Forbes Marshall FMTD64 Thermodynamic Steam Trap

Overview

The Forbes Marshall FMTD64 is a thermodynamic steam trap with an inbuilt strainer and full stainless steel construction, which Forbes Marshall recommends for steam header and mainline drains. Steam mains need traps in large numbers, and each one must clear the heavy condensate load at start-up as well as the smaller running load, while losing as little heat as possible through its own body. Forbes Marshall describes its thermodynamic traps as the most widely used and best suited type for this duty: they remove condensate quickly, help prevent water hammer, are compact, robust and maintenance free, and have only one moving part, the disc.

Seven Star LLC supplies the Forbes Marshall FMTD64 to refineries, power and desalination plants, food factories and hospitals across Oman and the GCC, with engineering support in Muscat. Steam networks in the region often run at medium to high pressure and are exposed to outdoor conditions, so a stainless steel trap rated to PN63 with a protected disc and seat is a practical choice for long trap lines.

Operating Principle

A thermodynamic trap works on the difference in behaviour between condensate and steam passing under a flat disc. When cool condensate or air arrives, the inlet pressure lifts the disc off its seat and the liquid is discharged freely. As hotter condensate reaches the trap, some of it flashes to steam; the high velocity flow beneath the disc lowers the pressure there, while flash steam collects in the control chamber above the disc. The pressure acting on the larger upper area of the disc snaps it down onto the seat and the trap closes.

The trap stays shut until the steam in the control chamber condenses as it loses heat, the pressure above the disc falls and the cycle repeats. In the Forbes Marshall FMTD64, condensate enters below the disc, concentric with the disc and seat, so the disc lifts cleanly and parallel to the seat and local wear is avoided. The disc and seat are induction hardened to about 45 RC, which lets them withstand continuous water hammer, and the seat is integral with the body, removing leak-prone joints and gaskets.

Engineering Design of the Forbes Marshall FMTD64

The Forbes Marshall FMTD64 has a stainless steel body to ASTM A743 Gr CA40, a stainless steel cap and strainer cap to BS 3146 ANC2, a disc in ASTM A240 SS420 and a strainer screen in ASTM A240 Type 304. The large area integral strainer screen protects the disc and seat from scale and debris and can be cleaned by removing the strainer cap without disturbing the piping. The bare screwed trap weighs about 0.8 kg, and an optional ISOTUB insulating cover shields the cap from wind, rain and low ambient temperatures that would otherwise make it cycle more often.

Standard sizes are DN15, DN20 and DN25 with screwed BSPT, BSP or NPT ends or socket weld ends to Class 6000. The FMTD64FL flanged version places the trap between carbon steel ASTM A105 flanges to ANSI 150, ANSI 300 (ASME B16.5) or PN40 (EN 1092-1), with flange to flange dimensions to ISO 6554, and the FMTD64SW25 has DN25 socket weld ends ready to install. The trap is preferably installed on a horizontal pipe with the cap on top, and IBR certification is available.

Key Features

The design points that make the Forbes Marshall FMTD64 suitable for mainline drainage are:

• Complete stainless steel construction gives good mechanical strength and corrosion resistance.
• An induction hardened disc and seat at about 45 RC withstand continuous water hammer conditions.
• The seat is integral with the body, eliminating leakage-prone joints and gaskets.
• Concentric condensate entry below the disc ensures a clean, parallel lift and even wear.
• A large inbuilt strainer screen gives long, trouble-free operation in dirty steam lines.
• The single moving part, the disc, keeps maintenance simple and spares to a minimum.
• Screwed, socket weld and flanged versions with IBR certification suit most piping standards.
• The PN63 body is rated 63 bar g at 100°C, with 42 bar g recommended operating pressure.

Industrial Applications

The primary application of the Forbes Marshall FMTD64 is draining steam mains and headers, where condensate collects at drip legs, low points and the ends of lines. Typical installations in Oman include steam lines in refineries and petrochemical plants in Sohar, boiler house headers in power and desalination plants, process steam networks in food, beverage and dairy factories, and laundry and kitchen steam systems in hospitals and hotels in Muscat. Its compact stainless body is also well suited to outdoor pipe racks in coastal locations where carbon steel traps corrode.

Because the Forbes Marshall FMTD64 is available in flanged form to ANSI 150, ANSI 300 and PN40, it can replace existing traps in plants built to American or European standards without modifying the pipework. Seven Star LLC supplies the Forbes Marshall FMTD64 together with disc and screen spare kits and ISOTUB covers to maintenance teams in Duqm, Salalah and across the GCC, so trap surveys can be followed by replacements with lead time confirmed at quotation.

Technical Specifications

The Forbes Marshall FMTD64 data below is taken from the Forbes Marshall technical information sheet (TIS-FMTD64 R4).

Other steam trapping products in our range include the Spirax Sarco BT6-B thermostatic steam trap, the Yarway Series 751/761 drip and tracer trap and the Spirax Sarco STS17.2 steam trapping station.

How to Order

To order the Forbes Marshall FMTD64, send Seven Star LLC a formal RFQ with the size, end connection, operating pressure and any IBR requirement, and our team will confirm the order description and spares. We provide supply on request and engineering support in Muscat for customers in Oman and the GCC. Download the Forbes Marshall FMTD64 technical information sheet from this page, and contact our steam and instrumentation division for trap surveys and delivery times.