Hi friends,

With introduction to spring isolated inertia base centrifugal pump foundation.
The pump set up is, foundation is mounted with springs, suction and discharge nozzles are mounted with expansion rubber joint, and both the nozzles are horizontal in plane.
With the above criteria I am stucked with the following
1. How to model the pump with spring foundation
2. For both suction and discharge side, what type of support (first support near to pump nozzle) will be used in the piping, (whether spring or +Y restraint)
Please give me any mandatory guidelines to solve the problem.

Regards
Rathish.G

Why do you want to model pump with springs. Check with the vendor, the spring mounted pump is to reduce the pump vibrations. You can do conventional analysis and check the nozzle loads.

I suggest you make some rigid elements to hook up nozzles and springs. Wish this is a good idea.

Is the concept acceptable to your client?

Regards

When i discussed with client they are asking for Spring supports near to the nozzle, but my worry is that,

when the spring is mounted near to the nozzle, whether the expansion bellow will work.

Because, when both the pump foundation and first support of pipe near to the nozzle is not a fixed restraint or anchored, so expansion bellow will not fullfill its activity. But when we have a Rest as a first support near to the nozzle instead of spring, then the displacements of the pump will affect the support and the first elbow and so on.

can you please suggest me the supporting phenomena for the above problem, it will be very much usefull for me

See EJMA and any good book on piping design or engineering as it regards expansion joints...

can you guide me about the things to consider in conventional analysis

First of all it will be too dangerous to use springs both for the foundation and for pipe support, coz misalignment or mis-coordination between piping support spring and foundation spring can affect the nozzle. as "PKU" rightly said rightly said y do u need springs for foundation?
In conventional analysis lot of this are to be care of, but most important is "Provide the suction side with a straight run of pipe, in a length equivalent to five to 10 times the diameter of that pipe, between the suction reducer and the first obstruction in the line"..... then for supports u u can use adjustable supports but in Caesar only +y will mention it.
if the situation is that much critical which u are telling then use spring supports for pipe.

Dangerous yeah sure!!!

Your kidding right?

To Rathish.G,

There are a number of evaporator- crystallizer units with the circulating pumps either mounted on springs or fitted with flexible expansion joints in the inlet / outlet piping at pump. Typically the vessels are set at 30 to 40 ft elevation to provide adequate NPSH to the pumps. The piping expands thermally downward from the vessel to the pumps. The slurry solids flow requires the piping to be kept short and straight - no pockets. The flexible expansion joints were used in small to medium diameter lines, while for larger diameter inlet /outlet lines the pump would be put on a base fitted with 4 or 6 springs. (The pumps would be horizontal end suction, or axial flow elbow pumps, depending on flow volume and head.) The flexible expansion joints in piping would also have the concerns for solids settling and filling the convolutions of expansion joints.

The piping should be modeled from the vessel to the pump, and the pump would be modeled with rigid elements having weights of pump, motor, and base. As stated by SIF, the base plate springs would be located by added rigid elements with the spring stiffnesses as defined by the pump vendor. Since the pump vendor is likely supplying the pump with motor on the base, it is recommended the pump vendor integrate all with the spring design and base plate. A 200 hp motor could weigh more than the pump. You will need to define the required vertical movement to the pump vendor.

Any required piping spring supports on the inlet / outlet piping will need to be designed to meet allowable loads on the pump. If there are not any heavy valves or components near the pump connections, there might not need to be any piping supports close by the pump.

When modeling a spring supported pump, don't forget to preload those springs. I would imagine the pump/motor/baseplate combination will be leveled while on the springs before pipe fitup. If you run a deadweight analysis of the pump alone, the preloads should give zero deflection at your connection points. If they were not preloaded, the pump will sag down until the springs provide the balancing load.

You can have CAESAR II help "size" the pump springs. If you try it, I suggest you set up Node/CNode anchors at both pump connection points and "release" those anchors during hanger sizing.

As I understand it, the reliability of a spring supported pump may be a (vibration) problem.

Ratish, i must agree with PKU regarding need to model pump with springs. In my opinion, there is no need to model pump at all. What one may need to get from modeling pump with springs is Pump nozzle displacements due to thermal expansion, nozzle support reactions and finally pump nozzle load evaluation.

Modeling the whole piping with nozzle, which is restrained with support having stiffness provided by pump vendor for foundation springs will do. Use resultant stiffness here, not the individual spring stiffnesses. It is worth noting that the springs are preloaded with pump/motor/foundation dead weight. The pump nozzles should however be modelled with zero -Y displacement disregard of initial -ve Y displacement by the amount of spring preloading which, you would have already accomodated in detrmining elevation of nozzles. Spring foundation for pumps are typically used for resolving vibration problems, in some cases for accomodating some pump thermal expansions; however this donot seem to be your case where you r using expansion rubber joints.

More flexible piping system with pump would aggrevate vibration problems and make the application of spring foundation useless in general. In my opinion first support with pump having expansion joints should be rigid one. This however would also depend on the type of EJ used in horizontal run; with untied EJ, your support would have to accomodate pressure thrust, which would also be applied at pump nozzle in axial direction. If the pressure thrust is huge and exceed your nozzle allowbles, you can model your nozzles and first pipe support as rigid, leaving the vibration and thermal expansion of pump to be accomodated by the pump spring base(assuming pump and motor share a commom foundation base)and thermal expansion of pipe run to be absorbed by expansion joint you are using.

Hope that your question is answered.

Regards

Something i would like to add is regarding huge size pumps and large size piping attached with it carrying dense heavy fluids. If this is your case, Ratish, then you must worry about heavy weight of fluid in pump and piping. In various operating conditions, this can impact your system integrity and probably this is the reason of recommending spring support adjacent to pump by pump vendor.

The solution that comes to my mind in this situation is using directional anchor at pipe elbow which resists pressure thrust but allows vertical/lateral movement, EJ having guides as per EJMA recommendations and the nozzle pipe supported through spring for compensating vertical movements due to presence/absence of fluid weight under various operating conditions. The suggested support system would also make your system stiff enough to avert vibration problems.

Thanks for all suggestions,

I modeled the system as mentioned above by our sky of stars
The first support on the pump is made with rigid one, by providing 3mm gaps on the stop and guide to make the pump nozzle under allowable.
Also i considered the nozzle part anchored. I sended the report to vendor for their review and approval.

Please guide me, whether any piping loads or any critical loads to be conveyed to vendor for their spring(4 nos) selection on the pump foundation which is vendor scope.

The solution in my reply #12236 - Today at 10:43 AM should work if pump base springs are stiff enough to allow zero vertical travel in both Fluid filled & empty pump condition.

When considering fluid weights, I fear you have not gone through my reply #12237 - Today at 12:50 PM. As per it, the solution should look like this:


Pipe
\ |
/ |
\ Spring support(+Y) |
/ |
\ |
--|| | Guides | | Guides |
-----------------------| EJ |----------------------|<- Direc. anchor
--|| | | ^
|(+Y support)

Nozzle not anchored,
Spring stiffnesses of pump
base (get fr vendor) applied at restraints
on nozzle and vertical
travel due to effects of fluid wt. on base springs
in operating & no fluid content condition
applied as displacement on nozzle.

The pressure thrust on pump shall be taken by pump base. In this case, keep Effective ID for EJ zero and apply thrust force at elbow after calculation. You should convey of pressure thrust at pump base due to EJ to pump vendor here.