A screw oil press is a simple, robust machine, so when it stops making oil the cause is nearly always mechanical and fixable on site. This field guide walks through the seven faults operators report most — what each one looks like, how to diagnose it, and how to fix and prevent it. It applies to single- and multi-stage screw oil presses for peanut, soybean, rapeseed, sunflower and sesame.
Quick symptom → cause → fix table
| Symptom | Most likely cause | First fix to try |
|---|---|---|
| Low / no oil output | Wrong moisture; worn screw; seam clogged; cold barrel | Check moisture, pre-heat, narrow cake outlet, inspect wear |
| Jam / stall / noise | Foreign object; over-feeding; worn screw | Power off, clear chamber, sieve seed, slow feed |
| Oil backflows to inlet | Cake outlet too tight; rough seam; cold barrel | Open cake outlet slightly, polish seam, pre-heat |
| No / soft cake | Outlet too wide; wet material; worn ring | Narrow outlet, dry material, replace ring |
| Seeds won't feed | Too wet; worn inlet flights | Dry material, roughen/replace screw inlet |
| Cloudy oil / sediment | No filter; worn cage gaps; soft cake | Add/clean filter, reset bars, firm cake |
| Shaft won't turn / wrong way | Belt slip/broken; wrong phase rotation | Re-tension belt; swap two phase wires |
Low or no oil output
Low yield can have several interacting causes, including: seed moisture, screw/cage wear, the cake-outlet (oil-seam) setting, or barrel temperature.
- Moisture wrong. The suitable moisture target is specific to the seed, preparation method and press. Too wet and the meal clumps and pressure bleeds off; too dry and seeds slip without building pressure. Condition or dry the seed and re-test.
- Worn pressing screw or cage bars. Flights and bars gradually wear, which can reduce the chamber's ability to build pressure. Pull the screw and inspect the flight edges and bar gaps; replace as a set when rounded.
- Cake outlet too open / oil seam clogged. If the cake-thickness gap is too wide, pressure never peaks; if the oil-discharge seam is packed with fines, oil cannot escape. Narrow the cake-outlet nut a little at a time and polish the seam with an oil stone.
- Cold barrel. On a cold start the oil is too viscous to flow. Follow the approved start-up and preheating procedure before full feeding.
Machine jams, stalls or makes abnormal noise
A sudden stall, grinding or knocking usually means something physical is wrong inside the chamber — stop and cut power before opening anything.
- Foreign object (stone, bolt, metal) carried in with the seed is the classic cause. Clean and sieve seed through a vibrating screen before pressing.
- Over-feeding chokes the screw. Reduce the feed rate and let the chamber clear.
- Material too hard/dry or a worn, misaligned screw can bind. After power-off, disassemble, clear the chamber and check screw alignment and bearings.
Oil flows back to the feed inlet
When oil creeps back toward the hopper instead of out the seam, back-pressure is building in the wrong place.
- The cake-outlet gap is too tight, forcing oil backward — open it slightly.
- The oil seam is rough or scaled, so oil takes the path of least resistance back up the screw — polish the seam with an oil stone.
- A cold barrel raises viscosity and encourages backflow — pre-heat before feeding.
No oil cake forms, or the cake is too soft
If the cake crumbles or never forms a firm ring at the outlet, the chamber is not reaching pressing pressure.
- Cake-outlet gap too wide — narrow it so the meal compacts.
- Material too wet — dry/condition it to spec.
- Worn pressing ring or cone — replace it so the cake can build back-pressure.
Seeds will not enter the pressing chamber
If the hopper bridges and seed stops feeding, the screw cannot grab the material.
- Moisture too high makes seed sticky and clumpy — dry it.
- Screw inlet flights worn smooth lose their grip — roughen or replace the feed section of the screw.
- Check the feeder/auger and clear any bridging in the hopper.
Pressed oil is cloudy or full of sediment (foots)
Some fine solids are normal in screw-pressed crude oil, but heavy sediment means solids are getting through or the cake is too soft.
- No filtration or a clogged filter — add or service a pneumatic / plate-and-frame filter downstream.
- Cage bar gaps too wide or worn let solids pass — inspect and reset/replace bars.
- Cake too soft (see above) lets fines escape with the oil — firm up the cake.
Motor runs but the main shaft will not turn (or turns the wrong way)
If the motor hums but the press shaft is still, the problem is in the drive or the power phase — not the pressing chamber.
- Belt slipping or broken — re-tension or replace the V-belts.
- Wrong three-phase rotation direction on a new install: the main shaft turns backward. Power off and swap any two of the three phase wires, then restart.
- Overload trip / undersized supply — check the thermal overload and that voltage is stable under load.
Prevent most faults: routine practice
- Clean & sieve seed through a vibrating screen to keep stones and metal out of the chamber.
- Condition moisture to the right range for each seed before pressing (see how a screw oil press works).
- Pre-heat the barrel and feed steadily — avoid cold starts and surges.
- Inspect the screw, cage bars and oil seam on a schedule and replace wear parts as a set.
- Filter the crude oil promptly with a pneumatic or plate filter to protect downstream equipment.
Related: How a screw oil press works · Screw press vs hydraulic press · Oil press machine buying guide · Our oil press machines · Talk to an engineer.