close coupled vs base mounted pumps 4

[Geby]

Pump manufacturers such as B&G offer the same pump in either a base mounted or a close-coupled design. I am wondering why close-coupled pumps are used so infrequently when compared to base mounted pumps. Base mounted pumps need to be aligned, which requires special skills and tools. I suspect that the alignment step of a base mounted pump installation is frequently skipped by the contractor, since in many cases he could get away with it. Close coupled pumps will not accept a standard motor, but how big of a deal is this really? I am not sure what the cost difference is between the two, but maybe this is a factor.

I appreciate any input that anyone can contribute.

Thanks,

Geby

 

[FACS]

Close coupled pumps require the pump manufacturer to have it's motor supplier fit the motor with a machined hub. The hub is machined from a casting, and guess what, usually the replacement motor can only come from one source. The motor is more expensive since it is now an OEM and not readily available.

When a pump leaks, and it probably will, it may leak into the motor, depending on how it is mounted. It is also harder to detect leaks as the pump hub is mounted inside the motor casting.

Mounting and aligning the motor/pump combo should not be as hard as you expect. Mounting a close coupled pump inside the motor casting takes some precision machining, and repair alignment is not always guaranteed.

I also do not like the small tang used to drive close mounted pumps. Using a coupling to run the pump from the motor shaft is better because there is no stress riser on the pump/motor shaft.

Space restrictions sometimes play a role as close mounted pumps have a smaller footprint.

Close mounted pumps can be rotated for piping alignment without rotating the motor.

Removing a close mounted pump is easier.


Charlie

http://www.facsco.com

 

[TenPenny]

In my experience, I find that most process plants have large populations of motors, and try to make them as interchangeable as possible, so foot mounted horizontal motors are the preferred choice.

Also, in the example of end suction pumps, using pumps that are designed for back pullouts with spacer couplings means that, in the event of pump maintenance, the motor does not need to be moved, so fewer trades are involved in the maintenance operation.

 

[SteveWag]

I work in the municipal water/wastewater area and make the selection based on the competence of the operators. In larger plants having designated mechanics I specify coupled units. In the case of smaller plants I use close coupled pumps unless I know the operators. My personal preference is coupled motor and pumps. A little more expensive but cheaper as soon as a motor needs replaced. Also allows the pump to be removed without disturbing the motor wiring.

Steve Wagner

 

[pumpking]

The modern close coupled pumps use standard shaft motors to avoid the 'special motor' scenario.

While they offer space saving, cost saving, automatic alignment and are nice compact units, they do have limitations for use, especially on plant that are operating 24/7 on critical duties.

The back pull out (long coupled) design are made for ease of maintenance, especially during the middle of the night, where simply the pump rotating assembly can be removed, leaving pipework in situ still attached to the casing, motor can stay in place avoiding the need for electriciants to assist, and replacement pull out unit can be installed within half or so, with equipment that has been prior repaired and tested so operators are confident that plant will operate correctly first time.

The down side of long coupled pumps is that ideally, units should be laser aligned to improve MTBPM and also the initial cost is higher due to the additional baseplate, coupling, guards etc - thats simply a decision to be made on the criticallity of the installation.

Examples of both designs can be seen on

http://www.cdrpumps.co.uk

where we manufacture pumps for nasty chemical applications, and these kind of questions are commonly discussed with customers - hope this answers sufficiently ??

 

[TenPenny]

"The modern close coupled pumps use standard shaft motors to avoid the 'special motor' scenario."

While that is generally true, it's not the shaft I was concerned about. Most close coupled pumps require a C face motor, and, while it is generally only a matter of changing the end cover, it still makes the motor a 'special' to most electrical departments.

 

[PumpSmart]

Geby,
The real thing is that pumps creates 2 kind of hydraulic dinamic loads in shaft.
Sometimes in little pumps, motor shaft (and motor bearings) can stand these little loads. In high pressure or high capacity or high energy leveld , you will never see a coupled design pump.
Coupled, Foot mounted and certerline mounted has advantages depending the application pump is used for.

 

[pumpking]

TenPenny, interesting comment you make re the 'C' face, Im guessing this is American specification close coupled pumps ? European pumps tend to have 'D' flange motors which are a standard available mounting method - would agree 'C' face availability is somewhat more difficult, but only a couple of days or so.

Perhaps the pump manufacturers should look at this problem and identify a resistance to the market - modifying for 'D' flange is not a major project !!!!

http://www.cdrpumps.co.uk

detail the designs with 'D'flange motors...

Ash Fenn

http://www.cdrpumps.co.uk