Minimum Shims requirement for Pumps as per API-686 2

[skpatel]

Dear Experts,

During Pump to motor alignment, we achieved the alignment with just 0.5 mm shims under motor base but Client inspector insists to provide minimum 3 mm shims as per API-686 and Project specs requirement.

Can you advise me the reason behind minimum 3 mm shimming is must even if we achieved the alignment with 0.5 mm ?

 

[Artisi]

I am unaware of the reason why 3mm and not 1, 2, 4 or 5 of shim is specified in the standard, but it is and if you only have 0.5mm then the pump installation is not to spec. and can be / has been rejected by the inspector. Sounds as though you need the motor pads to be reduced in height so that a minimum or 3mm can be achieved.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[skpatel]

Thanks Artisi.

Actually I wish to get some technical explanation which can help me to get concession through TQ from client, Machining of Motor pads is the last option.

 

[ApplicationENG]

I believe this is required is so that the motor can "float".

There would be a +/- 3 mm tolerance or larger, i.e. +5/-3. By only having 0.5 mm of float as your negative tolerance, this may create problems during future alignments for whatever reason. I guess 3mm was decided as a practical number.

 

[Artisi]

in theory 0.5mm should be sufficient, motors centre height tolerance is normally +00, -0.5 to 1mm and pump centre heights are + xx, -0.
What this means is, if you changed a motor, the centre height - underside of mounting pad to motor shaft centre will be the same or less than the existing motor ie, maybe needs more shim. Changing a pump the centre height, underside of mounting pad to pump shaft centre will be the same or more than the existing pump - this means means more shim under the motor to get shaft centres in alignment.

To put it in numbers, a D180 motor centre height is 180 +00 -0.5 mm, I don't have a pump book handy so assuming a pump centre height of 300mm the tolerance would be something like 300 +1.00 -00mm.

However, the code stipulates 3mm and that's it - sorry.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[CaracasEC]

API 610 11th edition paragraph 7.3.6 All pads for drive-train components shall be machined to allow for the installation of shims at least 3mm thick under each component. If the vendor mounts the components, a set of stainless steel shims at least 3mm thick shall be furnished. Shim pack shall not be thicker than 13 mm nor contain more than 5 shims.

 

[CaracasEC]

Hi skpatel, machining of motor pad should not be the last option since api 610 11th edition paragraph 7.3.6 If specified, in addition to shim packs, a stainless steel spacer plate not less than 5mm thickness machined on both sides of the same length and width as the specific mounting plate shall be furnished and installed under all equipment feet including the pump, the driver and any speed increaser...hope this will help

 

[TenPenny]

In the old days, it was 'good' practice to put 1/8" shims under the pump and motor so that proper field alignment can be made once the piping is done; the 1/8" was deemed to be enough to allow for lowering the equipment train if required. Obviously, the 1/8" has continued, and lives today as 3mm.