The Pattison rotary pump uses an eccentric inside a hollow winged cylinder. As the eccentric turns about the shell axis, a piston and socket guide the wing. Explore this motion and calculate the diameter, distance and speed of the eccentric center’s circular orbit.
Pattison Eccentric-Motion Explorer
Enter outer-shell radius, eccentricity and crank speed. The worksheet reports exact eccentric-center orbit geometry and speed without inferring hydraulic delivery.
Equation Used
- The outer shell is circular with fixed central axis O.
- The eccentric center follows a circular orbit of radius e around O.
- The hollow winged cylinder follows the eccentric center in the schematic.
- The wing remains collinear with the pivoting guide socket and slides through the piston guide.
- Clearance, sealing, pressure, displacement, leakage, flow, torque, materials and safe operation are excluded.
The outer-shell radius changes the schematic geometry. The orbit calculations depend on eccentricity and rotational speed; playback is slowed for clarity and does not simulate hydraulic flow.
Hiscox item 541: eccentric inside a hollow winged cylinder
Hiscox describes a hollow winged cylinder containing an eccentric that rotates about an axis central with the outer shell. The piston and socket serve as a guide for the wing.
The eccentric center orbits the fixed shell axis. The wing remains connected to the hollow cylinder while the socket pivots and the piston guide accommodates sliding.
A historical eccentric rotary-pump topology
The Pattison entry appears among several distinct rotary pumps in Hiscox's hydraulic devices section. Its defining feature is the guided wing and internal eccentric, not a generic spring-loaded sliding-vane rotor.
The illustration shows the relationship between the eccentric, hollow cylinder and wing guide. Its dimensions do not establish suitability for a particular fluid or service.
Eccentric-center orbit
These identities describe only the circular path of the eccentric center. They do not determine swept volume or pump flow.
Declared motion example
For e=20 mm at 60 rpm, the eccentric center follows a 40 mm diameter orbit, travels 125.66 mm per revolution and moves at 125.66 mm/s.
From eccentric motion to pump performance
The eccentric-center orbit alone does not determine how much fluid the pump transfers. Calculating delivery would require the working chamber geometry, port arrangement, clearances and a hydraulic model.
The calculator reports center motion only. It does not predict flow, leakage or self-priming, or select materials for a fluid service.
Pattison mechanism questions
Which parts make up the mechanism?
Hiscox 541 shows a hollow winged cylinder, internal eccentric and guided wing.
What rotates about the shell axis?
The eccentric.
What guides the wing?
A piston and pivoting socket below the shell.
Does orbit speed equal pump flow?
No.
Pattison pump references
- Gardner D. Hiscox, Mechanical Movements, item 541, printed page 146: Pattison hollow winged cylinder, central-axis eccentric and piston/socket guide.
- US Patent 4,309,152, historical background: classifies Pattison among eccentric rotary-pump mechanisms.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
