What it is
The Zurn Wilkins 375 is a large reduced pressure assembly in 2½" through 10" with a relief valve mounted under the body between the checks. It comes as the 375 (flanged ductile iron), the 375A (grooved ductile iron, longer), and the 375AST (stainless, shorter), plus DA detector versions of each for fire service. Shutoffs are NRS or OS&Y gates, with butterfly and post-indicator options.
The relief valve is deep: 9½" below the pipe centerline at 2½", 15⅜" at 8" and 10". That is several inches deeper than the matching 350 double check in the same body.
What matters for the cover
Three lengths. At 8" the flanged 375 is 60⅞" end to end, the grooved 375A about 62", and the stainless 375AST 52¾". The 120 × 50 cover is the price-list match for 8" and clears all three, but on 4" and 6" the difference between families is enough to change which cover sits well. Read the tag for the letter after 375.
Depth plus discharge. The relief valve under the body has to drain. Set the cover so the base closes to the pad around the assembly but never seals under the relief port. Zurn calls for 12" of clearance under the relief valve for the discharge; the cover's base has to respect the same gap on that side.
OS&Y height. Open stems reach 21" above centerline at 8"; NRS gates are lower. The 40" and 50" cover heights are built around a standard pad-mounted stack.
375DA. The detector bypass adds 12"–15" of width on one side. Photos first on the DA.
Stocking
The 375 is the large RP on commercial domestic service across Wilkins-spec territory, and the 375DA is the fire-line RPDA. Plumbing houses see 2½" through 4"; fire protection distributors see 4" through 8". Keep the 70 × 40, 85 × 40, and 100 × 50 on the shelf and quote the 120 × 50 and 130 × 55 to order.