Is a "water hammer" actually a hammer made of water? Is it a hammer that will indeed drive a nail? No, of course not—it is an evacuated glass tube partially filled with water that illustrates how water can make clanking noises in household pipes. Have you ever turned off the water quickly and heard the pipes bang? Investigate the common phenomenon called "water hammer."
- Properties of fluids
Water hammer is the term used to describe the banging noise that is heard as a result of rapid pressure differences in a water line. The pressure dramatically increases above the steady state when a valve is closed and dramatically decreases when the valve is opened. Water hammer can range from a house-shaking bang to a large bang followed by a series of smaller echoing bangs.
Water travels down the pipes in a house at a certain velocity. When a valve is closed, the water crashes into the valve, resulting in a loud banging noise. The faster the water is traveling, the louder the noise. Since water is essentially incompressible, most of the energy from the collision is transformed into a tremendous increase in water pressure. The energy is expended by striking the side of the pipe.
Water hammer may occur during manual operation of a faucet or, more commonly, from the automatic operation of a valve, as is the case with dishwashers and washing machines. Water hammer puts stress on the pipes in a home and will damage them over time. To alleviate this problem, homeowners can install air chambers or water hammer arresters in the pipes. These devices absorb the spike in pressure and eliminate reverberation in the pipes.
The evacuated glass water hammer in this kit is partially filled with water. When the water hammer is suddenly jerked downward, the water hits the bottom of the tube just as a solid would and creates a "ping" comparable to that of a hammer hitting a nail.
Glass water hammer*
*Materials included in kit.
Although the materials in this activity are considered nonhazardous, please observe all normal laboratory safety guidelines. Handle the glass water hammer with care to prevent breakage. Since the glass tube is under a partial vacuum, be sure to wear safety eyewear during the demonstration.
The water hammer is reusable and should be stored in a manner to prevent breakage and to avoid extreme temperatures.
- Hold the water hammer with the glass bulb pointing up and the tube perpendicular to the floor.
- Firmly grasp the tube portion of the water hammer with the fingertips and thumb a few inches below the bulb (see Figure 1).
- With a quick, sharp motion, jerk the hammer downward a few inches.
- Avoid shaking the water hammer. A quick, sharp jerk will produce a sound similar to that of a hammer hitting a nail. Practice the motion a few times to get it just right.
- Allow a few seconds for the water to return from the bulb to the tube before repeating the procedure.
- The glass water hammer can also be used as an example to demonstrate the properties of the meniscus. The meniscus is clearly visible and shows students exactly what they are looking for when reading a graduated cylinder.
- Just as a part of a house amplifies the sound of water crashing into the sides of the pipe, the bulb amplifies the sound of the water crashing into the glass tube. Hold one hand over the glass bulb and jerk the hammer downward—notice that the sound is muffled.
The American Heritage® Dictionary of the English Language, Fourth Edition, Houghton Mifflin Company, 2000.
Scott, John M. Everyday Science; J. Weston Walch; New York, 1988, p. 112.
Webster’s Revised Unabridged Dictionary, MICRA, Inc., 1998..