PTO retrofit solution solves downtime dilemma.

* A MECHANICAL power take-off retrofit on a diesel-driven vacuum blower has allowed the blower to more reliably salvage in-accurately stored agricultural products from grain elevators.

The mechanical pto gives more reliable service because its design provides support for side loads with two heavy-duty tapered roller bearings on the take-off shaft. The vacuum blower's original pto, which used a pilot bearing to handle side loads, experienced repeated pilot bearing and friction disc burn-out during the year it was in service.

Since it was installed over two years ago, the new pto has provided reliable, uninterrupted blower operation and has required only routine maintenance.

The retrofit was done for the Windsor Grain Terminal of the United Co-operatives of Ontario, which uses the vacuum blower to salvage product that has been inadvertently stored in the wrong silo. Beans, for example, may be placed on top of corn in a silo designated for corn. Unless the beans can be separated and reclaimed, the silo's contents will have to be sold at a large discount. The financial loss can be considerable since up to 2,000 tons of product may be involved. This makes the maintenance department's portable vacuum blower a critical piece of equipment.

To retrieve a product, a crew constructs a pipeline to the silo's interior. The first leg of this distance is covered by a permanently mounted, 125-ft. aluminum pipe running up the outside of each silo. To this pipe, other aluminum pipe sections, totaling as much as 200 feet, are added to cover the remaining horizontal and vertical distance. Depths as much as 90 feet have been reached with this piping.

Connections between these pipe sections are made with flexible hose. When the pipeline has been completed, the blower is wheeled into position at the base of the silo and connected by flexible hose to the bottom of the pipe. The blower's engine is started, the pto engaged, and the inaccurately stored product is vacuumed out of the silo.

According to Stan Mitchell, maintenance supervisor, the blower could not be run for more than three or four hours without overheating of the original pto's three-piece, segmented clutch.

Heavy side loads carried by the take-off shaft were focused right on the pilot bearing and engine crankshaft, causing excessive pilot bearing wear and, ultimately, bearing burn-out. As the pilot bearing wore, oil leaks developed, causing slippage between the clutch plate and friction discs. The result was heat buildup on the discs and deterioration of the friction surface. Within a year, the blower was down twice for pilot bearing replacement and twice for replacement of friction discs.

On the recommendation of a Dana Corp. power transmission sales division distributor, Mitchell decided to install a Wichita mechanical pto, which uses the Spicer Angle-Spring truck clutch.

The Wichita pto does not use a pilot bearing. Instead, flywheel and clutch are attached at the clutch outside diameter via a flange. All side loads are carried by the flange and the two heavy-duty tapered roller bearings supporting the take-off shaft. Side loads are thus effectively isolated from the engine crankshaft, and excessive heat buildup at the pto/flywheel connection is prevented.

The vacuum blower uses a 175-hp, 1800-rpm diesel engine to power its two-stage positive displacement fan. Power is transmitted by a 10-groove sheave and V-belt pulley driven by the pto's take-off shaft. The pulley drive provides a 1:2 speed increase, for a maximum fan speed of 3600 rpm.

The two-stage fan creates the air movement necessary to draw silo product through the blower. Product is drawn through the silo pipeline into a duct entering the topside of a funnel-shaped cyclone collector. This duct is slightly to the side to force product into a spiral, or cyclonic, path as it moves through the collector.

A rotary airlock at the bottom of the collector conveys product into the outlet chute directly underneath it, through which it is discharged into a new storage facility. The airlock is a rotating drum with isolated V-shaped compartments that enable it to convey product while maintaining a vacuum in the collector.

Movement of air in the cyclone collector is controlled by the fan's suction stage. The fan draws air through a right-angle duct connecting the top of the collector and the fan's hub. Because of the seal created by the rotary airlock, fan suction creates the vacuum needed to pull silo product into the collector. As the product "cyclones" through the vessel, it falls by gravity to the bottom, while entrained dirt, moisture and airborne particles are drawn out the top and discharged at the fan outlet.

Air movement in the outlet chute is created by the discharge stage of the fan. As the rotary airlock conveys product into the chute entrance underneath it, the fan discharges air into this opening, forcing product up the chute and out its funnel-shaped end.

The rotary airlock is driven by a hydraulic motor through a chain and sprocket. The motor, in turn, is driven through a 3:1 speed reduction pulley by the fan drive shaft. Rotary airlock rpm is, thus, a precise ratio of fan drive speed.

In addition to virtually eliminating clutch maintenance on the vacuum blower, the Wichita pto has proved easier for operators to engage. With the original pto, clutch engagement was accomplished by applying leverage against the force of the clutch's springs. Because of the high force requirement, operators occasionally engaged the clutch only part way, causing disc slippage and overheating.

Mitchell recalls that he was constantly worried that one of his men would burn up the clutch in this manner. The Spicer Angle-Spring clutch used in the Wichita pto is spring-actuated, assuring complete engagement.

In the Spicer clutch, load springs are placed at an angle to the clutch centerline, maintaining constant plate load as the clutch wears and reducing release bearing load during disengagement. Because springs apply load at an angle, only the axial component of this force contributes to plate load and release bearing load.

Facing wear does not alter the spring angle enough to decrease the axial force on the pressure plate. Axial force approaches zero during disengagement because the spring angle is moving toward the perpendicular with respect to the clutch centerline.

Constant clearance between pressure plate and intermediate plate is assured by the Spicer clutch's self-adjustment feature. As release bearing travel increases with clutch wear, an actuator arm is triggered, rotating a worm gear on the clutch OD. The worm gear engages an adjusting ring, rotating the ring so that it exerts leverage on the pressure plate. Pressure plate/intermediate plate clearance is thus constantly readjusted.

The Angle-Spring clutch used in the Wichita pto has specially dampened friction discs to prevent torsional vibration from damaging engine or transmission components or causing spline wear.

Dampening is accomplished by an assembly of coaxial oil springs mounted in the disc hub. Each spring set has an outer spring housing an inner spring for increased vibration dampening. Each friction disc has six trapezoidal ceramic buttons per side for increased facing surface area and longer life. The clutch's intermediate plate is extra thick for high heat dissipation.

The Wichita mechanical pto is inexpensive, quick, and simple to maintain. Should roller bearings need to be serviced or replaced, the bearing assembly can be removed from the take-off shaft housing without disturbing pto installation. Clutch and clutch housing are also individually mounted for in-place clutch repair or replacement. An oil reservoir within the take-off shaft housing provides lubrication for roller bearings. Oil level can be checked simply by removing a plug.

The Wichita pto uses a 15 1/2-in. Spicer clutch rated for engine speeds to 2600 rpm and constant torques of 1650 lb.-ft. Clutch plate load is 3600 lbs., with a release bearing load of 480 lbs.