Hayward HCF Series HCF234 34" Commercial Fiberglass Sand Filter 2" Bulkhead. Hayward HCF series of filters have been engineered to fit todays demanding applications. Overhead multi-diffuser distribution is combined with a horizontal lateral grid array that improves water distribution over the filter bed resulting in linger filter cycle time, improved filtration, and a more efficient backwash cycle. The twist-lock, tool-free rapid open/close lid mechanism with positive O-Ring seal simplifies operation and ensures long-term durability and reliability.