Selective Rack VS Pallet Flow Rack VS Pallet Shuttle – A Case Study

 Solution at a Glance:

  • Services Provided: Assessment, Design
  • Location: Yabucoa, PR

Concern: A Distributor of Motor Oil Required a Higher Density Storage Solution to Replace Their Existing Selective Rack System

The company stores barrels of motor oil on pallets. Their inventory consists of several SKUs, and they have 26+ pallets of each SKU. Considering these inventory characteristics, their 1-deep selective rack system was not providing the highest density possible in their storage space.

The company came to REB looking for pallet flow rack. They thought this would provide the highest density in their storage space. REB surveyed their space, products, and throughput. Based on this, REB suggested that a pallet shuttle system may be the best solution.

Solution: Comparison of Material Handling Systems

REB provided a comparison between their existing standard selective rack, pallet flow rack, and pallet shuttle system in their space. The following was measured: pallet positions, layout and pick flow, and cost. Read further for the findings on each of these.

Pallet Positions

Selective Rack System

  • 12 bays
  • 2 pallets wide
  • 12 rows
  • 3 levels high
  • 864 pallet positions

Selective Rack Scope DrawingPallet Flow Rack System

  • 120 lanes
  • 11 pallets deep
  • 3 levels high
  • 1,320 pallet positions

Pallet Flow Scope DrawingPallet Shuttle System

  • 20 lanes
  • 26 pallets deep
  • 3 levels high
  • 1,560 pallet positions

Pallet Shuttle Scope DrawingLayout and Pick Flow

Selective Rack System

Standard selective rack is 1-deep, and therefore requires a pick aisle in-between each row. This allows for easy accessibility to each pallet but decreases the number of pallet positions.

Because the company had many pallets of each SKU, this high amount of selectivity is not needed. Therefore, the company would benefit from a system that provides less selectivity and higher density.

Selective Rack - PlanPallet Flow Rack System

Pallet flow requires two aisles: one for loading the pallets and one for picking. This system consists of racking and rails, which the pallets are placed on.

The rails are required to have a pitch, which is assessed and designated depending on the weight of the pallets and depth of the system. This pitch allows gravity to move products from the loading aisle to the picking aisle.

Pallet flow is ideal for 1 SKU per lane. The company had enough pallets of each SKU to fill each lane of the system, so no pallet positions would be unused.

The available length of the company’s storage area is 107’-8 ¼” wide, 81’-4 ½” deep, 21’-1 ¾” tall (to top of box). Given this available height versus depth, coupled with the size and weight of their pallets, the pitch necessary to glide the pallets.

To get the highest number of pallet positions in their space with pallet flow rack, it was designed with two equal sections of pallet flow that flow towards each other into a central aisle. Each section consisted of 60 lanes at 11 deep with a 14’ aisle in between them. require a longer pallet flow rail than the height of their space would allow. It would not be able to reach the full depth of their space, and therefore a certain number of pallet positions would be lost.

Pallet Shuttle System

The pallet shuttle system provided the highest number of pallet positions in their space. This system is semi-automated, meaning it includes a mixture of automation and human interaction to operate.

The system consists of racking and shuttles that run along rails within the system. Each shuttle is designated to one lane, although shuttles can be relocated to different lanes when needed. In a system utilizing semi-automated pallet shuttles, pallets are loaded into the system by a lift truck then transported and placed on the rack by an automated cart.

Like pallet flow, pallet shuttle requires 1 SKU per level of each lane. Since the company had enough pallets of each SKU to fill the 26 pallet positions in each lane, this solution made sense for them.

The pallet shuttle system yielded the highest number of pallet positions in their space. This is because the shuttles transport pallets via automation, instead of gravity. Therefore, no pitch is required in this system. This allows for the entire cube to be utilized and resulted in one less aisle than with the pallet flow system.

Pallet Shuttle - PlanCost

Selective Rack System

The company had to make room for more product, which meant either move to a new building or better utilize the space they have. The cost of increasing density in their existing space by switching to a pallet flow system or shuttle system is less costly than having to move operations to a new building.

Pallet Flow Rack System VS Pallet Shuttle System

REB provided the company with a cost comparison between the pallet flow rack system and the pallet shuttle system.

The customer assumed that because a pallet shuttle system is a semi-automated system, it would cost more upfront. They were surprised to learn that the total material for the pallet shuttle system was less than the total material for the pallet flow system. In fact, the entire lot of material (racking, rails, shuttles, and required componentry) for the pallet shuttle system was only 8% higher than the rails for the pallet flow system (not including racking).

This outcome can be the case in other instances. Although we can’t provide the exact reason for the higher cost of the pallet flow material, in general there are four reasons that can account for this:

  1. Pallet flow rails consist of a fair amount of componentry. Typically, not all the components needed for the rails are manufactured in the same plant. Therefore, extra costs incur from the freight to bring parts from multiple locations to a central location to be assembled.
  2. Pallet flow rails generally require more preassembly at the factory. For example, all the wheels must be connected. Conversely, a pallet shuttle system consists of folded rails, racking, and shuttles, all of which do not require as much preassembly at the factory.
  3. More componentry is needed to move pallets through a pallet flow system compared to a pallet shuttle system. More specifically, the rails and wheels are required to be present in the entire pallet flow system. In a pallet shuttle system, however, the mechanism to move the pallets is contained within the shuttle, which moves about the system. Therefore, extra componentry is not needed to be present throughout the entire system.
  4. The mechanism necessary to move the pallets in a pallet flow system, that being the rails and wheels, are required to be present in the entire system at the time of installation for it to be usable. In a pallet shuttle system, shuttles can be added or removed as needed. This makes the pallet shuttle system scalable.

Outcome: Informed Decision Making

The company is educated on their options and can make an informed decision based on the specifics of their operation.

They understand that converting their distribution center to a semi-automated operation is a viable option that will allow them to streamline operations.

How You Can Get the Best Storage System for Your Needs

If you’re concerned that you’re using an inefficient system, or unsure which system is the best for your operation, contact REB today.

Our dedicated team of material handling experts can work with you to provide you with a solution that optimizes your picking operations. We are highly experienced in identifying inefficiencies and implementing improved systems.

We’d appreciate the opportunity to help you further, whether that be more information or a quote. Fill out the contact form on this page or call us at (800) 252-5955 to get in touch with a REB representative.

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