Float Steam Traps

Continuous, proportional condensate discharge — the reference solution for heat exchangers, autoclaves and any application where immediate condensate removal is critical to process performance.

How a float steam trap works

A float steam trap (also called a ball-float trap) contains a hollow metal ball resting in the condensate that accumulates in the trap body. As condensate enters, the level rises and the float lifts, opening the discharge valve via a lever — proportionally to the condensate level. When the level drops, the float sinks and the valve closes, preventing live steam from passing.

The mechanism is purely mechanical and continuously proportional: the higher the condensate inflow, the further the valve opens. This ensures no condensate accumulates upstream — whether in a heat exchanger, autoclave or dryer — keeping the full heat transfer surface free at all times.

An integral thermostatic element (balanced pressure capsule or bimetal, depending on model) sits at the top of the body. It stays open when cold, venting air at startup, and closes automatically as the body temperature approaches steam saturation temperature at operating pressure.

Float steam trap Spirax Sarco — Roffia srl

Spirax Sarco FT14

  • Max pressure: 14 bar
  • Max temperature: 200 °C
  • Connections: screwed ½"–1"
  • Body: spheroidal graphite iron or carbon steel
  • Air vent: bimetal element
  • Applications: HVAC, small heat exchangers, building services

Spirax Sarco FT43

  • Max pressure: 32 bar (special versions 43 bar)
  • Max temperature: 250 °C
  • Connections: screwed ½"–2", flanged DN 15–80
  • Body: carbon steel or AISI 316
  • Air vent: balanced pressure capsule (PTFE)
  • Applications: industrial heat exchangers, chemical processes

Spirax Sarco FT44

  • Max pressure: 40 bar
  • Max temperature: 250 °C
  • Connections: flanged DN 15–100
  • Body: carbon steel or stainless steel
  • Capacity: up to 30,000 kg/h
  • Applications: large industrial exchangers, heavy process duty

Typical applications

Steam-heated heat exchangers

On steam-heated heat exchangers, the float trap is the standard choice. Continuous discharge keeps the condensate section drained at all times, maintaining maximum active heat transfer area. An undersized or failed float trap floods the exchanger, reducing thermal performance by up to 70% and creating water hammer risk as cold condensate meets live steam.

Autoclaves and sterilisers

Autoclaves require rapid air purging before sterilisation cycles (air reduces the effective temperature at any given pressure) and continuous condensate removal throughout. The float trap with integral air vent handles both: it purges air at startup and maintains a dry chamber throughout the cycle. For large autoclaves, a separate thermostatic air vent may also be installed at the top of the chamber.

Dryers and heated rolls

Paper drying cylinders, calendar rolls and industrial dryers handle variable condensate loads as production speed changes. The float trap responds instantly to rate changes. Very large cylinders (paper machines) use FT44 or rotating syphon arrangements to manage high condensate volumes at the cylinder periphery. Temperature uniformity across the heated surface depends on complete condensate removal.

Tank and vessel heating coils

Steam-heated tanks with submerged coils or half-pipe jackets need continuous condensate drainage to maintain the coil free of water. In food, chemical and pharmaceutical vessels, stainless steel FT43/FT44 bodies with CIP-compatible gaskets (EPDM or PTFE) and flanged connections to EN 1092 or ASME B16.5 are specified.

Domande frequenti

Why is a float steam trap preferred on heat exchangers?
A float steam trap provides continuous, proportional condensate discharge: the hollow ball rises with the condensate level, progressively opening the discharge seat. Unlike intermittent-discharge traps, condensate is removed instantly and continuously from the exchanger, keeping the full heat transfer surface active at all times. A flooded exchanger can lose 50–70% of its rated thermal performance. Where the condensate load varies significantly (common on modulating control valves), the float responds instantaneously — no risk of the "steam locking" that affects some other trap types. The integral thermostatic air vent (balanced pressure capsule or bimetal) ensures rapid air purging at startup — essential for heat exchangers and autoclaves where air pockets create cold zones.
What is steam locking and how does the float trap handle it?
Steam locking occurs when live steam — rather than condensate — enters the trap body and prevents the float from falling, blocking discharge. This happens when condensate drains too quickly into the trap, entraining steam from upstream. A standard float trap has a Balance Pressure Connector (BPC) — a controlled connection between the float chamber and the steam space that equalises pressure, allowing condensate to drain even when steam is present. Spirax Sarco FT43 and FT44 traps incorporate this feature. For critical applications (dryers, hot presses) where steam locking risk is high, a manual bypass valve allows operation to continue and condition verification while the trap is isolated.
What is the difference between the FT14, FT43 and FT44 Spirax Sarco models?
FT14: float trap with bimetal air vent, cast iron or steel body. Maximum 14 bar. Compact, for low-to-medium pressure applications (HVAC, small exchangers). FT43: balanced pressure capsule air vent, carbon steel or AISI 316 body, up to 32 bar (special versions to 43 bar). Wide flow ranges. More responsive air venting than bimetal, suitable for demanding duty and frequent cycling. Available DN 15 to DN 80. FT44: heavy-duty version with higher flow capacity for large heat exchangers and intensive industrial applications. Maximum 40 bar. DN 80 and DN 100 versions handle condensate rates up to 30,000 kg/h.
How is a float steam trap sized?
Correct sizing requires two key values: the maximum condensate load (kg/h) and the available differential pressure between trap inlet and the condensate return back-pressure. Condensate load is calculated from the exchanger duty and the latent heat of steam at operating pressure: G = Q / r, where Q is thermal duty in kW and r is latent heat in kJ/kg. The maximum condensate rate used for sizing must include a safety factor of 2–3× the steady-state load, to account for the cold-startup condensate flood when the exchanger mass absorbs heat before reaching operating temperature. Available differential pressure is the steam pressure minus the condensate return back-pressure — often underestimated in existing systems with elevated return headers.
What are the signs of a failed float trap?
Common failure modes: Failed closed — corroded or damaged float, or blocked seat. Symptoms: cold exchanger, condensate backing up onto steam line, violent water hammer as condensate floods the steam space. Failed open — punctured float (water-filled) or eroded seat. Symptoms: live steam passing through to condensate return, elevated downstream temperature, energy waste. Failed air vent — air not purged; symptoms: slow warm-up, exchanger never reaching target temperature despite adequate steam supply. Diagnosis is best done with ultrasonic testing (a healthy float trap produces a smooth, continuous flow sound) or infrared thermography (abnormally high or low temperature downstream of the trap).
Can a float trap be installed in any orientation?
Float traps must be installed with the cover uppermost — the float must hang below the seat. The body can be on a horizontal or vertical pipeline, but must not be installed upside down or with the axis rotated 90° (sideways), as the float would not move correctly. Always install a Y-strainer upstream (200–800-μm mesh, per manufacturer specification) to protect the seat and float from magnetite, pipe scale and debris. On horizontal pipelines, install the trap at the lowest point of the condensate collection line with a minimum 300 mm drop from the exchanger to encourage gravity drainage.

Float steam trap selection

Tell us the operating pressure, estimated condensate load, application type and return line back-pressure. Roffia technical team selects the right model and size with a dedicated quotation.

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