There are three configurations of couplings commonly used on these pumps. For the smaller ones (less than about 150 HP), they often use a greased spline drive. This is not desirable for a couple of reasons. First, the greased spline requires frequent maintenance. It is basically a greased gear coupling. It should be cleaned out, inspected and packed with fresh grease once per year for continuous operation. The second problem with this arrangement is the difficulty in fully inspecting it. There is not a good way to properly inspect the internal spline in the end of the motor shaft. The last problem is the fact that this makes the motor a special order that is more expensive and has a much longer delivery time.
Other pumps of this type use a non-lubricated disk-pack type couplings for a close-coupled arrangement. This type has a spacer housing and perhaps a gap of about 3/8” between the shaft ends. This type of coupling is difficult to assembly and disassemble. It has a spacer, of sorts. But, you have to disassemble the bolts and washers through the disk packs to take it apart. But, at least this lets you use a standard motor with a short shaft.
The last type of coupling commonly used is a standard spacer coupling. This could be any type. We commonly use disk pack couplings with drop out spacers (Thomas Series 71).
There are many reasons to use the spacer coupling. It is more reliable than the spline and requires much less maintenance. It is quicker and easier to disassemble and reassemble than the close-coupled arrangement. It has a longer span between flex planes which reduces the load on the bearings if the alignment across the pilot fit from the motor to the gearbox is not perfect (and they are not). I would not consider purchasing a pump of this type without a spacer coupling.
Johnny Pellin
