Making a water pump to play with and to explore concepts is easy. Simply gather and assemble a few household items in a different way. This project is a useful way for your children to spend some time. It also illustrates a principle that you can discuss together.
Choose the cups. The more steep and subtle the taper on the cup, the higher the amount per pump you should get from the finished product. Stack the two cups together, with one inside the other. Pull the cups apart to see the strength of the vacuum generated. This will give you a good indication of the amount of pressure you will be able to produce by pulling and pushing these two cups in relation to each other.
Carefully drill a hole in the center of the bottom of the two plastic cups with the drill and 1/4-inch bit. Make sure no cracks form around the hole. If cracks do form, seal them with the glue and allow the glue to dry. Do not get any glue on you or anything valuable.
Make the top valve. Cut a strip of duct tape the length of the cup's base. Half way down the tape fold it in half. Tear off a small tab of tape that you will use to make a hinge for the folded strip. Place the tab on one side of the strip so that it allows the strip to act as a one-way valve over the hole. To do this, it must allow water to move one direction. When the water tries to go the other direction, it must create resistance.
Tear a strip of duct tape half the width of the cup and the same length as the cup. Fold the tape in half on itself with the sticky side together, but keep 1-centimeter at the far edges of the tape from touching. Use these 1-centimeter tabs on either side of the strip of tape to attach the tape to the cup. Attach the strip on the cup to the side of the hole in the second cup and lay the tab of tape over the hole. Crease the tape so that the tab lays down over the hole.
Do the same thing with the other cup.
Place the two cups, one inside the other. Drill a hole in a third cup at the corner of the base of the cup. This will allow you to aim the water. Place this third cup on top of the other two. Use a hot glue gun to glue the top two cups (one of the valved cups and the one with a hole in it.
Fill a tub with water until it covers the bottom cup when you put the cup into the water. Make sure that the open mouths of the cups are facing down. Start pumping by moving the bottom cup together and apart from the top two cups. The water will come out in spurts through the hole in the cup that you have on top.
The flatter the tape lies on the hold inside the cup, the higher the pressure you can get during pumping. You can make modifications like handles for convenience. If the tape leaks around the edges, pump faster or get the tape to lay flatter.
Do not let the water get on anything that should not be wet, including electrical devices and other items. This object has small parts and is not intended for small children or children without adult supervision and appropriate maturity to keep themselves safe. Everyone should wear safety goggles while using this device, and adults should be the ones to do steps requiring hot glue, sharp or small parts, or anything else that might be dangerous to children. Do not burn yourself on the glue gun or glue. Read and follow all instructions that come with your tools. Only use this device with room temperature water.