Metering pump glossary
Quick answer: A metering pump delivers a fixed, adjustable volume per stroke. Flow is set by stroke length and stroke rate, accuracy follows standards like API 675, and the liquid end material must suit the chemical.
- Metering pump
- A positive displacement pump that delivers a precise, adjustable volume of liquid per stroke; also called a dosing or proportioning pump.
- Plunger pump
- A metering pump in which a reciprocating plunger is in direct contact with the liquid. Suits high pressure.
- Diaphragm pump
- A metering pump in which a flexible diaphragm separates the liquid from the drive, giving leak-free dosing.
- Hydraulic diaphragm
- A diaphragm moved by hydraulic oil driven by a plunger, allowing higher pressure than a mechanically actuated diaphragm.
- Liquid end
- All parts that touch the pumped chemical: pump head, valves, balls, seats, diaphragm or plunger.
- Stroke length
- The distance the plunger or diaphragm travels per stroke; adjusting it changes flow, usually from 0–100%.
- Stroke rate
- The number of strokes per minute (SPM). Flow = displacement per stroke × strokes per minute.
- Turndown ratio
- The ratio of maximum to minimum accurate flow, for example 10:1 means accurate from 10% to 100% of capacity.
- Steady-state accuracy
- How repeatable the delivered flow is at a fixed setting, often ±1% for API 675 pumps.
- API 675
- The American Petroleum Institute standard for controlled-volume positive displacement pumps used in refineries and process plants.
- NPSH
- Net positive suction head: the pressure available at the pump suction above the liquid vapour pressure. Too little NPSH causes cavitation.
- Suction lift
- The height the pump must lift liquid from the tank to the pump inlet; flooded suction is preferred for metering pumps.
- Flooded suction
- Installation where the tank liquid level is above the pump inlet so liquid flows into the pump by gravity.
- Check valve
- One-way valve (ball or disc) on the suction and discharge of the pump head that makes each stroke deliver a fixed volume.
- Back pressure valve
- A valve on the discharge line that keeps constant pressure so the pump does not over-deliver or siphon.
- Pressure relief valve (PRV)
- A safety valve that opens when discharge pressure exceeds a set value, protecting the pump and piping.
- Pulsation damper
- A gas-charged vessel that smooths the pulsing flow of a reciprocating pump and reduces pipe vibration.
- Calibration column
- A graduated cylinder on the suction side used to measure the actual pump flow.
- Siphoning
- Uncontrolled flow through the pump when discharge pressure is lower than suction pressure; prevented by a back pressure valve.
- Simplex / duplex / triplex
- Number of pump heads on one drive: one, two or three. Multiplex pumps give higher flow or dose several chemicals.
- Dosing skid
- A pre-assembled package of tank, pumps, valves, instruments and panel on a common base frame.
- Degassing valve
- A valve that releases gas from the pump head, used for chemicals like hydrogen peroxide and hypochlorite that give off gas.
- Gear box (worm reduction)
- The reduction drive that converts motor rotation into reciprocating stroke in motor-driven metering pumps.
- LPH
- Litres per hour, the usual unit for metering pump capacity.
- ppm
- Parts per million; in water treatment, milligrams of chemical per litre of water.