How to select a horizontal self-priming centrifugal oil pump？

1. First, confirm the medium and operating conditions (to determine if the pump can be centrifugal self-priming).

The following must be clearly stated:

Oil type: diesel, gasoline, kerosene, lubricating oil, heat transfer oil, etc. (whether it is volatile, whether it contains gas/water/impurities).

Temperature range: minimum/maximum (affects viscosity, vaporization pressure, seals, and materials).

Viscosity (cSt): Very critical.

Higher viscosity significantly reduces the flow rate, head, and efficiency of the centrifugal pump, and also worsens its self-priming performance.

Empirically: >50–100 cSt often recommends evaluating gear pumps/screw pumps; if a centrifugal pump is insisted upon, viscosity correction should be performed, and a larger pump size or speed reduction should be selected.

Solid content: Sand/iron filings accelerate wear, requiring filters or wear-resistant designs.

Leakage tolerance: Determines whether a mechanical seal, double-end seal, or magnetic pump solution is used.

2. Define Flow Rate Q and Head H (Pump “Operating Point”)

Flow Rate Q: Normal/Maximum/Minimum (m³/h or L/min).

Head H: Not simply “vertical height,” it must include:
Static head (including suction head/discharge head) + Pipeline friction loss + Local losses at elbows and valves + Pressure drop from filters/flowmeters/loading arms + Outlet back pressure (e.g., tank pressure).

Aim for the operating point as close as possible to the BEP region of the pump curve to avoid prolonged low flow rates (self-priming pumps are more prone to overheating at low flow rates).

3. Self-priming Capacity and Suction Pipeline (Determines “Whether it can be drawn up”)
The most common pitfalls with self-priming pumps are:

Pay attention to the self-priming height/self-priming time provided by the manufacturer, but consider the conditions (medium, speed, pipe diameter, whether it’s the first time priming). You need to calculate/confirm:
Actual suction height (height difference between liquid level and pump centerline)
Suction pipe losses (small pipe diameter, many bends, and clogged filters can all cause self-priming failure)
Oil volatility: Gasoline/light oils are more prone to cavitation and vapor lock, making self-priming more demanding.
Suction side recommendations:
Diameter not smaller than the pump inlet, as short, straight, and with few bends as possible
Suction pipe sloping upwards towards the pump to avoid air pockets
Whether a foot valve/check valve is needed: Many self-priming pumps do not require a foot valve, but long suction pipes or conditions prone to backflow may still require a check valve
Reserve a priming/exhaust port; priming should be performed as required during initial startup.
Reminder: Self-priming ≠ being able to pump dry for a long time. Most self-priming centrifugal pumps still require a certain amount of liquid in the pump chamber to form a liquid ring in order to establish a vacuum.

4. Structure selection: Choose the right “self-priming type”
Common horizontal self-priming centrifugal oil pump structures:

Gas-liquid separation external mixing type/self-priming chamber structure (common self-priming pumps): Suitable for intermittent pumping, where air may be introduced during suction.

Vacuum-assisted priming: More stable with high suction head and long pipelines (but system complexity).

Alternatives: Vane pumps/gear pumps/screw pumps are often more suitable for high viscosity or when stronger self-priming and stable metering are required.

5.Materials, Seals, and Explosion-proof (essential for oil pumps)

Materials: Commonly used for pump bodies are cast iron/ductile iron; stainless steel can be selected for sulfur-containing or corrosive materials, or for applications requiring higher cleanliness. Seal materials must be matched to the oil type and temperature (NBR/FKM/PTFE, etc.). Mechanical Seal: Normal Operating Conditions: Single-face mechanical seal. Volatile/Zero Leakage Required/Environmentally Friendly: Consider double-face mechanical seals (API Plan) or magnetic pumps (but magnetic pumps also require attention to viscosity and dry-running risks). Explosion-proof: Motors generally need to meet site requirements: Ex d / Ex e, etc. (select according to the area’s explosion-proof rating). Static grounding, coupling protection, venting, and ventilation should also be considered.

6. Temperature Rise, Backflow, and Protection (Self-priming oil pumps are prone to “stuck pump overheating”) Oils with low specific heat and high viscosity are more prone to temperature rise:

Long-term operation with the outlet valve partially closed is not recommended; add minimum flow backflow/bypass if necessary.
Configuration: Outlet pressure gauge, temperature protection, dry-running/idle-running protection (liquid level interlock, power/vibration monitoring, etc.)

7. Key acceptance points (to be specified in the technical specifications before purchase): Performance curves for your medium at different viscosities and temperatures (Q-H, efficiency, power, NPSHr, self-priming height/time); Allowable suction head and self-priming time (with piping conditions); Sealing type and leakage rating; Explosion-proof certificate, material report, test report; Spare parts list (mechanical seals, bearings, wear rings, etc.).