QUICK ANSWER
Match flow and total dynamic head before selecting stage count or motor power
A CDLF vertical multistage pump should be selected around the required flow at the system's total dynamic head, then reviewed for inlet pressure, system pressure, liquid temperature, wetted-material suitability, stage count and motor duty. The number of stages is not a standalone starting point: it is the result of matching a multistage pump curve to the required operating point. A sound selection also considers whether the application is pressure boosting, RO feed, water treatment, industrial water supply or circulation, because the upstream and downstream system conditions are different.
Do not calculate a final model from one pressure figure or a pipe diameter alone. Confirm the real operating point and configuration with the relevant product data before purchase or installation.
Start with required flow, not a nominal connection size
Required flow is the volume the system needs over its real operating range. For a booster or supply system, identify normal demand and the possible minimum and maximum demand. For an RO or water-treatment package, distinguish the process feed requirement from recirculation, flushing or intermittent demand. For circulation, identify the design circulation flow and the conditions that can change resistance.
Connection size may influence pipe velocity and losses, but it does not set the pump duty by itself. Flow must be paired with the total dynamic head at that flow.
What belongs in total dynamic head?
Total dynamic head is the system duty that the pump must overcome at the required flow. It commonly includes the difference in static elevation where applicable, discharge pressure requirement, inlet pressure contribution, friction loss in pipes and fittings, and losses across equipment such as filters, valves, treatment components or heat exchangers. The system pressure must be expressed consistently with the head calculation.
| Input | Why it matters | Check before selection |
|---|---|---|
| Required flow | Defines the target operating point | Normal, minimum and maximum process demand |
| Static elevation | Can add to the pumping duty | Liquid-level and discharge-level conditions |
| Pipe and equipment losses | Rise with system flow | Pipe route, valves, filters and treatment equipment |
| Inlet pressure | Affects the pressure balance | Source condition and permitted inlet arrangement |
| System pressure | Sets discharge requirement | Required pressure at the defined control point |
How do stage count and motor power follow the operating point?
In a vertical multistage pump, the selected stages must provide the required head at the required flow on the applicable curve. More stages are not automatically better; an operating point should be reviewed against the pump's intended range and the system's likely variation. Motor power is then assessed from the selected hydraulic duty, liquid properties and the confirmed configuration. Avoid treating a motor rating as a substitute for duty calculation.
For the current product range, start with the vertical multistage pump category. It provides the appropriate CDLF family entry point for a final model and configuration discussion.
How application type changes the questions
Water pressure boosting
Define the required pressure at the control point, source pressure variation, peak flow and any control method. A changing source or demand can move the operating point.
RO systems and water treatment
Define feed flow, required pressure at the relevant component, pre-treatment losses, water temperature and possible filter fouling allowance under the package design.
Industrial water supply and circulation
Identify the process flow, elevation, pipe route, valves and equipment losses. For circulation systems, confirm whether fluid temperature, additives or system pressure change the pump configuration review.
Common selection mistakes
- Using flow alone without calculating total dynamic head.
- Adding stages simply to create a pressure margin without reviewing the operating point.
- Ignoring inlet pressure or source variation.
- Omitting filters, valves and treatment equipment from friction-loss review.
- Using a motor power figure as a complete pump selection method.
- Assuming water-treatment or circulation liquid conditions match clean, ambient water without confirmation.
Practical CDLF inquiry checklist
Provide required flow, system head or required discharge pressure, inlet pressure, source arrangement, liquid name and temperature, operating schedule, power supply, control needs and the full pipe/equipment layout. If the system includes RO equipment, filtration or heat exchange, state the relevant pressure-loss data. Shanghai Shangcheng Pump & Valve Manufacturing Co., Ltd. can then relate the duty to the existing multistage pump range without assuming an unsupported stage count or performance point.
FAQ
How do I know how many stages a CDLF pump needs?
Determine the required flow and total dynamic head first, then review the applicable pump curve and configuration. Stage count follows the operating point.
Can I select from discharge pressure only?
Not reliably. Pressure must be considered with required flow, inlet conditions and system losses.
Why does inlet pressure matter?
It affects the pressure balance across the system and can affect the pump's inlet operating conditions.
Is a CDLF pump only for water boosting?
No. Vertical multistage pumps can be considered for several clean-liquid duties, including boosting, water treatment, industrial supply and circulation, subject to the actual liquid and operating conditions.
Should motor power be chosen before the pump stages?
No. Establish the hydraulic duty and appropriate pump configuration first; then review motor power for that confirmed duty.
Review a multistage pump duty
Send your flow, pressure and system details to shscpv@gmail.com.