A Hancock inspirator feeds a steam boiler using two steam-jet stages. The lifting stage draws water into the apparatus and supplies the forcing stage. The forcing jet transfers energy to that water, and the delivery passage converts part of its velocity into pressure. The animation shows these connected paths; the calculator compares pressures you choose, rather than predicting injector performance.
Hancock Inspirator Interactive Calculator
Choose boiler pressure and two comparison ratios. Read the resulting lower and upper delivery pressures and their difference from boiler pressure. The animated flow shows the delivery phase of a double-tube inspirator.
Equation Used
The two ratios are sorted to give lower and upper results. Defaults of 110% and 115% are comparison settings, not a Hancock performance specification or an allowance for a particular check valve. All pressures use the same gauge reference. Flow, lift, steam consumption, temperature, nozzle dimensions and losses are not calculated. At 100%, the selected pressure equals boiler pressure and provides no allowance for delivery losses.
Two connected steam-jet stages
The lifting nozzle sends a steam jet into its combining tube. Water enters around the nozzle and mixes with the jet. Condensation and momentum transfer produce a moving stream of water and condensed steam, which passes to the forcing stage.
A separate steam nozzle supplies the forcing tube. Water from the lifter enters around that nozzle, and the mixed stream continues through the delivery passage. A diverging passage can recover static pressure from a fast liquid stream. Successful delivery requires sufficient pressure at the boiler connection to overcome boiler pressure and the intervening losses.
Hiscox shows an upper lifting tube and lower forcing tube in figure 389, and another locomotive arrangement in figure 391. The animation follows the parallel, double-tube principle of figure 389. Transfer passages are separated and enlarged to make their connections visible; it is not a manufacturing section.
Boiler feed without a reciprocating pump
Steam injectors provide boiler feed without a crank-driven pump. Their energy source is the steam jet, so feeding does not depend on a locomotive crankshaft turning. An inspirator still has control and overflow valves; the absence of a reciprocating pumping mechanism does not mean every component is stationary.
The lifting stage matters when the water supply lies below the apparatus. Actual capacity and permissible lift depend on the specific injector, steam and water conditions, pipework and valves. Use the matching equipment data when selecting or operating a unit.
What the pressure calculator measures
Enter a boiler gauge pressure Pᵦ and two percentage ratios. After sorting the ratios, the calculator multiplies Pᵦ by each ratio divided by 100. Subtracting Pᵦ gives the corresponding pressure surplus.
This is a pressure comparison. It does not derive delivery pressure from steam expansion, mixing or condensation. It also does not calculate a combining-tube diameter or feedwater rate. Those tasks require the actual nozzle geometry, inlet states, flow conditions and losses.
Example at 150 psi gauge
With a boiler pressure of 150 psi gauge and selected ratios of 110% and 115%, the calculated pressures are 165 and 172.5 psi gauge. Their surpluses are 15 and 22.5 psi.
These are the consequences of the selected percentages. They do not establish that a Hancock inspirator will produce either pressure, nor that a particular valve or delivery line will pass the required flow. Swapping the two ratios leaves the displayed lower and upper results unchanged.
Reading the flow animation
Gold markers follow the two steam supplies. Blue markers enter through the water connection at the top. Green markers follow the lifted water through the transfer passage and then the forcing tube to the delivery connection on the left. The short lower branch represents an overflow passage closed during delivery.
The animation repeats steady flow rather than a startup procedure. Hiscox describes an initial lifting and overflow condition followed by admission to the forcing nozzle. The drawing omits the detailed valve linkage, control handles and external boiler check valve. Its flow markers indicate direction, not measured velocity, flow rate or a pressure distribution.
Changing the pressure sliders updates the comparison results. It does not change the drawn jets or prove successful pickup. Water temperature, air leakage, deposits and unsuitable operating conditions can affect a real injector; this model does not diagnose them.
Frequently asked questions
What distinguishes a Hancock inspirator?
Its separate lifting and forcing steam-jet stages. The lifter supplies water to the forcer. Each stage has its own steam nozzle and combining tube.
Does it contain moving parts?
It has control and overflow valves, although its pumping action comes from steam jets rather than a reciprocating piston or rotating impeller.
Does the calculator guarantee 110% to 115% of boiler pressure?
No. Those are adjustable example ratios. The results are arithmetic comparisons, not a measured or predicted operating range.
Why is the overflow shut in the animation?
The animation shows the delivery phase. Startup uses a lifting and overflow condition before full forcing action; that operating sequence is not simulated.
Can I size the nozzles from this page?
No. Pressure ratios alone do not determine nozzle dimensions, feedwater capacity or permitted suction lift. Use data for the actual equipment and operating conditions.
Why do the flow markers keep the same speed when pressure changes?
They show connected flow paths at an explanatory speed. The calculator contains no steam-expansion, condensation or liquid-flow model.
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