A steam injector uses a steam jet, condensation and pressure recovery to feed water toward a pressurized boiler. The illustrated arrangement includes delivery and overflow balls. Follow the pickup and delivery sequence, then compare boiler pressure with an equivalent water speed and head, a chosen volume ratio and a projected seat gap. These calculations do not determine injector capacity or prove that it will pick up and deliver.
Ball-valve Injector Interactive Calculator
Compare the water velocity and head equivalent to boiler pressure, condensation volume ratio and normal delivery-seat gap. The animation illustrates pickup and delivery; the inputs do not solve injector performance.
Equation Used
Boiler gauge pressure is converted to an ideal water-speed and head equivalent. A separately entered vapor-to-liquid volume ratio gives 100 divided by that ratio as a percentage. Ball lift is projected normal to the seat using the chosen seat angle; none of these outputs predicts injector pickup or delivery rate.
- Uses an incompressible water energy comparison, not a calculated delivery-jet requirement.
- Pressure is treated as gauge pressure acting against the boiler.
- Losses in cones, turbulence, heating, and check valves are not included.
- The chosen volume ratio is illustrative and depends on the vapor and liquid states; it is not calculated from boiler pressure.
The pressure-equivalent water speed is an ideal energy comparison, not an injector performance prediction. The user-entered collapse ratio is not a constant property of steam. Startup and check-valve timing are illustrative.
Entrainment, condensation and pressure recovery
Steam expands through a nozzle and transfers momentum as it mixes with feedwater. Condensation converts the steam into liquid while exchanging heat with that water. The mixed stream then passes through a delivery cone that recovers pressure from its motion.
Delivery requires pressure sufficient to overcome the boiler-side pressure and the connected delivery-system losses. The energy comes from the steam supply; the injector does not produce energy merely because steam occupies less volume after condensing.
In this animation the delivery ball opens after delivery pressure is established. The second ball controls the overflow path: it is shown open during pickup and closed during delivery. It is not an inlet check ball. The displayed sequence is explanatory and is not solved from the calculator inputs.
Flow-path components
- Steam nozzle: accelerates the motive steam.
- Water inlet and combining region: bring feedwater into the steam jet.
- Delivery cone or diffuser: recovers pressure in the mixed stream.
- Delivery ball: controls the path toward the boiler in the schematic.
- Overflow ball and passage: provide the illustrated pickup route.
This layout does not reproduce every dimension or valve arrangement of a historical injector. Cone shape, thermal mixing and actual valve behavior require a specific design.
Boiler-feed applications
Steam injectors have been used for boiler feed service where motive steam is available. Their operating range depends on the injector model, steam conditions, feedwater temperature, supply arrangement, suction lift and delivery pressure.
Lifting and non-lifting arrangements have different water-supply requirements. The type name alone does not establish a permitted suction height, capacity or feedwater temperature. Manufacturer performance data are needed for the intended installation.
The Penberthy automatic-injector literature is one example of model-specific selection data. It should not be treated as a specification for every historical ball-valve injector or as a claim that the animation reproduces a Penberthy product.
Four comparisons, not an injector-sizing equation
Pressure-equivalent speed and head
Convert the entered gauge pressure P from psi to Pa. With water density ρ = 1000 kg/m³ and g = 9.80665 m/s², pressure-equivalent speed v = √(2P/ρ), and pressure head H = P/(ρg).
These express the same pressure as kinetic energy per volume or hydrostatic head. They omit inlet velocity, elevation, heat transfer and losses. The speed is not predicted steam velocity, actual mixed-jet velocity or a complete injector delivery requirement.
Volume ratio
If R means initial vapor volume divided by final liquid volume for the chosen states and mass, the final volume percentage is 100/R. R is supplied independently by the user. It is not a universal steam property, a steam-to-feedwater mass ratio or a calculated condensation percentage.
Seat-gap projection
Normal Gap = lift × sin α, using millimetres for lift and gap. For this projection, α is the angle between the seat surface and the ball’s axial lift direction. The relationship describes separation normal to a straight conical-seat section. It does not calculate annular flow area, valve coefficient or ball motion under pressure.
Worked example: interpret each output separately
Choose hypothetical boiler gauge pressure 160 psi. The converted pressure is about 1.10316 MPa. The pressure-equivalent water speed is 46.9715 m/s, and the head is about 112.491 m. These are pressure-energy equivalents, not an injector’s measured operating speed or suction lift.
At 100 psi the equivalent speed is about 37.1342 m/s and head 70.3070 m. Increasing pressure to 200 psi doubles that head to 140.614 m and raises speed by √2 to about 52.516 m/s.
Separately, choosing R = 1600 gives a volume-ratio result of 0.0625%. Choosing R = 800 gives 0.125%. This arithmetic does not specify the steam and water states or prove complete condensation.
For an entered ball lift of 2 mm and seat angle 45°, normal gap is 2 sin 45° = 1.4142 mm. Halving lift halves the projected gap. Neither value is a valve-lift recommendation or a delivery-flow calculation.
Use tested performance for feed-system decisions
| Question | What is required | What the calculator provides |
|---|---|---|
| Will the injector pick up? | Actual cone geometry, steam and feedwater conditions, supply and overflow behavior. | No pickup prediction. |
| How much water will it deliver? | A validated coupled flow/thermal model or appropriate tested performance data. | No mass-flow or volume-flow rate. |
| What does boiler pressure mean as water head? | Pressure and a chosen water density. | The ideal pressure-head equivalent. |
| How does lift separate a ball from a conical seat? | A defined lift and local seat angle. | A normal-gap projection only. |
A mechanical feed pump and a steam injector use different driving methods. Choosing between them requires the boiler’s approved feed arrangement and operating requirements. An electric linear actuator is not a direct substitute for the injector’s thermal and fluid process.
Injector questions
Steam expansion supplies energy and momentum to the mixed stream. After condensation, the delivery cone recovers pressure. Successful delivery depends on the complete flow and thermal process.
No. It is the ideal water velocity whose kinetic energy per unit volume equals the entered gauge pressure. No steam expansion calculation is performed.
No. Vapor and liquid specific volumes depend on their states. The ratio here is a user-selected comparison and is independent of the pressure calculation.
In this schematic it controls overflow during pickup and delivery. Other injector designs can use different valve arrangements.
No. It is the boiler pressure expressed as a water-column height. Suction lift depends on the injector and supply conditions.
No. Use the specific injector drawings, compatible replacement parts and approved service instructions. Changing diameter or material can affect fit and operation.
No. Several fluid, thermal and mechanical conditions can produce those symptoms. Follow the boiler’s approved operating and service procedure; do not improvise tests with a closed delivery path or by touching hot piping.
No. The tool has no feed-capacity calculation or boiler-level model. It cannot establish a safe firing condition or a feed-system rating.
Manufacturer reference
Penberthy Automatic Injectors: manufacturer explanation and model-specific steam-pressure, feedwater-temperature, suction and capacity information. Use the applicable injector’s current documentation for an installation.
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