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Spray-Jet Dishwasher Arm
Josephine Cochrane's machine, already published, held the dishes in wire racks and threw water at them from fixed jets while the rack was turned. Robert Tatham's rung makes the water do the moving: jets angled off the radius push the arm round, so a pump and one moving part wash a stationary load from every direction.
**US 1,900,529**, "Dishwasher", Robert L. Tatham, filed 29. June 1929, granted 7. March 1933: apparatus for "washing dishes by discharging water with considerable force, in the form of jets or sprays", delivered by a pump. Every domestic dishwasher since has a reaction-driven spray arm.
**You build the arm** from PVC pipe on a bearing, fed by a submersible pump, and measure its speed and how much of a dirty plate it actually cleans.
Intermediate
3 hours
Instructions
1
1
Drill the arm
Drill the arm
Cap both ends of a 200 mm length of 20 mm PVC pipe. Drill six 2 mm holes along it, three each side of centre, all angled about 20 degrees off straight-out and all the same way round.
Materials for this step:
PVC Pipe1 piece
PVC Pipe Fittings Assortment1 setTools needed:
Cordless Drill
Drill Bit Index
Steel Ruler2
2
Hang it on a bearing
Hang it on a bearing
Fit a ball bearing at the arm's centre on a short stub of pipe so it spins freely, and connect the pump to the stub with vinyl tubing. Keep the tubing slack so it cannot drag.
Materials for this step:
Ball Bearing1 piece
Clear Vinyl Tubing1 meterTools needed:
Hot Glue Gun3
3
Measure the flow
Measure the flow
Run the pump into a graduated cylinder for 15 seconds and work out litres per minute. Do it again with the pump half-throttled by pinching the tube.
Tools needed:
Water Pump (Submersible)
Bucket
Graduated Cylinder
Stopwatch4
4
Dirty a plate
Dirty a plate
Paint a ceramic plate with a paste of flour and food colouring and let it dry hard. Stand it in the bucket above the arm.
Materials for this step:
Plain Flour50 g
Food Colouring5 mlTools needed:
Ceramic Tray5
5
Run, count, compare
Run, count, compare
Run for one minute, counting arm revolutions in 30 seconds. Photograph the plate and estimate the share cleaned. Repeat with the arm locked still, and at half flow.
Tools needed:
Stopwatch
Masking Tape6
6
Reaction speed and coverage
Reaction speed and coverage
Loading Jupyter Notebook...
7
7
History & Context
History & Context
**What the patent specifies:** washing by forceful jets or sprays delivered by a pump against dishes held in a tray. **Modern build (derived):** a reaction-driven PVC arm and an aquarium pump.
Later machines added a second arm above, a heater to keep the wash hot, and a detergent dispenser timed to the cycle. Its limits: a jet cannot clean what it cannot reach, so loading matters; burnt-on food still needs soaking; and the arm stalls if cutlery drops through the rack.
Materials
6- 1 piecePlaceholder
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- 1 meterPlaceholder
- 50 gPlaceholder
- 5 mlPlaceholder
Tools Required
10- 1 vendor sell this, none ship to you yetPlaceholder
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