Pump on Stilt with spring and sliding pads

[Pumpsonly]

Hi,
I have a requirement to mount a pump on Stilts with springs and sliding pads for the following reasons
which can be found in the HI web site.

http://www.pumps.org/content_detail.aspx?id=3992

· Spring mounted bases provide vertical displacement
under applied loads associated with thermal expansion of the piping.
· Optional addition of slide bearing plates may also be provided below
the stilts or springs to allow horizontal displacement associated with
thermal expansion of the piping.

The pump is a OH2 type with 55Kw motor at 2900 RPM and with VFD. Baseplate is heavy duty per API design. Total weight is about 1200kg. Operating temperature is 150C.

Appreciate if you can share your experience of such arrangement.
Who are the supplier of such mounting system?

Thanks !

 

[desertfox]

try these people

http://www.watson-marlow.com/Documents/knowledge-hub/Datasheets/us - USA/wd-521cc-us-02.pdf

I've no experience with free standing pump base plates, only ever used grouted in base plates.

 

[DubMac]

There are a lot of folks that make "anti-vibration" baseplate supports (Mason, Kinetics, etc). Google the same or "inertia baseplates". Most of these are used in the HVAC industry for <50HP pumps on water services. Seldom do they take into account any kind of vibration analysis other than asking about total weight. Many are nothing more than coil spring supports; but they seem to use a lot of them without issue.

Not saying these won't work for you, but at your temperature I would be careful looking at allowable forces and moments on the pump. Even though your baseplate is API, it is most likely not designed to support the total load at 4 distinct points; design is usually for evenly distributed load and grouting.

If this were a critical service pump and money was secondary to reliability (haha)it should have an FEA structural modal analysis to look at critical speed issues, and baseplate stress and deflection analysis to ensure API allowable forces and moments and coupling deflections are within allowables. Not a plug at all here, but a company such as Mechanical Solutions in NJ, is very good at this kind of analysis for $$$.

Also check out Trelleborg. They make "anti-vibration" mounts in marine environments for pump skids on FPSO decks; they are used to dealing with very heavy equipment mounted on 3 or 4 points and having some degree of freedom of movement.

Or you might just get away with some cheapo, coil spring HVAC mounts. Will be interested to hear in what direction you decide to go.

 

[Pumpsonly]

DubMac
Thanks for your input. I had experience with the inertial baseplate or inertial block for the HVAC industry for high rise building where equipment are installed at high floor level. We mount the concrete filled baseplate , like a grouted baseplate or an inertial block,which is 2-3 time the weight of the pump + motor and sit on top of 4 springs. The function was just to isolate / reduce vibration transmission to the floor.

This case here is for a chemical plant and the reason for such installation is requested mainly to cater for the thermal expansion of the piping so as to reduce the pipe stress as described in the HI statement.

The vertical displacement required is less than 1mm. So is not so much of an issue.
But the horizontal displacement is about 7mm. Spring mounts will not tolerate lateral displacement.
To allow horizonatl movement, a PTFE plate has to be attached to the bottom of the spring mounts and resting on a smooth finish mounting plate fixed to the floor. The whole pump assembly is suppose to slide forward and backward when the suction piping expands and contracts between ambient and operating temp.

This is still in discussion stage.

Other smaller and low temp pumps are just mounted on free standing stilts.

 

[TenPenny]

I would expect that ALL of the major manufacturers do this routinely. The stilt mounted bases are quite common, and spring mounted ones are also pretty much 'straight out of the catalog' options.

 

[Pumpsonly]

I can find a few stilts only vendor but not with the springs and the sliding pads.

 

[TenPenny]

Make sure you're clear with your terminology.

With ITT/Goulds, 'stilts' are simply feet under the baseplate that sit on the floor, they are not on springs. What you are describing is what they call their 'spring mounted baseplate'. Standard option out of the catalog.

With your reference to OH2 pumps, are you looking at API 610 pumps? If so, remember that those are centerline mounted, and I don't think 610 covers spring mounted baseplates, but I could be wrong.

 

[DubMac]

Understand the service a little better. Having been formally trained by API pump manufacturer back in the dark ages.....one of the biggest credos was: "ALWAYS advise against using the pump as a pipe hanger, or to offset thermal growth displacements". Also disavow warranty if nozzle allowables were exceeded in the design stage.

With an end suction, especially at your temperature, will you be adding stresses or applying some kind of moment to the casing from the nozzles alone, before the support has a chance to alleviate? This could be designing in a never-ending misalignment nightmare.

One thing I would for sure not do is use a "catalog" solution to an elevated temp, API pump service. My first tack would be to tell the piping guys not to use the pump to solve a piping problem. If determined however to let baseplate supports absorb the displacement, ask the manufacturer of the supports to gaurantee there will be no casing distortion or alignment issues from thermal displacements. I imagine they will back off quickly.

Again, in a perfect world, or if this was a NASA project and the $$ warranted, a full structural modal analysis with stress and deflection analysis of the complete unit should be performed. Otherwise buy a lot of spare bearings, seals, and couplings.

Just my armchair QB opinion.

 

[Pumpsonly]

The pump is not a API 610 spec. Just a ISO standard end-suction pump with center line casing mounting.
Decided to use API spec baseplate for rigidity due to elevated support on stilts.

See attached similar arrangement from Flowserve and Goulds.

It was a HI suggested solution for piping thermal expansion..

We need additional requirement for lateral movement which I don't think the slender spring and stilt assembly will allow.

 

[DubMac]

Pumpsonly....I don't want to make a mountain out of molehill, but API service or not, it's still operating at 300DegF right? Allowing the nozzles to absorb the piping thermal expansion displacements is going to put a strain on the pump casing before the stresses can be transferred even to the mounts. If the displacements are small and infrequent, then a centerline pump may work well; but if not.........

Not from an API rule-breaking stance, but just looking at reliability, can it be gauranteed that the pump casing will not be continually distorting and screwing up rotor alignment?

If someone cannot gaurantee that their mount will keep the pump casing within the nozzle allowables for this service ; I would ask them why not.

Just as an exercise, I would pester the local Goulds or Flowserve Sales Office Application Engineering Group and ask them if they would quote that baseplate in the picture, on a 300 degree service given the displacement forces to the nozzles. Ask them if they'll gaurantee the seals & bearings for a year, or even for a month.

Maybe I'm just a scaredy cat, but this one scares me.

 

[JJPellin]

We have about 1500 API pumps in service. Of those, two have spring mounts and two have slide plates. In both cases, the process temperature is over 500 F and the piping is very stiff. The ones on springs seem to work pretty well. They are very old pumps (circa 1955) and have been redesigned many times. The two on slide plates have had terrible reliability. The slide plates don't slide. After the first couple of years, they were rusted in place. All four of the pumps I am describing are 400 HP or larger, so they may not be representative of your equipment. I am old fashioned. I like a nice solid foundation with flexible piping.

Johnny Pellin

 

[TenPenny]

PumpsOnly, looks like all you need to do is go with a standard spring mounted base from Flowserve or Goulds. Thousands of them are installed in similar services with no issues.

Make sure, of course, that your pump materials and configuration including seal are good for the temps and pressures. Personally, I would avoid referring to an API style base for an ANSI/ISO pump, unless you wish to pour money on it. The spring mounted bases from the big manufacturers will be heavy duty fabricated steel construction anyway.

 

[Pumpsonly]

Thanks for all your valuable input. I personally prefer the traditional solid foundation. But for this case, because of the short suction piping space,there are limitation to design a more flexible piping.

Because the pump is center line mounted,the vendor can just use one of their standard API base for OH2 pump without adding many dollars.

We were asked to look into this simply because it is prescribed by HI.

Alternative is to put a flexible connector in the suction piping.

 

[DubMac]

Pumpsonly, I talked to a cohort at Dow Freeport and he said they use Teflon sliding plates under some of their Goulds pump bases for high temp services where the baseplates can "walk". He couldn't remember if it was Goulds or not that made them, but they were used with the Polyshield baseplates (super-thick non-metallic).
He did mention that the piping did not impart any unacceptable loads to the nozzles however.

 

[TenPenny]

If you spec an API base for an ANSI pump, you are asking for a custom design, and it will cost you a fortune.