Steam Pump Mechanism: How Direct-Acting Duplex Pumps Work, Parts, Formula & Uses

Selected swept-volume ledger

One-way swept volume per selected cylinder is piston area pi D squared over four times stroke L. Multiplying by selected cylinder count and one-way strokes per minute gives theoretical volume rate. The entered delivery multiplier scales that value; the difference is arithmetic reduction.

What the calculator determines

Use it to inspect selected displacement geometry and unit conversions. It cannot establish actual pump capacity.

Selected relationships

A=pi D^2/4; V_s=ALN_c; Q_t=V_s n/231; Q_f=eta Q_t; reduction=Q_t-Q_f.

Selected-input example

At 4 in bore, 6 in stroke, 50 selected one-way strokes/min, two cylinders and 90% multiplier, selected swept volume is about 150.796 in3/stroke, theoretical rate is about 32.640 gpm, factored rate is about 29.376 gpm and arithmetic reduction is about 3.264 gpm.

Not a pump-capacity model

Single- versus double-action details, rod area, clearance volume, check-valve dynamics, leakage, compressibility, suction conditions, cavitation, pressure, steam use, power, piping and safety are excluded.

Questions

Why are strokes labeled one-way?

The retained equation contains one swept length per counted stroke. Calling the same input double strokes would require additional action geometry not represented by the equation.

Is the multiplier measured efficiency?

Not unless independently supplied; it is only an entered arithmetic factor.

Is factored rate actual delivery?

No. Actual delivery requires pump configuration and operating evidence.

Authoritative references

• NASA Glenn Bore and Stroke — gives piston area and swept volume A times stroke.
• U.S. government reciprocating-pump maintenance manual — defines volumetric displacement as piston area times stroke and requires allowance for double action.
• NIST Handbook 133 Appendix E — defines one U.S. gallon as exactly 231 cubic inches.