A Pattison Rotary Pump is a positive-displacement vane pump where an eccentrically mounted rotor carries spring-loaded or gravity-extended sliding vanes inside a circular housing, sweeping fluid from inlet to outlet on every revolution. You will find this layout in early 20th-century hand-cranked oil transfer pumps, marine bilge units, and tanker drum pumps. It moves viscous liquids smoothly without pulsation and self-primes from dry. A 75 mm bore Pattison body typically delivers around 0.25 L per turn at 60 RPM — roughly 15 L/min by hand crank.
Pattison Rotary Pump Interactive Calculator
Vary displacement, crank speed, and volumetric efficiency to see delivered flow and a live eccentric-vane pump diagram.
Equation Used
The pump delivery is the displacement per revolution multiplied by crank speed and volumetric efficiency. Use eta_v as a percentage to account for leakage across vane tips and end plates.
- Positive-displacement vane pump with stable chamber filling.
- Displacement per revolution is supplied directly as Vd.
- Volumetric efficiency accounts for vane-tip and end-plate slip.
Inside the Pattison Rotary Pump
The trick is the offset. The rotor sits inside a circular bore but its axis is shifted — usually 4 to 8 mm — so one side of the rotor nearly touches the housing while the opposite side leaves a crescent-shaped cavity. Slots cut radially through the rotor hold flat vanes that slide in and out as the rotor turns. Centrifugal force, springs, or in older Pattison units simply gravity, pushes the vanes outward to keep them sealed against the bore wall. As each vane sweeps past the inlet port, the cavity behind it expands and draws fluid in. As it sweeps toward the outlet, the cavity shrinks and pushes fluid out. Two or four vanes are typical — the original Pattison patents used four.
Why this design? Because it self-primes, handles viscous fluids like lubricating oil and diesel fuel, and produces near-pulseless flow at low RPM. A gear pump will fight you on cold thick oil; a centrifugal pump will not prime at all. The Pattison layout was the standard hand-crank oil dispenser for garages and ships from roughly 1910 through the 1950s for that reason.
Get the tolerances wrong and the pump fails in predictable ways. If the vane-to-bore clearance opens past about 0.1 mm, slip flow climbs sharply and volumetric efficiency drops below 70% — you will crank harder for less output. If the vane slot is too tight (less than 0.05 mm clearance on the vane thickness) the vane jams on cold oil and the pump locks up. End-plate clearance is the silent killer — 0.04 mm is the target, and a worn end plate at 0.15 mm bypasses fluid axially around the vane tips no matter how good the radial seal is.
Key Components
- Eccentric Rotor: The cylindrical rotor mounted off-centre inside the housing bore, typically with 4 to 8 mm of eccentricity on a 75 mm bore. Its offset creates the crescent-shaped working volume that defines displacement per revolution.
- Sliding Vanes: Flat rectangular vanes — usually 4 of them in a Pattison — riding in radial slots in the rotor. They extend outward against the bore wall to seal the working chambers. Phosphor bronze or hardened cast iron is standard, with a vane thickness around 4 to 6 mm.
- Cylindrical Housing (Bore): The fixed cast-iron or bronze body the rotor turns inside. Bore roundness must hold within 0.02 mm or vane sealing breaks down on the loose side and the vane drags on the tight side.
- End Plates: The two flat covers that seal the rotor cavity axially. End-plate clearance to the rotor face must hold around 0.04 mm — too tight and the rotor scuffs, too loose and fluid bypasses around the vane tips and volumetric efficiency collapses.
- Inlet and Outlet Ports: Kidney-shaped slots cut into the housing or end plates positioned to align with the expanding and contracting cavities. Port timing controls cavitation at the inlet and back-pressure spikes at the outlet.
- Drive Shaft and Crank Handle: On hand-operated Pattison pumps the shaft carries a crank with a 150 to 200 mm throw, geared 1:1 to the rotor. Cranking at 60 RPM delivers the rated flow at a comfortable pace.
Where the Pattison Rotary Pump Is Used
The Pattison layout shows up wherever you need to move a viscous liquid by hand or low-speed motor without electrical infrastructure or pulsation. It dominated bulk oil dispensing for half a century and still earns its keep today in marine, agricultural, and heritage settings. The self-priming behaviour and tolerance for dirty fluid are the reasons it has not been displaced by gear or centrifugal alternatives in these niches.
- Marine: Hand-cranked bilge and fuel transfer pumps on traditional fishing vessels — the Edson Patterson-style brass rotary pumps fitted to Maine lobster boats are direct descendants of the Pattison design.
- Petroleum & Lubrication: Drum-top oil dispensers used in the 1920s through 1950s by Texaco and Shell service stations, mounted on 55-gallon barrels for engine oil decanting.
- Agriculture: Diesel and kerosene transfer pumps on farms — Lister and Petter sold Pattison-pattern crank pumps for filling stationary engine tanks from drums.
- Heritage Industrial: Restoration of cotton mill lubrication systems where original Pattison pumps still feed bearing oil to overhead line shafts at sites like Quarry Bank Mill in Cheshire.
- Chemical Handling: Hand-operated transfer of viscous chemicals — glycerine, molasses, and printing inks — at small batch facilities where electrical pumps are over-spec.
- Aviation Heritage: Refuelling cart pumps for piston-engine warbirds at airshow operations, where original-pattern brass rotary pumps move 100LL avgas without sparks.
The Formula Behind the Pattison Rotary Pump
The displacement formula tells you how much fluid one revolution of the rotor moves, and from there how much you get per minute at a given crank speed. What matters in practice is the operating range. At the low end — slow crank speeds, cold thick oil — you lose almost nothing to slip but you are limited by how fast the operator can turn the handle. At the high end the rotor speed rises and so does slip, because fluid leaks back across vane tips and end plates faster than the cavities can refill cleanly. The sweet spot for a hand-cranked Pattison is 50 to 80 RPM with SAE 30 oil at room temperature — fast enough to be productive, slow enough that volumetric efficiency stays above 90%.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Q | Volumetric flow rate delivered by the pump | L/min | gal/min |
| Vd | Displacement per revolution — geometric volume swept by the vanes in one full rotation | L/rev | in³/rev |
| N | Rotational speed of the rotor (or crank, since they are 1:1 on a Pattison) | RPM | RPM |
| ηv | Volumetric efficiency — accounts for slip flow past vane tips and end plates | dimensionless (0 to 1) | dimensionless (0 to 1) |
| e | Rotor eccentricity - used to compute Vd as Vd = 2 × π × e × D × L approximately, where D is bore diameter and L is rotor length | mm | in |
Worked Example: Pattison Rotary Pump in a brass Pattison drum pump for a vintage tractor museum
You are sizing a brass Pattison-pattern hand pump to dispense SAE 30 lubricating oil from 200 L drums at a vintage tractor museum in Saskatchewan, where volunteer staff need to fill the sumps of restored John Deere Model D engines during winter open-house events. The pump bore is 80 mm, rotor length 90 mm, eccentricity 6 mm, and the design crank speed is 60 RPM with assumed volumetric efficiency of 0.92 at room temperature.
Given
- D = 80 mm
- L = 90 mm
- e = 6 mm
- Nnom = 60 RPM
- ηv = 0.92 —
Solution
Step 1 — calculate displacement per revolution from the rotor geometry. The crescent volume swept by the vanes is approximately Vd = 2 × π × e × D × L:
Step 2 — at the nominal 60 RPM crank speed, multiply by rotational speed and volumetric efficiency:
Step 3 — at the low end of the typical operating range, 30 RPM (a tired volunteer cranking slowly with cold oil at 5°C, where ηv rises to about 0.96 because slip drops with viscosity):
That is enough to fill a 6 L Deere Model D sump in about 46 seconds — slow but predictable, and the operator is not breathing hard. Step 4 — at the high end, an enthusiastic 100 RPM, slip starts winning and ηv drops to about 0.84 because vane-tip leakage scales with the square of speed once you cross the design point:
In theory you have gained 50% over nominal, in practice the operator cannot sustain 100 RPM on a pump moving SAE 30 — the crank torque demand peaks above what one arm can comfortably push, and you will see the handle slowing on the up-stroke.
Result
Nominal output is 14. 96 L/min at 60 RPM — a 6 L sump fills in 24 seconds, fast enough that the visitor demonstration stays interesting and slow enough that the volunteer is not winded. Across the operating range the pump delivers 7.8 L/min at the slow end and around 23 L/min if you push it, with the sweet spot sitting at 60 to 70 RPM where volumetric efficiency, operator comfort, and flow steadiness all line up. If you measure 10 L/min instead of the predicted 15, the most common causes are: (1) end-plate clearance worn beyond 0.1 mm letting fluid bypass axially around the vane tips, (2) a cracked or chipped vane edge that no longer seals against the bore, often caused by a previous dry-running incident, or (3) the inlet check valve sticking partly closed because dried varnish from old oil has gummed the seat — pull the inlet fitting and inspect before assuming the rotor is at fault.
Pattison Rotary Pump vs Alternatives
The Pattison rotary pump sits in a specific niche between gear pumps and centrifugal pumps. Knowing where each one wins saves you from picking the wrong tool for a viscous-fluid transfer job.
| Property | Pattison Rotary Vane Pump | External Gear Pump | Centrifugal Pump |
|---|---|---|---|
| Typical operating speed | 30–200 RPM (hand or low-speed motor) | 500–3000 RPM | 1500–3600 RPM |
| Self-priming from dry | Yes — up to 5 m suction lift | Yes - up to 3 m once wet | No — must be flooded |
| Viscous fluid handling (SAE 30+) | Excellent — designed for it | Good but high torque demand | Poor — flow drops sharply |
| Volumetric efficiency at design point | 88–94% | 90–96% | Not applicable (not PD) |
| Pulsation in delivered flow | Low (4-vane gives smooth delivery) | Moderate (gear-mesh frequency) | Very low |
| Tolerance to dirty fluid | Moderate — vanes wear but keep working | Poor — gear teeth chip on grit | Good — open impeller passes solids |
| Maintenance interval (commercial duty) | 1000–3000 hours before vane replacement | 5000+ hours | 10000+ hours |
| Capital cost (75 mm class) | £200 × 400 (hand) / £600–1200 (motor) | £300–800 | £200–600 |
| Best application fit | Manual oil/fuel transfer, drum decanting | Continuous-duty hydraulic and lube circuits | High-flow water and low-viscosity transfer |
Frequently Asked Questions About Pattison Rotary Pump
Cold oil thickens dramatically — SAE 30 climbs from about 100 cSt at 40°C to over 1000 cSt at 5°C. The vanes have to shear that fluid out of the slots as they extend, and at high viscosity they cannot extend fast enough to seal the bore. You get partial seal, partial flow, and a heavy crank.
Two fixes: store the pump and drum somewhere heated overnight, or fit thinner vanes with stronger extension springs. Original Pattison units relied on gravity and centrifugal force only, which is why they were always rated for indoor service above 10°C.
Vane count trades pulsation against drag. A 2-vane rotor has lower internal friction and is easier to crank, but you get noticeable flow pulses twice per revolution — fine for filling a drum, annoying if the discharge feeds a sight glass or a metered dispenser. A 4-vane rotor smooths the delivery to near-continuous flow at the cost of about 15% more crank torque because you have twice the vane-tip drag.
Rule of thumb: 2 vanes for transfer service, 4 vanes when downstream equipment cares about flow steadiness or when you are running a motor drive above 100 RPM where pulse frequency starts to vibrate piping.
You are losing it to slip and air entrainment. The displacement formula assumes perfect sealing and full chamber filling on every revolution. In reality, end-plate clearance bypasses fluid axially around the vane tips, and at higher RPM the inlet cannot feed the expanding cavity fast enough so you draw a partial vacuum and pull air past the suction-side seal.
Diagnostic check: rerun the bucket test at half speed. If output per revolution rises toward 0.27 L/rev, your problem is inlet starvation — open up suction piping or shorten the lift. If output per revolution stays at 0.22, your problem is internal leakage — measure end-plate clearance with a feeler gauge, target 0.04 mm.
You can, but watch the speed. Hand-pattern Pattison pumps were designed for 60 to 100 RPM with bronze-on-cast-iron sliding contact. Drive one at 1750 RPM off a standard induction motor and the vane tips will gall within hours — surface speed exceeds the lubrication regime the bronze was designed for.
Use a gearmotor or belt reduction to keep rotor speed below 200 RPM, and add a relief valve on the discharge side. A hand pump operator notices a blocked outlet and stops cranking; an electric motor will happily generate enough pressure to split the housing.
Counterintuitively, thicker fluid is easier for a vane pump to prime once it has wetted seal — but harder to prime from dry. On the first stroke the dry vanes need a film of fluid to seal against the bore. Water films thinly and instantly; cold oil sits in droplets and the vanes slide over dry metal for the first few revolutions, drawing air past the tips.
Trick used in service stations: pour 50 ml of light kerosene or the working oil into the pump body through the discharge port before the first crank of the day. Once the seal wets, the pump pulls a vacuum strong enough to lift oil 3 to 4 m up the suction tube without further help.
Better than a gear pump, worse than a diaphragm pump. The vanes will pass particles up to about 0.5 mm without immediate damage because the vane retracts into its slot if it hits something hard — there is no rigid mesh point like gear teeth have. But repeated grit ingestion scores the bore and rounds the vane edges, and within a few hundred hours your volumetric efficiency drops below 80%.
If the source tank is dirty, fit a 200 micron strainer on the suction side. It is the cheapest insurance you will buy and it preserves the bore finish that keeps the pump efficient.
References & Further Reading
- Wikipedia contributors. Rotary vane pump. Wikipedia
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