The Sellers restarting injector uses fixed steam, combining and delivery tubes. Historical descriptions identify two concentric check valves guided by the combining tube; pressure in that tube closes the overflow checks as the water current becomes established.
Sellers Injector Geometry and Delivery Threshold
Compare selected circular throat areas and the static pressure threshold at a boiler delivery check.
Equation Used
- Selected throats are circular.
- Pressures are gauge values using one consistent reference.
- The animation is a qualitative staged schematic of documented valve closure.
- Fluid dynamics, heat transfer, performance and safety are excluded.
Check crack pressure is a selected increment, not a validated component specification.
Documented restarting sequence
Steam and water initially discharge through the open overflow path. As water reaches the combining tube, pressure operates concentric valves C and D and closes the overflow, allowing the established jet to proceed toward the boiler delivery check.
The animation is an educational cross-section of that documented sequence. It is not a computational fluid-dynamics or boiler-operating model.
What the calculator determines
Select steam-nozzle and combining-throat diameters, boiler gauge pressure and an assumed delivery-check crack pressure. The calculator reports the two circular areas, their area ratio and the minimum static delivery-pressure threshold.
Throat areas alone do not determine water delivery or steam velocity.
Geometry and pressure threshold
For each selected circular throat, A = πd²/4. Combining-to-steam area ratio is Ac/As = (dc/ds)². The boiler check can begin opening only when delivery gauge pressure exceeds Pboiler + Pcrack.
Selected-input arithmetic
For 4.5 mm steam and combining throats, each area is about 15.90 mm² and their area ratio is 1.000. At 150 psig boiler pressure with a selected 5 psi crack increment, the static delivery threshold is 155 psig.
What throat geometry cannot predict
Throat areas and a check threshold do not predict injector operation. Steam state and quality, feedwater temperature and lift, nozzle profiles, cone spacing, condensation, compressible choking, two-phase momentum transfer, diffuser recovery, losses, valve dynamics and manufacturer calibration are absent.
The calculator therefore cannot predict capacity, steam consumption, jet velocity or reliable restarting. Use manufacturer performance data for the intended steam and feedwater conditions when selecting an injector.
Questions
Does reaching the static threshold guarantee delivery?
No. It is necessary for the check to open but does not prove the injector can generate that pressure or sustain flow.
Are equal throat diameters required?
No design rule is inferred here; the ratio is reported only as selected geometry.
Can this size an injector for a boiler?
No.
References & Further Reading
- Wikipedia contributors. Injector. Wikipedia
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