Pentair SD35 Standpipe Assembly

The Pentair SD35 / Cristal-Flo® II Standpipe Assembly (part number 152229) is a critical internal fluid-distribution conduit engineered exclusively for the vertical center columns of compact, top-mount sand filtration systems. This genuine original equipment manufacturer (OEM) replacement part is tailored to fit the exact interior tank depth of Pentair Sand Dollar® Model SD35 aboveground filters (specifically those manufactured after October 2004) and Sta-Rite® Cristal-Flo II 16-inch high-rate sand filter vessels.

Primary Operational Role

The standpipe serves as the primary vertical channel connecting the multi-port control valve at the top of the tank to the lateral collection hub at the very bottom. During the standard pool filtration cycle, water enters through the top valve, pushes down through the active silica sand bed to filter out dirt, and flows into the lower lateral arms. The standpipe assembly then routes this collected, purified water directly up through the center of the tank, where it exits the multi-port valve and returns to the pool. Conversely, during the backwash cycle, the valve reverses the flow, pushing high-velocity water down through the standpipe to expand and clean the sand bed from the bottom up. By maintaining an aligned and secure path for the water, the assembly prevents media bypass, minimizes hydraulic friction, and ensures the pressurized tank can safely manage high circulation velocities up to 50 PSI without leaking at the critical valve junctions.

Materials & Performance

To endure the harsh, buried environment within a sand filter, the assembly is injection-molded from heavy-walled, high-impact PVC and chemically inert engineering polymers. Measuring approximately 16 inches in internal functional length, the rigid pipe is highly resistant to structural bowing, cracking under sudden pump startup surges, and abrasive wear from hundreds of pounds of moving sand media. Its resilient plastic formulation fully resists advanced chemical oxidation, material brittleness, and bleaching from continuous exposure to high-strength sanitizers like liquid chlorine, bromine, and routine seasonal scale-removing acid washes. Due to its hollow cylindrical profile and integrated structural molded couplings, this replacement standpipe assembly carries a standalone product weight of approximately 1.15 to 1.50 pounds.