CRFlex inline multistage pumps

The CRFlex is a vertical (inline) multistage centrifugal pump designed specifically to operate under variable power conditions, including solar (DC), conventional AC, or hybrid systems.

In essence:

• Inline / vertical multistage: The pump’s suction and discharge ports are on the same horizontal plane, which simplifies installation in many piping layouts.

• Non–self-priming surface pump: It must be installed such that it remains flooded (i.e., it cannot draw water from a lower level by suction alone).

• Renewable-ready / dual mode: It is equipped with a MGFlex motor / VFD drive that accepts both DC (from PV / solar arrays) and AC power, switching or blending as needed.

Because of its flexibility, CRFlex is ideal for solar water pumping systems, where grid access may be unreliable or absent. Its ability to operate on AC also allows fallback or hybrid operation when solar output is low.

To understand why CRFlex stands out, we need to look inside its architecture — the motor, hydraulic design, control electronics, and protective systems.

The MGFlex Motor (VFD)

At the heart of the CRFlex is the MGFlex variable frequency drive motor. This motor integrates a variable frequency drive (VFD) that:

• Adapts pump speed dynamically based on power input (especially from solar)

• Implements MPPT (Maximum Power Point Tracking) to extract the maximum possible energy from PV arrays under varying irradiance

• Accepts a wide voltage range (for DC: ~30–300 VDC; for AC: 90–240 VAC)

• Offers protection features such as over/under voltage, system overload, temperature protection, and more built-in (minimizing the need for external protections)

Because the drive is built into the motor, fewer external components are needed, simplifying installation and reducing the risk of wiring errors or mismatches.

Pump Hydraulic Design

The hydraulic section uses a multistage centrifugal arrangement, where multiple impellers are stacked in series. This design allows:

• Higher pressures (heads) without excessive speeds

• More compact size for a given head

• Balanced axial thrust (often via balancing holes or balance drums) — reducing bearing loads

• Flexibility in matching pump stages to required system head

Grundfos’ CR / vertical inline pumps (the base family from which CRFlex is derived) are known for high efficiency, robust construction, and laser-welded impellers in some cases.

Control Electronics & Protection

The integrated control electronics manage:

• Real-time monitoring of voltage, current, temperature

• Dynamic speed adjustment (especially when solar power varies)

• MPPT algorithms for solar arrays

• Switching between power sources (e.g. AC vs DC) if designed in hybrid mode

• Soft start / stop functionalities to prevent hydraulic shocks

• Fault detection (overload, under/over voltage, temperature)

This embedded intelligence improves system robustness and prevents damage from extremes or erratic power input.

One of CRFlex’s greatest strengths is its ability to run under multiple power regimes:

• DC Mode (Solar / Wind): When sufficient DC input from solar PV or wind is available, the pump runs directly on DC via the MGFlex driver. The VFD ensures optimal speed using MPPT.

• AC Mode (Grid / Generator): If DC supply is insufficient or unavailable, the same pump can run on AC mains or backup generator, via the internal drive.

• Hybrid / Fallback Mode: In many systems, the controller may switch automatically between DC and AC modes (or combine them) to ensure continuous operation.

This flexibility means the CRFlex system can operate in off-grid, grid-tied, or hybrid configurations — a major advantage in remote or intermittently powered settings.

Because of its adaptability, the CRFlex is suitable across many domains. Below are common use cases:

Solar Water Solutions

For homes, farms, or remote installations without reliable grid access, CRFlex enables water pumping powered by solar energy, reducing reliance on diesel generators or grid extension. Especially for:

• Domestic water supply

• Livestock watering

• Garden and greenhouse irrigation

Community / Rural Water Supply

In rural or semi-urban communities, CRFlex can serve boreholes or reservoirs to supply communities with potable water, especially in off-grid regions. Its hybrid capability helps maintain service during low solar periods by switching to backup power.

Rotor & Spray Irrigation

For agricultural irrigation systems (sprinklers, drip, micro-sprinklers, spray lines), CRFlex can supply the required pressure and flow, adjusting dynamically to solar input or fallback power. It’s well suited to medium-head irrigation schemes.

Pressure Boosting & Water Transfer

Even in grid-connected settings, CRFlex can be used as a pressure booster in buildings, or for water transfer (e.g. from low reservoirs to elevated tanks). Its ability to draw power from solar while on-grid improves energy efficiency and lowers electricity costs.

Below is a summary of key performance metrics, followed by caveats and fine print to consider when designing systems.

Flow, Head & Efficiency

The CRFlex series covers different models (e.g. CRNF1-17 Flex, CRNF3-11 Flex, CRNF5-6 Flex, CRNF10-02 Flex, CRNF15-01 Flex) each optimized for varying combinations of flow and head.

As an example, the CRF10-2 is often cited: it’s suitable for water transfer, irrigation, and pressure boosting in solar applications.

Efficiency is boosted by the motor’s variable speed operation and the MPPT algorithm under solar input, allowing operation close to optimum pump curves even under partial solar power.

Operating Envelope

• Maximum Input Power: ~1,730 W (max)

• Nominal Motor Power: around 1,250 W (for many models)

• Voltage / Current Ranges:
   • DC: ~30–300 VDC 
   • AC: 90–240 VAC, 50/60 Hz 
   • Max current: ~8.9 A in some specs

• Temperature & Fluid Conditions:
   • Pumped liquid: clear, non-aggressive fluids, free of fibers/particles (sand content < ~20 ppm) 
   • Liquid temperature: 0 °C to +40 °C 
   • Ambient temperature: up to +40 °C 
   • Max input pressure: ~25 bar

Always refer to the manufacturer’s datasheet for precise values for your particular model.

Materials & Construction

• Hydraulic parts: stainless steel for corrosion resistance and durability

• Pump head & base: cast iron in many models

• Impellers: well-engineered, often laser-welded or precision machined in high-grade materials (depending on the CR lineage)

• Seals, bearings, and auxiliary parts are selected for durability under variable-speed operation and intermittent duty conditions.

Environmental Conditions & Limits

• Must avoid cavitation (maintain sufficient Net Positive Suction Head)

• Avoid running dry or under low flow for extended periods

• Ambient and fluid extremes (e.g. freezing conditions, chemical aggressiveness) must be accounted for

• Protection and monitoring are critical (temperature sensors, overload protection)

Understanding the edge that CRFlex brings is vital when pitching to clients, designing systems, or justifying investment.

Energy Efficiency & MPPT

By dynamically adjusting pump speed according to real-time power, CRFlex efficiently uses solar input, extracting maximum from PV arrays under changing irradiance. This means less wasted solar energy and more consistent flow.

Flexibility in Power Source

The ability to run on AC, DC, or a hybrid configuration gives designers and clients far more operational flexibility:

• Off-grid (solar only)

• Grid-tied with solar supplementation

• Backup power (generator / mains) support

This flexibility reduces the risk associated with solar-only systems and helps in maintaining reliability.

Low Maintenance & Durability

With fewer external components, fewer external drives, and simpler wiring, CRFlex systems tend to require less maintenance. The robust materials (stainless steel hydraulics, cast iron housings) provide durability in harsh environments.

System Integration

CRFlex can integrate with sensors, level controllers, remote monitoring, and control systems (e.g. SCADA, IoT) — making it well-suited for modern smart water systems.

Economic & Ecological Benefits

• Lower operating cost (reduced electricity / fuel)

• Reduced carbon footprint via solar use

• Improved resilience in areas with poor grid infrastructure

• Long-term ROI through durability and efficiency

To build a reliable system around CRFlex, careful planning is essential.

Understanding Head and Flow Requirements

• Define daily water demand (volume)

• Identify system head (static + friction + elevation)

• Use pump curves of candidate CRFlex models to match flow & head

• Consider seasonal and peak demands

Sizing the Solar Array

• Determine total consumed energy over pumping hours

• Account for solar irradiance profile, system losses, and derating

• Size PV array (voltage, current, number of modules) to provide sufficient DC input for desired flow even under suboptimal insolation

• Ensure DC voltage remains within the MGFlex’s operating range

Pipeline & Hydraulic Design

• Use appropriate pipe diameters to limit friction losses

• Include check valves, non-return valves, foot valves if needed

• Design for surge protection or damping (especially for on/off operation)

• Ensure suction side NPSH (Net Positive Suction Head) is satisfied

Control & Protection Strategy

• Use level sensors for reservoirs

• Implement a supervisory controller to switch AC/DC modes

• Include alarms, emergency stop, dry-run protection

• Monitor current, voltage, temperature to avoid damage

Safety & Redundancy

• Plan for redundancy (parallel pumping) in critical systems

• Include bypass or manual failover options

• Design safe maintenance access, electrical protection (circuit breakers, grounding)

A correctly installed system maximizes performance and longevity.

Site Preparation & Mechanical Alignment

• Ensure stable foundation, vibration dampening

• Confirm vertical alignment (for inline installation)

• Ensure piping is stress-free (no misalignment, minimal bending forces)

Electrical / Solar Connections

• Proper wiring: size conductors, fuse/circuit protection

• Connect PV modules in series/parallel to meet voltage/current specs

• Ensure proper grounding and lightning protection

• Route cables to avoid shading, overheating

Start-up & Tuning

• Fill the pump and prime (if required)

• Ramp speed gradually, observe current and voltage

• Monitor behavior under different solar conditions

• Fine-tune MPPT / speed algorithms

• Set safety thresholds (over-current, over-voltage, temperature)

Monitoring & Maintenance Practices

• Periodic inspection of hydraulic parts (impellers, seals)

• Clean solar panels to maintain irradiance

• Track performance to detect degradation

• Software/firmware updates (if applicable)

• Replace wear parts as needed

Troubleshooting Common Issues

Agricultural Irrigation Project

A farm in a remote area lacked grid access. MHC designed a CRFlex-powered solar pump to deliver 20 m³/day at 50 m head. Two CRNF5-6 Flex units were paired with a PV array sized to maintain flow during cloudy days, combined with a small generator backup. The system provided consistent irrigation, reduced diesel costs, and freed farmers from manual pumping.

Community Water Supply in Remote Village

In a rural village, MHC installed a CRFlex pump to draw from a borehole and fill an elevated storage tank. With DC solar supply and AC backup, the system ensures continuous drinking water supply even during grid outages. Remote monitoring allows early fault detection and reduces downtime.

Pressure Boosting for Building Complex

In a new residential complex, MHC used CRFlex to boost pressure to upper floors. During daytime, the pump draws partially from solar panels on the rooftop; at night or low solar, it shifts to grid power. This hybrid approach reduces grid consumption and ensures stable pressure at all times.

Electromechanical Works

At MHC, our electromechanical division handles all wiring, motor controls, instrumentation, and integration. With CRFlex, we can offer turnkey solutions inclusive of pump, control, solar array, and monitoring systems.

Contracting & Turnkey Projects

In our contracting works, we integrate CRFlex systems into building projects, industrial parks, or community infrastructure. From civil foundations to final commissioning, MHC ensures seamless delivery.

Integration with Schneider Electric & Grundfos Portfolio

Through our partnerships (e.g. with Grundfos and Schneider Electric), we can pair CRFlex with smart instrumentation, SCADA systems, medium-voltage integration, and inverters, offering clients holistic and scalable solutions.

You can see more of our electromechanical work in Electromechanical Works, and our contracting projects in Contracting Works.