Axial Load
Axial Load
(OP)
Hi , is there a device to measure the axial thrust of a vertical pump? I know it can be done using axial load cell , but ...:(.i need to measure the total thrust generated by a vertical pump. Thank you for any idea/ help





RE: Axial Load
RE: Axial Load
RE: Axial Load
You could place a load cell under the thrust surface of the bearing, run the wire thru the housing, seal it against lube or process fluid leaks, install the pump and connect all the piping and wiring, calibrate the load cell, then run your test and tear everything down.
OR
As JJPellin says, the pump supplier should have the thrust values readily available for the actual duty conditions since these are required during the design process to calculate the bearing sizes. A simple email or phone call would save a lot of time!
"If A equals success, then the formula is: A = X + Y + Z, X is work. Y is play. Z is keep your mouth shut."
-- by Albert Einstein
RE: Axial Load
As a vertical pump manufacture I do this everyday! I would recommend you calculate thrust load based on worst-case scenario!
Worst case thrust load occurs at shut-it. Why not just calculate it? Get the impeller area from the manufacture and multiply it times the pressure. You will also need to include the shaft area and physical weight of the rotating assembly.
Note:
At shut-in there is no up-thrust or fluid velocity lifting effect.
D23
RE: Axial Load
i did calculate the thrust load , but i wanted to check it by measuring it. I came across an old technical paper where hydraulic fluid was used along with a thrust gage, just like a piston.Strain gage and elctronics wont do it if you have a rotating shaft at 1700rpm.Thank you all for your inputs
RE: Axial Load
So far I understand the biggest one is the difference in pressure*area, producing downthrust. Biggest when d/p is highest at shutoff. That part makes sense.
what is fluid velocity lifting effect? what are the other components and how do they vary with flow?
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RE: Axial Load
RE: Axial Load
To answer electricpete's question, there are generally two main components of centrifugal pump axial hydraulic thrust loading, ie.,unbalanced pressure across unbalanced front and back face (shouds and hubs) and the fluid turning reaction force in the impeller channel. Equations are:
T=0.433*A*H + 0.00139*Q^2*sin theta/Ae where
T=Thrust(lbs), H=Head(ft.), Q=Flow (GPM), A=Unbalanced area(in.^2), Ae=Impeller eye area(in.^2) , theta =impeller channel turning angle (degrees). Calculation of impeller unbalaced pressure area becomes increasingly complicated as specific speed of the pump increases because of the curvature of the front shroud in shrouded impellers. Since the dominant factor in axial thrust is pump head the shape of the thrust curve versus flowrate, when normalized should be about the same as the pump head-flow curve. However flow instabilities in impeller channels often affect thrust more than head so dips in thrust curves often reveal unstable flow ranges not evident in the head curve.
RE: Axial Load
Sorry for the delay. I’m kind of hit and miss for available time on the internet.
When I think of vertical pumps I tend to think closed type radial or mixed flow multi stage pumps. That may not be the case here.
With a closed type impeller in a vertical position there will be X-amount of thrust applied in an upwards fashion. This is due to the velocity or fluid momentum of the fluid entering the eye of the impeller. Guess a simple way to think about a single stage pump would be to consider what happens as fluid enters the eye for a closed impeller.
With a closed type centrifugal stage in a vertical position there will be three sources of thrust.
• Gravity is always downward.
• Down thrust resulting from the net pressure differential.
• Up thrust resulting from fluid momentum entering the eye of the stage.
Typically I expect my multi stage pumps to operate with a little down-thrust; however if one of my pumps (closed impeller type) operates at too high of a flow the fluid momentum entering the eye of the impeller will lift the impeller in an upward motion. In cases where we have operated with 0 head or open flow I have seen pumps self-destruct in up-thrust. They will try to lift the shaft and impeller out of the pump housing.
Sorry about the confusion. Mottto did not say anything about closed impellers. I made an assumption and you know where that left me!
D23.
RE: Axial Load
I like the idea of downthrust curve looking like the head curve, makes it easy to remember.
Tell me if this is the correct way to understand the momentum part of it:
Water enters the impeller going up and leaves going at some angle away from up and toward radial.
F = M dv/dt = d/dt(mv) = rate of change of momentum
force exerted on fluid is change in momentum accross the pump
If fluid is changing it's momentom from upwards toward radially, then change in momentum is downwards. Downwards force on fluids requires equal and opposite upwards reaction force on the shaft.
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RE: Axial Load
Your explanation is true for volute pumps, not true for turbines, axial flow, etc. There is no radial thrust on turbines (almost none), because the flow through the impeller is concentric, all radial thrust is balanced by the concentric flow.
PUMPDESIGNER
RE: Axial Load
Thanks!
I can explain a low easier with pictures.
D23
RE: Axial Load
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RE: Axial Load
RE: Axial Load
I saw your post and I was wondering if you know where I can find a copy of the paper you referenced. Thank you