Equal Wall Thickness Screw Pumps
Cat:Single Screw Pumps
Screw pumps equipped with equal wall thickness stator, the same kind of pump specifications pump flow, and pressure are increased. The equal wall thic...
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A single screw pump (also known as a progressive cavity pump) performs three primary functions: metered flow of viscous fluids, low-pulsation transfer of shear-sensitive materials, and self-priming lifting of multi-phase mixtures. Unlike centrifugal pumps, a single screw pump delivers a constant, linear flow rate directly proportional to its rotational speed—typically achieving volumetric efficiencies above 95% across a wide pressure range.
This unique performance makes it indispensable in industries ranging from oil & gas to food processing and wastewater treatment. Below, we explore each function with measurable data and practical examples.
Single screw pumps function as positive displacement metering devices. Each rotation displaces a fixed volume (from 0.005 to over 2,500 liters) regardless of discharge pressure. Flow rate accuracy typically stays within ±0.5% to ±1% when properly sized.
In enhanced oil recovery (EOR), operators inject polymer solutions with viscosities up to 10,000 cP. A single screw pump doses at precisely 2.5 L/min against pressures of 40 bar (580 psi). Centrifugal pumps would lose efficiency above 1,000 cP and cannot maintain linear dosing. The result: consistent polymer injection reduces chemical waste by up to 15% annually per well pad.
The gentle pumping action of a single screw pump is one of its most valued functions. Unlike piston or lobe pumps, the fluid moves axially without turbulence or rapid pressure spikes. Shear rates are typically below 200 s⁻¹—comparable to low-shear mixing. This preserves product integrity for delicate materials.
In a controlled test pumping yogurt cultures (a shear-sensitive biological fluid), a single screw pump maintained viable cell counts above 95% after 10 hours of recirculation. A lobe pump under identical conditions reduced viability to 72%. For food processors, this means longer shelf life and better product consistency.
| Pump Type | Maximum Shear Rate (s⁻¹) | Pulsation Amplitude (% of flow) | Product Degradation after 5 cycles |
|---|---|---|---|
| Single Screw Pump | 180 | ±2% | 3% loss |
| Twin-Lobe Pump | 450 | ±8% | 12% loss |
| Centrifugal Pump | 2,000+ | N/A (non-positive displacement) | 45% loss (emulsion broken) |
Single screw pumps can lift fluids from suction lifts as high as 8.5 meters (28 feet) of water column under dry conditions, and 9.5 meters (31 feet) when primed. More importantly, they handle gas, liquid, and solid mixtures simultaneously—a function called multi-phase pumping. Gas volume fractions (GVF) up to 80% are possible without vapor lock.
In a municipal treatment plant, scum contains 40% air, 55% water, and 5% grease/solids. A single screw pump transfers this mixture from a DAF (dissolved air flotation) tank to a digester at 12 m³/h. Centrifugal pumps lost prime within 10 minutes, while diaphragm pumps clogged every 2 hours. The single screw pump ran for 2,000 hours without failure, reducing maintenance costs by €8,000/year.
Yes, but only for short durations (30-60 seconds). The stator (typically elastomer) requires fluid lubrication and cooling. Extended dry running damages the stator and rotor. For applications with intermittent dry periods, specify stators made of high-temperature elastomers (e.g., FKM or HNBR) or add a dry-run protection sensor.
Single screw pumps offer volumetric efficiency between 85% and 98% under normal operating conditions. Overall mechanical efficiency (including motor and gearbox) ranges from 55% to 75%, which is 10-20% higher than centrifugal pumps when handling viscosities above 1,000 cP.
Unlike centrifugal pumps, flow rate of a single screw pump remains nearly constant with viscosity changes. Doubling viscosity from 1,000 cP to 2,000 cP reduces flow by less than 2% at constant speed. This makes them ideal for dosing additives where feed viscosity varies with temperature.
A single-stage single screw pump typically delivers 6 to 12 bar (87 to 174 psi) differential pressure. Each additional stage adds similar pressure. For high-pressure applications like reverse osmosis feed (up to 40 bar), use a 4-stage or 6-stage configuration. Each stage contains one set of rotor-stator cavities.
To select the correct single screw pump for your function, evaluate three parameters against the table below:
| Primary Function | Key Design Feature | Typical Material Pairing | Performance Target |
|---|---|---|---|
| Metering/dosing | Close-tolerance rotor/stator (interference fit 0.1-0.3 mm) | Hard chrome rotor + NBR stator | Flow accuracy ±0.5% |
| Shear-sensitive transfer | Large cavity (L/D ratio < 3:1) & low speed (50-200 rpm) | 316L rotor + food-grade EPDM stator | Shear rate < 200 s⁻¹ |
| Multi-phase (gas + solids) | Open throat hopper or auger feeder + hard-faced rotor | Stellite rotor + HNBR stator (abrasion-resistant) | Handle 80% GVF + 15 mm solids |
For most industrial applications, the single screw pump’s combination of metering precision, low shear, and multi-phase capability makes it the most versatile positive displacement pump. When your fluid is too thick for centrifugal pumps or too delicate for piston pumps, a single screw pump is the functional answer.