Grundfos DMH 251-B Hydraulic Piston Diaphragm Dosing Pump 3 Phase with External Motor

The Grundfos DMH 251-B Hydraulic Piston Diaphragm Dosing Pump is a heavy-duty, industrial dosing solution engineered for applications requiring high pressure, maximum reliability, and long service life. Designed for continuous operation in demanding process environments, the DMH series combines hydraulic diaphragm technology with a robust mechanical drive for precise and repeatable chemical dosing.

Unlike mechanically actuated diaphragm pumps, the DMH 251-B uses a hydraulically driven diaphragm, where the diaphragm is fully supported by hydraulic oil. This design eliminates mechanical stress on the diaphragm, resulting in superior durability, improved dosing accuracy, and extended maintenance intervals—especially in high-pressure applications.

Flow rate is adjusted manually via a mechanical stroke length adjustment knob, allowing reliable fixed-rate dosing with excellent repeatability. The pump is driven by a high-efficiency three-phase AC motor coupled to a precision gear-eccenter system, ensuring stable operation even under fluctuating process conditions.

The liquid end features a PVDF dosing head, PTFE diaphragm, and ceramic ball valves, offering excellent chemical resistance for aggressive and corrosive media. With an aluminium pump housing, IP65 motor protection, and industrial construction, the DMH 251-B is ideally suited to water treatment plants, chemical processing facilities, and OEM dosing skids where reliability is critical.

APPLICATIONS

• High-pressure chemical dosing systems
• Water and wastewater treatment plants
• Industrial process dosing
• Chemical manufacturing and processing
• pH correction and coagulation systems
• Cooling tower and boiler water treatment
• OEM dosing skids and engineered systems
• Applications requiring maximum diaphragm reliability

FEATURES

• Hydraulically driven diaphragm dosing pump
• High-pressure operation up to 16 bar
• Manual stroke length adjustment (1:10 ratio)
• Robust gear-eccenter and piston drive system
• Aluminium pump housing for industrial durability
• PVDF dosing head for chemical resistance
• PTFE diaphragm with hydraulic support
• Ceramic ball valves for accurate dosing
• Designed for continuous industrial operation
• IP65 motor enclosure
• Three-phase motor for stable performance

SPECIFICATIONS

Performance

• Maximum flow: 4.9–23 LPH (variant dependent)
• Maximum pressure: 16 bar
• Stroke adjustment range: 1:10
• Dosing accuracy: ±1.5% (FS)
• Linearity: ±2% (FS)
• Maximum viscosity: 300 mPas

Hydraulic

• Liquid temperature range: −10 to 20 °C
• Maximum suction lift: Up to 4 m
• Maximum permissible inlet pressure: 8 bar

Materials

• Pump housing: Aluminium
• Dosing head: PVDF
• Diaphragm: PTFE (hydraulically supported)
• Valve balls: Ceramic (Al₂O₃)
• Valve seats & gaskets: PTFE composite

Electrical

• Supply voltage: 3 × 230/400 V, 50 Hz
• Power input: ~0.09 kW
• Enclosure class: IP65
• Frequency converter: Not prepared for VFD