Pump Foundation API RP686

[penpe]

Chapter 4 of API RP686 section 6.3 states that "The width of the foundation should be at least 1.5 times the vertical distance from the base to the machine centerline, unless analysis demonstrates that a lesser value will perform adequately."

Are they referring to the base of the foundation? Or the base of the pump/motor skid?

The base of the foundation is dictated by the client at 6" below frost, and top of concrete 12" above grade. Centerline of shaft is 43" above T.O.C., so the foundation width is almost twice as wide as the skid if they are referring to the base of the foundation - which isn't completely outlandish, but not what I was expecting....

 

[dauwerda]

The reference of 1.5 times the vertical distance from the base to the machine centerline is referring to the base of the machine (in your case the base of the pump/motor skid). As you noted, this is 43" so the foundation's minimum width should be 43"*1.5 = 64.5".

 

[penpe]

Thank you for responding. The pump/motor skid is 7 feet wide, so it will easily meet that requirement in order to provide the required anchor bolts, which makes me skeptical. The correct interpretation of such "Recommended Practices" is imperative for proper application, and it's pretty unclear due to sentence structure whether "base" refers to machine or foundation. If they are in fact referring to the base of the machine wouldn't they say "vertical distance from the machine's base to its centerline"?

 

[dauwerda]

I agree that the wording is a bit vague. As the depth of the foundation is somewhat arbitrary based on frost depth and/or required mass (could be no frost and only need to be 12" deep or there could be 4+ feet depth required) it would not make sense to base the required width on the distance from the bottom of the foundation to the equipment. Also note that this requirement is a rule of thumb and generally a good minimum to follow (see section 6.1 and the end of section 6.3). My experience is that most pump skids are sized such that the foundation size due to geometry of skid is large enough to meet the above requirement (i.e. a 8' wide skid would get a 9' wide foundation).

 

[penpe]

I do follow your logic that required depth of foundation, and its relation to frost depth, shouldn't drive the pump foundation width. So measuring from the base of the machine would eliminate geographical location from the equation, and that provides a constant for the rule of thumb. I'm convinced that your interpretation is correct. Thanks.