Middleby Marshall PS555, PS570 manual Air finger operation, PS300/350 air finger with shutter plate

SECTION 2 - AIR FLOW AND HEAT TRANSFER

B.PS360-series ovens

PS360-series ovens feature two blower motors. Ablower wheel is fastened onto the end of the motor shaft. In order to adjust the amount and speed of heated air that is directed by the blower wheels, it is necessary to change the size of the wheels and/or change the speed of the motor. See Figure 1.

Each PS360-series oven model has a specific combi- nation of blower motor and blower wheel. Field modifi- cations to these approved combinations are not per- mitted unless under the specific directions of the Middleby Technical Service Department. Any changes to convection air delivery MUST be made using the air fingers.

C.PS555/570-series ovens

PS555/570-series ovens have one blower motor mounted inside each of the end compartments of the oven, with a pulley on the end of the motor shaft. The oven has two blower wheels; a belt connects each motor pulley to a pulley on the end of one of the blower wheel shafts. The air velocity can be changed by using a larger or smaller pulley on the motor shaft, and chang- ing the length of the belt to match the new pulley. See Figure 1.

Some customers have a specific belt/pulley combina- tion approved by Middleby Marshall, while others use a “standard” configuration. Field modifications to these approved combinations are not permitted unless under the specific directions of the Middleby Technical Ser- vice Department.

Figure 2

Air finger operation

Hot air flow from blower wheel(s)

Vertical

columns of high-velocity hot air

III. AIR FINGERS

A.Description and Function

Air fingers direct the heated air from the blowers into vertical jets that are directed at the top and bottom of the conveyor belt. Each air finger configuration has been tested to optimally cook a specific customer’s product. As a rule, air finger configurations should NOT be changed from customer specifications without di- rect instructions from the Middleby Technical Services Department.

Middleby uses two main types of air fingers:

•PS300/350 and early PS310/360 ovens used a shut- ter-type air finger assembly. The finger is as- sembled from a manifold, inner plate and outer plate. The inner plate is assembled from two sepa- rate plates, each with a series of holes, that are riveted together. The plates can be repositioned relative to each other to restrict the air flow through the holes as necessary. These fingers are no longer in general use, but may still be found in older ov- ens in the field. See Figure 3.

•All current ovens use an air finger which is com- posed of a manifold, inner plate, and outer plate. No adjustments are necessary or possible to these fingers, but a wide variety of styles is available to meet different customers’ baking needs. See Fig- ure 4.

Figure 3

PS300/350 air finger with shutter plate

Outer plate

Lower air fingers have wire rack as shown to prevent conveyor belt from rubbing on outer plate.

Rivets

Inner plate

Shutter

Manifold

Figure 4

Current standard air finger (all oven models)

	Outer plate
	Width and hole
	configuration varies.
	Inner plate
	Width and hole
	configuration varies.
	May have inner dam.
	Manifold
	Width varies to match inner
	and outer plates. Baffle may
	be solid, perforated, partially
	perforated, or absent.
	Several special shapes are
	available to meet specific
8	customer needs.