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#73208 - 04/30/19 06:27 AM spring on pump vertical line : fluid weight?
vermaccio Offline
Member

Registered: 09/05/17
Posts: 39
Loc: italy
vertical line starting from pump top vertical nozzle: weight for spring?

i have to install a spring on a vertical pipe starting from top nozzle of pump to decrease load on pump top nozzle.
the pipe run vertically for about 3 meters and then goes horizontally.

For a (variable) spring hanger: have i to consider the vertical pipe full of fluid (a liquid having double weight of water) or have i to consider it empty?
Vertical fluid column (inside the vertical pipe) insist on bottom of pump and not on flange connection between pipe flange and pump flange nozzle (where i have to check flange load) : so, the spring hanger, i think, should not "feel" the weight of this fluid column inside vertical pipe.

Have i to set the fluid density =0 inside the vertical pipe (to avoid spring to support fluid weight that really will insist on pump bottom instead of spring)? or will this affect other caesar results? eventually can i set density (=2) and set a force on spring node equal and opposite to fluid weight so to discharge the fluid weight from spring?
what is the best way to have a correct spring load in this case? the pipe diameter is big (12") and fluid weight is high so i risk to order a wrong loaded spring hanger....

thank you

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#73210 - 04/30/19 07:45 AM Re: spring on pump vertical line : fluid weight? [Re: vermaccio]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 710
Loc: Louisiana, US
For pump nozzle protection, you have 2 goals:
1) To prevent over-distortion of the casing
2) To protect the impeller and rod

Ideally, your pump manufacturer selection will include verbiage to enhance the nozzle loads for your pump.

With that said, you should have an earnest discussion with the end user / operator to explain that if the pump lines are to be evacuated, the springs should locked after cool-down, if the pump can't handle the cold spring, or if you don't check to see if it can. That's not our call.

Two notes of caution:

1. With such a heavy liquid that you calculate dynamic effects at bends. Normally we ignore these because we're flowing too slowly with too light a liquid to account for the extra 0.1% of load this will cause. I don't know this for your application, and you shouldn't assume, either, and it sounds like this additional load can be the final straw.

2. Normally pump manufacturers should use the hydrotest case to validate their pin. You should consider using the greater of WW+HP and W+PX+TX where PX and TX is the greatest pressure/temperature they will choose to release the pins.

If they don't tell you, then you should provide the numbers you choose and insist they get put onto the P&IDs.
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#73213 - 04/30/19 08:47 AM Re: spring on pump vertical line : fluid weight? [Re: Michael_Fletcher]
vermaccio Offline
Member

Registered: 09/05/17
Posts: 39
Loc: italy

thank you.
but what about spring hanger load? have i to run caesar calculus with or without fluid density (for vertical pipe only, i mean)? or have i to insert a force equal and opposite to fluid weight on pipe near spring hanger node?

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#73220 - 05/01/19 09:58 AM Re: spring on pump vertical line : fluid weight? [Re: vermaccio]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 710
Loc: Louisiana, US
If you are going to tell them to pin the springs before evacuation, no. If you are going to not tell them to pin the springs before evacuation, it wouldn't be a bad idea to analyze this.

How you manage it is up to you, but either method seems viable to me.


Edited by Michael_Fletcher (05/01/19 09:59 AM)
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#73223 - 05/02/19 04:19 AM Re: spring on pump vertical line : fluid weight? [Re: Michael_Fletcher]
vermaccio Offline
Member

Registered: 09/05/17
Posts: 39
Loc: italy
all you said is perfect but i still have some doubt for pump flange load:
here link for a pdf drawing to explain better my question.

https://ufile.io/ibrjdavo

thank you

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#73225 - 05/02/19 09:45 AM Re: spring on pump vertical line : fluid weight? [Re: vermaccio]
mariog Offline
Member

Registered: 09/29/07
Posts: 669
Loc: Romania
vermaccio,

This question has been posted several times in forum. See for example an old one
http://forums.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=1400&page=1
which hasn't a clear conclusion.

But I have also a question for you: you are focused on weight of fluid column, however what about the pressure of fluid? Are you ready to accept fluid exerts pressure on pump nozzle but no weight effects on it?

Maybe you would find my question as non-trivial because fluid height can be converted as pressure at flange level....


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#73228 - 05/03/19 12:33 AM Re: spring on pump vertical line : fluid weight? [Re: mariog]
vermaccio Offline
Member

Registered: 09/05/17
Posts: 39
Loc: italy
uh! i searched but i didn't find such an insteresting thread. thank you smile smile

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#73232 - 05/03/19 08:17 PM Re: spring on pump vertical line : fluid weight? [Re: vermaccio]
mariog Offline
Member

Registered: 09/29/07
Posts: 669
Loc: Romania
Sometime you would find helpful in doing search directly in Google with an approximate string matching your topic, beginning the string search with "Caesar II". In your case would be something as caesar II vertical run fluid column pump.

BTW What do you think of pressure load on pump nozzle?

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#73239 - 05/06/19 08:55 AM Re: spring on pump vertical line : fluid weight? [Re: vermaccio]
Michael_Fletcher Offline
Member

Registered: 01/29/10
Posts: 710
Loc: Louisiana, US
An even more direct way to Google through the forums is to include the string site:forums.coade.com in your search.

For the same reason we do not include actual pressure thrust in the nozzle loads, we should not incorporate hydrostatic pressure thrust in the pump nozzle. This load is exclusively taken up by the bolts.

With respect to the original question, if you want the most realistic analysis, first analyze with the vertical pipe full. Then analyze with the vertical pipe empty. Then subtract the vertical loads and apply it as a force at the pump center.

If you were to replace the vertical column of liquid with solid metal, it's clear to see how the load pans out. When we convert solid interior metal to liquid metal, the liquid metal fails to hold itself up, and then exerts pressure laterally to its container.
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