View Full Version : Pump couplings
07-29-2004, 11:28 AM
When installing or repairing a flexable type pump coupling (the Lovejoy kind with two flanges and a rubber sleeve insert) should the keyways be lined up opposite each other or 180 deg. apart from each other? I am trying to reduce any imbalance and vibration on the shafts.
The shafts are different diameters, if that matters.
07-29-2004, 06:51 PM
I would worry more about the alignment tolorences. Also if this is a 3500 rpm pump your alignment becomes more critical.
Are you aligning both the parallel and the angular alignments to the coupling mfg's tolorences? Are you sure you have your soft foot on the motor down to a minimum.
07-29-2004, 07:50 PM
The pump is 40 hp 1750 rpm 1600 gpm condensor water pump. The bearings are very noisey and I will replace them and install a new seal tomorrow. I will align the coupling as close to specs as I can get it using a 6" steel rule, feeler guages and spacer blocks. I do not have dial gauges or lasers (and don't really know how to properly use them).
What is Soft Shoe? Is that a procedure or a shim product? Can you give me any tips or methods to make the alignment any easier? I usually keep playing with it, adding or removing shims, tigtening down the motor feet, check measurements (always to high or low!) then do it all over again and again until I feel it's "as good as I'm gonna get it".
I think I was getting anal about the keyway positions!
07-29-2004, 08:25 PM
i've had issues with couplings blowing out..just make sure the flanges are clean, make sure the coupling is pressed up on the the flanges..i've had no problems using a torpedo level..but that was my situation..had no problems since.
07-29-2004, 08:52 PM
Dont know the term soft shoe but when shimming the motor, my experience is to snug the motor bolts when tightening it back down in a cross pattern. Motors have a tendency to shift as you tighten them down. If you are using a black rubber insert they need to be as close to perfect as possible. The harder orange inserts take misalignment better. Oh, and dont just press the coupling halves together after aligning it..Make sure you follow the coupling manufacturers tolerances ..
07-29-2004, 11:28 PM
can't be done wothout calipers. more than likely will have to be within 4000th.
Most coupling manufacturers allow a maximum of .0010" difference between coupling halves on a 1750 drive but the closer the better. No calipers? Go buy a set, can't do the job right without the proper tools. Save the laser for 3450 drives and the like. Follow the coupling manufacturers recommendations for the coupling spacing, failing to can cause premature failure of the insert. Misalignment can cause bearing failures.
07-30-2004, 01:06 PM
I will use a vernier caliper to get the angular measurement but will still use the steel rule and feeler gauges for parallel. Hope I can get it within spec! What about the keyways though?
07-30-2004, 01:12 PM
Are you sure you have your soft foot on the motor down to a minimum.
What do you mean?
[Edited by powerhead on 07-30-2004 at 01:15 PM]
07-30-2004, 07:39 PM
I always have the coupling alined with a dial indicator or lazer set up. The pump will last alot longer with less vibration and wear. Any company that does vibration analysis
or sets up mechanical equipment can do it if you don't have the equipment.
07-30-2004, 08:05 PM
A motor will rarely ever set perfectly on the base with all four feet. Since you do not have a dial indicator you are going to have to use feeler gauges. Soft foot occurs when there is an abnormal space between the motor feet and the shims. There are two kinds of soft foot, parallel and angular. Angular is harder to correct because you have to step shim the foot of the motor.
Soft foot over .005 will put stress on the motor housing thus causing stress in the bearings and shaft, because when you tighten the motor down it pulls the foot down to the base. Soft foot must be corrected before you do any final alignment. Get the motor somwhat close in parralel and angular alignment. Then tighten all four feet down. Start on one foot and loosen the bolt, leave the other three tight. Put your feeler gauge inbetween the foot and the top shimm. If you are over .005 then you should correct it. You will notice that if you have a soft foot, the foot diagonally across will also have soft foot if it is parallel soft foot. The other two will most likely be fine. If you have an angular soft foot you will notice this when you try to slide the feeler gauge under neath the foot it will go easy on one side and stop on the other. You will have to step shim the open side. They do make a product called soft shoe that you can buy from graingers that is supposed to eliminate soft foot. I have never had that much luck with it. I have not found a science in correcting soft foot, but if it is parallel I will take the foot that has the most soft foot and insert a shim double the measurement to start with. If you have severe soft foot you will notice it if you are able to move the shims around with your fingers when the motor is not bolted down.
Make shure that you always use stainless steel precut shims. Brass shimstock is maleable and should be avoided.
Most coupling mfg's want to see no more than .004" TIR (total indicator reading) for parralel alignment. The angular will vary with the diameter and rpm of the coupling. If you do not have a coupling over 5 inches in dia. then I would limit the angular to a max of .010" There again, check the mfg requirements.
Also when final alignment is acheived, shove the coupling halves together until they stop on the insert then pull one coupling back about 1/8 of an inch and tighten the couplings. This will allow for the thrust of the motor shaft upon startup.
P.S. Graingers also sells a fairly inexpensive Starret dial indicator kit. If you are interested I can get you the part number.
07-31-2004, 07:10 AM
I use a caliper on bigger motors but on one that is 50 hp or smaller I use a straight edge. Have never had any problems. The literature that comes with the coupling does not recommend any play in the coupling insert, keeping it pulled tight to both coupling halves.
The keyway position is not supposed to matter, but I have eliminated some vibration by moving them to different postions. 180 degrees of one another will not always do it. Have to try different postions till you get the best results.. If you still cannot get rid of the vibration try using the new bolt on coupling. There are two types. The one you want actually bolts to the coupling halves..The other one uses a Dodge insert and it is pinched together by using a flat metal plate inside the coupling insert.
just used one the other day. Worked perfectly. Will try and get you more info if you like..
07-31-2004, 09:52 AM
Thank you all,
all this advice is great. I'm sure the job will be O.K. after your help.
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