FT46 Stainless Steel Ball Float Steam Trap

FT46 stainless steel ball float steam trap

Spirax Sarco FT46 is an austenitic stainless steel ball float steam trap for continuous condensate drainage in steam systems. It combines an integrally flanged body, stainless steel working internals and a built-in automatic air vent in one maintainable assembly. The documented size range is DN15, DN20, DN25, DN40 and DN50, with differential-pressure designations from 4.5 bar to 32 bar. This makes the FT46 a practical choice where condensate must be removed as it forms, air must be cleared during start-up and the trap must tolerate a demanding stainless-steel process environment.

The product is intended for engineers selecting a complete drainage point rather than a nominal-size fitting in isolation. The correct choice depends on the condensate load, inlet pressure, backpressure, available differential pressure, connection standard, temperature, flow direction and the orientation of the drain point. The pressure designation and size must be selected together: for example, the documented FT46-14 option is limited to DN15, DN20 and DN25, while the 4.5 bar, 10 bar, 21 bar and 32 bar designations are shown for the relevant size groups. The technical information below keeps those conditions visible instead of treating the model name as a single universal rating. For a replacement duty that needs a different connection route, compare the published FT14 ball float steam trap page for its documented threaded or flanged options and pressure-class path. Where stainless construction and the installation boundary are the deciding factors, the published FTGS14 stainless steel ball float steam trap page provides a separate model-specific comparison route; neither model is an FT46 variant.

Continuous drainage with automatic air removal

A ball float trap responds to the density difference between hot condensate and steam. At start-up, the thermostatic air vent opens so air can bypass the main valve and leave the system. This reduces air binding while the system is warming. When hot condensate reaches the trap chamber, the air vent closes and the float rises. The float movement is transferred through the lever mechanism to the main valve, allowing condensate to discharge continuously as it forms. When steam reaches the chamber, the float falls and the main valve closes. The result is a drainage cycle that follows the load instead of waiting for a batch of condensate to accumulate.

This operating pattern is useful on heat-transfer equipment, process plant and steam distribution points where standing condensate can reduce heat transfer, disturb temperature control or contribute to waterhammer. It also helps the trap respond to changing loads without requiring an electrical signal. The air-vent arrangement is not a minor accessory: it affects start-up behaviour and temperature capability, so it must be confirmed against the chosen pressure variant. The current installation guide identifies a BP99/32 capsule for the 4.5–21 bar variants and a bimetallic air vent as standard for the 32 bar variant. The bimetallic element can also be requested on other variants, subject to the documented restrictions.

Stainless construction for flanged steam service

The FT46 body and cover are documented as austenitic stainless steel, with stainless steel float, lever, air-vent, support and related working parts. The exact technical data sheet also records the component material grades and the distinction between the DN15–DN25 mechanism and the DN40/DN50 mechanism with its inlet protection arrangement. This construction provides a robust basis for applications that require stainless wetted and internal surfaces, while the material still has to be checked against the actual condensate chemistry, cleaning regime and plant environment.

Connections are integrally flanged. The standard route is EN 1092 PN40 with face-to-face dimensions to EN 26554 Series 1. ASME B16.5 Class 150 and Class 300 flanges are available as documented options, with tapped UNC holes for the flange bolts. The body marking identifies the flow direction. When facing the body, DN15 to DN25 flow from left to right; DN40 and DN50 flow from right to left. This size-dependent direction is important when a replacement is planned for an existing line: the flange pattern alone does not confirm that the installed pipework is suitable.

The trap can be maintained without disturbing the pipework when the installation provides safe isolation and the required cover access. That feature reduces the amount of line breaking during planned maintenance, but it does not remove the need to isolate pressure, vent trapped fluid and allow the metal to cool. The installation and maintenance section below gives the working precautions, component procedures and torque values that govern the intervention.

Choose the pressure and air-vent arrangement

The current FT46 data in the installation guide defines a PN40 body design condition, a maximum allowable pressure of 40 bar g at 100 °C and a maximum allowable temperature of 400 °C at 27.4 bar g. For saturated steam, the maximum operating pressure is 32 bar g at 239 °C. The minimum allowable temperature is -10 °C and the minimum operating temperature is 0 °C; lower-temperature duties require confirmation. These values describe conditional boundaries, not independent targets. The pressure-temperature chart, connection class, air-vent type and actual operating point must be checked as one selection.

For the pressure designations, the maximum differential pressures are FT46-4.5 at 4.5 bar, FT46-10 at 10 bar, FT46-14 at 14 bar for DN15–DN25 only, FT46-21 at 21 bar and FT46-32 at 32 bar. DN40 and DN50 are limited to the options shown in the technical table. The product is documented as safe under full vacuum conditions. The maximum cold hydraulic test pressure is 60 bar g, but a complete trap with its internal mechanism fitted must not be subjected to more than 48 bar g. A cold test limit must never be repurposed as an operating rating.

For superheated steam, the BP99/32 capsule is documented for 150 °C superheat at 0 bar g, reducing to 50 °C at 32 bar g. The bimetallic air vent extends superheat resistance to more than 400 °C in the conditions shown by the guide and has a separate 400 °C at 27.4 bar g operating limit. The manually adjustable needle-valve version, designated FT46-C, adds a steam-lock-release feature to the standard air vent. The steam-lock-release arrangement and bimetallic air vent cannot be used together, so the desired air-removal and steam-lock strategy must be specified before ordering.

Where the FT46 adds engineering value

The main benefit of the Spirax Sarco FT46 is the combination of continuous drainage, automatic start-up air removal, stainless construction and flanged serviceability. Continuous discharge is valuable when a heat exchanger, jacket, coil or process vessel needs condensate removed immediately to preserve heat-transfer area. Automatic air venting helps the plant warm through without leaving a pocket of non-condensable gas in the steam space. Integral flanges give a defined face-to-face installation and make the valve straightforward to isolate and service in a correctly arranged line.

The model is also suited to an installation programme where component access matters. The cover withdrawal distance for maintenance is a maximum of 200 mm in the installation guide. The trap should be fitted as close as possible to the drain point, with a short drop leg—typically 150 mm—immediately before the trap. An upstream strainer is recommended to protect the mechanism from line debris. Where condensate discharges into a return system with backpressure, a downstream check valve prevents the steam space from flooding when inlet pressure falls or steam is shut off.

These benefits depend on correct layout. A trap installed too far from the plant can steam-lock, allowing steam to occupy the connecting pipe and preventing condensate from reaching the float chamber. The FT46-C option can provide a controlled bypass for steam-lock release in suitable low-speed cylinder and similar duties. High-speed cylinder applications may need a separate external bypass because the adjustable needle valve cannot handle the larger blow-through requirement described in the installation guide. That distinction belongs in the application review, not in a default assumption that every FT46 needs the C option.

Application boundaries and selection checks

The installation guide describes the product for steam, air or water/condensate in the applicable Group 2 boundary. Before selection, check the fluid, material compatibility, maximum and minimum pressure, maximum and minimum temperature, differential pressure at the trap and any return-line backpressure. Consider whether the system can create waterhammer, whether the discharge is safe, whether the exposed valve needs protection from freezing and whether the valve is in a position where maintenance personnel can work safely. If the duty is still at the family-selection stage, compare the documented ball float steam trap family before fixing the FT46 connection and pressure designation.

FT46 should be installed in the direction marked on the body, with the float arm in a horizontal plane so that it rises and falls vertically. The body orientation and nameplate should read correctly when the installation is complete. The standard FT46 arrangement described here is horizontal with size-dependent flow direction; no vertical variant is being added to this single-model page without a verified product-specific source. The full installation block retains the source safety and orientation requirements.

When comparing materials or pressure classes, use the published FT43 selection page only as a clearly separate comparison route; it is not part of FT46 and its cast-iron construction must not be substituted for the stainless specification. For a wider choice of drainage principles, review the steam-trap range and the related steam trap selection guidance. These links support selection decisions while leaving FT46 as the sole product identity of this page.

Dimensions, maintenance and ordering

The exact FT46 data sheet records approximate weights from 10.8 kg for DN15 and DN20, 15.0 kg for DN25, 33.0 kg for DN40 and 43.0 kg for DN50. The dimension table in the technical block should be used for layout and lifting planning, with the usual allowance for gasket, bolt and surrounding pipework clearances. The body, cover, air vent and main valve assemblies are service parts in the documented maintenance system. DN15–DN25 use the main-valve assembly with float, while DN40 and DN50 use the separate main-valve assembly and float/lever arrangement with the specified inlet baffle components.

Before an enquiry is released, state the FT46 pressure designation, nominal size, flange standard, air-vent arrangement, any FT46-C steam-lock-release requirement, and any balance-line or drain-cock tapping requested at the time of order. State the installation direction and allow for the required maintenance withdrawal space. The price reference currently contains spare-part rows mentioning this family but no exact FT46 complete-unit row, so this page intentionally exposes no inferred price-table specification selector. The Spirax Sarco FT46 should be quoted only after the actual whole-unit configuration is confirmed.

FT46 selection summary

• Austenitic stainless-steel ball float steam trap with stainless working internals and built-in automatic air venting.
• DN15, DN20, DN25, DN40 and DN50 integrally flanged sizes with EN 1092 PN40 standard connections and ASME Class 150/300 options.
• Continuous condensate discharge, start-up air removal and online maintenance access when the line is safely isolated.
• FT46-4.5, -10, -14, -21 and -32 differential-pressure designations, selected with the size and operating conditions.
• BP99/32 capsule, bimetallic air-vent and FT46-C steam-lock-release arrangements subject to their documented compatibility limits.
• Confirm flow direction, pressure-temperature boundary, condensate load, return-line backpressure, strainer, check valve and maintenance access before ordering.