A Note on Pump Selection (1)

Selecting Centrifugal or Reciprocating?

Although centrifugal pumps are the first option in a pump selection process because of lower cost, simplicity, reliability and smooth flow characteristics, there are some occasions when positive displacement pumps (reciprocating or rotary) might be more desirable. These occasions can be classified as follows:

1. Very high head, especially when combined with a low capacity; 
2. Low speed drivers;
3. High efficiency requirements over a range of pressures;
4. Constant capacity requirements over a wide range of heads;
5. Variation of head requirements over a wide range;
6. High viscosity;
7. Emulsification;
8. Accurate control of flow requirement in low flow applications.

There are some notes that should be considered together with the above-mentioned selection criteria:

• There is a specially designed type of centrifugal pumps for low-flow, high-head applications. This is high speed integrally geared vertical inline pump which is identified by API classification OH6 and is known as “Sundyne” in industry. As a guideline, reciprocating pumps are selected for low-flow, high-head applications when service conditions are outside the hydraulic coverage range of Sundyne pumps as presented in below Figure. Of course NPSH and minimum flow requirements should be carefully investigated when selecting a Sundyne pump.
• Although initial costs of small reciprocating pumps are competitive with centrifugal pumps, for capacities over 200 gpm they are usually more expensive.
• When service requirements permit using either a centrifugal or a reciprocating pump, the operation and maintenance cost should be carefully considered. Maintenance costs of reciprocating pumps are usually higher because of moving parts, valves and sliding contacts.
• For viscosities above 500 SSU and below 8000 SSU usually reciprocating pumps are considered. For viscosities above 8000 SSU rotary pumps are the better options.

 Sundyne pumps hydraulic coverage