Armstrong CD-33 Controlled Disc Steam Trap, Stainless, 600 psig

A disc trap engineered to cycle less

Ordinary disc traps wear out because they open and close very often. The Armstrong CD-33 is a thermodynamic disc steam trap designed to control that cycle rate: three discharge ports give stable disc operation, and capacities are sized for the application so that the trap is not oversized. Armstrong states that the reduced cycle rate gives the CD-33 a longer service life than typical disc traps, which keeps maintenance time down and cuts steam cost.

The body is stainless steel with an electroless nickel-plated finish, with an integral seat and a hardened disc and seating surface. Armstrong lists it as freeze-resistant and available in 1/2 in, 3/4 in and 1 in NPT connections only. Four variants share the body style: CD-33, CD-33S with an integral 30 x 30 mesh type 304 stainless steel strainer, CD-33L for low capacity, and CD-33SL, the low-capacity version with strainer.

Technical specification

Dimensions and weights

Further printed dimensions: withdrawal distance for the rain guard insulating cap (E) is 3 in (76 mm) on the strainer versions, the blowdown connection (F) is 1/4 NPT (6 mm), and the blowdown valve withdrawal distance (G) is 3-1/2 in (89 mm). The temperature and pressure values in the sheet appear in two forms, 41 bar in the table and 42 bar in the text, so use the certified drawing for design work.

Which CD-33 variant to order

Capacities of the standard CD-33 were engineered for three duties: large steam main drips, process equipment, and HVAC heating equipment on constant pressure. The CD-33L was sized for the smaller loads of steam main drips and steam tracing lines, and Armstrong makes the point that not over-sizing is what keeps the trap lasting longer than a disc trap with an excessive capacity rating.

Pick the S versions when a strainer is wanted in the same body, for example when pipe scale could foul the disc; the S body is 4-1/4 in (108 mm) high in the small size against 2-1/2 in (63 mm) without it. Choose the blowdown plug or blowdown valve to suit how often the strainer will be cleaned. In outdoor installations the optional rain guard insulating cap limits radiant heat loss and is meant for outside applications.

Applications and handling notes

A 63 bar vessel rating and 2,500 lb/hr ceiling put the CD-33 in medium- and high-pressure drip and tracing duty in oil and gas processing, petrochemical plants and power stations, as well as large HVAC heating coils fed with constant-pressure steam. Because a disc trap needs a minimum operating pressure of 3.5 psig (0.24 bar) and tolerates back pressure up to 80% of inlet pressure, it is not for very low-pressure lines below that minimum; the data sheet gives both limits.

The sheet does not claim ATEX, fire-safe or other third-party approvals for this trap, so none is stated here. Selection should follow the project steam specification and the certified drawing.

Reading the limits as a selection check

Four numbers from the sheet decide whether a CD-33 fits a line: a minimum operating pressure of 3.5 psig (0.24 bar), a maximum back pressure of 80% of inlet, a maximum operating pressure of 600 psig (41 bar) and a vessel rating of 915 psig (63 bar) at 752 F (400 C). The body and cap are ASTM A743 Gr. CA40 and the disc is ASTM A276 Gr. 420, both hardened stainless grades. The heaviest variant is the 1 in CD-33S at 3.25 lb (1.5 kg) and the lightest is the 1/2 in CD-33 at 1.4 lb (0.64 kg).

Selection and installation notes

Specify a steam trap from the steam pressure, the condensate load and the connection size, and check the body material and the pressure rating against the system. Fit a strainer upstream, a union or flange for easy removal and isolation valves either side, prime the trap with condensate before start-up where the type requires it, and protect it from freezing. Inspect traps on a regular schedule to find failures early, because a failed trap wastes steam or floods the line.

A disc trap works best when fitted in a horizontal or vertical position that the maker permits, with its discharge lines free to drain.

Information needed for a quotation

Send the full model code, the quantity, the delivery location in Oman or the GCC, the intended use and any accessories needed, so that the complete package can be quoted together.

Documents and supply information

The manufacturer data sheet is attached to this page and should be read together with the project specification and the site risk assessment before a purchase is confirmed. Ratings, standards and dimensions are quoted as printed on that sheet. Lead time, stock position and certificates available with the shipment are confirmed in the quotation, and we supply to Oman and the wider GCC region for industrial, utility and building services projects.

Documents and quotation

The official data sheet is attached. For related steam equipment browse pipes and fittings. Seven Star LLC is an independent supplier in Muscat; tell us the variant, connection size and working pressure and we will check the exact model against the manufacturer data before we quote.