Are rollers and scrapers used in large diameter (>12")resilient seat gate valves that are mounted horizontally?
Depending of service type, pressure and fluid, you would be able to select from a wide range of constructions.
The upper end being special construction knife-gate or o-port all stainless steel valves for high-pressure, high temperature liquids with a high degree of solids sticking on the blade. Built in scraper effects in sealing constructions.
A European / Scandinavian approach would be to use resilient seated gate valves, where the gate itself is compleately covered in elastomere (normally EPDM or NBR), stem stainless, non-rising stem, stem nut in softer gun metal allaoy, stem nut 'floating' inserted in upper part of wedge, guides for wedge incorporated in housing, in best constructioned valves with elastomere (PTFE or similar) sidewise guides incorporated or mounted in housing wall.
Full bore, free bottom, vertically mounted, stem up.
This type is also used for sludge and waste water, and will normally give no problems.
For larger diameters, say 20 inches and above, (but also for smaller if automated), double eccentric, double flanged butterfly valves, epoxy lined, soft sealed, certified for drinking water, shaft mounted horizontally, will be a cheaper and lighter choice.

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