Double Disc Pump™ vs. Rotary Pump

Double disc pumps and rotary pumps are different types of positive displacement pumps. Both types operate relatively smoothly and quietly and are ideal for dewatering feed applications and moving higher percent solids sludge through wastewater plants, but this is where the similarities end.

Double Disc Pump Technology

Our double disc pump is a reciprocating pump technology, based on a ‘non-captive’ free disc design where two discs are staged in the pump housing.

These discs work in unison to perform the duties of both the pumping element and valving element. The hydraulic interaction between the discs creates vacuum and pressure simultaneously to move fluid from suction to discharge. This hydraulic interaction provides for a very low friction inside the pump chamber, which leads to a long operating life.

By using small offset eccentric cams pinned to the drive shaft, the double disc pump has a short stroke length which produces rapid, small pulses. The use of pulsation dampeners further attenuates the pulses to provide a relatively smooth flow pattern.

This unique design allows the pump to pass larger solids (up to 2″ diameter, depending on the pump model), rags and debris that would routinely cause problems like clogging and failure on rotary pump styles.

Progressive Cavity and Rotary Lobe Technology

Though based on two different types of rotary technology, progressive cavity and rotary lobe pumps share many of the same technology style characteristics, including:

A close tolerance design that incorporates a rubbing action or very tight tolerance to generate flow
They cannot run dry for any period of time without becoming damaged
They cannot pass larger solids
Abrasive materials, like grit and sand, can drastially increase the pump’s wear rate

By design, rotary pumps experience ‘friction wear’ even on relatively clean sludges. They also lose efficiency during operation since the tolerances open up and result in a drop in flow. When this happens, pump speed needs to increase to achieve the desired flow rate. As speeds increase in rotary pumps, so do the wear rates.

The typical operating life for these pump designs can range from 3,000 to 5,000 hours before a rebuild is required. Rotary pumps are very expensive to rebuild, with spare parts costing anywhere between 50% to 100% of the initial capital purchase price of the pump. The initial investment in a rotary pump can be low, but the total cost of ownership over the lifetime of the application can increase rapidly as maintenance is required.

Lower Cost of Ownership with Double Disc Pumps

On typical applications, double disc pump technology will operate on the low end of approximately 10,000 hours and can achieve an operating life of 15,000 to 20,000 hours between rebuilds. This is three to four times the normal operating life of a close tolerance rotary pump.

Additionally, the spare parts costs are approximately 10% of the initial capital purchase price. The pump is gland-less and seal-less, with no oil lubrication or re-greasing requirements. There are virtually no routine maintenance requirements. Plus, the Maintain In Place housing design allows for quick and straight forward disassembly and reassembly in the ultimate event of parts replacement. This all leads to less downtime, lower replacement parts costs and a much lower total cost of ownership.

View details and specs of Double Disc Pumps

PUMP COMPARISON: Double Disc Pump vs. Progressive Cavity vs. Rotary Lobe Technology

Features	Double Disc Pump	Progressive Cavity	Rotary Lobe
Operation	Relatively smooth, quiet.	Smooth, quiet.	Smooth, quiet.
Maintenance	Simple design with few moving parts. Easy disc removal without disturbing piping. Housings hinged for quick access to internal components.	Close tolerance design, rubbing action between rotor and stator. Many parts to include bearings, seals, O-rings, and spacers. New designs have split stator that allow removal without removing piping, if not jammed with rags or debris.	Close tolerance design between rotors and housing. Wear plates require adjustment and replacement. Many parts, bearings, seals, O-rings, and spacers. Rotors can be replaced without removing piping, if not jammed with rags or debris.
Flow Variability	No fall off in flow as pump wears, given reciprocating design.	Flow decreases as rotor and stator wear requiring increased speed that exponentially increases wear.	Flow decreases as rotors wear requiring increased speed that exponentially increases wear.
Seals	Leak-free, maintenance-free “trunnion” sealing design requires no adjustment or seal water system.	Either a stuffing box with packing that leaks and requires adjustment or expensive flush-less mechanical seals or mechanical seals that require a seal water flush system.	Mechanical seals with pressurized oil canister lubrication or that require a seal water flush system.
Lubrication	All bearings are sealed for life with NO lubrication required.	Gear reducer requires oil and bearings require lubrication.	Gear reducer requires oil and bearings require lubrication.
Cleanliness	Seal-less "trunnion" design does not leak, requires no seal water and is maintenance free.	Packing gland leaks during operation or seal water system leaks.	Packing gland leaks during operation or seal water system leaks.
Abrasive Material	Long lasting given no close tolerances in pumping chamber.	Poor life given close tolerance rubbing action between rotor and stator.	Poor life given close tolerances within pumping chamber between rotors and housing.
Solids, Rags and Debris Handling	Depending on model, can pass up to 2” solids and line size semi-solids to include stringy material, rags and debris.	Very poor, large solids create damage, stringy debris gets wrapped around rotating shaft.	Very poor, large solids create damage; stringy debris gets wrapped around rotors. Requires routine cleaning.
Run Dry Capability	Runs dry indefinitely without damage.	Cannot run dry, will seize quickly.	Can only run dry for a few minutes before damage when elevated connection flanges are used.
Drive Type	Simple V-belt and pulley drive system with electric motor.	Normally direct coupled to gear reducer and electric motor.	Normally direct coupled to gear reducer and electric motor.
Power Consumption	Lower HP requirement on same application, no break-out torque requirements.	Higher HP requirement for break-out torque due to close tolerances.	Similar to higher HP requirement for break-out torque due to close tolerances.
Space Requirements	Compact with small footprint. Elevated for maintenance.	Long and narrow. Low to ground.	Small footprint when connection flanges are not used.
Operating Life Between Rebuilds	Typically between 10,000 hours and 25,000 hours.	Typically between 3,000 hours and 5,000 hours.	Typically between 3,000 hours and 5,000 hours.
Spare Parts	Inexpensive. Infrequent replacement. All parts in stock, same day shipment guaranteed.	Expensive, frequently approaches cost of new pump. Frequent replacement due to wear characteristics.	Expensive, frequently approaches cost of new pump. Frequent replacement due to wear characteristics.
Warranty	Two (2) years.	One (1) to two (2) years depending on manufacturer.	One (1) to two (2) years depending on manufacturer.
Origin of Manufacture	Warrington, PA USA.	Over 100 different brands, both domestic and foreign. Large variations in quality.	Over 100 different brands, both domestic and foreign. Large variations in quality.