FT450 Float and Thermostatic Steam Trap

FT450 float and thermostatic steam trap

The Spirax Sarco FT450 is a cast steel float and thermostatic steam trap for continuous condensate removal from steam equipment. Its mechanical float modulates a double-seated main valve so condensate leaves at approximately steam temperature as it forms, while a separate thermostatic air vent discharges air and other non-condensable gases during start-up and operation. This makes the FT450 a practical choice for process duties where the drainage point, differential pressure and service access can be defined clearly before ordering.

The model is documented across two size envelopes. The smaller range covers 3/4 in to 2 in connections and uses model-specific pressure limits from FT450-4.5 through FT450-32. The high-capacity range covers 3 in (DN80) and 4 in (DN100). These ranges share the same float and thermostatic operating principle, but their connection arrangements, pressure-temperature limits, dimensions and capacity information must be selected from the correct technical section.

Continuous condensate removal at steam temperature

A float trap responds directly to the level of condensate in its body. As condensate enters, the float rises and positions the main valve to discharge the incoming load continuously. The discharge behaviour is therefore suited to equipment that needs condensate removed as it is produced rather than held for an intermittent cycle. The independent thermostatic air vent helps clear start-up air and non-condensable gases that would otherwise reduce heat-transfer performance and delay warm-up.

The FT450 can operate against back pressure provided the outlet pressure remains below the inlet pressure. For a Spirax Sarco FT450 capacity review, the usable capacity is governed by differential pressure, defined as inlet pressure minus outlet pressure, as well as by the selected orifice and connection. A pressure number without its size, model pressure class and outlet condition is not enough to select a trap. The capacity tables and curves below should be read with the actual steam pressure, return pressure, condensate load and warm-up requirement.

Applications and engineering value

For the 3/4 in to 2 in range, the documented applications include process equipment, equipment controlled by modulating temperature-control valves, unit heaters, air-heating coils, heat exchangers and steam main drip stations. The continuous discharge characteristic is useful where condensate backing up into a heat-transfer surface would affect temperature control or where a drip point must drain reliably while the steam main remains in service.

The 3 in and 4 in versions are intended for higher condensate loads from reboilers, large heat exchangers, other large process equipment and large absorption chillers. The large-trap technical sheet also identifies use in combination with a 4 in pressure powered pump. Where the wider system requires condensate transport beyond the trap, the related condensate pump options should be considered alongside the available differential pressure and return-system back pressure. That application reference identifies a possible system arrangement, not a universal selection rule.

Selection should start with the wider steam trap range and then narrow to a float and thermostatic configuration that matches the duty. For a Spirax Sarco FT450 order review, the high-capacity steel body and relatively large service footprint make space, lifting and maintenance access part of the selection rather than afterthoughts.

Construction for demanding steam service

The FT450 body is cast steel or carbon steel, with stainless steel internal parts. The large-range technical information identifies the body as ASTM A216 WCB and the float as ASTM A240 Type 304. The internal arrangement includes the float, linkage, main valve mechanism and thermostatic air vent. For the small range, an optional bimetal air vent is identified for the FT450-4.5, -10, -14, -21 and -32 configurations when superheated-steam service requires it. The broader steam air vent and air eliminator range provides related system context, but the FT450 air-vent choice must still be part of the order review rather than assumed from the base model name.

The body is designed for horizontal in-line installation. The documented design also allows service without disturbing the connected piping, which can reduce the scope of a maintenance intervention when isolation, lifting access and replacement parts have been planned correctly. Serviceability does not mean the trap can be opened under pressure: both supply and return sides must be isolated, trapped pressure relieved and the body allowed to cool before disassembly.

Pressure and temperature boundaries

These values are conditional operating limits, not a blanket rating for every FT450 arrangement. The small-range document gives a separate pressure/temperature graph and limits for NPT, socket weld and ANSI 300/600 construction, with ANSI 150 units limited by the flange rating. The large-range document gives its own pressure/temperature curve and allowable limits. The correct document section must be used for the selected size and connection.

Connections, capacity and physical space

Small FT450 sizes are described with NPT, socket weld connections to ANSI B16.11 and ANSI 150, 300 or 600 raised-face flanges. The 3 in high-capacity version is available with NPT, socket weld or flanged connections, while the 4 in version is flanged in the large-range data sheet. Connection selection affects the pressure envelope, face-to-face dimensions and installation method. It should be confirmed together with the line standard, drain arrangement and available downstream pressure.

Capacity is not selected from nominal pipe size alone. Use the hot-condensate capacity table or curve for the FT450 configuration, then check that the connection piping can carry the resulting flow. The large-range capacity graph explicitly marks a region where trap capacity may exceed the flow capacity of the connection piping. A sound enquiry therefore includes the condensate load, steam pressure, return pressure, required safety margin, start-up load and whether the load is hot or cold condensate.

Physical dimensions matter particularly for the 3 in and 4 in trap. The large unit weighs approximately 485 lb (220 kg), has mounting legs and requires overhead access for cover withdrawal. The installation guide also gives a 32 in (813 mm) withdrawal distance and notes the cover weight. For a smaller unit, the technical sheet gives size-specific dimensions and separate NPT/SW and flanged weights. The technical information below should be used to reserve the final envelope.

Installation and maintenance planning

The trap should be installed firmly and horizontally, with the inlet at or preferably below the equipment drain point. The body flow markings must be followed. The inlet line should be blown down before installation, and a strainer should be installed upstream to protect the mechanism from pipe debris. Full-flow isolation valves should permit service, and a downstream check valve is recommended in the large-trap installation arrangement to help prevent backflow.

Reserve access above the cover and provide a stable support for the mounting feet. Outdoor installations need protection against freezing because condensate may not drain completely from the body when operation stops. Bypass piping is not recommended because of the possibility of misuse; if a bypass is required by the plant design, its valve must shut off tightly and the bypass should be at least one line size smaller than the trap line.

For upstream protection, review the available pipeline strainer and filter range alongside the trap arrangement. The strainer is a system accessory and is not an FT450 option. It should be sized and installed for the actual steam and condensate duty, with blowdown access that allows the inlet line and strainer to be cleaned without exposing personnel to pressure.

Routine service includes inspection and cleaning of the valve mechanism, valve heads and seats, float, air vent and gasket seating surfaces. The large-trap guide specifies that the bimetal air vent is factory calibrated and not repairable; suspected failure calls for replacement of the complete assembly. Worn valve mechanism parts are likewise addressed through complete assembly replacement where specified. These instructions are provided in the installation and maintenance section below and should be followed with the current document available to the service team.

What to confirm before ordering

1. Confirm that the product is the Spirax Sarco FT450 float and thermostatic trap and identify whether the duty falls in the 3/4 in to 2 in or 3 in to 4 in document range.

2. Provide inlet steam pressure, outlet or return pressure, condensate load, start-up load and the required operating temperature. Calculate differential pressure from the actual inlet and outlet conditions.

3. Choose the nominal size and connection type, then verify the applicable ANSI flange rating or socket-weld/NPT standard, pressure envelope and face-to-face dimensions.

4. For the small range, confirm the FT450 pressure trim and whether the documented optional bimetal air vent is required for superheated service.

5. For the large range, confirm support steelwork, lifting method, 32 in cover withdrawal clearance, certification/inspection requirements and any pressure powered pump arrangement.

6. Confirm upstream strainer, isolation, downstream check valve, drain/blowdown access and safe maintenance isolation before release for manufacture or supply.

FT450 selection summary

A Spirax Sarco FT450 selection is strongest when the model trim, size envelope, connection, differential pressure and service temperature are treated as one engineering decision. The product offers continuous mechanical condensate discharge, integral air removal and service access without disturbing the pipe connections, but the published limits remain conditional on the exact range and installation. Use the technical tables and installation instructions below to turn the duty data into an auditable configuration.