Pool Filter Separations & Explosions

Pool Filter Separations & Explosions


Most types of pool-related injuries occur to bathers in a pool. Pool/spa filter separations, however, occur not in the water but at the pool equipment location and pose the greatest risk to someone servicing the pool equipment. Dr. Rowley and Mr. Reynolds have over 50 years of combined design experience, are dedicated to properly designing swimming pool filtration systems, and emphasize the importance of following manufacturer guidelines for servicing and repair.

Pool filters operate under pressure and are designed to be able to be opened for maintenance. If the clamping mechanism, which secures the filter lid to the filter base fails during operation, the pressure inside the filter will force the filter lid to separate from the filter base. These types of incidents occur typically during startup and not during normal operation. Water is non-compressible, so if a failure occurs during normal operation (i.e., when the filter tank is full of water), the filter lid will leak but will not fly off during separation.

If a filter lid becomes airborne upon a clamp failure, a pneumatic separation has occurred:

– A pneumatic separation can only occur when a pool filter has compressed air in it (which typically occurs when the filter tank is refilled with water after being taken apart for servicing/maintenance. After a filter tank is serviced, it is reassembled, and the pump is started in order to circulate water through the filter tank.)

– Filter tanks are manufactured with an air-relief valve (manual or automatic), which is used to bleed the air out of the filter tank as it is refilled with water. If water fills the tank faster than the air can be bled out (or if the valve was plugged or left closed so that air could not bleed out), then the air becomes compressed as water fills the tank.

– If the clamping mechanism that secures the filter lid to the filter base fails while compressed air is inside the filter, then the compressed air will expand and launch the filter lid into the air. This is the pneumatic separation.

filter examples

When a filter pneumatically separates, anyone near it is at risk of receiving a serious or even fatal injury. For example, a typical 20-inch residential pool filter can easily exert over 6,000 pounds of force against its filter lid.

Dr. Rowley has been consulted in such cases for more than 40 years. His experience in the field of pool filtration dates back to 1970 when, as director of engineering for a major swimming pool manufacturer, he oversaw the engineering and production of more than 300,000 filters (approximately 30,000 per year) for 10 years and oversaw quality control and testing as part of the production process.

He has tested to failure (literally blown apart) hundreds of filters in the course of his testing and research. The National Sanitation Foundation (NSF) awarded Dr. Rowley the 1985 Spes Hominum (For The Good of Mankind) Award for his doctoral dissertation on hi-rate sand filtration. He served on the National Sanitation Foundation’s (NSF) Standard 50 Joint Committee (Circulating System Components for Swimming Pools, Spas or Hot Tubs) from 1974 to 1992. During that time, he helped write pressure test protocols and requirements for the NSF’s Standard 50.