Choose the right KSB ECOLINE steam trap by application. Inverted bucket vs ball float vs thermodynamic. Answer four questions and get a specific model recommendation in 30 seconds.
Where in your steam system will this trap be installed?
Steam pressure at the trap inlet. Bands match KSB ECOLINE rating cut-offs — if unsure, the boiler outlet pressure is a safe upper estimate.
How much condensate (kg/hr) does the trap need to discharge at full duty? Estimate from heat duty if exact figure unknown.
Pick the closest match. These factors override the default recommendation when relevant.
A steam trap is an automatic valve that discharges condensate (and air, on startup) from a steam system while preventing the loss of live steam. KSB's ECOLINE range covers the three principal trap mechanisms — inverted bucket (SIB-S), ball float (SBF-S) and thermodynamic (STH-S) — and between them they cover essentially every industrial steam application from boiler superheaters to instrument tracers. The right choice depends on application type, pressure, condensate load, and a few special factors like dirt, modulating control, superheat and back-pressure.
| Feature | SIB-S Inverted Bucket | SBF-S Ball Float | STH-S Thermodynamic |
|---|---|---|---|
| Operating principle | Density difference | Buoyancy | Flow velocity (Bernoulli) |
| Body materials | Cast iron, cast steel | Cast iron, ductile iron, cast steel | Stainless (CA40), WC6 alloy, F22 alloy |
| Max pressure (CI / SG) | 17.5 bar (CI) | 14 bar (CI), 16 bar (SG) | — |
| Max pressure (CS) | 42 bar | 32 bar | — |
| Max pressure (alloy) | — | — | 62 bar (WC6), 170 bar (F22) |
| Max temperature | 425°C (CS) | 300°C (CS) | 540°C (WC6 / F22) |
| Sizes available | ½″ to 2″ | ½″ to 2″ | ½″ to 1″ |
| Discharge pattern | Intermittent | Continuous, immediate | Intermittent (cyclic) |
| Dirt tolerance | Excellent | Moderate | Good |
| Air venting | Continuous (small vent) | Built-in thermostatic vent | On startup only |
| Water hammer | Tolerates well | Float can be damaged | Tolerates well |
| Modulating load | Marginal | Excellent | Poor |
| Freeze risk (idle) | Low (drains by gravity) | High (water-filled) | Very low (compact) |
| Best for | Drip legs, dirty condensate, process heating | Heat exchangers, modulating loads | Mains, tracers, HP superheater drains |
For high-pressure superheater drips on a utility boiler at 100 bar, only the thermodynamic trap (STH-S) in F22 alloy steel reaches that range — rated to 170 bar. The cast steel SIB-S maxes out at 42 bar and SBF-S at 32 bar, so the pressure window forces the choice. Conversely, on a 5-bar sugar juice heater with sticky scale, ball float would normally suit a heat exchanger, but inverted bucket is preferred because of the dirt tolerance — SBF-S would foul within weeks. The selector tool above accounts for these overrides automatically.
The same trap model has very different ratings in different body materials, so the recommendation always comes paired with a material. Cast iron is the cheapest and suits low-pressure utilities up to 14 bar (SBF-S) or 17.5 bar (SIB-S). Cast steel is the workhorse for industrial steam from 14 to 42 bar. For pressures above 42 bar or temperatures above 425 °C, only the alloy-steel thermodynamic trap applies — WC6 to 62 bar / 540 °C, F22 to 170 bar / 540 °C. Stainless steel STH-S CA40 (42 bar / 427 °C) is selected for chemically aggressive condensate at moderate pressure rather than for the pressure rating itself.
Always size the trap for two times the calculated full-load condensate discharge to handle startup loads, control valve cycling, and mid-life fouling. Undersized traps waterlog the equipment, reduce heat transfer, and cause water hammer. Oversized traps cycle too rapidly, wear faster, and waste live steam through brief blow-throughs. For ball-float traps in particular, oversizing creates rapid float wear; pick the next-smaller size if the calculated load is on a boundary. For final sizing, send your duty data and we will run the KSB sizing tool with the pressure differential and back-pressure to confirm orifice and trap size.
The two most frequent steam-trap selection mistakes in Indian process plants are: choosing a single trap type for the entire plant (creates premature failures in 30-40 percent of services), and ignoring back-pressure. A trap rated 25 bar inlet but installed in a system with 18 bar back-pressure has only 7 bar driving pressure — capacity drops by 60 percent. The selector flags high back-pressure in step 4 and reduces the recommendation accordingly.