Centrifugal Pump Bases

[nucleareng78]

We have a 900 rpm pump and are wanting to re-do the piping so that we have 5 feet of suction piping before it hits the impeller (let the flow settle out).

The problem is, in order to get that 5 feet we need to raise the pump's suction level pretty high (around 2.5-3 feet). We are considering a 1 foot concrete pad with a 2 foot metal platform.

Has anyone had experience mounting a pump to a metal platform? Or had a concrete pad higher than 1 foot? It's not a very large pump but would be have to do some sort of additional calc to verify it would not topple over? It's only 2 feet of metal platform though.

 

[cloa]

People might want a few more details like how big is the pump especially the dimension that it is being attached, how much does it weigh and is it centrifugal or positive displacement.

 

[BigInch]

Concrete is cheaper and generally provides a more solid foundation against vibration, but it would look kind of stupid if it was for a 100 mW pump.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[nucleareng78]

It is a skid mounted pump. 90 inches long. Height from base to discharge flange is 52 inches. Total weight with motor is approximately 3700 lbs.

It is a centrifugal pump with a 40-50 hp motor. I can try to provide a quick sketch on paint if needed.

I'm just trying to figure out if the reaction forces for a smaller pump would be that high. And is there usually a limit on how high the concrete pad can go? I know at certain heights it can fail something called a "slab test."

Also, am I correct in wanting 4-5 feet of straight piping before the suction of the pump?

 

[TenPenny]

Many of the pumps I see have concrete pads that are at least 2 ft high, and these can include pumps up to 200 hp. I'd just make sure you design the pad properly (but that's not my area, so I have no advice on that).

 

[BigInch]

CONCRETE. NO QUESTION.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[nucleareng78]

I was pushing towards concrete as well. A metal platform seems to rsiky.

One question, will having a concrete that is 2 feet high imposed any cracking issues when the pump is operating? I've honestly never seen a pump pad that high before, if anyone has any pictures that could share just so I can put it into perspective.

BigInch, do you know of any resources regarding pump concrete pads? I've searched around and could not locate any helpful sources.

 

[pennpiper]

There are tall "Stilt mounted Foundations" for Coke Drums, some as much as 100'-0" high.
There are 15' to 20" high Stilt mounted Foundations for Centrifugal Compressors.
There are many, many Reciprocating Compressors around the world sitting on foundations that exceed 5'-0" in height.

All of these types of equipment generate a lot of vibration but I have yet to hear of any real failures due to height.

I suggest that the original poster should discuss the height of the foundation with the Structural Engineers on the project.

As for the mythical "5'-0" issue" for the pump suction piping he has not given us enough information for us to comment.
- What is the Commodity?
- What is the Operating Temperature?
- What is the Operating Pressure?
- What is the suction line size?

prognosis: Lead or Lag

 

[BigInch]

6 ft, 8 ft, 10 ft, 12 ft are common, counting footing thickness.
Up to 250 HP pumps are not usually considered critical enough to require a dynamic foundation design, with many foundations in that range sized on proportional dimensions and weight rules. for example such a foundation might have at least a width of 1.5 x bottom of foundatin footing to height at machine centerline and a foundation weight of 2.5 x the weight of motor + pump + gear box.

The maximum lateral load at the machine centerline for overturning stability check would be calculated from the torque generated from a short circuit condition.

The US Army Corps of Engineers has a design manual concerning dynamic machine foundation design. I think it is engineering manual EM#515 or is it EM#517. Let me know if you can't find it. I have a copy somewhere around here.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[1gibson]

Don't forget to transfer piping loads imposed on the nozzles, down to the anchor bolts.

 

[BigInch]

I don know... Pump nozzles allowables arn't usually high enough to impact foundation design. At least they won't be forgotten now. Short circuit loads can be quite high though. Or seismic shear forces, if earthquake zone.

I was going to mention that reinforcement steel in the concrete usually isn't complicated. Enough for temperature expansion and shrinkage steel (0.0018 x cross-sectional area of concrete) is required in all the lateral and top faces (both ways) to account for most of it. Then just add dowels between footing and pedestal joint For that size pump, you could level with normal grout rather than epoxy grout for larger machines, but be sure to have your foundation engineer take a look.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[nucleareng78]

Is this the Army Corp of Engineer papers you were talking about?

http://publications.usace.army.mil/publications/eng-manuals/

I don't see a 515 or 517...


Also, would additional calculations be needed with a pad that high? From a structural standpoint it almost turns into being a foundation to a column. I'm not structural but a column could be a mess of problems right?

 

[BigInch]

Seems I can't remember my manual numbers. TM 5 - 818 attached

No columns. No eccentric loadings, just a chunk of concrete with a balanced soil bearing load for normal weight loads, ie. CG of foundation footing directly below CG of equipment, plus a check of overturning stability from short circuit load.



"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[nucleareng78]

Found out that there are 90" tunnels underneath where we are putting our pumps.

At 125 lb/cf for concrete and the pump/motor weight over 3600 lb, we are looking at 6 tons for the whole skid if we were to make them 3 feet tall.

Apparently we only have 6 inches of stab to anchor our bolts too...that being said, under the 6 inch of slap is just filler concrete. Looks like 3 feet of concrete may not be possible. And we really would want to stay away from a metal platform.

If all else fails we'll have to lower the pump and install flow straighteners at the suction to prevent air pockets from hitting the impeller. I mentioned that it is a good rule of thumb to have straight pipe before the suction flange, but does this depend on the flow rate?

 

[Artisi]

If you have airpockets - 5ft of pipe or 50ft of pipe or flow straighteners won't do anything to help the situation.

Build a steel structure, can't see what your problem is for a very basic engineering undertaking.

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.)

 

[BigInch]

Back to square 1. Concrete weighs 150 pcf.
How far below floor are the tops of the tunnels?

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[nucleareng78]

I'm trying to confirm this about the tunnels. My structural guy said we have avaliable 6 inches of slab to bolt into. There is fill concrete below that though.

This is why I would much rather go with a 8" concrete pad and then bolt a metal platform about that...bolts going only to the pad or straight through the pad and slab underneath?

A 900 rpm pump should not generate much vibration in the platform. Would need to find the natural frequency of the platform to make sure this doesn't happen. Hopefully the client doesn't freak out when they see this!!

 

[BigInch]

My aquarium pump vibrates.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[Artisi]

I just don't believe this thread, it sounds like the wheel is being invented.
A simple fabricated steel to be bolted to a concrete floor to mount a smallish pump on.
A first year eng. student exercise

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.)

 

[BigInch]

No, it's the same fire pump from the thread next door. I've always thought that the most responses are generated from the silliest threads. This one is proof of that theory. Add the two together and we will soon easily reach 100+. I'm going to see how long we can keep them going.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek