Without any doubt perhaps the most import requirement in operating a steam car (or any steam engine powered piece of equipment for that matter) is insuring sufficient water is carried in the boiler.  Locomotives and traction engines generally used devices called "injectors" to add water to the boiler when it was at pressure and delivering steam to the engine.  Injectors are problematic and a more positive and reliable means to add water to a boiler is with a pump of some sort.  Stanley steam cars have always relied on a pair of piston pumps to supply water to the boiler.

The power water pumps only operate when the car is in motion as they are driven off the rear axle of the car (on early Stanleys the pumps were driven from the engine crosshead).  While a single pump is generally sufficient to handle the water pumping required for flat level driving at 30 to 35 MPH, two pumps insure sufficient water is available when steam demands are stronger such as hill climbing.  Both pumps are plumbed in parallel meaning that water is pumped on both the forward and return strokes of the pump drive rod.  When pumping water to the boiler, both pumps are capable of delivering water at greater than 600 PSIG pressure so that water can be forced into the boiler when the boiler is at maximum operating steam pressure.



The pumps used on Stanley steam cars manufactured through 1914 are referred to as "short stroke pumps".   A 9/16" diameter piston was used up through 1907 with a 5/8" diameter piston being used on the short stroke pumps from 1908 through 1913 for the 20 horsepower cars.  These pumps used 7/16" diameter brass balls for the check valves.  Driven from the right-hand crosshead wrist pin of the engine, a rocker arm arrangement reduced the 5" engine stroke to the required 1-1/4" stroke of the pump's piston.

In 1915 Stanley introduced the "long stroke pump" which ran at a much slower speed and was therefore a lot quieter than the short stroke pump.  Long stroke pumps have a 4" stroke and use a 5/8" diameter piston.  The check valve balls were increased to 1/2" diameter.  Mounted on the right rear axle is the pump drive box.  The pump drive box provides gearing and a crank arm to drive the power pumps.  At the end of the crank arm the pump drive rod is attached.  The result is that the pumps operate at a much slower speed as a result of this design making them quieter (see photo and discussion at the end of this article on the pump drive box).

Each Stanley power water pump operates like most standard piston pumps.  As the piston is drawn out of the cylinder a vacuum is created which draws water from the supply tank to fill the volume within the cylinder that the piston occupied.  The water is drawn in the water supply line to the pump through the suction check valve while the delivery check valve keeps water from being drawn in from the delivery piping.

As the piston is pushed back into the cylinder the water that has been drawn in now tries to run back out of the cylinder through the suction check valve that was open.  This action forces the suction check valve to close and pressure begins to build on the water in the cylinder as the piston continues its motion into the cylinder.  When the pressure within the cylinder becomes greater than the water pressure of the delivery piping after the pump, the delivery check valve opens allowing the water just drawn into the pump's cylinder to escape and flow into the delivery piping.  Once the piston is fully inserted in the cylinder no more water is supplied by the pump to the delivery piping and the cycle starts over with the piston being pulled out of the cylinder to draw in more water.

The power water pumps in a Stanley are generally located below or at least at the same level as the water supply tank.  This affords an easy way for them to be initially primed with water.  Rings of graphite impregnated packing are used at the end of the cylinder to for a seal between the cylinder and moving piston.  Maintenance is generally required every couple hundred miles to snug up on the packing nut.

Water from the power water pumps is routed to a check valve just in front of the firewall on the right side of the car.  This check valve is shown on the color diagram and serves to insure that hot water doesn't flow back into the pumps if the boiler check leaks or if the water in the feed water heater begins to turn to steam.  From this check valve the water has two paths it may flow.  If the boiler has sufficient water that the feed water automatic is not calling for water to be added to the boiler, then water from the pumps is routed through the feed water automatic's water valve and back to the supply tank.  If the boiler needs water added, the feed water automatic's water valve closes off the path to the supply tank.  This causes the water discharged from the two water pumps to be routed to the feed water heater and then onto the boiler through the boiler check valve.  As there is steam pressure on one side of the boiler check valve, the check valve remains closed until the pressure in the piping between the power water pumps and the boiler check valve becomes greater than the steam pressure in the boiler.  The boiler check valve opens to allow the water from the power water pumps to enter the boiler.

It will be noted in the power pump diagram above and in the right hand photo above there is a valve attached to the front power pump.  This valve controls water flow to and from the hand water pump.  Generally the hand water pump is not needed and thus the water supply to it is closed off.  This reduces the amount of effort needed to operate the pump handle as the hand water pump is pumping air and not water.  If use of the hand water pump is required the valve is opened.  Opening the hand water pump valve allows water to flow to the hand water pump and water can be manually pumped into the boiler.  The plumbing location of the hand water pump valve is between the suction and delivery check valves thus eliminating the need for check valves in the hand water pump.  Operation of the hand water pump relies on the operation of the front power pump's check valves to pump water.

Pictured to the left is a close up of a rear power water pump from a condensing car.  Missing in the photograph is the pump's plunger or piston which would move in and out at the left end of the pump's cylindrical brass casting pictured.  The lower and right-most hex-nut on the top of the pump casting provides access to the suction check valve ball.  The suction connection to the pump is attached to the lower rear part of the pump housing and points upward at a slight angle.  The upper and left-most hex-nut on the top of the pump casting provides access to the discharge check valve ball.  The threaded port for the discharge of water can be see above the cylindrical pump housing to the left of the discharge check valve.  At the far left is the packing nut that allows pressure to be applied to the packing rings so that the pump does not leak as the piston moved in and out of the pump housing.  A spring engages slots in the packing nut preventing the nut from loosening as the pump operates.  To the far right of the pump at the center of the cylindrical pump casting is a plug.  The power pumps are designed such that they can serve as either the front or rear pump and the plug in the end of the pump casting is where the hand pump valve would be placed if this pump were configured to serve as the front pump.

The power water pumps will not pump water if the water supplied to the pumps becomes too hot. The operation of the pump requires that the pumpís piston be drawn out of the pumpís cylinder or casting. This creates a vacuum in the cylinder that is normally filled by water drawn into the pump. However, if the supply water is close to boiling temperature it will flash into a vapor (from the air entrapped in the water) due to the drop in pressure created within the cylinder. Once flashed to vapor an air pocket forms in the cylinder. As air is many times more compressible than water, the air expands and compresses to the motion of the pumpís piston and full slugs of water are not drawn into the pumpís cylinder. If the air pocket becomes too large the pump can become vapor locked and stop pumping water altogether.

There are a couple of factors that contribute to vapor lock of the water pumps. Supply water being close to the boiling point is the prime cause since it takes water close to the boiling point for vaporization to occur. For the non-condensing cars the piston motion is much quicker than that of the condensing-era cars (condensing car pumps operate at approximately one-quarter the speed of a non-condensing carís pumps). The quicker piston motion of the non-condenser car pumps can aggravate the situation making non-condenser pumps more prone to the problem than condensing car pumps. Thus the speed at which the car is operated directly affects the potential for pump vapor locking to occur. Sometimes slowing down will allow the pumps operate slower and not vapor lock as quickly.

In addition to hot supply water causing vapor lock, if the pumps have difficulty in drawing in water, vapor lock can occur. Looking for any suction line obstructions such as a partially collapsed hose from the tank to the pumps or a clogged screen on the inlet to the pumps in the bottom of the water tank will cause the pumps to have a harder time sucking in water and thus increase the potential for vapor lock. Water pump supply lines need to be properly sized and kept clear of sharp bends, restrictions, and obstructions to prevent pump vapor lock from occurring. If a pumpís inlet check valve is removed with the water supply tank full of water, a generous flow of water should occur when the check valve cap is removed.

In some models the steam siphon steam line is routed in close proximity to the water suction lines to the pumps. Running the steam siphon allows the heat of the steam line to transfer to the water line heating the water in the water line to near boiling. When the pumps try and pump this hot water they vapor lock.

While the condensing cars have slower operating pumps, the condensing action of the car causes the water in the water tank to become heated as the car is driven. As non-condensing cars do not condense the steam back into water and return it to the water tank, the water tank generally remains at the temperature of the air. For condensing cars the water leaving the condenser is just below the boiling point of water. Thus the water returning to the water tank from the condenser serves to heat the water in the tank. As the car is driven and water is lost from the water tank due to escaping steam the water in the tank becomes hotter and hotter. As the water level gets lower in the tank the potential for pump vapor lock increases.


The aluminum casting at the right bolts to the rear drive axle housing and provides the mounting means for the power pump drive box when assembled.  Pictured to the left is the power pump drive assembly which bolts to the casting at the right.  A 31-tooth gear on the right rear axle shaft mates with the 70-tooth gear of the power pump crank gear.  The crank arm is designed with a 2-inch distance between the 70-tooth gear shaft and the bearing at the end of the crank arm.  This provides for a 4" stroke of the power pump drive rod.

The short stroke pumps used in the early Stanleys were driven from the engine's crosshead wrist pin.  This meant the pumps were cycled at engine speed or one pump cycle per revolution of the engine crankshaft.  With the long stroke pump design being driven from the rear axle the cycling of the pumps is greatly slowed.  With a 40-tooth gear on the engine crankshaft mating with the 60-tooth gear of the differential, combined with the 31-tooth tooth gear on the axle and the 70-tooth gear that drives the pump crank arm, the effective gearing reduces the pump stroke to 3.38 engine RPM to one cycle of the pumps.  Due to the differential being part of the gear train this number is an average as differing rear wheel rotation rates will change the engine to pump drive ration slightly.

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