An often asked question is "What's the valve handle do that is between the driver's and left rear passenger's door?"  This valve operates the steam engine's drip valve.  The Stanley Steam Car's drip valve is functionally equivalent to the cylinder cocks seen on steam locomotives.  As a steam locomotive leaves the station the engineer has the cylinder cocks open and one sees steam rushing from the front sides of the locomotive until the engineer closes the cocks.  The drip valve provides the same function on the steam carriage.

When a steam car has been at rest for a while the high-pressure steam piping between the boiler and the engine, as well as the engine's cylinder block have cooled.  When the throttle is opened and steam fills the pipe and engine cylinders, the steam contacting the pipe and cylinder walls is cooled and condenses back to water until the pipe and cylinder walls warm sufficiently.  The condensate (water) that is created will ruin the engine if not released.  The drip valve provides a means to release condensate before it can do damage to the engine.

The clearance space between an engine's piston and the end of a cylinder allows for about an ounce of water volume.  If more than an ounce or so of water is blown into or accumulates in the cylinder the clearance space fills with water before the piston reaches the end of its stroke.  Since water is not compressible, the end of the cylinder can be blown off with further movement of the piston.  The drip valve is located at the lowest point of the steam engine and thus any condensate coming from the steam supply line as well as any condensate generated in either of the engine's two cylinders collects in the domed area at the bottom of the engine and is vented through the drip valve when the valve is opened.

An additional use of the drip valve is to insure the car doesn't move when parked.  Throttle valves can leak and in doing so will send steam to the engine.  Over time the continuous leak will build pressure in the steam supply line to the engine and in the engine's cylinder.  If sufficient pressure is created the engine can move the car even though the parking brake has been set.  By opening the drip valve whenever the parking brake is set, steam pressure is released from the system and unless the throttle is intentionally opened full the car is unlikely to move since any steam pressure is immediately vented through the drip valve.

In the video below the rear axle of the car is supported on a pair of jack stands so that both rear wheels are free to turn.  Due to the operation of the differential the left wheel has been chocked to keep it from rotating so that only the right wheel rotates.  Steam has been applied to the engine and it is running to move the car forward.  The clip includes audio and you'll hear the steam at approximately 500 PSIG rushing from the drip valve.  After a few seconds of operation the valve will be closed (you'll see the valve's stem rotate in the video).  The steam will stop being released from the drip and the engine will run somewhat quieter. 

This clip includes the sound of the steam escaping the drip valve.  Be prepared to adjust the volume of your computer's speakers.  During the video you will hear some "clanking" going on.  This is due to the alternating load being applied to the right axle by the pump drive.  As the right axle turns it also powers the pump box drive.  The pumps are maintaining proper boiler water level, proper burner fuel pressure, and providing steam cylinder oil to the steam engine for lubrication.  The clanking heard is the pump drive alternately pushing and pulling on the pump drive rod.  The pushing and pulling causes the differential to first be mechanically loaded in one direction and then the opposite direction.  The clanks are the gears of the differential making noise.  This is not heard when both wheels are on the ground and the car is actually moving forward.

One thing you will not hear is the "locomotive choo-choo" sound.  A Stanley condensing car was used to make the video and the steam exhaust from the engine is directed to a heater and then to the condenser and finally to the water tank.  All the piping and the radiator design of the condenser effectively muffle any steam sounds the engine might make.  In order to hear the classic locomotive sound from a steam car a non-condenser would have had to be used.  Non-condensing Stanley Steamers have a very distinctive choo-choo exhaust sound.

To view the video, click the START button (lower left triangle).  The video will start and run to conclusion.  The video is 4 megs in size and will take a few minutes to download.