The Brownley injector shown in Hiscox figure 385 has two steam jets: an upper lifting stage and a lower forcing stage. Its distinctive common overflow cock relieves both stages. This animation follows the separate paths for steam, incoming water, intermediate mixture, delivery and overflow. The calculator compares mass and thermal energy through the two stages.
Brownley Injector · Two-stage Thermal Balance
Follow the lifting and forcing stages, then compare an ideal complete-condensation balance. Fixed illustrative steam enthalpy: 2750 kJ/kg. Results do not rate actual injector pressure or capacity.
Equation Used
- Same entered total steam supply split between two stages.
- Steam share is an assumed mass allocation, not an added regulating valve.
- Both stages fully condense steam at steady state.
- No heat or overflow loss.
- Constant liquid cp and fixed illustrative steam enthalpy.
- Animation is an explanatory sequence rather than a transient solution.
The paired end sections show two levels of the same overflow cock. The historical source describes one common control.
Two jets share one steam supply
Steam enters the chamber at the right and supplies both nozzles. Water enters above the upper lifting tube. That stage forms an intermediate stream which passes through the connecting chamber toward the lower forcing tube. The lower stage receives more steam and directs the resulting mixture toward the delivery connection at the left.
Hiscox identifies the overflow cock as the regulating device and says that it relieves both the lifting and forcing tubes. The diagram shows both branches leading to the common overflow control. The cock is removed from the main fluid cutaway to expose the routes. The two enlarged end sections below show two passage levels of that same cock, linked to the same angle.
Autoplay demonstrates open overflow, turning the cock, established delivery with both overflow passages closed, and a return to the starting state. Valve travel, proportions and timing are illustrative, not measurements or a dynamic startup simulation.
Compare a two-stage condensation balance
Choose total steam flow, the assumed proportion reaching the lifting jet, incoming water per kilogram of total steam, and incoming water temperature. The calculated stage temperatures assume complete condensation in each stage, with no heat or overflow loss.
The steam-share input represents an assumed allocation of mass flow. It does not add a regulating valve to either nozzle. Both stages use the same fixed illustrative inlet steam enthalpy, 2750 kJ/kg. No pressure is inferred from that number.
Changing the share changes the intermediate temperature, but not the final mixture temperature when total steam and water flows are unchanged. Changing total steam flow scales the mass flows while preserving their ratio and the two temperatures.
Mass and energy through each stage
Let ms be total steam flow, f the lifting-stage fraction, R incoming water per kilogram of total steam, and Tw incoming water temperature. Then ms1=fms, ms2=(1−f)ms and mw=Rms.
With hs=2750 kJ/kg and liquid cp=4.18 kJ/(kg·K), the first-stage mixture temperature is T1=(mw cp Tw+ms1 hs)/((mw+ms1)cp). The second stage gives T2=((mw+ms1)cpT1+ms2 hs)/((mw+ms)cp).
Combining the equations gives T2=(mw cpTw+ms hs)/((mw+ms)cp). Final mixture flow is mw+ms. The intermediate stream includes the condensed steam from stage 1; it is not just the original incoming water.
The constant-cp liquid approximation uses a near 0°C reference. It omits kinetic and potential energy changes between the external balance boundaries. No nozzle-capacity coefficient, momentum transfer, delivery-pressure recovery or suction-height calculation is included.
Example: split 20 kg/h of steam between two stages
With 25% of 20 kg/h sent to the lifting jet, stage 1 receives 5 kg/h and stage 2 receives 15 kg/h. At a water/steam ratio of 15, incoming water is 300 kg/h and final mixture flow is 320 kg/h.
For incoming water at 20°C and the stated steam enthalpy, the first-stage mixture is about 30.46°C and the final mixture about 59.87°C. Increasing the lifting share moves more of that heating into stage 1; total final temperature remains unchanged.
These figures satisfy an ideal thermal balance. They do not establish that the assumed flow split or total flow can be produced by a particular historical injector.
Diagram and calculation assumptions
The external connections and two-stage arrangement follow Hiscox figure 385. The passages are opened out for visibility and the separate cock sections are explanatory views, not manufacturing details. Dots indicate direction; their number is not a measured mass-flow scale.
The calculator assumes steady, complete condensation in both stages, identical steam enthalpy, no overflow loss and no external heat loss. It does not predict starting behavior, capacity, lifting height or delivery pressure. Those depend on the nozzles, fluid states and hydraulic performance of the injector.
Brownley injector questions
Are there two independent overflow valves?
No. The source describes one cock relieving both tubes. The enlarged views show two controlled passages on the same rotating control.
Why does changing steam share leave final temperature unchanged?
With the same total steam enthalpy and water input, the overall energy balance is unchanged. Only the distribution of heating between the two ideal stages changes.
Does the steam-share slider represent a physical nozzle valve?
No. It is an assumed flow allocation for comparison. Hiscox describes steam flowing to the two nozzles without a separate regulating device other than the overflow cock.
Is this a boiler-feed sizing tool?
It is a thermal and mass-flow comparison. Actual injector delivery requires hydraulic, condensation and device performance information that is not supplied here.
References
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, printed page 106, figure 385, Brownley injector: two jet nozzles and common overflow cock.
NIST, NISTIR 5078, Thermodynamic Properties of Water, for steam-table enthalpy conventions. The calculator uses a stated fixed illustrative steam enthalpy and constant liquid specific heat; it does not implement a steam-property or pressure-state solver.
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