Progressive Cavity Pump vs Screw Pump - Liberty Process

The Progressive cavity (PC) pump is a positive displacement pump. The pumping element is a single "screw" that has a round cross section and rotates inside of a stator made of rubber which has a double cross section. Cavities are created between the geometry of the rotor and stator that travel along the length when rotated, to move the fluid. There is slight interference fit between the rotor and stator which seals the cavities. The rotational speed of a progressive cavity pump is typically determined by the size of the pump and pumping application. Smaller pumps tend to run at higher RPM's, Some PC pump designs run at direct motor speeds like RPM. Most PC pumps run at reduced speeds, lower than 500 rpm. The speed is reduced by using a gearbox or v-belts between the pump and the motor.

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A screw pump typically refers to a 3 rotor or 2 rotor screw pumps. These differ from a progressive cavity pump in that they are typically used for pumping lubricating fluids. Screw pumps are all metal pumps and are typically used for nonabrasive fluids. They also can pump at much higher discharge pressures that a progressive cavity pump. Screw pumps typically run at direct motor speeds.

Advantages of a Progressive Cavity Pump

The advantages of a progressive cavity pump are the ability to pump highly abrasive fluids and fluids with large solids and have reasonably long service life on these difficult pumping applications. The low speed results in low velocities through the pump and this helps extend the pump service life on abrasive applications. Progressive cavity pumps are also used for applications where the flow varies and the pump flow can be easily changed by changing the pump speed, typically by using a variable frequency drive (VFD). The progressive cavity pump is a great, low cost alternative for applications that require a measured flow. Another advantage of a progressive cavity pump is that when it is turned off, the fluid will not flow through it, it acts like a valve in this way.

Advantages of a Screw Pump

The advantages of a screw pump are they can pump at extremely high pressures. They are also very good for oil-based fluids like lube oil, fuel, oil, hydraulic oil and any hydrocarbon in refinery applications like asphalt. Screw pumps are very mechanically efficient, meaning they require much less power than a centrifugal pump, they are also very quiet in operation where noise is a concern and when properly applied, they are very reliable for long service life. High pressure applications are typically hydraulic fluid, Bearings on heavy machinery and as high-pressure coolant pumps for machine tool applications.

Advantages of Both

An advantage of both progressive cavity pumps and screw pumps is they can easily pump about the same flow no matter what the discharge pressure is or if the discharge pressure varies. Centrifugal pumps have dramatic changes in flow with changes in discharge pressure. They PC and screw pumps both have little or no pulsation. The disadvantage of both progressive cavity pumps and screw pumps is that they can not be run dry or they will be damaged. They also can not pump against a closed discharge or they will be damaged.

Pumps and pump parts offered for sale by Liberty Process Equipment, Inc. are made in the United States, Germany, India, Spain, Argentina and Brazil.

*Liberty Process Equipment, Inc. is not affiliated with nor distributor for Seepex®, Allweiler®, Moyno®, Tarby®, Netzsch®, or Continental Inc.® All referenced product names, brands, models, or part numbers is solely for identification purposes. Seepex® is a registered trademark of Seepex®. Moyno® and Tarby® are registered trademarks of Robins and Myers® and NOV®, Netzsch® Incorporated is a registered trademark of the Netzsch® Group, Allweiler® is a registered trademark of Colfax® Corporations Continental® Pumps is a Trademark of Continental® Ultra Pumps.

Screw pumps are used to transport high-viscosity liquids, pastes, neutral or corrosive liquids, liquids mixed with air, liquids with foam, and even medium containing fiber solid components. The screw pump is also known as Progressing Cavity Pump, Mono Pump, and Rotary Positive Displacement Pump, according to the different structural form which are divided into single screw pump, double screw pump and three screw pump.

By selecting different materials like carbon steel, AlSl 316 stainless steel, 22Cr duplex and 25Cr duplex stainless steels to suit a wide range of applications, the goal is to provide the best viscous medium handling solution for end users. Progressive cavity pumps perfectly handle with viscous mixtures in petroleum, water management, hydrocarbon sludge, and other industries.

A single screw pump belongs to positive displacement pumps, whose wetted parts are composed of stator and rotor. The rotor is a screw with large lead, large tooth height and small inner diameter of thread. The stator is an elastic bushing with double-headed spiral. The rotor and the stator cooperate with each other to form a sealed cavity without communication. When the rotor turns inside the stator, the cavity progresses spirally along the axis of the pump without changing either shape or volume.

Working principle of a single screw pump

When the rotor rotates in the stator, the sealing cavity moves from the suction end to the discharge end, and the high viscosity medium transported is discharged continuously in the sealing cavity. Screw pumps are reversible and could discharge mud or sludge in reverse.

The structure of the single screw pump

Application

Waste water treatment

The sludge produced in all aspects of the sewage treatment plant, including concentrated sludge, floating sludge, dilute sludge and dehydrated sludge, which are transported and treated by single screw pumps. The single screw pump meets the requirements of complete closure, no leakage, no odor, continuous operation and automatic management when conveying sludge in medium and short distance.

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Coal water mixtures, coal water slurry and coal water transportation

The coal water slurry refers to the mixture of pulverized coal and water, and a certain amount of additives are added. The phenomenon of soft precipitation and stratification should be avoided during the transfer of coal water mixtures. The single screw pump is the best choice for coal water mixtures transportation because the volume of the pump chamber remains constant and the medium is almost not stirred in the pump.

Pulp, paper and board industry

Stoichiometry; Coating and coloring process; 10~25% medium concentration pulp transport

Oil, gas, crude oil and other petroleum industry

Oil and gas mixed transport; 

Oil-water separation and waste oil recovery system;  

Polymer transport.

All kinds of chemical paste; 

All kinds of milk; 

All kinds of suspension; 

All kinds of gas-containing and solid-containing liquids; 

All types of media not subject to agitation and shearing.

Production and preparation of titanium dioxide, kaolin, calcium carbonate, etc. in mineral engineering, feed the swirling fluid and filter body; Chemical dosing; Loading and grouting

The flow parts are made of food-grade stainless steel material, which is used in food industry dairy products; Fruit juice, fruit puree, vegetable pulp; Ground meat and condiments.