Maintenance and Troubleshooting Guide for Single Orifice Float Trap (SOFT)

Single Orifice Float Traps (SOFT) are continuous discharge mechanical steam traps designed to efficiently remove condensate from process equipment. Utilising the buoyancy principle, these traps maintain optimum process efficiency by preventing condensate backup whilst ensuring zero live steam loss when operating correctly.

This comprehensive technical guide covers the essential maintenance and troubleshooting procedures for the complete line of Forbes Marshall Single Orifice Float Traps, including the SOFT31, SOFT53-HC, SOFT54, SOFT510, and SOFT53-X variants.

How to Identify Your SOFT Model Number

Before executing any maintenance or ordering replacement spares, it is important to identify your exact model configuration to match pressure limits and dimensional parameters. Every SOFT unit is fitted with a permanent stainless steel nameplate riveted to the base casting. Use this nameplate to identify the model, size, maximum allowable pressure and temperature.

SOFT Variants and Material of Construction (MoC)

SOFT31 (Cast Iron Series): Recognisable by its cast iron body construction and dome-shaped cover layout. Smaller nominal sizes (DN15–25) are physically compact and stamped with EN-JS1025, while DN40–50 iterations feature a distinct rectangular-to-hexagonal flange profile.
SOFT54 (High-Pressure Carbon Steel – Small): A single-size DN25 cast steel high-pressure module engineered for high-pressure applications up to 42 bar g. It features a robust, diamond-profile 4-bolt base-to-cover orientation.
SOFT510 (High-Pressure Forged Steel): Constructed entirely from forged steel (ASTM A105N). Unlike side-dome variants, it uses a straight vertical cylindrical body profile with a circular top cover secured by heavy-duty 8-bolt arrays.
SOFT53-HC (High Capacity Series): Massive cast steel traps built for high condensate loads in DN80 and DN100 sizes. They are easily identified by integrated mounting feet designed for floor level horizontal installation.
SOFT53-X (High-Capacity Steel with Thermostatic Vent): Sized at DN100, this high-capacity cast steel unit is easily distinguished by its wide twin-chamber body geometry designed to handle extensive automatic air venting.

Single Orifice Float Trap (SOFT) Troubleshooting Guide

Failure Mode	Possible Cause	Recommended Technical Remedy
Not Discharging At All (Surface temperature of the trap body is low)	Incorrect mechanical installation or reversed process flow. Complete blockage within the upstream strainer or main valve seat orifice. System differential pressure exceeds the maximum design limit, meaning float buoyancy is inadequate to lift the valve mechanism off its seat (trap fails closed). Punctured or water-hammered ball float.	Check casting arrows and verify the nameplate orientation arrow points directly downwards. Isolate the unit, open the trap body, and clear out all foreign pipeline debris from the strainer mesh and seating. Review process operating pressures to ensure compliance with the trap's rated pressure limits. Replace the damaged ball float; investigate and rectify upstream water hammer to avoid future failure.
Not Discharging At All (Surface temperature of the trap body is high)	The steam trap has become "steam locked" because steam has entered the trap mechanism ahead of the condensate.	For SLR units (SOFT31, SOFT54): Calibrate the Steam Lock Release needle valve. Screw the stem clockwise until fully seated, then back it off anti-clockwise by exactly 1/4th of a turn. For SOFT53-HC: Inspect, clean, or replace the fixed bleed unit/air vent assembly to ensure non-condensable gases can escape.
Leaking Live Steam (Live steam continuously blowing into the return line)	Trap orientation is upside down or misaligned. Heavy deposition, scale, or particulates trapped between the valve ball and seating area. Faulty setting or mechanical leakage across the SLR assembly or air vent thermopod.	Ensure the casting flow marks match pipeline flow and the nameplate points downwards. Open the trap body, thoroughly clean the main valve internals, and lap the seating area. Tip: Lightly stamp a new stainless steel ball onto the main valve seat face to restore a tight metal-to-metal seal. Recalibrate or renew faulty SLR or thermostatic air vent assemblies.
Steam Leaking from Flange	Cover bolts are under-torqued or have loosened under thermal cycling. The body cover gasket is crushed, burnt, or eroded.	Tighten cover bolts in a cross-pattern sequence to the specified torque rating. Replace the old gasket with a new original component; ensure joint faces are completely clean.
Reduced Capacity / Condensate Flooding	Trap is structurally undersized for the peak condensate load. Elevated backpressure within the condensate return network. Adjacent broken or blowing traps on a common return manifold are pressurising the line. Bypass valve lines left open or passing steam internally. Partially blocked inlet strainer or thermostatic air vent orifice.	Re-evaluate sizing calculations and verify trap selection against standard capacity charts. Ensure all manual bypass valves are isolated and fully sealed. Locate and repair passing steam traps connected to the same condensate manifold. Ensure an independent Non-Return Valve (NRV) is active on the discharge side of each trap feeding a common return header. Clean the inlet strainer screen and lap the thermostatic valve seating.

Important Operational Rules for Diagnosis

Flash Steam vs. Live Steam Identification:
Because condensate discharges at or near steam saturation temperature, a physical pressure reduction across the seat orifice naturally causes a portion of the fluid to immediately boil into flash steam. This produces a high-velocity, turbulent mixture of condensate mist and steam at the outlet. This normal thermodynamic phenomenon should not be misdiagnosed as a live steam leak.
SOFT53-HC Double-Seated Design Characteristic:
The SOFT53-HC utilises a double-seated internal valve mechanism. By design, double-seated assemblies may experience microscopic passing in their fully closed orientation. If your process condensate load drops below the residual leakage threshold (roughly 0.5% of the trap’s full capacity), the unit will naturally vent a nominal trace of steam.

Single Orifice Float Trap (SOFT) Routine Maintenance Guide

Parameters / Tasks to Execute	Immediately	Daily	Weekly	Monthly	Quarterly	Half-Yearly	Annually
Visual Inspection for External Joint Leaks	-	Y	-	-	-	-	-
Arresting/Repairing Confirmed External Leaks	Y	-	-	-	-	-	-
Testing Medium-Pressure Traps (up to 17.5 bar g)	-	-	Y	-	-	-	-
Testing High-Pressure Traps (above 17.5 bar g)	-	Y	Y	-	-	-	-
Repair/Replace Traps showing Internal Leakage	Y	-	-	-	-	-	-
Clean Upstream Strainer Screens	-	-	-	Y	Y	-	-
Dismantle and Clean Internal Mechanisms	-	-	-	-	Y	Y	Y