How to choose a diaphragm vacuum pump
A diaphragm pump flexes an elastomer or PTFE membrane over a head with two check valves. Nothing rubs and nothing is lubricated, so the gas path can be made completely inert. Ultimate vacuum improves with the number of stages in series; corrosion-resistant heads with PTFE-faced diaphragms and valves handle solvents and acids that would destroy an oil-sealed pump.
Match pumping speed at your working pressure rather than at open flow — a diaphragm pump's speed falls steeply as pressure drops. Pick the number of stages for the ultimate you need, and specify chemistry resistance honestly: what solvent, what concentration, what temperature. Check the inlet and outlet connections, noise level, duty cycle and whether the pump is offered with a vacuum controller, an inlet separator or an exhaust waste-vapour condenser. Diaphragms and valves are consumables with a stated service life.
Typical duties: rotary evaporators, vacuum drying ovens, filtration and solid-phase extraction, gel dryers, and as the oil-free backing pump for turbo pumps on analytical instruments. Where the sample cannot tolerate any hydrocarbon, this is usually the first pump to consider.
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FAQ
What vacuum can a diaphragm pump reach?
Two-stage diaphragm pumps typically reach around 10 mbar and four-stage models a few mbar. That is rough vacuum only — for high vacuum a diaphragm pump is used as the oil-free backing pump for a turbo, not as the main pump.
Why choose a diaphragm pump over a scroll or rotary vane pump?
Because the gas path touches only the diaphragm and valve plates, which can be PTFE for aggressive chemistry, and there is no oil and no wearing seal strip. That makes it the standard choice for solvent-laden laboratory work — rotary evaporators, filtration, gel dryers. The trade-off is much lower pumping speed.
How long does a diaphragm last?
Typically 8,000 to 15,000 running hours on clean duty, shorter with aggressive solvents or if the pump runs continuously at its ultimate pressure. Diaphragms and valve plates are the service items and are supplied as a kit.
Can a diaphragm pump handle corrosive vapour?
In a chemistry-resistant version, yes — PTFE diaphragms and valve plates with a fluoropolymer-lined head. Standard versions with elastomer diaphragms will swell and fail. Tell us the solvents involved and we will specify the right head material.
Do you supply diaphragm kits for Vacuubrand and Pfeiffer pumps?
Yes — diaphragms, valve plates and seal sets for the common Vacuubrand, Pfeiffer and KNF laboratory diaphragm pumps. Send the pump model from the nameplate; several models use different diaphragm diameters across stages.