Can - Liquid Time Delay

Section VI

No. 10

A time delay device for electrical firing circuits can be made using a can and liquid.


  • Can
  • Liquid (water, gasoline, etc.)
  • Small block of wood or any material that will float on the liquid used
  • Knife
  • 2 pieces of solid wire, each piece 1 foot (30 cm) or longer


1. Make 2 small holes at opposite sides of the can very close to the top.

22 11 Can   Liquid Time Delay

2. Remove Insulation from a long piece of wire for a distance a little greater than the diameter of the can

22 21 Can   Liquid Time Delay

3. Secure the wire in place across the top of the can by threading it through the holes and twisting in place, leaving some slack. Make loop in center or wire. Be sure a long piece of wire extends from one end of the can.

22 31 Can   Liquid Time Delay

4. Wrap a piece of insulated wire around the block of wood. Scrape insulation from a small section of this wire and bend as shown so that wire contacts loop before wood touches bottom of container. Thread this wire through the loop of bare wire.

5. Make a very small hole (pinhole) in the side of the container. Fill container with a quantity of liquid corresponding to the desired delay time. Since the rate at which liquid leaves the can depends upon weather conditions, liquid used, size of hole, amount of liquid in the container, etc.. determine the delay time for each individual case. Delays from a few minutes to many hours are possible. Vary time by adjusting liquid level, type of liquid (water, oil) and hole size.

22 41 Can   Liquid Time Delay


1. Fill can with liquid to the same level as during experimental run (step 5 above). Be sure that wooden block floats on liquid and that wire Is free to move down as liquid leaves container.

2. Connect wires to firing circuit.

NOTE: A long term delay can be obtained by placing a volatile liquid (gasoline, ether, etc.) in the can Instead of water and relying on evaporation to lower the level. Be sure that the wood will float on the liquid used. DO NOT MAKE PINHOLE IN SIDE OF CAN!

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