Worked Progressive Cavity Pump Sizing Example – 40 GPM Raw Sewage at 125 PSI
This worked example follows a complete progressive cavity pump selection from application data through final element size, stage count, operating speed, drive end and horsepower.
The application is raw sewage at 40 GPM, 125 PSI differential pressure, medium abrasion and 0.2-inch maximum solids.
Application Data
| Parameter | Application Requirement |
|---|---|
| Flow | 40 GPM |
| Fluid | Raw sewage |
| Viscosity | Approximately 1 cP |
| Suction pressure | 5 psig |
| Discharge pressure | 130 psig |
| Differential pressure | 125 psig |
| Abrasion | Medium |
| Maximum particle size | 0.2 in. |
| pH | 6–8 |
| Temperature | Ambient, approximately 70°F |
| Duty cycle | 18 hours/day, intermittent operation |
Step 1 – Select the Basic Pump Model
The application uses raw sewage, which behaves essentially like water at approximately 1 cP but contains some solids. The worked selection chooses a Moyno 2000 Series industrial pump with a standard round suction housing rather than an open-throat inlet.
Step 2 – Select Materials of Construction
The fluid pH is between 6 and 8, so the application is treated as non-corrosive for this example. The selected material combination is cast-iron body with carbon-steel internals, designated CDQ in the example configuration.
The stator selection uses the standard industrial nitrile family represented by the Q elastomer code in the selection tables.
Step 3 – Determine the Minimum Element Size from Solids
The largest expected solid is 0.2 inch. The smallest available 2000 Series element in the example is the 008 element, and its published particle-size capability exceeds 0.2 inch.
Result: the 008 element is acceptable from a particle-size standpoint.
Step 4 – Adjust for Medium Abrasion
The raw sewage is classified as medium abrasion. For the 2000 Series 008 element, the abrasion table gives a suggested maximum speed of approximately 528 RPM and a corresponding capacity of approximately 42 GPM.
The required duty is 40 GPM, so the 008 element can still meet the required capacity while remaining within the medium-abrasion speed recommendation.
Result: retain the 008 element.
Step 5 – Check Viscosity
The fluid viscosity is approximately 1 cP, essentially water-like. No high-viscosity speed correction is required for this example.
Result: abrasion, not viscosity, controls the preliminary speed limit.
Step 6 – Determine the Number of Stages
For the selected industrial elastomer group, 008 element and medium abrasion, the recommended pressure per stage is 43.5 PSID.
Stage Calculation
125 PSI ÷ 43.5 PSI/stage = 2.87 stages
A 2.87-stage pump is not a standard offering, so the selection must move to the next higher available configuration.
Result: select a 4-stage 008 pumping element.
Step 7 – Determine Actual Pump Speed
Using the applicable 2000 Series performance curve at 125 PSI, the operating point for approximately 40 GPM occurs at about 500 RPM.
This is below the medium-abrasion maximum of approximately 528 RPM for the 008 element, so the selected operating speed is acceptable.
Result: approximately 500 RPM.
Step 8 – Select the Drive End
The selected pumping configuration is a 4-stage 008 element. The drive/element pressure table shows that an E drive end with an 008 element is suitable for substantially more than the required 125 PSI differential pressure.
The worked example therefore selects the E drive end.
Interim pump configuration: 4E008G1-CDQ.
Step 9 – Determine Horsepower
The performance-curve calculation in the worked example gives approximately:
| Horsepower Component | Calculated HP |
|---|---|
| Hydraulic and friction horsepower | 4.5 HP |
| Drive-end horsepower | 0.75 HP |
| Total calculated horsepower | 5.25 HP |
The worked selection then compares 5.25 HP with the minimum recommended horsepower from the performance curve. The curve requires approximately 8.4 HP for the sizing check, so 8.4 HP is used for the drive-capacity calculation.
At 500 RPM:
Drive-End Horsepower Check
8.4 HP ÷ 500 RPM × 100 = 1.68 HP per 100 RPM
The E drive end with carbon-steel internals is rated at 3.8 HP per 100 RPM, so the E drive remains acceptable.
Because the required motor horsepower is 8.4 HP and the next available standard motor size is used, the worked example moves to a 10 HP drive.
Final Pump Selection
| Selection Item | Final Result |
|---|---|
| Pump family | Moyno 2000 Series / ACCA-compatible configuration |
| Element size | 008 |
| Stages | 4 stage |
| Drive end | E |
| Configuration | 4E008G1-CDQ |
| Operating speed | Approximately 500 RPM |
| Required flow | 40 GPM |
| Differential pressure | 125 PSI |
| Calculated pump horsepower | 5.25 HP |
| Minimum horsepower used for sizing check | 8.4 HP |
| Selected drive motor | 10 HP |
| Materials | CDQ — cast-iron body / carbon-steel internals / Q elastomer selection used in the example |
What This Example Demonstrates
This selection shows why progressive cavity pump sizing cannot be based on flow alone. A 40 GPM requirement first appears modest, but the final configuration is controlled by several interacting limits:
- 0.2-inch solids establish the minimum usable element size.
- Medium abrasion limits the acceptable operating speed.
- 125 PSI differential pressure drives the selection to four stages.
- The performance curve establishes the actual operating speed near 500 RPM.
- The E drive end must satisfy both pressure and horsepower-per-100-RPM limits.
- The final motor size is selected above the calculated minimum horsepower.
Related Engineering References
Maximum Particle Size & Solids Handling →
Abrasive Fluid Speed Selection →
Viscous Fluid Speed Selection →
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