Pump base designs 1

[nucleareng78]

Trying to get pointed in the right direction about bases used for pump skids.

I will first start by saying I am a mechanical engineer but with high interest in structural. I know most pump skids use a concrete pad to anchor too. Problem is that we want to use a 8" concrete pad and then mount a metal platform on top (around 2.5-3 feet tall).

I was assuming there are some sort of guidelines/standards for bases that may tell us the natural frequency of the platform.

Any good sources to start looking at?

 

[JedClampett]

Natural frequencies are pretty hard to calculate, with lots of assumptions (end conditions, cracked section properties, etc.) and involved number crunching. If the pump is on an elevated platform or upper story, you need to hire a structural engineer. But I won't kid you, if the equipment is light, cheap or slow (less than 1200 rpm), you might be better off taking a chance. I'm in water and wastewater treatment with lots of pumps and rotating equipment and we don't do a vibratory analysis for every piece.
Besides that, if you make your foundation three times the weight of the equipment, you're going to be all right most of the time.

 

[WARose]

I don’t think I’ve ever run a dynamic analysis on supports for a light (500-1500 pound) pump. Of course, what I normally do is put it on a heavy mat/footing; therefore there is no issue (that I have ever been advised of).

Why the platform by the way? Are you trying to get some elevation to match up?

As far as calculating the natural frequency goes….most software (like STAAD) can do that for a multi-degree of freedom system (which a platform unquestionably is). But if you are going to that length you should probably (also) do a time-history analysis (to get an idea as to what kind of displacements/velocities/accelerations you’ve got and to compare them to allowables). You’ll need to make a guess at the unbalanced force to do that.

 

[nucleareng78]

We are raising the pump elevation to get a straight suction line. The current setup has an elbow very close to the suction of the pump. This elbow we think is causing the pump to operate poorly (air pockets).

Raising it up this height will help us tremendously. Pump with motor weight is around 3900 lbs (fairly light).

Would it be wise to have a concrete pad under a metal platform though? I'm trying to find any type of book or source that may have standard base structures? Such as, how many beams are needed, etc.

My structural guy seemed worried that it would be pretty extensive calculations but since it is non-safety related and non-seismic I don't see any issue with the calculation.

 

[WARose]

Some sort of concrete base (for the platform to anchor to) would be just about absolutely necessary. I’d make it heavy and as broad as possible.

I can’t think of too many books that have pump base details. I’ve just always relied on some standard details that were developed at some large companies I’ve worked for.

Some pump bases I’ve seen: I’m not even sure they could go on steel (it was obvious they intended them to go on concrete)….so check that first.

 

[nucleareng78]

The main slab floor is concrete but I was saying we add an additional pad on top instead of anchoring directly to the main floor. Also, making the platform broad may require handrails or steps if OSHA requires it.

 

[WARose]

Ok, I didn’t know you were on an elevated slab (I thought you were on the ground)……when I said “broad” I was thinking of a base [on the ground] supporting a platform that supports the pump. In that case, it probably wouldn’t help things.

Depending on the thickness if the slab (and what the calculations show), a pad on the floor may not be necessary…..but it probably wouldn’t be a bad idea either.

 

[desertfox]

Try This

http://www.scribd.com/doc/14882252/63/Design-and-dimensions-of-pump-foundation

 

[desertfox]

another

http://www.waterworld.com/articles/...installation-can-impact-pump-reliability.html

 

[desertfox]

pipework:-

http://www.mcnallyinstitute.com/14-html/14-07.htm

 

[JedClampett]

The concrete base isn't a bad idea to add a little mass to the system. But you're frame is much more likely to contribute vibration than the concrete. I'd either use a very stiff section (i. e. piece of 24 inch pipe) or have your structural guy get off his duff and design you a braced frame that's so stiff, there's no way it can vibrate.
I was in the Nuclear business for 20 years. We would spend countless hours designing supports for 3/4 inch instrumentation pipes. This sounds important enough, even if it's in the NS side of the plant, to put in a couple of days.

 

[nucleareng78]

Are there any special nuclear codes to follow when dealing with centrifugal pumps in a nuke plant?

This is non-safety related so if our pumps were to fail it would have no effect on the reactor or other vital components.