How to Deal with Pallet Flow Jams
In deep lane flow systems, jams can be a time-consuming problem. Here's how to clear them safely
Pallet flow racks are the ultimate in high-density, space-saving storage. When you need to concentrate storage of similar SKUs into a tight space, flow systems are ideal. A single SKU can be loaded into the back of the system and stored multiple pallets deep in a pick position, first-in, first-out order. Like any gravity flow equipment, there is a possibility of jams, and those jams can sometimes be in the center of a packed rack system — and difficult to reach. What are some safe methods to deal with this problem?
Ways to prevent obstructions and jams
Pallet flow jams happen for a number of reasons, and it’s always better to prevent a jam than fix one. Some tips for jam prevention:
- Load the rack correctly. Forklifts should be square to the face of the rack with the pallet squared and centered on the lane. Poor angles and off-center pallets are more likely to jam than those loaded correctly. Train drivers to never approach the rack at an angle. Load the pallet 4″ to 6″ above the wheels/rollers. Set the pallet down gently.
- Use pallet flow entry guides on the infeed side to help square the loads. In some applications, full-length guides may be needed to make sure that pallets track directly in a deep lane rack.
- Don’t allow damaged or substandard pallets to be loaded into the flow system. If they break, a messy jam is inevitable. If you are using containers, have them regularly inspected for damage. One spill/jam can make inspections worth the time.
- Make sure your loads are evenly distributed. Even if you have great-quality pallets loaded flawlessly, an uneven load may not track. Make sure the load is adequately secured on the pallet so that cartons or other units can’t fall off and jam the system.
- Do any maintenance prescribed by your rack manufacturer. This can keep the rack functioning longer, and also allow you to spot issues before they cause jams and delays in production.
Even if you take all these precautions, jams sometimes still happen and will need to be resolved. Let’s discuss some safe ways to clear them.
Clearing jams safely and efficiently
Pallet flow is robust; when specified and used correctly, it transports very heavy loads on a deep lane structure from the “charging” side to the pick face. We have plenty of installations that have operated without issue for years, with deep pick positions and heavy loads. It can jam for a number of reasons, including:
- Debris or loose cartons on the tracks
- A broken wheel or roller
- Temperature (or humidity) changes
- A broken pallet stringer
When your system jams, what are some safe ways to deal with it?
Don’t climb into a loaded, live rack system
This probably seems like the fastest, easiest way, but it’s dangerous and should be a last resort, under strict safety conditions (see below). The potential for serious injury is simply too high, and you have other methods at your disposal that should be explored first.
Plugging
Plugging nudges the load to attempt to clear it. Position a forklift squarely at the pick face of the jammed lane. The driver should lift the first pallet slightly (about 1″) off the rollers, then gently nudge the second pallet with the first, by no more than four inches. After that, the driver should back out with the first pallet on the forks. Ideally, the pallets behind it will flow to the front and the jam will clear.
This technique is a reliable way to clear jams, but if it doesn’t work, put the pallet back into position and visually inspect the lane to find the issue.
Flow from behind
This goes at the issue from the infeed side. Load a full pallet into the charging side of the system and let it glide down to the jammed area. This can cause the jam to clear by applying force from a different direction onto the stuck pallet. If it doesn’t work, then load more pallets to apply pressure to the obstruction.
Enter the rack safely to diagnose the issue
We discussed not entering the rack earlier, but at this point you are out of options — someone may have to enter the system.
While entering a loaded and live rack system is never recommended, you can do so with the right safety precautions. To do this, remove the last pallet loaded at the infeed side of the obstructed lane. Then, clear all pallets from one of the adjacent lanes. Secure that lane with ties and any other mandated safety procedures. Safe behaviors include:
- The person entering the lane should be trained for the task and have an understanding of the system and its functions.
- Make sure the entire flow rack is shut down. No loading or picking from any lane. Post signs, guard the system and string tape to ensure it’s understood that the rack can’t be used while someone is inside the system.
- Always enter from the infeed side of the rack. Never have a person on the flow side of a jam, unless the jammed pallet has been secured.
- Access the elevated height correctly. Use a warehouse ladder or approved maintenance cage to reach the jammed lane. Leave the ladder or forklift in place while someone is in the system.
- Use an approved walkway over the rollers to ensure they don’t move when walked on. You can also fill the lane with empty pallets or sheets to provide a stable walkway that prevents movement.
- Wear appropriate PPE, including hard hats or goggles.
- Use fall protection systems for elevated lanes.
- Position people on each end of the lane to monitor the operator’s progress and safety.
Once the obstruction has been found, the operator should clear it if that can be done safely. The jammed pallet should be strapped before anyone touches it, any obstruction, or its load.
The jammed pallet may need to be unloaded onto a pallet in the empty lane. This should always be a pallet in front of the operator, and should always be done with caution. If a small jam forward of the stuck pallet can be removed, use a pole or extension device. Never allow an operator to place themselves in front of the jammed pallet, particularly if they are pulling debris from the tracks and could dislodge the pallet toward themselves or an extended hand.
Once the pallet clears, survey the rollers and rack structure for any damage.
Force from the discharge side
If the operator can’t clear the jam from within the system, next up is front pressure. To do this, re-load pallets from the pick face end of the rack system until they make contact with the obstruction. This lets your forklift push from the front against the stuck pallet. Since you have an operator in the rack system, he or she can communicate with the driver about what the pressure is doing, and guide the process. This should be enough force to clear it, assuming the components are not severely damaged.
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Scott Stone is Cisco-Eagle's Vice President of Marketing with 35 years of experience in material handling, warehousing and industrial operations. His work is published in multiple industry journals an websites on a variety of warehousing topics. He writes about automation, warehousing, safety, manufacturing and other areas of concern for industrial operations and those who operate them.