How to Select the Right Metering Pump: Solenoid vs. Mechanical vs. Hydraulic Diaphragm

Selecting the correct metering pump type is critical for dosing accuracy, chemical compatibility, and long-term reliability. This guide compares the three main drive technologies used in diaphragm metering pumps: solenoid, mechanical (motor-driven), and hydraulic diaphragm.

Solenoid diaphragm metering pumps use an electromagnetic coil to drive the diaphragm directly. This design is compact, low-cost, and well-suited for flow rates up to 60 L/h at back pressures up to 16 bar. The stroke frequency is adjustable via a potentiometer or external 4-20mA signal, making solenoid pumps ideal for swimming pool chlorination, drinking water disinfection, and small-scale industrial dosing. Key limitation: the solenoid drive produces a pulsating flow, which may require a pulsation dampener in sensitive applications.

Mechanical diaphragm metering pumps use a motor-driven eccentric mechanism to actuate the diaphragm. This design supports higher flow rates (up to 1,200 L/h) and continuous duty cycles. The stroke length and speed are independently adjustable, providing a wide turndown ratio. Mechanical diaphragm pumps are the standard choice for wastewater treatment chemical dosing, cooling water treatment, and agricultural fertigation. They are more robust than solenoid pumps for 24/7 operation but require periodic diaphragm inspection.

Hydraulic diaphragm metering pumps use hydraulic oil to transmit force to the diaphragm, eliminating direct mechanical contact and allowing operation at pressures up to 100 bar. This design is essential for high-pressure applications such as boiler feed chemical injection, reverse osmosis antiscalant dosing, and offshore platform chemical treatment. The hydraulic oil cushion also protects the diaphragm from pressure spikes, extending service life significantly.

Selection criteria summary: For flow rates below 60 L/h at moderate pressure, choose a solenoid diaphragm pump. For flow rates from 60 to 1,200 L/h in continuous duty, choose a mechanical diaphragm pump. For pressures above 16 bar or critical high-pressure injection, choose a hydraulic diaphragm pump. TL Environment offers all three types — contact our engineering team for a selection recommendation based on your specific flow rate, back pressure, chemical, and control requirements.