Sprinkler heads often utilise a sprayer that pops up when water pressure is applied. The pop up sprinkler device allows the sprayer to be retracted below ground level when not in use. As sprinkler heads are often used in grass areas over which there may be cars driving or people walking, the retraction reduces the likelihood of damage to the sprinkler device due to inadvertent impact.
The most common form of pop up sprinkler comprises a cylindrical housing having an internal slidable piston. The piston is spring biased to pull it into the housing and has a sprayer head on the end. Water pressure within the housing pushes the piston out of an aperture in the top of the housing in use. In order to minimize water leakage between the housing and the piston the abutting surfaces have to form a water-tight seal, e.g., through the use of an o-ring.
A regular problem with such pop up sprinklers is that any debris around the sliding piston can cause it either not to slide out when water pressure is applied, or not to retract when the water is turned off. Regular maintenance is therefore required to keep such sprinklers in good working order.
As a further issue, as such sprinklers must be constructed of an inflexible plastic material, walking or driving over the sprinkler device even when in the retracted position can result in damage to the sprinkler head.