The RD1800 Series features an exclusive comolded, pressure activated Triple-Blade Wiper Seal to assure a positive seal without excess "flow-by", which enables more heads to be installed on the same valve. The Triple-Blade Wiper Seal precisely balances flushing, flow-by and debris protection to optimize performance and durability at pop-up and retraction. Precision-controlled flushing at pop-up and retraction clears debris, assuring positive stem retraction in all soil types. Debris pockets in the base of the spray body prevent recirculation of harmful debris during operation to reduce wear on the wiper seal and stem.