What it is
The Ames 2000SS is a double check valve assembly in 2½" through 12" on a 300-series stainless body with cam-check modules under a single grooved-coupling top cover. The 3000SS is the same body with a side-mounted metered bypass, making it a DCDA for fire service; it is the assembly the trade calls the Silver Bullet. NRS or OS&Y gates; horizontal or vertical flow-up installation.
The body is long for its class, 37" at 2½" and 40" at 4", and shallow: 3½" to 8" below the pipe because there is no relief valve. OS&Y stems supply the height, 16⅜" above centerline at 2½" and 37¾" at 8".
What matters for the cover
Length first. The 70 × 40 is the price-list match at 3" and clears the 37"–38" body with gates; the 85 × 40 at 4"; the 100 × 50 at 6". Same covers as the 4000SS size for size.
Base closes. No relief discharge, so the cover base can close all the way to the pad. Do it; it is what lets a covered DC ride out wind.
3000SS bypass. The Silver Bullet's bypass and meter add width and height along one side. On 2½" through 4" the stock cover usually accommodates it; at 6" and up we want a photo with the bypass side showing.
Fire lines stay charged. A 3000SS on fire service cannot be drained for winter. In sustained cold the fire authority may require a heated enclosure or heat trace under the cover; see fire protection before quoting a cover alone.
Stocking
The 3000SS is one of the most common fire-line DCDAs in the country, so fire protection distributors drive the volume: 4" and 6" covers, occasionally 8". Plain 2000SS units show up on irrigation mains and commercial low-hazard service through plumbing houses. The DCDA covers page covers the fire-line category as a whole.
Ordering
Name the size, the shutoff type, and whether it is the 3000SS. The 70 × 40 covers 2½" and 3" with gates, the 85 × 40 the 4", the 100 × 50 the 6", and the 120 × 50 the 8". For the 3000SS, add the bypass-side photo so the meter clearance is confirmed before the cover ships.