Loader arms: z-link vs. parallel lift

In the world of wheel loaders there are two different styles of arm configurations – Z-linkage and parallel lift. And while either style can do most of the work of the other, there are advantages to choosing the best design for the applications at hand. To find out more about these differences, we talked to Gary Bell, vice president and general manager for Kawasaki Construction Machinery. He compared their 65ZV, single Z-linkage machine with their 65TMV Task Master which uses an in-line parallel linkage. There are two types of parallel linkages on the market. In-line places the linkage in-line with the lift arms and a parallel lift linkage that use a single cylinder and linkage mounted between the lift arms.

PARALLEL LIFT PROS

· Visibility. In-line, parallel-lift linkage offers operators great visibility down the center of the lift arms. This is particularly useful in pallet handling and pipe laying where you need to see the ground or work area in front of the machine.
· Parallel lift. When you pick the work tool off the ground with a parallel-lift machine it rises flat rather than rolling back. Again this is helpful in loading pallets or lifting anything you want to keep level.

PARALLEL LIFT CONS

· More parts. With two hydraulic cylinders and two sets of linkages, the parallel lift design has twice as many cylinders, pins and bushings to service and maintain as a single link design.
· Less efficient breakout force. The geometry in a parallel-lift arrangement can result in less mechanical leverage than a Z-bar configuration. And since the digging or rollback of the bucket is achieved by charging the smaller rod end of the tilt cylinder, a larger cylinder or higher operating pressure is required to achieve the same digging force as if the larger base end of the cylinder is charged.

Z-LINKAGE PROS

· Simple, efficient breakout force. The mechanical advantage of the Z-configuration produces higher breakout force more efficiently. The larger base end of the tilt cylinder is charged in the digging or rollback function and makes it a better choice for applications where you’re digging hard or heavy material.

Z-LINKAGE CONS

· Visibility. On single Z-Link machines or in single link parallel linkages, the hydraulic cylinder is dead center in your field of vision, so you can’t see directly in front of you as well.
· Fork arc. The rolling action of the fork makes it difficult to hold a load level for pallet handling.

MISCONCEPTIONS
Parallel-lift loaders have been marketed as “tool carriers,” says Bell. But couplers and attachments can be used on either style (except for attachments that need to be lifted flat, such as pallet forks.) Also, third-spool hydraulics were once marketed for couplers as necessary to actuate the locking pins. “But most couplers can be handled with a less expensive diverter valve, unless you have an attachment with a third function.”

VERDICT
Choose the machine based on your application needs: parallel-lift for its material handling finesse and better visibility, Z-linkage for simplicity and efficient digging force. Bell also advises that you consider the resale value of the machine you buy. If you’re in an area where parallel lift machines are popular, it may be harder to sell a used Z-linkage machine and vice versa.