A return steam trap sends collected condensate back to a boiler. Hiscox’s Blessing-pattern example uses a counterweighted vessel that falls as it fills and rises as it empties. Below, compare that historical principle with a separate float-trap illustration, where a float moves inside a stationary body. The display controls illustrate positions; they do not calculate condensate capacity.
Float-Trap Level Illustration
Move the liquid-level slider to compare float and valve positions. The period control changes the water ripple only. This is a float-trap illustration, not the moving-vessel Blessing return trap.
Equation Used
- The main valve remains below the selected liquid level.
- Changing the level sets the drawn float and valve positions. Playback alone does not move them.
- The thermostatic vent is identified separately; its temperature response is not simulated.
- Capacity, Cv, pressure, temperature, flash steam, leakage, materials and ratings are excluded.
The historical return trap
Hiscox figure 407 identifies a Blessing-pattern return trap above the boiler waterline. Its vessel is carried on a weighted lever. Filling makes the vessel descend; emptying lets it rise. That movement trips valves to alternate between receiving condensate and discharging it into the boiler.
This moving vessel differs from the float-trap illustration above. In a float trap, condensate raises a float within a stationary body to operate the main outlet valve. A separate thermostatic vent releases air. The manufacturer references below explain that float-trap principle.
Using the float-trap display
The level slider sets the waterline, float and valve positions. The period slider sets the speed of the surface ripple. Pause and the cycle slider control that ripple; they do not create a fill-and-drain cycle.
The displayed valve percentage is a chosen illustration scale. A value of 100% does not mean a particular trap can pass a stated mass of condensate. Equipment selection requires manufacturer data for the intended service conditions.
Display relationships
For a display period T seconds, ripple frequency is 60/T cycles per minute. The level L is the entered percentage. The float-rise readout scales the available level range from zero to 100%: (L − 20) × 100/60.
The valve-position readout is 2.5 × (L − 30), limited to the range zero to 100%. It stays at zero up to L = 30% and at 100% from L = 70% upward. These thresholds define the illustration, not a physical valve characteristic or measured operating levels.
Worked display example
With T = 8 seconds, the surface ripple repeats 7.5 times per minute. At L = 55%, the readouts show 62.5% illustrative valve opening and 58.3% float rise within the displayed level range. The float stays at that chosen position during playback.
Interpreting the illustration
The schematic identifies a float, linkage, main outlet and thermostatic vent. It is not a product cross-section: the connecting lines change length as the level changes, and the display does not solve a rigid linkage or buoyancy balance.
The vent symbol does not model a thermal response. At the highest level settings the drawn waterline reaches part of that symbol, so its displayed position should not be treated as an installation detail. A working float-trap air vent needs access to the space above the condensate.
The main valve position and waterline do not establish flow, pressure, leakage or a steam seal under actual operating conditions. Use the relevant manufacturer’s capacity and installation information for an identified trap.
Return-trap and float-trap questions
Is the illustration the Blessing return trap in Hiscox?
No. Hiscox figure 407 shows a whole vessel moving on a weighted lever. The interactive illustration here shows a different arrangement: a float and valve inside a stationary body.
What changes when I move the level slider?
The drawn waterline, float and valve positions change with the selected level. The percentage outputs describe those chosen display positions; they do not calculate buoyancy, discharge rate or a real valve characteristic.
What does the display-period control do?
It changes the repeating water-surface ripple. At a fixed level setting the float and valve stay in place; playback does not simulate a filling and draining cycle.
Why is a float-trap outlet kept below the waterline?
In a float trap, retained condensate helps keep live steam from passing through the main outlet. The separate thermostatic vent releases air from the space above the condensate.
Does this calculate trap capacity?
No. It reports display frequency, selected level and illustrative position percentages. Use manufacturer capacity data for the required pressure difference and service conditions when assessing a particular trap.
Historical and technical references
Hiscox, figure 407: Blessing-pattern return steam trap — moving vessel, weighted lever and alternating collection and boiler return.
- Spirax Sarco, Mechanical Steam Traps — float, lever, flooded main valve and thermostatic air-vent operation.
- Spirax Sarco, Steam Trapping — An Overview — staged ball-float operation.
- U.S. Department of Energy, Steam System Survey Guide — follow each trap manufacturer's piping recommendations and assess condensate return.
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