Boilers and the Plumbing Thereof

Photo #1 shows a 3-drum Yarrow semi over-discharge water-tube boiler (identical to the one in my steamboat). It is made of copper and it has 39 sq.ft. of heating surface. The mud drums are 3in. dia. and the steam drum is 6in. dia. The downcomers are 2in. dia. and the four rows of water tubes are 1/2in. o.d.

When I first got my hands on this boiler I tried to fire it with a kerosene vaporizing burner and thereby hangs a tale for another day...

Nowadays I fire with wood, preferring to use what Dick Vennerbeck calls &quotGourmet Racing Wood", i.e. those varieties which burn clean, long and hot. So far the best I have found is Pear wood, although I hear Manzanita is the best. Unfortunately, although it may be a common &quotweed" in other parts of the state it is an endangered species in Santa Barbara!

This boiler was made by Pete Moale, who now lives in Northern California, in blissful ignorance of the web! ;-)

Boiler under hydro test

Water Tube boilers are great steamers, but they have a limited &quottop end" of about 200psi. To get more pressure it takes a monotube or pipe boiler (I hope to build one some day!) Photo #2 shows a selection of bending tools built by my steam guru, Jim Tangeman. These are used to bend the serpentine sections used in uniflow or pipe boilers, which consist of butt-welded sections of black iron pipe or stainless tubing. The trick is to bend the tubing as tightly as possible without causing stress cracks or deformation. This is done by supporting the tube all around its circumference, during the entire bending operation, with inner and outer dies having semicircular channels all around. A tang is welded to the fixed inner die, and a gnarly big handle is welded onto the forming die so that it may be held in a bench vise.

The work to the left of the photo is a section of 1/4in. black iron pipe which has been bent to a typical radius.

In practice, bends would be alternating left- and right-hand in order to produce a grid. To do so requires two die sets, one right and one left-handed, otherwise as the boiler grew in size and became more convoluted it would become impossible to free the mess after each new bend. Photo #3 illustrates the offset of one inner bending die, relative to the section that holds it in a vise.

Photo #4 shows a set of dies suitable for 1/8in. black iron pipe. Jim says that a boiler made out of 1/8in. pipe can be bent up without a formed semicircular channel in the tool, since the pipe is sufficiently strong and small to be bent without excessive deformation. The pin to the bottom of the photo is the pivot that aligns the outer to the inner bending die.

Photo #5 illustrates Jim's completed boiler, which is barely 12in. wide and 18in. deep. Through the open top can be glimpsed the top row of water tube bends. Note also the neatly bent pipe leading to the pressure gauge.

Of course, if you do build one of these beasties you can expect *very* high temperatures and pressures. I have seen Jim's Stuart single-cylinder engine: high steam temperature has burned the paint off of its cylinder! Temperature gauges are common for these ranges, but safety valves are not. Jim says that the one essential feature of such a safety valve is an external spring in its design. Without this feature, steam blowing past the spring would be hot enough to anneal the metal, causing it to quickly fail. Photo #6 shows Jim's home-made safety valve, which is set to pop at 600psi. The projecting handle allows him to trip the valve by hand, in order to test it and to reseat the valve if it doesn't behave.

Since I built it more than a decade ago, my boat's steam plant has been condensing, i.e. I use a closed-loop system that recirculates exhaust steam with the aid of a keel condenser and other parapernalia, whose purpose is to separate condensate into lubricating oil (which is captured in a series of filter media) and pure feedwater for re-use in the boiler. Keel condensers have a few drawbacks, however, not the least of which is the drag they cause by hanging underneath an otherwise well-formed hull.

In addition to this liability, it is possible for some feedwater to make it through the filters and still have some residual oil mixed in. As time passes, the sticky residue can build up and cause check valves and pump components to misbehave and in extreme circumstances, oil deposits within boiler shells can cause structural failures due to local heating which can cause brazed joints to come loose...

In 1996 at the Great Delta Steamboat Meet, my feedpump packed it in (literally) and failed to function properly. Disassembly revealed deposits of steam oil around the spring-loaded stainless disks that "check" water from flowing back in to the pump. This contamination caused improper sealing of these disks and the pressure within the boiler actually caused water (and steam) to flow backwards and into the pump. Before contamination could cause further and more serious problems, I decided to convert my steamboat to a non-condensing, open-loop system. This will not only eliminate the problem of oily feedwater, it will also make the hull fair and it will allow me to re-plumb the engine's exhaust up the smokestack, which will have the benefit of increasing draft and making the fire more efficient.

Photo #7 illustrates proof of oil contamination when I disassembled the keel condenser and cut it in two. On the "steam" side the i.d. was spotless, but on the "water" end of the condenser, the evidence was there: oil leeches out of the system during the condensation process, before the mixture ever gets to the filters. Before too much longer, this could have caused far more damage.

If anyone out there in the audience uses a condenser, I would like to know how your system is behaving...

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