Several arguments are used to justify having the belt return inside the kettle on large French fry fryers.  With inside return, the whole conveyor assembly can be lifted out of the fryer; the conveyor frame is a single weldment.  With an outside return the frame has to be hinged.  The middle of the belt lifts out of the kettle and the head and tail shafts remain in the operating position.  Safety is used for a justification.  With an outside return, there is a hot belt returning outside the kettle.  Smoke and oil dripping off the belt has to be addressed.  Contending with this oil requires a large drip pan, a drip pan pump and piping to return the oil back to the system.  An outside return makes the conveyor track inside the fryer more complex, hence more expensive and adds considerable cost for the large drip pan, pump and piping.  Not only do these items increase the purchase price of the fryer, they also add to maintenance and operating cost.

So with all this added hassle, why would anyone purchase a large fryer with an outside belt return?  Two reasons: oil volume and carbon.  The new frying oils are putting an increased premium on reduced oil volume.  Compared with an outside belt return, returning the belt inside the kettle adds significant oil volume.  On a Gem fryer moving the belt return inside adds about 2 inches of oil depth.  This does not allow enough clearance for either inspection or clean-up access between the belts.  On a 6 foot wide 15 foot long cook length fryer the inside return would add approximately 160 gallons of oil, approximately 7 % of system oil volume.  On an 8 foot wide fryer, the width most often used for high capacity battered french fries, the situation becomes much worse.  Fryer belts wider than 6 feet require a center support.  With an outside belt return, the center of the belt can be supported from the bottom of the kettle.  An inside return would make it necessary to run beams the full width of the fryer to support the center of the belt, adding considerably more oil volume.  One method used (not by Gem) is providing two 4 foot wide belts for an 8 foot wide fryer.

Carbon may be a more important reason than oil volume for returning the belt outside the fryer kettle.  This is doubly true for fryers cooking battered product.  For various reasons, loose batter ends up in the fryer.  If this loose batter is not somehow removed from the fryer, it ends up being cooked until it becomes carbon.  Unless the fryer is properly designed, operated intelligently and the oil kept clean, the carbon will cause a couple of problems.  If the carbon concentration reaches a high enough level, it will leave the fryer, in the form of black spots on the product.  The other concern is fires.  If carbon forms in the oil and does not leave the fryer, there is a high risk of fire.  A mixture of carbon and oil at 390 degrees F. only needs air to ignite.  With an outside belt return, carbon drags can be suspended on the under side of the belt to help drag the carbon to the oil outlets.  This coupled with good oil flows will remove the carbon from the kettle so the filtration system can remove the carbon from the oil.  While an inside return makes the fryer simpler, an outside return makes the fryer more effective for cooking product.

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