QY Oil‑Immersed Submersible Pumps for Irrigation & Water Supply

Introduction: The Oil-Filled Advantage in Submersible Pumping

The QY series oil-immersed submersible pump is an integrated pump-motor unit designed for shallow-water drainage and irrigation applications where portability, reliability, and thermal performance are paramount. Unlike dry-motor submersible designs, the QY series features a motor cavity fully filled with insulating transformer oil, which simultaneously serves as a dielectric medium, heat transfer fluid, and bearing lubricant.

This oil-filled architecture delivers superior cooling capacity, extended bearing life, and enhanced overload tolerance compared to air-cooled or water-filled alternatives. With power ratings from 2.2 kW to 75 kW, flow capacities from 10 m³/h to 500 m³/h, and heads up to 260 meters, the QY series addresses the complete spectrum of agricultural irrigation, municipal water supply, construction dewatering, and industrial fluid transfer requirements.

1. Oil-Immersed Motor Technology: Thermodynamics & Performance

1.1 Thermal Management Principles

The defining engineering characteristic of the QY series is its oil-filled motor cavity. The thermal behavior of this system is governed by convective heat transfer from the stator windings to the oil bath, followed by conduction through the motor housing to the surrounding water. The heat transfer rate is described by:

Q_thermal = h × A × (T_winding − T_oil)

Where: 
Q_thermal = Heat dissipation rate (W) 
h = Convective heat transfer coefficient (W/m²·K); oil typically 100–300 W/m²·K vs. air at 5–25 W/m²·K 
A = Heat transfer surface area (m²) 
T_winding = Winding temperature (°C) 
T_oil = Oil bath temperature (°C)

Critical Advantage:

The oil medium achieves a convective heat transfer coefficient approximately 10–20× higher than air, enabling the QY motor to sustain higher continuous loads without exceeding insulation temperature limits. This translates to:

• 50% longer continuous operation time compared to dry-type submersible pumps under equivalent load conditions
• Significantly lower temperature rise during startup and transient overload events
• Extended insulation life per the Arrhenius equation: insulation life approximately doubles for every 10°C reduction in operating temperature

1.2 Bearing Lubrication & Life Extension

Bearings in the QY series operate fully immersed in clean transformer oil, eliminating the need for grease replenishment and providing superior lubrication film formation. The bearing life calculation follows the ISO 281 standard:

L₁₀ = (C / P)^p × (10⁶ / (60 × n))

Where: 
L₁₀ = Rated bearing life (hours); 90% reliability 
C = Dynamic load rating (N) 
P = Equivalent dynamic bearing load (N) 
p = Life exponent; p=3 for ball bearings 
n = Rotational speed (RPM)

Oil-lubricated bearings typically achieve L10 lives exceeding 100,000 hours under rated conditions, substantially outperforming grease-lubricated alternatives in continuous-duty applications.

2. Hydraulic Fundamentals: Pump Performance Equations

2.1 Hydraulic Power & Specific Speed

P_hydraulic = (ρ × g × Q × H) / (1000 × η_p)

Where: 
ρ = Fluid density (kg/m³); 1000 kg/m³ for clean water 
g = 9.81 m/s² 
Q = Flow rate (m³/s) 
H = Total dynamic head (m) 
η_p = Pump hydraulic efficiency (decimal)

Practical Calculation Example: 
For a QY65-42/2-11 pump operating at Q=65 m³/h (0.0181 m³/s) and H=42 m, with estimated η_p=0.68: 
P_hydraulic = (1000 × 9.81 × 0.0181 × 42) / (1000 × 0.68) ≈ 11.0 kW 
The installed 11 kW motor provides adequate service factor for startup torque and wear-induced efficiency degradation.

2.2 Specific Speed & Impeller Classification

N_s = n × √Q / H^0.75

Where: 
N_s = Specific speed (metric units) 
n = Rotational speed (RPM); QY series operates at 2860–3000 RPM (2-pole, 50 Hz) 
Q = Flow at Best Efficiency Point (m³/s) 
H = Head at Best Efficiency Point (m)

For the QY series, typical N_s values range from 500 to 3000, indicating single-suction, radial-to-mixed-flow impellers optimized for moderate-to-high head applications. Lower specific speed models (e.g., QY10-165/6-11, N_s ≈ 300) employ multi-stage configurations to achieve very high heads, while higher specific speed models (e.g., QY250-5-5.5, N_s ≈ 2500) utilize single-stage designs for high-flow, low-head irrigation duty.

2.3 System Head Calculation

H_total = H_static + H_friction + H_velocity

Darcy-Weisbach Friction Loss:

H_f = f × (L / D) × (v² / (2g))

Where: 
f = Darcy friction factor (Moody diagram) 
L = Equivalent pipe length including fittings (m) 
D = Pipe internal diameter (m) 
v = Flow velocity (m/s)

Velocity Head:

H_v = v² / (2g)

For QY series applications, recommended discharge velocities range from 1.0 to 2.5 m/s to balance hydraulic efficiency against erosion and noise considerations.

3. QY Series Technical Specifications

3.1 General Operating Parameters

3.2 Model Nomenclature

The QY series model designation follows a systematic coding convention: 
QY [Flow]-[Head]-[Power]

Example: QY65-42/2-11 
QY: Oil-immersed submersible pump 
65: Rated flow = 65 m³/h 
42/2: Head = 42 m; /2 indicates 2-stage impeller configuration 
11: Motor power = 11 kW

Multi-stage models (denoted by /n suffix) employ serial impeller arrangements to achieve heads exceeding the practical limits of single-stage centrifugal design.

4. Performance Data Tables

4.1 Low-Power Range: 2.2 kW – 7.5 kW

This range encompasses the most commonly specified QY models for agricultural irrigation, garden fountains, and small-scale municipal water supply.

4.2 Medium-Power Range: 11 kW – 22 kW

Suitable for medium-scale irrigation districts, water tower supply, construction site dewatering, and industrial process water.

4.3 High-Power Range: 30 kW – 75 kW

Engineered for large-scale agricultural districts, municipal water supply systems, and high-head industrial applications.

Note: All performance data represents nominal values at rated voltage, frequency, and clean water conditions (ρ = 1000 kg/m³, 20°C). Actual field performance varies with fluid properties, system geometry, and wear state.

5. Structural Design & Sealing Technology

5.1 Integrated Pump-Motor Architecture

The QY series features a vertically integrated design with the pump section positioned above the motor section:

• Pump section (upper): Single-stage or multi-stage centrifugal impeller(s) with volute casing
• Motor section (lower): Oil-filled three-phase asynchronous motor with sealed stator cavity
• Seal interface: Internal mechanical seal assembly separating the pump hydraulic chamber from the motor oil chamber

This "pump-over-motor" configuration ensures that:

• The motor operates in a thermally stable oil bath regardless of pumped fluid temperature fluctuations
• Bearing lubrication is independent of pumped fluid quality
• Motor repair or replacement does not require pump disassembly

5.2 Mechanical Seal System

The overall mechanical seal design ensures that external water cannot ingress into the motor oil chamber, internal oil cannot leak into the pumped fluid, and seal face wear is minimized by the oil lubrication film.

5.3 Noise & Vibration Characteristics

The oil-filled motor cavity provides inherent vibration damping due to the viscous properties of the insulating oil. The oil medium absorbs approximately 80% of mechanical vibration energy, resulting in operating noise levels below 55 dB(A) at 1 meter distance, reduced structural fatigue on mounting hardware, and improved operator comfort in noise-sensitive environments.

6. Application Engineering & Selection Guidelines

6.1 Duty Point Selection

The optimal pump selection positions the system operating point within the recommended flow range specified for each model. The recommended operating range is typically defined as:

Q_min ≈ 0.7 × Q_rated to Q_max ≈ 1.2 × Q_rated

6.2 Motor Service Factor & Overload Capacity

The oil-filled thermal management system enables the QY motor to sustain temporary overloads beyond the nameplate rating. The overload capacity is thermally limited by:

t_overload = (ΔT_max × m_oil × c_oil) / (P_overload − P_rated)

Where: 
t_overload = Permissible overload duration (s) 
ΔT_max = Maximum allowable oil temperature rise (K) 
m_oil = Oil mass in motor cavity (kg) 
c_oil = Specific heat capacity of oil (~2000 J/kg·K) 
P_overload = Overload power (W) 
P_rated = Rated power (W)

6.3 Typical Application Scenarios

7. Material Selection & Corrosion Resistance

7.1 Standard & Optional Material Configurations

Special Execution Codes: 
J suffix: Corrosion-resistant material configuration (stainless steel wetted parts) 
N suffix: Agricultural simplified version (economy construction, reduced features)

8. Installation, Operation & Maintenance

8.1 Installation Requirements

8.2 Oil Maintenance Protocol

The insulating oil in the QY motor cavity requires periodic monitoring:

Oil Replacement Procedure:

1. Disconnect power and remove pump from water
2. Drain existing oil through drain plug
3. Flush cavity with clean transformer oil
4. Refill with specified grade insulating oil to correct level
5. Verify seal integrity before return to service

9. Ordering Information & Custom Engineering

9.1 Required Specification Data

9.2 Custom Engineering Options

• Special voltage/frequency: 220 V, 415 V, 460 V, 660 V; 60 Hz designs
• High-temperature execution: Up to 80°C fluid temperature with Class H insulation
• Corrosion-resistant construction: Full stainless steel (CF8/CF8M) or duplex 2205 for seawater and chemical applications
• Extended cable: Custom cable lengths up to 50 m with submersible-rated insulation
• Float switch integration: Automatic level control for sump and tank applications
• VFD compatibility: Reinforced winding insulation for variable-speed operation

10. Why Choose QY Series for Your Water Management Needs?

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