MINI STEAM JEEP (STEMKA) 2
Apart from the steering wheel, the instruments and controls consisted of pressure gauge, speed and distance meter, foot and hand brakes, foot and hand throttle controls, engine cylinder lubrication pump and feed-water metering and bypass valve. Other controls included a boiler scale-trap blow down, chimney blower jet valve, feed-water priming pump, engine reversing and notching up lever, cylinder drain cocks lever, fire door, furnace air control and excess steam release valve. The cylinder drain cocks were made in the form of pop safety valves with variable spring loading from the hand lever and notched quadrant. If they were momentarily set at below boiler pressure they went off like small bore rifle shots.
Main dimensions were, wheel base 52”. Track 40”. Overall length and width were 70½” and 46”. The furnace extended rearwards from the generator section with the hinged fire door on top. The cylinder drain cocks lever, the hand brake, and the furnace air control levers were grouped close to the reversing lever. Apart from lighting up there was no smoke emission. The occasional burning of macadamia nut shells did create a little brown smoke as well as plenty of heat. Touring around the local streets produced memorable events. One found one’s self leading two or three cars showing no tendency to pass and they would loiter alongside. On one occasion pulling into a friend’s home and treating him and neighbours to rides up and down the street the fuel supply ran out with still a kilometre to get home. No problem, kindly people rummaged in their garden sheds and enough scraps of wood and pine-cones quickly appeared to continue the entertainment and complete the journey. They were apologetic over the tree bark included but to Stemka’s boiler that was good hot ember producing fuel. A friend, also a steam buff who frequently rode with me shares the memory of a Sunday afternoon jaunt about the village when we had to stop at an intersection for cross traffic. There was a full head of steam causing the release valve to blow off the excess which due to the cool air temperature and no breeze, enveloped the vehicle in a fog much to the obvious astonishment registered by the occupants of passing cars.
After six years of enjoyable driving and tinkering I became dissatisfied with the temperamental characteristics in this application of the flash type generator. Schemes for various configurations of small volume boilers were studied. I wanted a generator of a type that was inherently stable without the necessity of cause and effect control systems. I also wanted to devise a steam generator that had the manners of time honoured volume boilers and firmly believed as I still do that this could and should be the path to follow. Records of the successes of Winslow boilers and their derivatives the Derr boilers brought me to favour these types for replacement. Time and circumstances caught up with me and I terminated my workshop activities to give fulltime care to my then ailing wife. Now since 2005 my steam interests and fellowship with steam buffs and my third generation younger families fill my daily life.
A fellow enthusiast who owns a museum in Northland bought the little steam jeep and keeps it among his display pieces. So that leaves me enjoying being a nonagenarian pounding out on my computer themes and schemes and things the way they were and possibly could have been. I hope to discuss some of these meanderings in future instalments.
Friday, July 16, 2010
Sunday, July 4, 2010
MINI STEAM JEEP (STEMKA) 1
The steam-powered mini-jeep here described was not intended to be a contribution to the cause of motoring. It was the realisation of a desire to produce a steam-powered vehicle that gave a riding experience to its driver and passenger with freedom from the constraints of an earlier 7¼-inch gauge railway. The design was based on the American army jeep. No accessories requiring other installed power were included.
The actual construction time was 2050 hours spread over 5 years from 1987 to 1992. The total cost of materials and purchased trade components came to 2050 dollars, by coincidence a dollar spent for each hour of productive work. Double the workshop time was spent on scheming, planning and drawing. It was a labour of love, my idea of leisure and pleasure. Following the preliminary design work a wood and cardboard scale model was made and construction commenced with the details being determined as the project advanced. The objective was to create a fun machine relying on solid fuel firing, and not aimed at highway travel or commercial operations.
The flash type steam generator consisted of 65 feet of ¼” nominal bore steam pipe formed into a stack of ten zigzag grid elements located in the combustion gas flue of a wood burning furnace. The heating surface area was 9.2 square feet and the fluid content was 1.1 litres. The maximum working pressure was 600 pounds per square inch. The furnace volume was 1 cubic foot. The engine was a duplex open frame type with twin double acting cylinders of 1 5/8” bore X 2” piston stroke. The ¾” diameter X 7/8” travel piston valves were actuated by the Marshall variant of Hackworth valve gear that provided for expansive working and reverse. The 1 to 2½ ratio chain drive from crankshaft to differential gave an engine speed of 1100 RPM at 40 KPH on 16” diameter road wheels.
At start-up the wood chip fire was established and some water was pumped into the boiler by a few strokes of the foot pedal operated feed-water pump. Steam immediately generated and was blown through the engine to warm up. As pressure increased the car literally chuffed off. When the vehicle was running the boiler feed-water supply was taken over by the rear axle driven feed pump. 100 PSI was sufficient to motor on flat road.
It is important that boiler feed-water supply is matched as closely as possible to the steam demands of the engine. Ideally such control should be completely automatic but it was difficult to achieve a balance in this application because of the inexact practice of hand firing solid fuels plus the wide variations in demand on the road motoring. Various patterns of boiler pressure actuated feed-water control valves were made and fitted before being abandoned in favour of a manually controlled water metering and bypass valve that returned acceptable results providing that the driver remained alert to the cause and effect performance signals. The state of the steam generator was judged from the pressure gauge, the feel of the throttle and engine responses and the forces required on the priming pump pedal. With all of this in mind the furnace conditions had to be sustained by the frequent addition of wood blocks or pine-cones. Fuel consumption worked out at eight to ten pine-cones per kilometre. It was true seat-of-the-pants motoring.
The forty litres of feed water carried served about 2 hours of start/stop motoring around local streets, grassed recreation fields or on hard sand flats of the local tidal estuary. The car was driven on the hand or foot-operated throttle with high boiler pressure, or with minimal boiler pressure and the throttle full open with the speed controlled by the regulation of feed water delivered to the boiler. My wife and I once drove the car by this method in a town festival street procession. She was the fire attendant.
The steam-powered mini-jeep here described was not intended to be a contribution to the cause of motoring. It was the realisation of a desire to produce a steam-powered vehicle that gave a riding experience to its driver and passenger with freedom from the constraints of an earlier 7¼-inch gauge railway. The design was based on the American army jeep. No accessories requiring other installed power were included.
The actual construction time was 2050 hours spread over 5 years from 1987 to 1992. The total cost of materials and purchased trade components came to 2050 dollars, by coincidence a dollar spent for each hour of productive work. Double the workshop time was spent on scheming, planning and drawing. It was a labour of love, my idea of leisure and pleasure. Following the preliminary design work a wood and cardboard scale model was made and construction commenced with the details being determined as the project advanced. The objective was to create a fun machine relying on solid fuel firing, and not aimed at highway travel or commercial operations.
The flash type steam generator consisted of 65 feet of ¼” nominal bore steam pipe formed into a stack of ten zigzag grid elements located in the combustion gas flue of a wood burning furnace. The heating surface area was 9.2 square feet and the fluid content was 1.1 litres. The maximum working pressure was 600 pounds per square inch. The furnace volume was 1 cubic foot. The engine was a duplex open frame type with twin double acting cylinders of 1 5/8” bore X 2” piston stroke. The ¾” diameter X 7/8” travel piston valves were actuated by the Marshall variant of Hackworth valve gear that provided for expansive working and reverse. The 1 to 2½ ratio chain drive from crankshaft to differential gave an engine speed of 1100 RPM at 40 KPH on 16” diameter road wheels.
At start-up the wood chip fire was established and some water was pumped into the boiler by a few strokes of the foot pedal operated feed-water pump. Steam immediately generated and was blown through the engine to warm up. As pressure increased the car literally chuffed off. When the vehicle was running the boiler feed-water supply was taken over by the rear axle driven feed pump. 100 PSI was sufficient to motor on flat road.
It is important that boiler feed-water supply is matched as closely as possible to the steam demands of the engine. Ideally such control should be completely automatic but it was difficult to achieve a balance in this application because of the inexact practice of hand firing solid fuels plus the wide variations in demand on the road motoring. Various patterns of boiler pressure actuated feed-water control valves were made and fitted before being abandoned in favour of a manually controlled water metering and bypass valve that returned acceptable results providing that the driver remained alert to the cause and effect performance signals. The state of the steam generator was judged from the pressure gauge, the feel of the throttle and engine responses and the forces required on the priming pump pedal. With all of this in mind the furnace conditions had to be sustained by the frequent addition of wood blocks or pine-cones. Fuel consumption worked out at eight to ten pine-cones per kilometre. It was true seat-of-the-pants motoring.
The forty litres of feed water carried served about 2 hours of start/stop motoring around local streets, grassed recreation fields or on hard sand flats of the local tidal estuary. The car was driven on the hand or foot-operated throttle with high boiler pressure, or with minimal boiler pressure and the throttle full open with the speed controlled by the regulation of feed water delivered to the boiler. My wife and I once drove the car by this method in a town festival street procession. She was the fire attendant.
Subscribe to:
Posts (Atom)