minimum shim pack thickness - why?

I saw the following statement in the Precision Brand Sof Shoe literature:

"For the driver, it is good standard alignment practice to always have a minimum of 1/8" thick shim pack (using no more than 5 shims) under eac motor foot for motors up to 250hp. For larger motors a minimum of ¼" shim pack thickness is recommended"

I have heard of a maximum number of shims but I don't remember hearing about a minimum shim pack thickness. What would be the reason for that?
Original Post
I knew that bases and pumps were set up that way to ensure the motor could always be lowered enough.

I thought it was kind of weird to present it as a driver alignment practice. If can get acceptable motor alignment with only 0.020 inches under one of the motor feet, I don't think anyone's going to go back and raise the pump just to get this minimum 0.125" under all the motor feet (are they?).
I think that is a theoretical approach far removed from reality. Wishing shim total thickness no greater than 1/8 inches is also wishing that the foundation is designed manufactured to perfection with only minor adjustments needed. Can this be a fact of life?

Not to this boy's experience anyway!

That is a standard: 0.125" for initial setup. After subsidance and after removals, then you will only make the 'pump rise' (always a last resort). Generally all piping will have to be re-aligned and pipe hangers re-adjusted.

And that is standard run-of-the-mill equipment. On large turbo-machinery I'd go with Bill's suggestion - plate and shim pack. Certainly its a long way from end-to-end on large machines whereas the smaller machine train may be only 5' end-to-end.

And speaking of pipe hangers: routine maintenance on some? Different topic; more later.
Hi Pete,
1/8 is standard procedure for new installation. Once the pre-alignment is done then you weld the piping of the pump or anything fixed. It will ensure that you have enough shim to compensate for any future changes as new pump or motor. Starting with a thick Stainless steel shim and just a few shim packs to finish it up. I don't like to have long steel plate that goes from one foot to another for there may be dirt in between that could cause a twist within the machine. I recently saw new elastomer shim pack that can be use for soft foot. Seem to be good but I never use it yet.

Best regard, Marcel


Yes the minimum and maximum thickness of shim pack and no of shims are mentioned as per the API RP 686- recommended practices for Machinery installation and installation design.

That says (API RP-686 - 5.4.2-shim requirements)
" The maximum allowable number of shims under any equipment support foot is five".
"The movable machine shall have a minimum of 3 millimeters (0.125 inch) of 300 series stainless steel shims under each support foot. The maximum shim stack height shall not exceed 12 millimeters (0.5 inch). Only one 3-millimeter (0.125-inch) or thicker shim per mountingfoot is allowed"

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