# Key Points for Selection of Multistage Centrifugal Pumps for Paper Mills

1.Confirm operating condition parameters first

1.1 Medium: clean water / white water / thick white water. Confirm solid content, pH value, temperature and impurity particle size. Paper mill white water contains fibers and abrasive particles, so it cannot be selected as a clean water pump. 

1.2 Flow (m³/h) and Head (m), with 10%~20% margin reserved. 

1.3 Inlet & outlet pressure, installation type and continuous operation duration. Most paper mills operate 24h non-stop.

2.Pump structure selection

2.1 For clean water and condensate water: use segmental multistage centrifugal pumps with cost-effective performance. 

2.2 For media containing fibers and a small amount of fine solids (paper mill white water): bolted-barrel multistage centrifugal pumps with wear-resistant structure are preferred. Wear-resistant materials shall be adopted for impellers and wear rings to reduce fiber clogging and abrasion. 

2.3 Material matching:

a.Clean water: cast iron casing + stainless steel impeller

b.White water & mild corrosion: ductile iron casing, 304 stainless steel for impeller / wear ring; upgrade to 316L for corrosive white water 2.4 Mechanical seal: Paper mill media are prone to clogging. Cartridge mechanical seals with flush plan (Plan11/Plan21) are preferred to prevent fiber entanglement and seal damage due to dry running.

3.Motor and drive 

3.1 Select the motor according to the calculated shaft power, taking medium density and margin into account. Reserve safety margin for motor power for long-term continuous operation in paper mills. 

3.2 Voltage and frequency shall match the on-site power grid. If variable frequency is required to adjust flow and head, use inverter-duty motor and verify motor heat dissipation. 

3.3 Protection class no less than IP55 due to high humidity in paper mill workshop. Explosion-proof requirement to be confirmed according to site area.

4.Performance and NPSH verification 

4.1 Verify Net Positive Suction Head Available (NPSHa) and Net Positive Suction Head Required (NPSHr). Ensure NPSHa＞NPSHr+0.5~1.0m to avoid cavitation. 

4.2 The operating point shall be within the high-efficiency range of the pump. Multistage pumps shall not run under low flow rate for a long time to prevent backflow, vibration and temperature rise.

5.Auxiliary matching requirements 

5.1 Bearing lubrication: oil lubrication is more suitable for long-time continuous operation.

5.2 Piping: install flexible joints and pressure gauges at inlet and outlet; reduce elbows and throttling on suction pipeline to lower cavitation risk. 

5.3 Spare parts: stock consumables including wear rings, mechanical seals and bearings.

6.Selection prohibitions

6.1 Ordinary clean-water multistage pumps cannot be directly used for white water service. Fibers will rapidly abrade wear rings and cause quick head drop. 

6.2 Long-term low-flow operation deviating from rated condition is forbidden, as multistage pumps tend to generate internal backflow and severe vibration. 

6.3 Insufficient NPSH leads to impeller erosion, high noise and drastically shortened pump service life.