Open bellows on Pump's Nozzle - Thrust Force

[Lore80]

Hi to everybody,
my name il Lorenzo, I am an Italian Aeronautic Engineer working in piping stress analysis since 2006. It is a plesure to take part at this interesting forum hoping to meet nice engineers and attending interesting topics.

My first topic, and sorry if it is not in the right section, is related the use of open bellows. Everybody knows the effect of thrust force introduced by an open bellow expansion joint under pressure; in Caesar 2 we find also suggesting for installation of open bellows on pumps but there is a theme that is not clear in my mind: the action of the thrust force on the Nozzle of the pump.

I have heard somebody saying that thrust force introduced by the open bellow installed on the pump's nozzle does not partecipate directly on pump's nozzle because it acts on pump's baseplate. And, according to this, I have seen to substract the value of the thrust force from the results obatined on pump's nozzle and after that, to compare the value to the allowables imposed on the nozzle itself....it is right in your opinion?

Sorry but it is difficult to believe that the thrust force does not act on the nozzle....this is the reason I prefer to work using lateral tied expansion joint located in different position in order to control the effective values on the pumps with substraction of nothing...

Regards

Lorenzo

 

[bimr]

Agree with your arguement. If you use a flexible connector between pump and piping, you must account for pipe thrust. Since the pump manufacturer does not account for the pipe thrust in the design of the pump, the flexible connector (and piping) must be anchored to avoid putting the thrust on the pump nozzle.

If the end of the expansion joint closest to the pump is not anchored securely, the pipe strain is passed through to the pump, thus defeating the objective of the expansion joint.

 

[Lore80]

Thanx bimr!
but the open bellows is installed at the nozzle itslef, so it is located between pump's nozzle and the pipe anchor, so ok regarding pipe side, we have the anchor and the thrust is solved on pipe side, but what about at pump side? If I check the caesar2 results on nozzle I will found the thrust value resulting in the exceeding of the allowables of the pump

 

[LittleInch]

Can you sketch out the arrangement here as I'm getting a bit confused.

From what you describe, I can't see where the thrust on the nozzle is coming from other than reaction force from the bellows itself??

Bellows (there are many different types) will normally reduce loads coming from the piping, but do not make them zero, depending on the amount of differential movement and stiffness of the bellows themselves.

If this is mounted directly on the nozzle itself, you shouldn't be getting any liquid thrust on the nozzle, unlike if there was an elbow or something.

The devil here is in the detail I think.

If this is a Caesar 2 issue, then there is a specific forum for that

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Lore80]

here is a scheme

pump + exp joint (open bellow) and a part of pipe with a pipe lock.
Thrust force is the red Arrow; the right one acts on the pipe lock, the left Arrow? does it act directly on Pump's nozzle (green circle) or it works on the baseplate of the pump (red circle)?
And, when I check the comparison with allowables, have i add the thrust force at the nozzle or not?

http://files.engineering.com/getfile.aspx?folder=29611fab-13bc-4354-8c43-00c1d338b9ac&file=pump.png

 

[LittleInch]

I suppose this is really like an end cap force which acts on the pump itself and hence through into the base plate.

Hence other than the forces coming from the bellows itself (should be low, but not negligible) there is no other direct force on the nozzle per se (IMHO), but there are other forces on the pump itself caused by Pressure of the fluid acting on a part of the pump.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Lore80]

Thanx for the answer; the force is not low...20 barg on a Ø10" ...is quite hight

 

[Artisi]

Not sure about the statement of it not loading the pump nozzle, it the pump is sufficiently anchored onto the baseplate and the base plate is sufficient to handle the thrust - ie, the pump and baseplate cannot be moved (a very unlikely scenario) - then high enough thrust into the pump nozzle with deform the case (concertina). You need restrained bellows - check google plenty of pictures.

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.)

 

[Lore80]

this is the reason for which I was trying to consider the acting of lateral tied bellows located in order to use the lateral displacement instead of the axial movement of the open bellow...in this way I am sure that the thrust will be projected only to ties while on nozzle I will find the effect of only lateral stiffness of the bellow