Cary’s historical rotary pump uses a concentric rotating drum with two sliding wings guided by a stationary heart-shaped cam. Each wing retracts as it passes a fixed separator between the inlet and outlet. This animation shows that arrangement; the calculator estimates flow from a displacement and volumetric efficiency that you supply.
Cary Rotary Pump Interactive Calculator
Set the illustrated drum size and vane travel, then enter a known displacement per revolution, shaft speed and volumetric efficiency. The dimensions control the teaching diagram and swept envelope. Flow is calculated from the entered displacement, not inferred from this simplified cam shape.
Equation Used
- Two radial wings rotate with the drum and follow a stationary cam; the central axis is fixed.
- Illustrated wings are ideal thin vanes with constant radial length and a selected smooth rise, dwell and return.
- The illustrated fixed separator occupies 30 degrees; a wing is fully retracted while passing it. These are teaching proportions, not original manufacturing dimensions.
- Displacement and volumetric efficiency are entered independently of the illustrated dimensions.
- Estimated flow assumes steady speed and the entered operating efficiency; clearance alone is not used as a leakage model.
- Playback is 40 times slower than shaft RPM; chamber colors and port arrows explain connections, not resolved fluid velocity or pressure.
A fixed cam controls two sliding wings in a concentric rotating drum. Flow is estimated from the displacement, speed and volumetric efficiency you enter. The illustrated diameter and wing travel show the swept envelope; they do not establish pump displacement or leakage.
How the fixed cam controls the rotating wings
The 1853–54 New-York Exhibition account shows a drum fastened to the rotating shaft and a heart-shaped cam fixed around that shaft. Two sliding wings turn with the drum. As each wing follows the cam, it extends into the pumping chamber and then withdraws to pass the stationary separator between the supply and delivery passages.
The original account describes fluid-loaded leather packing on the sliding parts. Hiscox’s later figure 535 also identifies the fixed cam, guided wings and separator. The wings slide relative to the drum as it rotates around the fixed cam.
The cutaway uses that arrangement with a smooth illustrative cam profile. The blue wing tips follow the working wall while their inner followers follow the fixed cam. Around the bottom separator each wing retracts flush into the drum. The other wing remains active in the chamber. Detailed packing, end-face seals and three-dimensional drive hardware are omitted.
Reading the historical pump drawing
The exhibition illustration shows the pump on an iron frame, driven by a belt pulley on a horizontal shaft, with separate supply and delivery pipes. Its large section view identifies the central drum, two sliding wings, stationary cam and fixed separator. The animation presents those functional parts in an open front section.
Historical performance claims are not a rating for a reconstructed pump. This page does not specify a pressure limit, self-priming depth, contamination tolerance, permissible speed or modern service suitability. Those require actual pump data and operating conditions.
Flow from known displacement
For a documented displacement Vd in cubic centimeters per revolution and shaft speed N in revolutions per minute, theoretical flow is Qt = VdN/1000 liters per minute. An entered volumetric efficiency ηv in percent gives estimated delivered flow Q = Qtηv/100. The difference Qt−Q is the assumed flow loss.
This is a mean-flow calculation. It does not resolve pulsation, pressure or internal leakage. Efficiency must be appropriate to the fluid, pressure, speed and condition of the real pump; a single radial-clearance value cannot determine it.
The illustration’s maximum vane-tip diameter is D+2 h, where D is drum diameter and h is radial wing travel. This dimensional envelope is separate from displacement. A chamber’s actual swept volume needs its axial depth, wall and cam profiles, vane thickness and port timing.
Read the default flow example
An entered displacement of 100 cm³/rev at 400 rpm gives 40 L/min theoretical flow. With entered volumetric efficiency 90%, estimated delivered flow is 36 L/min and assumed flow loss is 4 L/min. At 800 rpm with the same assumed efficiency, those three flow values double.
The illustrated 100 mm drum and 20 mm wing travel give a 140 mm maximum swept diameter. Changing either dimension updates that envelope and the drawing. It does not change the separately entered 100 cm³/rev displacement. Supply a new displacement if your real pump geometry changes.
What this model does and does not compare
The stationary cam coordinates wing motion positively, while the fixed separator distinguishes inlet and outlet passages. Packing and end-face sealing remain essential parts of the physical pump, even though they are simplified in the drawing.
The teaching cam has a short retracted region, smooth rise and return, and an extended region. It explains how a rotating wing can clear the separator; it is not an extracted manufacturing profile. Use the original pump drawing or measured geometry for restoration, and documented displacement and efficiency for a useful flow estimate.
Understanding the Cary pump calculator
Is the central drum eccentric?
No. The cited Cary arrangement has a concentric rotating drum and a fixed cam. Sliding wings provide the changing radial reach.
Why does the cam stay still?
Its fixed contour determines where each rotating wing extends or retracts. Rotating the cam with the drum would remove that required relative motion.
How does a wing pass the separator?
The cam withdraws it into its slot before it crosses the separator. In this ideal thin-vane model the tip becomes flush with the drum through the selected separator region.
Why do diameter and vane travel not change the flow result?
They describe the illustration and swept envelope. The flow result uses the separate known displacement input. Exact displacement cannot be recovered from those two dimensions alone.
Can clearance determine efficiency?
Not by itself. Leakage also depends on pressure, viscosity, leakage-path geometry, speed and other details. Enter a measured or documented volumetric efficiency for the pump and operating condition.
References & Further Reading
- The World of Science, Art, and Industry Illustrated from Examples in the New-York Exhibition, 1853–54, printed page 36: Cary’s Rotary Pump. Original description, section and machine elevation.
- Gardner D. Hiscox. Mechanical Movements, Powers, Devices and Appliances, printed page 145, figure 535. Fixed cam, rotating drum, guided wings and separator.
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