Syringe, peristaltic, vacuum: which lab pump do you need?
Four kinds of lab pump, four completely different jobs. Buying the wrong one is the most common mistake we see in used lab equipment.
“Lab pump” is not a category. It is four unrelated instruments that happen to share a verb, and buying the wrong one is one of the most common and most avoidable mistakes we see people make in used lab equipment.
We have several kinds on the bench. Here is how to tell them apart and which one your application actually wants.
Syringe pump
What it is: a motor that pushes the plunger of a syringe at a precisely controlled rate.
What it is for: delivering a small volume of liquid very slowly and very accurately, over minutes or hours. Think microlitres per minute.
Why you would want one: because nothing else is this precise at low flow. If you need to infuse a drug into an animal at an exact rate, feed a reaction slowly, or drive a microfluidic chip, this is the instrument. Harvard Apparatus is the name you will see most often, and their older Model 11 and Model 22 units are mechanically simple and still entirely usable.
What it will not do: move any real volume. If you need litres, this is not the tool.
What to check when buying: that the drive moves smoothly and does not stall, and that the syringe clamp is intact. The electronics on these are simple. The mechanics are the thing.
Peristaltic pump
What it is: a set of rollers that squeeze a flexible tube, pushing liquid along ahead of the squeeze.
What it is for: moving liquid continuously when the liquid must not touch the pump.
Why you would want one: this is the key property and it is the reason peristaltic pumps exist. The fluid only ever touches the inside of the tube. Nothing else. That means you can pump something sterile, something corrosive, or something you cannot afford to contaminate, and to change what you are pumping you just change the tube. There is no cleaning of a pump head, because nothing got in it.
Cole-Parmer’s Masterflex is the standard here, to the point where “Masterflex” is used as a generic term.
What it will not do: high pressure, or perfectly smooth flow. The rollers give you a gentle pulse.
What to check when buying: that the drive runs across its speed range, and that the rollers turn freely. The pump head is a wear part and is available separately, so a tired head is not fatal.
Vacuum pump
What it is: a pump that removes gas rather than moving liquid.
What it is for: pulling a vacuum. Filtration, evaporation, degassing, or feeding any instrument that needs one.
What to check when buying: vacuum pumps are the ones most likely to have been abused. Oil sealed pumps need their oil changed and frequently have not had it. Ask what the ultimate vacuum is and whether it has been serviced. A pump that will not pull down is often rebuildable, but factor the rebuild into the price.
HPLC pump
What it is: a high pressure piston pump built to push solvent through a densely packed chromatography column.
What it is for: exactly one thing, which is HPLC. It is a precision instrument operating at hundreds of bar, and it is not a general purpose pump.
Do not buy one of these to move fluid around. It is the most expensive and least suitable way to do that. We wrote about what these actually are in what an HPLC actually does.
The decision, compressed
| You need to… | Use a |
|---|---|
| Deliver microlitres, precisely, over hours | Syringe pump |
| Move fluid that must not touch the pump | Peristaltic pump |
| Remove gas, pull a vacuum | Vacuum pump |
| Push solvent through a chromatography column | HPLC pump |
Every one of these turns up in surplus, frequently in the same lot, described simply as “pump.” Knowing which is which is most of the skill, and it is the difference between buying an instrument and buying a paperweight.