Testing a Turbine Pump
Testing a Turbine Pump
(OP)
My company has purchased a 10 stage Turbine pump, 10 HP. The pump manufacturer has provided the pump curve. Their persons visited our site for commissioning of this pump. The problem is that the data point of commission test comes a bit lower than the pump curve. Can any body suggest why this is happening. Else the pump is running smooth.
Moiz khan
Moiz khan





RE: Testing a Turbine Pump
RE: Testing a Turbine Pump
Most industry standards allow for some +/- margin on the rated conditions. Test tolerances too may come into play in field testing, the location of the gauges used relative to ideal test lab conditions probably don't exist (i.e. straight runs of pipe up and down stream of flow meter).
10 stage & 10 HP means this is a fairly small pump... small castings are difficult to predict performance due to variations in vane thickness and geometry. Your company should have purchased a test at the manufacturer if this was a critical application. That would have ensured performance was guaranteed.
Did you know that 76.4% of all statistics are made up...
RE: Testing a Turbine Pump
RE: Testing a Turbine Pump
I am attaching the pump curve with the test points shown in circle.
RE: Testing a Turbine Pump
Johnny Pellin
RE: Testing a Turbine Pump
As pointed out by Johnny P, you need to sketch or describe more fully the installation and show the measuring points etc - this is the only way we can get an idea of what is being measured.
RE: Testing a Turbine Pump
Not necessarily. The Head axis on the curve may either say Bowl Assembly Head, or Total Pump Head.
In the first case, only the head generated at the last discharge stage impeller/bowl flange is shown. This is the most efficient curve, independent total pump design losses (type of discharge elbow, column size, etc) and often the mfg Sales Curve.
The second case is the actual Pump Head at the discharge flange. This is usually a mfg Test Curve and will include the head loss through the column and across the discharge head.
Did you know that 76.4% of all statistics are made up...
RE: Testing a Turbine Pump
I would have considered an 11 stage pump before a 10 stage at full dia.
Did you know that 76.4% of all statistics are made up...
RE: Testing a Turbine Pump
I would say this is a standard sales curve for 1 stage of turbine ( that is why it has the derating % for a low number of stages) and does not include any discharge head or column losses.
The test plot looks to be typical of a bowl assembly together with the losses for the discharge elbow, inlet strainer and column - deduct the losses and the turbine could well be on curve.
More info from the OP who seems to have vanished would help with a better understanding of what is actually being measured.
RE: Testing a Turbine Pump
RE: Testing a Turbine Pump
RE: Testing a Turbine Pump
As far as for your problem your field test points are not parallel to a pump curve and they droop more and more as the flow increases. I would bet you have some trash caught up in the impeller bowls. Pull the pump out of the pit and take a look. I had a similiar problem back in 1983
RE: Testing a Turbine Pump
RE: Testing a Turbine Pump
RE: Testing a Turbine Pump
1. Incorrect method of determining the points
2. Not enough minimum submergence and you are drawing air
2. Clogged pump suction
3. When you have a clogged pump suction you are in effect reducing the NPSHa which in turn could cause cavitation. The more the flow is, the more the reduction in NPSHa and,if you are cavitating, the worse the cavitation will be and the pump performance will become poorer as evidenced by the drooping curve as you go further to the right of the curve. I have marked up the points on the pump curve that was previously available to illustrate my point.
The problem with turbine pumps is that you can't "hear" any problems because they are down in a hole
RE: Testing a Turbine Pump
RE: Testing a Turbine Pump
RE: Testing a Turbine Pump
I don't know where to begin to correct you...
Mixed flow pumps run against a liner, though I'm not convinced this is even a mixed flow pump.
Blockages at the suction, cavitation, or increased clearance would be assoc. with high vibration and noise, which wasn't mentioned.
Forget looking into any bowls for trash... 10 stages and only 10 hp motor indicates these are very small bowls and impellers (even smaller hydraulic passages).... actually the curve shows the impellers are only 5" in diameter.
What is more likely, and I have seen in my many years of pump testing, is variations in castings (vane thickness and geometry) on the smaller impellers contribute to greater performance variations (+/- 1/4" deviation on a 5" dia impeller is a greater portion of the total area then on a 35" impeller).... or even more likely, the setup and test equipment in the field isn't ideal.
Did you know that 76.4% of all statistics are made up...
RE: Testing a Turbine Pump
I will respond to your comments:
1. The pump is certainly not a centrifugal pump. If it was, the curve would have started at zero flow on the x axis. If you look closely at the pump curve the pump manufacturer does not show the left hand side of the curve all the way back to the y axis.
2. You won't hear cavitation or anything because the bowl is submerged in a well. I also did not say there was any cavitation. It depends how severe the blockage is
3. I have had practical experience with blockages on vertical turbine pumps and the curve looked the same. In one of the municipal water treatment plants that I have built in my career the high lift vertical turbine pump was not performing to its curve. I had them pull out the pump and send to back to the pump shop. There was construction debris in the pump bowl. Once cleaned out, field tests showed the pump performing exactly to the pump curve. I think if you looked in some pump handbooks they will show you a classic curve of a blockage on the suction side and this curve looks pretty close to my experience. BTW, the same installation had mixed flow pumps there also...
4. While it is possible there could have been some manufacturing issues I would suggest that pump manufacturers invariably get their pumps to perform EXACTLY to a published pump curve. Otherwise what is the point of publishing a pump curve if you cannot depend on it performing to its curve. How can anyone design anything in this world if the pump does not perform as advertised.
5. By the way I have done many witness tests on all sizes of pumps all the way up to 4000 HP. In the 4000 HP instance, Fairbanks Morse could not get their pump to perform during witness testing according to the commercial curve that they tendered. It followed the left hand side of the curve exactly and then started to droop more and more the further it went to the right. They spent so much money trying to get the pump to perform and at the end of the day were ready to give up and started to babble about fitting the witnessed points to some 3rd order curve fitting equation???!!!. The potential liquated damages were stupendous. I did my own calculations at the Kansas City witness test site and told them the pump was not performing the further they went on the right hand side of the curve because there was not enough suction lift capability. I went over the calculations with them on a white board and immediately they looked at their own spread sheets and saw where they made the computational error. I told them the pump does perform and I would release the pumps for delivery. We retested the pumps on site where we had flooded conditions and the pump performed according to its curve. END OF STORY.
RE: Testing a Turbine Pump
Actually if you would like to check the specific speed you will find it is probably in the Francis-vane range.
As the OP hasn't responded other than;
"safiamoiz (Mechanical) 4 May 10 5:13
Thanks to all. Now the pump is running smooth."
then discussion of the problem, if there was a problem will require a crystal-ball.
RE: Testing a Turbine Pump
RE: Testing a Turbine Pump
I can tell you two things for certain working for OEM's for the past 10 years; 1.) No two pumps are exactly identical in performance and 2.) Even two tests on one pump will yield some variance. The combined tolerances allowed in test equipment and casting variations always yields some discrepancies in performance. Most published curves are conservative.
To your point #5... I have a dozen or so similar stories. more often then not, they are discovered during the preliminarily testing prior to the witness test. There's a BIG difference between a 10 HP pump and a 4000 HP pump, namely the size of the impeller... which goes back to my previous argument on casting variations on small sand castings vs. large ones. It's a fact, please take the time to go look this up... larger impeller pump performance is more predictable/repeatable then smaller impellers.
Artisi, I know we're arguing a moot point.
Did you know that 76.4% of all statistics are made up...
RE: Testing a Turbine Pump
And since when is a Francis-vane type impeller not considered a centrifugal pump??? did you mean a vertical tubine pump (enclosed impellers)??
Did you know that 76.4% of all statistics are made up...
RE: Testing a Turbine Pump
QT,
And to your point #3... I never said a blockage at the suction would not cause a similar curve characteristic.
I said for this small 5" bowl and impeller combination, you won't be able to look into anything. You cannot even run your finger thru the bowl diffusers to check for blockage it's so small.
Did you know that 76.4% of all statistics are made up...
RE: Testing a Turbine Pump
After 30 years in the pump industry, nothing surprises me any more when it comes to performance testing, particularly site testing or what some belive is "testing" - especially when "ëxpert" consultants are involved. I once had a largish vertical pump rejected on test because the pump tested out at 95% efficient whereas the spec. sheet we tendered said 93% - the reason "not to specification" - a quick phone call to the idiots boss soon sorted that problem.