Update: 2-28-2001

Some design changes have occurred since the below article was written. The fuel, water, air, and cylinder oil pumps will go in a pump box mounted on the car frame, and will be driven by a 4:1 stroke-reduction lever, connected to one crosshead at one end via a ball-joint link. The small end of this lever, on the engine, is connected to a ball-jointed reciprocating rod, which is connected to the pump plungers in the pump box. The pump box will be sealed with an oil bath inside, and the plunger rod will run through two stuffing boxes, one at front and one at back of pump box, to keep the oil inside.

The air pump will be a very small (1/4" bore x 1" stroke) single-acting spring-loaded plunger pump, located in this pump box. It is designed to give constant clearance and compression ratio despite slight variations in pump stroke caused by rear suspension travel. It is sized such that it could refill an airless fuel pressure tank in 32 miles of driving -- much more capacity than needed despite its shrimpy size and negligible horsepower consumption. (For starting out with no air in the fuel pressure tank, just work the hand pump handle; this one handle simultaneously operates manual fuel, water, air, and cylinder oil pumps connected to it. Or a home or service station compressed air source can refill the pressure tank, via a conveniently-located tire-type valve stem. Neither procedure will ever be needed, however, if the car is kept in good shape and driven regularly.) Oil splash in the crankcase will lube and cool the thin air cylinder and plunger, for longer service life and better compression efficiency.

The fuel and water pump plungers will be precision molded/bonded into a single piece with the drive plunger via a fiberglass/epoxy yoke, eliminating side thrust. The pivoting drive pin shown below has been eliminated. Cylinder oil and air pumps will be impact-driven by spurs to the side of the bonded-on pump yoke; they are small enough to be driven by this method without perceptible noise or vibration, or excessive wear. The adjustability requirement of the lubricating pump, and the constant-clearance requirement of the air pump, are the reasons why impact-drive was selected for them. Early condensing Stanleys use impact-driven lube pumps very successfully.

Many factors led to these changes. The liquid pumps, which will still follow the drawing below with slight modification, are too large to fit in the crankcase of my engine. It is also better to use durable solid metal pipe and tubing for high-pressure fuel and water lines, than to use the flex tubing which would have been necessary with the pumps-in-crankcase layout.

I think this pump layout is pretty much finalized, and I am now working on a full-scale engine/axle/pump box mockup to check out some design factors related to the pump drive (mainly how much extra clearance to add for the pump plungers due to brief variations in plunger stroke caused by rear suspension travel with this pump drive method).

The pumps, though not as interesting or exciting as engines, boilers, and burners, are the "heart" of a steam automobile, indeed, of any steam power system. In the Brow steam car, there will be power pumps for water, fuel, air, and cylinder oil, all integrated into a single unit driven from one of the engine crossheads via a speed-reduction lever. My design studies revealed that the engine crossheads move much faster than is allowable for the plungers of liquid pumps, so the simple lever drive was necessary. A link on the wrist pin of one engine crosshead drives the lever, and the lever drives the pump plungers via a second link. The links, lever, and pumps are very compact, and located in the crankcase for protection from dirt and for complete oil splash lubrication and cooling.

[See update above, 2-28-2001]

I was surprised by the amount of study and work required to design the power pump unit. Numerous pump types and actual pumps were evaluated in the process, and several preliminary pumps of various types were designed. Eventually I decided that plunger design is best for all the power pumps.

Workable pumps are available off the shelf, but are heavy, large, and very expensive, and not entirely suitable for a steam automobile. Therefore, after briefly considering off the shelf pumps, I decided to design and build my own pumps.

I had planned to put off designing the pumps until later in the design stage of the project, but then I realized that building the fuel system and burner first would lead to very short testing times for the burner until the power fuel pump was built. There would also be large amounts of tedious hand pumping between the short burner tests. Therefore I decided to design and build the power pump unit first. This will be run on a custom crank drive attached to my wood lathe, with the water pumps operating at no pressure, to eliminate hand gasoline pumping and allow long tests of the fuel system and burner. Since all the power pumps are integrated into a single unit, it was necessary to design the water, fuel, air, and cylinder oil pumps at the same time. It is interesting how design/construction priorities change as the project proceeds!

Here is a rough drawing of the power water pump. It had to be designed first as it is the main part of the power pump unit. Some of the detail dimensions are slightly off for ease of drawing, but this drawing is broadly accurate.

The inlet manifold is at the bottom, and the outlet manifold is at the top. These manifolds are made of drilled steel pipe with fiberglass/epoxy fittings molded onto them. The fittings bolt onto the valve body/cylinder units, and the manifolds also help to brace the unit against mechanical thrusts resulting from operating loads. The manifolds are of the same inner diameter as the plunger, to keep water flow speeds low for low fluid friction losses.

In the middle of the drawing is the horizontal plunger. This is a single piece of 440C stainless steel, case-hardened and precision ground. I found an excellent source for these plungers, in the right diameters and lengths, off the shelf. No cutting, turning, or grinding will be necessary in my shop.

Plunger and stuffing box lengths have been carefully arranged to insure that every part of the plunger bearing surface is lubricated by either water or crankcase oil, for minimum friction and wear and reliable sealing.

At the center of the plunger, a drive pin mount of carbon fiber/epoxy composite is formed and bonded onto the plunger. This gives tremendous strength and fabrication ease. The drive pin, of hard drill stock, fits into the lower link of the pump drive, and is pressed into the drive pin mount. It is easily removed and replaced when wear sets in, which should not occur for the typical life of the vehicle due to ample bearing surface area. Replacement should only be a consideration to owners of extremely high-mileage vehicles.

The drive pin and drive pin yoke are shown rotated 90 degrees for illustration purposes. Normally they are horizontal.

The valve body/cylinder units, to each side of the drawing, are of fiberglass/epoxy for light weight, corrosion resistance, and fabrication ease. The stuffing box caps are of the same material. Graphite yarn and ribbon packing are planned. A special method of securing the stuffing box caps, not illustrated, has been developed.

The valves required a tremendous amount of consideration. At first nylon ball valves were planned, but because of the flexibility and low surface hardness of the fiberglass/epoxy material, and the unavailability of balls in suitable diameter to give a zero-restriction valve, I decided to go with wing-guided poppet valves with flat seats for better load distribution. These valves are of fiberglass/epoxy and their flat seats have Buna-N (nitrile) O-rings recessed in shallow grooves for good sealing. Inlet and outlet valves are identical to cut moldmaking labor/cost. They should rotate slightly in their bores, preventing the guide wing ends from wearing grooves in the bores. An easy way to visualize these valves is to pull out and examine the drain stopper in your bathroom sink. Most drain stoppers have guide wings and poppet tops, similar to these valves.

Above the valves are some little rectangles which represent the valve stops. These are radial fins, parallel to the valve body axis, which stop the valves, when fully opened, from blocking the outlets of their valve chambers, and allow the water to pass out of the valve chambers. All these parts and passages have been carefully sized to keep the water flow path of the same cross-sectional area all the way from the water tank to the boiler water inlet. This is a zero-restriction feedwater system. This design keeps fluid friction to a minimum and thus cuts pump horsepower loss. At maximum engine speed, the fluid speed through this system is 186 feet per minute, which works out to about 2 miles per hour! This low flow speed eliminates the need for careful streamlining of the flow path, and thus greatly simplifies design and fabrication.

Ken't Mechanical Engineering Handbook (1936) advises keeping fluid speeds through pumps below 240 feet per minute on the suction side, and below 300 feet per minute on the delivery side, to minimize fluid friction losses and cavitation.

The next design job will be the fuel pump, which is a scaled-down, smaller-bore version of the water pump, except that it has only one cylinder and uses only one end of its plunger. The other end of its plunger will serve as a simple plunger-type air pump, which must be of very different construction. The fuel/air and water pump plungers are parallel and linked together by the drive pin and bonded carbon-fiber/epoxy yokes. From above, they are arranged in an "H" pattern, like the pumps on a Stanley steam car. The cylinder oil pump is very tiny, and will be driven from a spur on the fuel/air pump yoke. It will be adjustable as in the 1918 Stanley cylinder oil pump, and will probably use ball valves.

These pumps are designed with enough capacity to run the engine at 500 psi and 60% cutoff at the lowest speeds. Since the engine will automatically shift to 28% cutoff at about 15-20 mph, and 500 psi inlet pressure will rarely be encountered, the pumps supply a generous surplus of fluids, which will be bypassed through the control system. Despite this, the pumps will consume well under 10% of the developed horsepower under road conditions, varying according to estimated load/speed/pump hp charts I have developed.

The air pump, by the way, is included to automatically recharge the fuel pressure tank, and will act as an air spring most of the time, except on the rare occasions it is called into action. A fitting and auxiliary air tank could be added to the air recharge system, to accumulate compressed air for blowing out lines, clearing dirt in service work, and to refill the tires via an on-board air hose. The idea of a steam car which can fill its own tires was inspired by recent encounters with coin-operated (50 cent) self-serve air pumps at service stations!