Why do engineers select screw pumps instead of centrifugal pumps?

Drilling mud screw pump is an ideal pump to feed the oil drilling mud decanter centrifuge,the fluids flow along with the shaft ,inner flow speed is slow. Below is the advantages of screw pump compared with centrifugal pumps.

1. Slow Speed, Simple and Rugged design 

Probably the main and overall advantage of a screw pump is its superb reliability. The simple design, open structure and slow rotation speed makes it a heavy duty pump with minimal wear that operates for years without trouble.

2.  No collection sump required = minimum head 

A screw pump 'scoops' the water directly from the surface and does not need a collection sump. This keeps the pump head to a minimum.

Why do engineers select screw pumps instead of centrifugal pumps?

3.  Long lifetime ( > 20-40 years)

Screw pumps with typical lifetimes of between 20-40 years are not unusual.

4. Pump capacity is self-regulating with incoming level

When incoming water-level goes down, at dry weather flow, the screw pump 'automatically' pumps less water. Ergo: no control system required to adapt pump performance.

5.  Easy maintenance (no 'high skilled' staff required)

A screw pump requires very little maintenance. Compared to (submersed) centrifugal pumps it is next to nothing. Besides that no 'highly skilled' maintenance staff are required which makes this type of pump very suitable for remote locations.

6. Constant high efficiency with variable capacity 

The efficiency-curve of a screw pump is flat on the top. Due to that efficiency characteristic, the screw pump offers even high efficiency when it works at 50% of its capacity.