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An in-depth explanation of the differences between these two choices.
Flexible couplings can be broken down into elastomeric and metallic types. Both grid and gear couplings fall into the lubricated category of metallic couplings as outlined in Image 1.
Image 1. Hierarchy of flexible couplings (Images courtesy of HI)
Grid style couplings are often used in medium- to heavy-duty applications and use a spring style metallic element with looping segments that interlock with the hub teeth. An example of a grid coupling is shown in Image 2.
Image 2. Close-coupled grid coupling.
The grid element or spring is made of high tensile alloy steel. The grid element transmits torque and accommodates some misalignment and shock loading in the system.
Because of the relative movement between mating metal surfaces, the grids and teeth must be lubricated as specified by the coupling manufacturer.
Image 3. Close-coupled, flex-rigid gear coupling
A typical grid coupling consists of the following components:
- two hubs
- two seals
- two gaskets
- a grid element
- either an axially split or vertically split (perpendicular to the shaft)cover
Image 4. Spacer gear coupling
Gear couplings come in many different designs, but all transmit torque and accommodate some misalignment through gear teeth. A few examples of gear couplings are shown in Images 3 and 4. Each hub has gear teeth cut around the outside diameter, with the hub connecting to a sleeve with mating gear teeth cut into the inner diameter. These products also require lubrication due to the relative movement of mating metal surfaces and have seals between the sleeve and hubs.
Gear couplings are often used in applications where high torque and balance are required. In some cases, gear couplings are the only solution with enough torque capacity to accommodate demanding applications. There are many custom options available with gear couplings in addition to those described here.
This type of coupling can be configured as a flex-flex, flex-rigid or rigid-rigid gear coupling. A flex-flex configuration uses two flexible style halves, with one half consisting of a flexible hub and a matching flexible sleeve. A flex-rigid
style uses one flexible style half and one rigid half.
A rigid-rigid gear coupling uses two rigid style halves. Flexible style grid halves also have seals to retain lubrication, and both styles typically incorporate a gasket between the mating flange faces.
For more information on couplings used with pumps, refer to HI’s Flexible Coupling Basics Guidebook at www.pumps.org.
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