The historical Knott rotary pump uses a hollow circular piston or strap driven by an eccentric rotating about the outer shell's central axis. A wing from the piston slides and rocks through a small slotted packing cylinder while the eccentric piston wipes the shell's inner surface.
Knott Rotary Pump Interactive Calculator
Calculate flow, ideal pressure torque and hydraulic power from entered displacement, speed, pressure rise and assumed volumetric efficiency. The historical drawing does not determine displacement or efficiency.
Equation Used
- Entered displacement and volumetric efficiency apply at the selected operating point.
- Pressure rise is uniform for ideal torque arithmetic.
- The inlet and outlet passages are illustrative; no fluid particles or port-timing model are used.
- No chamber-volume law, mechanical loss, pressure-dependent leakage, viscosity, cavitation, sealing, wear or strength model.
Torque is ideal pressure torque; port timing, chamber volume and mechanical efficiency are absent.
Eccentric piston and sliding wing
A shaft centered in the circular shell turns an eccentric inside the hollow piston/strap. The piston orbits while remaining internally tangent to the shell. Its single wing slides through a rocking slotted packing, separating the inlet and outlet sides.
Historical pump topology
The animation explains the Knott arrangement and its constrained motion. It does not select, rate or manufacture a pump.
Displacement, flow and ideal torque
For displacement D in cm³/rev, speed n in rpm and volumetric efficiency ηv as a decimal, delivered flow Q=D n ηv/1000 L/min. The difference from theoretical flow is D n(1−ηv) mL/min.
With pressure rise p in bar, ideal pressure torque is pD/(20π) N·m. Hydraulic output power is pQ×1000/600 W. Torque excludes mechanical losses, while flow uses the entered volumetric-efficiency assumption.
Example and diagram
At D=12 cm³/rev, n=40 rpm, p=80 bar and ηv=90%, flow is 0.432 L/min, ideal torque approximately 15.28 N·m, hydraulic power 57.6 W and the flow difference 48 mL/min. These are illustrative inputs, not historical pump ratings.
The central shaft and orbiting eccentric move the circular piston against the shell. Its fixed-length wing slides through the rocking upper packing. The shaded cavity shows the space outside the piston; the upper passages indicate inlet and outlet without simulating fluid particles. Playback has a fixed seven-second cycle.
Historical arrangement and model limits
Hiscox’s entry 540 describes a hollow winged cylinder, an eccentric on the shell axis and a small slotted cylinder that packs the wing. It does not supply the numerical operating ratings used as illustrative settings here.
The calculator does not determine chamber-volume change, port timing, leakage behavior, cavitation, sealing or strength. Its volumetric efficiency is entered. It contains no mechanical-efficiency calculation, so the torque result is not actual shaft torque.
Frequently asked questions
Is this the modern trailer-brake equipment sold under the Knott name?
This page concerns the historical pump described in Hiscox’s entry 540. It does not document or size modern trailer-brake equipment.
Is this a multiple sliding-vane pump?
The cited historical form uses a single wing on a hollow cylinder driven by an eccentric, with a separate slotted packing.
Is the torque the actual shaft torque?
No. It is ideal pressure torque without mechanical losses.
Does the animation determine displacement or leakage?
No. Displacement and volumetric efficiency are inputs. The drawing shows the moving piston and wing, not a fluid-flow or leakage solution.
Historical reference
Gardner Dexter Hiscox, Mechanical Movements, Powers, Devices and Appliances, entry 540: Knott rotary pump.
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