One of the most common questions that we receive from customers during the consultation, design, and quotation process is whether they need a top running or under running overhead crane system.

When deciding whether a customer needs to choose a top-running or bottom-running overhead crane system, the following aspects need to be considered:

• Customer’s specific needs: First, you need to understand the customer’s specific situation and needs, including their work processes, material handling characteristics, factory height and space and other factors. If a customer needs to move heavy objects high above the ground, or needs to operate in a lower space, a top-running overhead crane system may be more appropriate. If the customer needs to move heavy objects to a higher location, or needs to operate in a higher space, then choosing a lower-running overhead crane system may be more suitable.
• Ease of operation and maintenance: There are differences in operation and maintenance between top-running and bottom-running overhead crane systems. The operation of a top-running overhead crane system is generally simpler because its trajectories are usually shorter and the operating height is lower. On the other hand, the operation of a lower-running overhead crane system can be more complex because of its longer trajectory and higher operating height. In terms of maintenance, maintenance of a top-operated overhead crane system is relatively simple as its components are easier to access and inspect. Maintenance of lower-running overhead crane systems can require more work and time.
• Safety Factor: Safety is one of the important factors to consider when choosing an overhead crane system. For top-running overhead crane systems, they may be safer due to their lower operating height. For lower-running overhead crane systems, due to their higher operating heights, more safety measures may be required, such as safety railings, protective nets, etc.
• Cost Factor: Finally, cost is also one of the factors to consider when choosing a bridge crane system. The cost of a top-running overhead crane system can be relatively low because of its relatively simple structure. A lower-running overhead crane system may cost more because its structure is more complex and requires more materials and workmanship.

To sum up, when judging whether a customer needs to choose a top-running or bottom-running overhead crane system, it is necessary to consider the customer’s specific needs, convenience of operation and maintenance, safety factors, and cost factors. The system ultimately selected should be able to meet the customer’s needs while ensuring safe, economical and efficient operation and maintenance.

Top Running Overhead Cranes

A top running overhead crane has a fixed rail or track system installed on the top of each runway beam—allowing the end trucks to carry the bridge and hoist along the top of the runway system. Top running cranes can be configured in a single girder or double girder bridge design. A single girder bridge utilizes an underhung trolley and hoist, while a double girder design most often utilizes a top running trolley and hoist.

Top running overhead cranes have no limiting capacity—meaning that they can be built to handle small capacity loads or large capacity loads. Top running cranes can be built to capacities of anywhere from 1/4-ton to excesses of 100-tons. These types of overhead cranes are supported by the building structure or runway support columns and are ideal for moving extremely heavy loads.

Top running cranes provide added lift height for buildings with limited headroom because they ride on rails on top of the runway beam. A top running double girder bridge design allows the greatest lifting height because the hoist and trolley run on top of the two bridges or girders—adding anywhere from an extra 3 to 6 feet of hook height.

Top running overhead cranes are typically larger than under running cranes, as they can be built to higher capacities and can accommodate wider spans.

Because the crane is supported on rails on top of the runway beams, there is no suspended load factor, so installation and future service or maintenance is easier and less time-consuming than an under running crane.

Over the course of its life, the track or rail system that the bridge moves on may need to be checked for alignment or tracking problems more frequently than an under running crane. Fortunately, the service and alignment inspections are fairly easy to perform and require less downtime than an under running crane.

Benefits of a Top Running Single Girder Crane:

• Typical Load Capacity: 1/4-ton to 20 tons
• Typical Span: Under 65 feet
• Typical Service: Light to medium duty
• Common Applications: Light manufacturing, fabrication and machine shops, light assembly line, warehousing facilities, maintenance and repair centers
• Low deadweight
• More overhead space
• Faster hoist and trolley speed
• Lower production cost / lower overall price with less material required

Benefits of a Top Running Double Girder Crane:

• Typical Load Capacity: 20-400 tons
• Typical Span: Over 65 feet
• Typical Service: Medium to heavy duty
• Common Applications: Steel and metal mills, coil handling, foundries, large fabrication and stamping facilities, paper mills, casting plants, large-scale tool and die facilities
• Allows for best hook and lifting height because hoist and trolley can run on top of the two bridge girders
• Provides the most overhead floor space
• High speed

Under Running / Underhung Overhead Cranes

An under running crane, or commonly referred to as an “underhung” crane, uses wheels that are supported by the bottom flange of the runway beam to move the bridge up and down the runway. Under running cranes are most commonly configured in a single girder design for lighter service and lower-capacity applications. They can also be built in a double girder design for higher capacities but it can become impractical and expensive to design and engineer.

An under running single girder crane will utilize an under running hoist and trolley which moves across the bottom flange of the bridge beam. A double girder under running crane can run its hoist and trolley along the top or the bottom of the bridge beams.

These underhung types of cranes can allow you to maximize your facility’s floor space for production and storage of material because they are most commonly supported from the existing ceiling trusses or the roof structure. Underhung cranes also offer excellent side approach and maximize utilization of the building’s width and height when supported by roof or ceiling structures. They’re ideal for facilities that lack vertical clearance to install a top-running overhead crane system.

Under running cranes can be designed in a free-standing configuration if the building’s existing support structure can’t be utilized, but this setup does require the use of support or mounting columns.

Hook height and lift height is less than top running cranes because the bridge and hoist hang underneath the runways.

When it comes to the installation and service of an under running crane system, it can be more of a complex procedure leading to longer downtime. Because the crane is suspended from the runways, it can take longer to check the alignment or service the wheels of the crane, but it is easier to dial in and maintain the alignment and there are fewer tracking problems because it runs on an I-beam which is secured to building structure—limiting movement.

Benefits of an Under Running Overhead Crane:

• Typical Load Capacity: 1/4-ton to 15-tons
• Typical Span: Under 65 feet
• Typical Service: Light to medium duty
• Common Applications: Assembly, fabrication shops, maintenance buildings, and manufacturing facilities
• Maximizes floor space if supported by existing ceiling trusses or roof structure
• Reduces material costs if no runway support columns are needed
• Increased end hook approach and bridge beam and hoist are underneath runway beams

Wrapping it Up

Hopefully you have a better sense of whether a top running crane or an under running crane will be the most beneficial for your material handling needs. Under running cranes offer flexibility, functionality, and ergonomic solutions, while top running crane systems offer the advantage of higher capacity lifts and allow for higher lift heights and more overhead room.

At Dongqi, we have over 30 years of experience in the overhead crane industry and can build custom solutions ranging from light-duty economical cranes to large-capacity, high-duty cycle cranes.

We rely on the experience and expertise of our team of draftsmen, estimators, engineers, and project managers to design and build an overhead crane system that fits your budget and your specific business needs. If you’re interested in receiving a quote on a new overhead crane system, contact one of our Crane Specialists today to set up a free consultation.