Ultra-high-molecular-weight polyethylene (UHMW) is commonly used in stainless steel sluice gate seat-seal designs. The UHMW seat is placed on the gate frame and either a round neoprene rope, cord, or flat piece is used to squeeze the slide, thereby minimizing leakage, but also adding friction. The top and side seals are a combination of UHMW and neoprene, whereas the bottom seal is only neoprene. The end result are leakage rates that are in compliance with AWWA standard for sluice gates (AWWA C-561 establishes leakage of no more than 0.1 GPM/foot of wetted perimeter for seating and unseating heads).
Leakage: The compression of the rope, cord, or flat sponge rubber used in the design that minimizes leakage also increases the coefficient of friction considerably. This seal design therefore relies on the resilience of the neoprene to achieve a “self-adjusting” seal feature. When closing action occurs, the force applied by the lift can slightly deform the flush bottom seal. When the resilient seal is attached to the frame and compressed, the natural deformation causes the bottom seal to pull away from the side seal resulting in a potential leak path. Corner assembly for UHMW seat-seal gates is a challenge, as UHMW cannot be bonded/glued to itself or other materials. The corner joints of UHMW seat-seal gates may not achieve a continuous seal, thereby allowing the potential for leakage at the four corners. The joint is sealed with a caulking or “goop” which by its respective nature will not be reliable over an extended period of time.
Operating: This compression adds resistance to the operation of the gate throughout the entire vertical travel, such that the effort required to raise or lower the gate is done so with a constant friction.
Maintenance: If the seals on a UHMW seat-seal gate ever need to be replaced, the structure in which the gate is located must be de-watered for access to the gate frame. A slot is required in the UHMW to retain the rope seal. Real world application results in the slot functioning as an entrapment zone for the collection of debris. The longer a product of this design is in use, the more substantial the collection of debris becomes, which clogs the slot, prevents flexing of the UHMW, and interferes with proper operation of the rope seal.