Constant Water Pressure



To demonstrate a mechanism which produces a constant water pressure.


Aspirator bottle with stopper and glass tube, pedestal, water, tank.



Before doing the experiment, let your students vote on whether the range of the water projectile will increase, decrease, or remain the same, as the water level drops.

Setup Time

5 min.




    Air enters the aspirator bottle, initially almost filled with water, through a tube inserted through a sealed stopper into the water bath, while the water leaves through a nipple near the bottom of the bottle. This arrangement provides a constant water pressure head, which is equal to the height of the water column between the nipple and the bottom end of the tube. Thus the water jet will have the same range as the water level in the bottle falls from its initial level to the level of the bottom of the tube.◙


    Wallace A. Hilton, Little Thinkers: Mental Gymnastics, TPT 2, 139 (1964). J. H. Wales, Device for Constant Flow of Liquids, Science, Volume 79, No. 2059, March 1934, pp. 545-546. E. L. McCarthey, Mariotte's Bottle, Science, Vol. 80, N0. 2065, July 27, 1934, page 100. ◙E. L. McCarthey, Digest of Periodical Literature: Mariotte's Bottle, AJP 2, 184-185 (1934). W. G. Cutler, Constant Rate of Flow Apparatus, AJP 27, 185 (1959).