate stock. The hot gasses flow from the burner to the rear of the fire box and then up and over the baffle along the crown sheet and then out the flues. The baffle support and support angles are oriented with the thin sides in the direction of the flow to minimize impedance to the flow.
The details of the baffle are shown in the drawing above. The large holes line up with identical holes in the front rail. The baffle attaches to the front channel with three 6-32 screws and nuts.
The design of the atomizer and blower regulator mounting arrangement and associated plumbing and the the design of the fuel valve and filter plumbing are the major unfinished parts of this area of the design. These last designs are postponed until the fire pan and burners have been constructed and installed ---- which should happen ion the next few months.