Choosing a Pump for Honey Transfer — It's Not Just Viscosity, Flow Rate Decides
When selecting pumps for honey, syrup, and other high-viscosity media, many engineers prefer to use one pump model across multiple duties to simplify procurement and maintenance. In practice, however, the deciding factor is often not viscosity but flow rate. A recent honey transfer project illustrates this well.
Project Background
Two honey transfer duties:
Parameter Duty 1 Duty 2
Medium Honey Honey
Flow rate 500 L/H 0.3–0.6 m³/h (300–600 L/H)
Temperature / Pressure Ambient Ambient
Motor Standard Standard
Viscosity 3000 cP 1000–1800 cP
For Duty 1, a CYB1.6-2y rotary lobe pump was selected: 25 mm port size, 304 stainless steel wetted parts, 1.1 kW motor with VFD, operating at 140 rpm.
For Duty 2, the recommendation was to switch to a small-flow magnetic drive pump, size 12.0, rather than reuse the CYB1.6-2y.
Why Duty 2 Needs a Small-Flow Pump
At first glance, Duty 2 looks easier — the viscosity is lower, so the honey flows more readily. But the critical difference is the flow range: 0.3–0.6 m³/h, far below the 1.6 m³/h maximum of the CYB1.6-2y.
1. Flow range mismatch
A
rotary lobe pump is a positive displacement pump, so flow varies linearly with speed. Running a 1.6 m³/h pump at 0.3 m³/h means dropping speed dramatically. If Duty 1 runs at 140 rpm, Duty 2 would need to operate below roughly 30 rpm. At such low speeds, pulsation becomes more pronounced and flow stability suffers.
2. Internal slip grows at low speed
Although Duty 2's viscosity drops to 1000–1800 cP, the flow is very small. The rotor clearances in a large pump are sized for higher displacement. At low speed and small flow, internal recirculation becomes a larger fraction of total output, and actual delivered flow can fall short of the setpoint.
The specified magnetic drive pump, size 12.0, is designed for small-flow, medium-viscosity duties. It handles 1000–5000 cP media well and delivers 0.3–0.6 m³/h with better metering accuracy than a large rotary lobe pump throttled down to minimum speed.
The Takeaway
The core challenge for Duty 2 is not viscosity — it is flow rate that is simply too small. Since the CYB1.6-2y already covers the higher-flow Duty 1, there is no reason to force Duty 2 onto the same platform. A small-displacement magnetic drive pump with VFD or servo speed control is the more appropriate choice for the 0.3–0.6 m³/h range.
When selecting pumps for honey and other high-viscosity media, match the pump's displacement to the required flow rate first, then confirm viscosity and material compatibility. An oversized pump will not save money — it will cost you in stability, accuracy, and reliable output.
