Two shakers can carry identical API RP 13C screens and perform completely differently — because the screen only decides what size gets cut, while the deck’s motion and G-force decide how much fluid it can handle, how dry the cuttings leave, and how fast the panel wears out. Screen selection gets all the attention; motion is the variable that quietly decides whether that screen ever reaches its potential.
The two levers: motion type and G-force
A shaker does two jobs at once — it has to convey solids off the end of the screen and process fluid through it. How well it balances those jobs depends on the shape of the motion the deck imparts and the intensity (G-force) behind it.
| Motion | How it behaves | Best at |
|---|---|---|
| Linear (two counter-rotating motors, straight-line throw) | Aggressive, fast conveyance; high fluid capacity; the modern default for primary shakers | High-volume top-hole, heavy returns, primary separation |
| Balanced elliptical | Gentler, longer solids retention on the deck | Drying duty, fine screens, sticky / gummy formations |
| Circular / elliptical (older) | Smooth on solids, lower capacity and poorer conveyance uphill | Legacy units; gentle handling of fragile cuttings |
Linear motion became the standard because it conveys solids fast enough to run finer screens without burying the deck. But “fast conveyance” is not always what you want: when the goal is a dry discard rather than maximum throughput, the longer retention of a balanced-elliptical deck can pull more fluid out of the cuttings — which is why dedicated drying shakers often use it.
Reading the G-force
G-force is the acceleration the deck imparts to the slurry, and it follows the same family of relationship as any vibrating or rotating separator:
(It is the same constant as the decanting-centrifuge bowl formula — only the dimension you plug in changes, stroke for a shaker, bowl diameter for a centrifuge.) Primary shakers commonly run in the region of 5–7 g; dedicated drying shakers push higher, often 8 g and above, to fling free fluid through the screen.
Why motion beats brochure capacity
A shaker’s rated throughput on a datasheet assumes ideal motion, level decks and sound screens. In the field, the things that actually limit it are mechanical: a failed or weakening vibrator motor turns clean linear motion into a lopsided wobble that kills both conveyance and capacity; an out-of-level deck pools fluid at one end and dries out the other; mismatched motor phase on a dual-motor linear unit destroys the straight-line throw entirely. None of these show on the screen label, and all of them make a correctly chosen screen flood or blind.
Key takeaways
The screen sets the cut; the motion and G-force decide whether the shaker can deliver it. Use linear motion for capacity and primary duty, reach for balanced-elliptical retention when a dry discard matters more than throughput, and treat G-force as a deliberate trade between dryness and screen life — not a dial to leave at maximum. And when a correctly screened shaker still floods, look at the motion first: a tired motor or an out-of-level deck defeats the best panel on the market.