The historical Bundy steam trap uses a weighted bowl that tilts as condensate collects. Explore the gravity-return sequence and calculate batch-cycle times from usable volume and entered flow rates.
Bundy Steam Trap Interactive Calculator
Enter usable batch volume and measured or assumed flow rates to estimate filling time, discharge time and average throughput. A separate switching allowance covers each transition. The animation shows the weighted-bowl sequence.
Equation Used
- Usable batch volume is the transferred volume between reset and tipping levels, not total vessel volume.
- Filling and discharge rates are constant within each stage and must be provided by the user. Inlet flow pauses during discharge.
- Each switch uses the same entered time allowance. Actual tipping, valve response and pressure equalization require measured data.
- The animation shows the weighted bowl and counterweight linkage with illustrative proportions and liquid shading. It does not establish pressure-vessel suitability or a product rating.
Condensate changes the bowl’s weight and position, operating the steam-admission and vent sequence. The calculator compares filling, discharge and switching times for a specified batch.
The weighted Bundy bowl
Bundy gravity-return traps were made by the A. A. Griffing Iron Company. Their pear-shaped bowl turns on trunnions and is balanced by a ball weight and lever. Collected condensate makes it descend. That movement admits boiler steam and closes the air vent; equalized pressure then permits gravity return. Emptying lets the weight raise the bowl, shutting steam admission and reopening the vent.
The drawing separates the valve sequence from the moving bowl so the operating stages remain clear. Its linkage lengths stay fixed. The small tipping angles and dimensions are illustrative, not dimensions for manufacturing a trap.
Return and separating versions
The manufacturer catalogued gravity-return and separating versions. Their valve arrangements and purposes differ. This animation follows the gravity-return sequence; it is not a modern balanced-pressure bellows trap.
Historical catalogue capacities are specific to their stated equipment and conditions. This page does not use them as a current selection rating.
A usable batch-cycle calculation
For usable transferred volume V in litres, filling rate Qin and discharge rate Qout in litres per minute, the stage times are tfill = 60V/Qin and tdrain = 60V/Qout seconds. With a switching allowance ts for each transition, total cycle time is their sum plus 2ts. Average throughput is 3600V/tcycle litres per hour.
The model assumes filling and discharge occur separately. Condensate arriving while the inlet is isolated needs upstream storage. The calculation does not derive the supplied rates, tipping threshold or valve lift from pressure or temperature.
Worked example: a specified 4-litre batch
Use V = 4 L, Qin = 2 L/min, Qout = 8 L/min and ts = 2 s. Filling takes 120 s and discharge takes 30 s. The total is 120 + 30 + 4 = 154 s. Average throughput is 3600 × 4 / 154 = 93.5 L/h.
This is an arithmetic example, not a tested Bundy product capacity. Flow rates, usable volume and switching times must be established for the installation before using a cycle estimate.
What changes the calculated cycle?
A larger usable batch increases both stage times. Increasing either entered flow rate shortens that stage. Switching overhead reduces average throughput even when both flow rates are high. The simulation preserves these timing proportions while playing the whole cycle in twelve seconds.
Pressure equalization, receiver storage, valve losses, flashing, leakage and the counterweight tipping threshold are outside the model. The entered rates and usable batch volume must account for the installation’s operating conditions.
Questions about the Bundy calculator
Is this a thermostatic bellows trap?
No. The historical arrangement shown operates through the changing weight of condensate in a pivoted bowl.
Which inputs determine the calculated cycle time?
Usable batch volume and the filling and discharge rates determine the two flow stages. The switching allowance adds time for each transition.
Does the animation show the actual cycle speed?
No. It plays a full cycle in twelve seconds. The result cards show calculated seconds; stage proportions follow those times.
Is usable batch volume the whole vessel capacity?
No. It is the volume transferred between the tipping and reset conditions, excluding any residual liquid.
Primary references
A. A. Griffing Iron Company catalogue, printed pages 114–118: Bundy return and separating trap forms.
W. T. Edwards, Modern Steam Traps, American Electrician, July 1905, pages 384–385, Figure 3: weighted bowl, counterweight linkage and return-trap valve sequence.
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