A centrifugal separator removes grit by spinning it out of the flow, and that mechanism has a specification most buyers skip: it works within a flow range and separates poorly outside it. Under the range there is not enough velocity to throw particles outward, and over it the turbulence carries them through. Sizing is therefore the whole decision.
Matching it to the pump, not the pipe
Size from the pump's actual delivery rather than from the diameter of the pipework it sits on, because the two are not the same and a separator on a large pipe fed by a modest pump spends its life below its separation range. Take the pump's rated flow at the system's working pressure, and account for a pressure tank, since a well system delivers in bursts as the pump cycles rather than continuously. Where flow varies widely, some designs cope better than others and the manufacturer's curve is worth reading.
What size particle it will catch
Separation works on density and size together, so it removes sand and grit efficiently and progressively less as particles get finer or lighter. Manufacturers publish a removal efficiency against particle size, and it is worth comparing rather than assuming. Fine silt and clay largely stay in suspension and pass, and organic matter of similar density to water passes too. Anything dissolved, including iron, hardness, tannins and sulfur smell, is entirely unaffected. It is a first stage that makes the rest of the train viable.
The purge and where it goes
Separated grit collects in a chamber at the bottom that must be purged, either manually on a schedule or with a timed automatic valve. A chamber left full passes grit through as though the unit were absent, and the failure is silent. Route the purge to a drain that will not block on grit and can take an occasional slug of water, and keep the run short and falling. In a pit or an unheated pump house, both the body and the purge line need protecting from frost.
Fitting it and asking the real question
The standard position is after the pressure tank and ahead of all treatment, protecting the media tanks, the softener, any membrane and the UV. Mount it vertically as specified with clearance below to service the chamber. Then ask why the well makes sand at all: a failed or wrongly sized screen, a pump set too low in the borehole, over pumping or a collapsing formation are the usual causes, and all of them wear out the pump while the separator quietly handles the output. Our well filtration guide covers the rest of the train.
Questions people ask about sand separator for well
How do I size a sand separator?
From the pump's actual delivery at working pressure, not from the pipe diameter. Outside its flow range it separates poorly.
What does it fail to remove?
Fine silt and clay, organic matter of similar density to water, and everything dissolved including iron, hardness and sulfur smell.
What happens if I never purge it?
The collection chamber fills and grit passes straight through as though the unit were not fitted. The failure gives no warning.
Where should it be installed?
After the pressure tank and before all treatment, mounted vertically with clearance below to service the collection chamber.