TD120M High Pressure Thermodynamic Steam Trap

Spirax Sarco TD120M high-pressure thermodynamic steam trap for superheated main drainage

Spirax Sarco TD120M is a maintainable high-pressure thermodynamic steam trap with an integral strainer and replaceable seat. It is a low-capacity model specifically documented for superheated steam main drainage applications up to 250 bar g. The replaceable seat and accessible strainer make the trap suitable for installations where the seat, disc, gaskets and strainer screen must be inspected or renewed as part of a planned maintenance programme.

The model is intended to be selected as part of a complete drainage point, not by nominal pipe size alone. The required connection, pressure-temperature case, available differential pressure, condensate load, return-line backpressure and access for maintenance all affect the final choice. The official installation instructions identify steam, air and condensate/water in Group 2 service as the intended media boundary; any other fluid requires a separate suitability review.

Thermodynamic operation with a maintainable seat

A thermodynamic steam trap uses a disc to control the discharge of condensate and retain live steam. Cool condensate, air and other non-condensable gases enter through the central orifice and lift the disc, allowing discharge through the outlet passage. As the condensate approaches steam temperature, part of it flashes. The high-velocity flash steam passes beneath the disc and builds pressure in the control chamber above it. The resulting pressure imbalance drives the disc onto the seat and stops the flow.

The disc is the only moving part identified in the installation guide. Heat loss from the body eventually lowers the control-chamber pressure, allowing inlet pressure to lift the disc and begin the cycle again. This gives the TD120M a periodic discharge close to steam temperature and tight closure between discharges. In a superheated main, the low-capacity characteristic is important: the trap is intended to remove the drainage load without being treated as a general-purpose high-volume condensate device.

The integral strainer helps prevent dirt and scale from reaching the disc and seating surfaces. It is still necessary to assess pipe cleanliness and the likely particle load. The installation guide notes that particles trapped between the disc and seat can cause rapid wear and erosion, so a separate strainer or dirt pocket may provide additional protection where the system requires it. The integral screen is part of the trap assembly; it does not remove the need to design the upstream drainage arrangement correctly.

Connections and configuration choices

TD120M is available with several high-pressure connection arrangements. Butt-weld ends are offered in 1/2 inch, 3/4 inch and 1 inch sizes to suit Schedule 160 pipe. Socket-weld ends are offered in the same sizes to ASME (ANSI) B16.11 Class 6000. The integral flange options cover DN15 and DN25 to EN 1092 PN160 and PN250, and DN15, DN20 and DN25 to EN 1092 PN100 or ASME (ANSI) Class 600, Class 900 and Class 1500.

These alternatives do not represent interchangeable dimensions. A welded installation must be checked against the pipe schedule and approved welding procedure; a flanged installation must be checked against the nominal diameter, flange class, bolt access and removal clearance. The dimensions drawing later in this page gives approximate A to F dimensions and weights for the documented connection groups. Confirm the exact connection and standard on the enquiry so the supplied trap matches the plant design.

The technical sheet describes the body, top cover and bottom cover as alloy steel to ASTM A182 F22. The disc is steel to BS EN ISO 4957, the strainer screen assembly is stainless steel to BS 970 304 S15 or sintered stainless steel, and the replaceable seat is steel to BS 4659 Grade BD2. Cover studs, nuts, gaskets and the stainless-steel ferrule are separately identified in the materials table. These designations support procurement and compatibility review; they are not a substitute for checking the complete system against corrosion, erosion and temperature conditions.

Pressure, temperature and backpressure limits

The TD120M body design condition is PN250. Its maximum allowable pressure is 250 bar g at 300 °C, and its maximum allowable temperature is 550 °C at 80 bar g. For saturated steam service, the current technical sheet gives a maximum operating pressure of 220 bar g at 374 °C. The maximum operating temperature is 550 °C at 80 bar g. These are conditional points on a pressure-temperature envelope, rather than independent values that can be combined without checking the graph.

The documented minimum allowable temperature is -29 °C, while the minimum operating temperature is 0 °C; lower operating temperatures require consultation with the manufacturer. Operating backpressure must not exceed 50% of the upstream pressure. The minimum operating differential pressure is 8 bar g. The product is documented as safe under full vacuum conditions, but the 375 bar g cold hydraulic test pressure is a test value and must not be used as a continuous operating rating.

When pressure is above 170 bar g, the technical sheet recommends regular inspection of the seat. This is especially relevant to a high-pressure drainage point because wear, contamination and seating damage can change shut-off behaviour. Review the pressure-temperature graph, the pressure class of the selected connection and the actual start-up, running and shutdown cases together. A maximum pressure number by itself does not establish suitability.

Capacity and selection of the drainage point

The capacity information is presented against differential pressure, with separate cold-water and hot-condensate curves and a corresponding table. Use the differential pressure actually available across the trap, including the effect of the return header and other discharges. Check both start-up and normal running conditions because the available pressure difference and condensate load can change as the steam main warms. The capacity chart is retained in the technical section so selection can be made from the documented relationship rather than from a single quoted flow number.

TD120M is described as low capacity for superheated main drainage. That description should guide the application review: identify the drain point, the pipe geometry, the expected condensate load and the consequences of retaining water in the main. If the load is close to the curve or the pressure difference is unstable, record the complete operating case for engineering review. Do not use the line size, the maximum allowable pressure or the hydraulic test pressure as a substitute for a capacity check.

Reserve the clearance shown in the dimensions drawing. Access is needed for the removable covers, integral strainer screen, replaceable seat and disc. A trap that fits between two connection faces but cannot be opened safely is not a maintainable installation. Include the withdrawal distance, lifting and working access in the pipe-rack or plant-layout review before the order is released.

Installation and system integration

The preferred installation is in a horizontal pipe with the nameplate uppermost. A small drop leg should precede the trap, and the installation guide shows an alternative drop-leg arrangement when the model is more than 2 m (6 ft) from the main vertical drain leg. The flow direction must agree with the nameplate and the intended layout. Other orientations may operate, but the installation guide warns that service life may be affected.

Provide suitable upstream and downstream isolation valves so the trap can be safely maintained or replaced. In a closed return system, fit a downstream non-return valve to prevent reverse flow. If the discharge is to atmosphere, route it to a safe place because the discharged fluid may be at 100 °C (212 °F). Welding, external pipe stresses, access, lighting, lifting arrangements, hazardous contents and protective clothing belong in the installation risk review, not only in the commissioning checklist.

During commissioning, air and debris may need to be vented from the drop leg. The installation guide specifies a controlled sequence using the upstream stop valve, downstream stop valve and drain valve, followed by slow opening to normal operating conditions. After the trap has operated for 24 hours at normal pressure and temperature, the cover nuts must be retightened to restore the correct gasket compression. This step is part of the maintenance plan for a newly installed trap.

Maintenance and ordering checks

Maintenance starts with safe isolation from both supply and return, pressure equalisation to atmosphere and sufficient cooling time. The top cover, disc and replaceable seat can be accessed for inspection or renewal; the bottom cover gives access to the integral strainer screen. The guide requires clean gasket contact surfaces, a new disc when the seat assembly is serviced and correct positioning of the disc grooves. It also warns that the thin stainless-steel support ring in the cover gasket can cause injury if handled or discarded carelessly.

Use only suitable tools and genuine replacement parts. The guide provides dedicated tightening torques for the screen assembly, cover studs and cover nuts, and requires the cover nuts to be tightened in a diagonally opposite sequence. Inspect the strainer screen as part of a scheduled maintenance programme, and check for leaks after the isolation valves are reopened slowly. The available spare categories include cover studs and nuts, the strainer screen and gasket, gasket sets, and a maintenance kit; a spare-parts enquiry should state the size and trap type.

For a Spirax Sarco TD120M enquiry, provide the connection type and size, pipe or flange standard, normal and maximum pressure, temperature, available differential pressure, condensate load, return-line backpressure, discharge destination and maintenance-access arrangement. State any EN 10204 3.1 certification or inspection requirement when ordering. This information allows the selected high-pressure thermodynamic steam trap to be checked against the actual drainage point instead of being specified by model number alone.

TD120M selection summary

• Maintainable high-pressure thermodynamic steam trap with an integral strainer and replaceable seat.
• Low-capacity design specifically documented for superheated steam main drainage up to 250 bar g.
• Butt-weld, socket-weld and integral flange connection options across the documented inch and DN sizes.
• Current saturated-steam operating limit of 220 bar g at 374 °C, with pressure-temperature conditions checked against the official graph.
• Maximum operating backpressure limited to 50% of upstream pressure and minimum operating differential pressure of 8 bar g.
• Horizontal installation with the nameplate uppermost, an inlet drop leg, isolation for maintenance and safe discharge planning.

Use the verified pressure-temperature envelope, capacity curve, connection standard, dimensions and installation instructions together. The detailed technical and installation sections below retain the full tables, drawings, safety conditions, operating description and maintenance sequence for the exact TD120M model.