Weekend Discussions Archieve

Week – 34 Common problems of pumps

[3:55 PM, 8/18/2018] TecKXpert Working Committee: Dear All, Good Evening Today’s Weekend TecKnow Discussion will be on the below subject. ” Common & Critical problems faced in Pumps & Pumping systems “. Kindly post the problems faced by you in pumps and pumping systems and how it was resolved. It would be a great learning for others.

[3:55 PM, 8/18/2018] TecKXpert Working Committee: General Rules of Discussion:
1. The objective of this discussion must be knowledge sharing only.
2. Please do not mention any brand name.
3. Not required to mention where ( which site) the failure happened.
4. Discussion must be subject specific and gentle. Pl do not hurt anyone.
5. Pl do not lead the discussion to other subject.
6. Pl do not post anything other than this specific subject during conversation is ON.
Thank you all in advance.
Let’s have a great knowledge sharing discussion.

Discussions:


[4:00 PM, 8/18/2018] TecKXpert Working Committee: In one offshore installation additional sea water lift pump was installed and piping was modified to suit the condition. One of the new pump was continuously facing problem and the MTBF was more often. OEM was called for servicing and the result was same. Unfortunately they missed the basic the bend before the pump suction nozzle was very close. Minimum requirement of the 5D length was not maintained. When it was corrected the failure frequency came down

[4:02 PM, 8/18/2018] TecKXpert Working Committee: The above case study was shared in our TecKXpert Group Singapore

[5:07 PM, 8/18/2018] Srinivasa Rajkumar B: When u aid pump suction with less resistance for the flow of liquid, the performance of the pump improves. Yes indirectly it gives u the benefit.

[5:07 PM, 8/18/2018] Srinivasa Rajkumar B: Piping has to facilitate the smooth flow of liquid. At suction it should have eccentric reducer and in discharge it should be concentric expander to reduce friction and air pockets.

[7:31 AM, 8/19/2018] TecKXpert Working Committee: I think this is by reducing Hf we are getting more NPSH available and suction pressure will be more. pumps capacity is difference in head. So the discharge head will go up.
Please add if we are having Any other reason

[7:31 AM, 8/19/2018] TecKXpert Working Committee: Sorry to ask this question.
This suction set up doesn’t have proper priming or self priming arrangement. May be a flapper type check valve can help. moreover pumps with suction lift doesn’t need an isolation valve in the suction side. That’s why we suggest after our energy audit to the industry, to replace this monobloc self priming pump to open well sub pump which doesn’t have the problem of NPSH And the power savings achieved compared to the existing pump is around 20 %

[9:11 AM, 8/19/2018] Srinivasa Rajkumar B: Open well submersible has its own limitations , specially on duty . These open well submersibles are mostly rated for intermittent duty. And the applications calling for continuous duty still has to go with surface mounted pumps.

[3:36 PM, 8/19/2018] TecKXpert Working Committee: Question from other TecKXpert group ? What is flow turbulence in centrifugal pumps? What is the impact on efficiency?

[4:08 PM, 8/19/2018] TecKXpert Working Committee: In fluid dynamics, turbulence or turbulent flowis any pattern of fluid motion characterized by chaotic changes in pressure and flow velocity turbulent flow can give problems of low efficiency, noise and structural damage on impeller. Deposits in water can amplify the problems of structural damages: we have experienced shaft impeller break-down in the case of “hard” (Calcium richness) water.

[4:12 PM, 8/19/2018] TecKXpert Working Committee: the turbulence can induce cavitation by the high centrifugal speed of the eddies, the generated vaccum will cause cavitation, and that type of turbulence is induced by the so called “pump flow recirculation”, it happens when the pump works actually at flow less than its design minimum flow, so the discharge pressure will be higher than the design pressure and forces the flow to return back to the impeller, causing recirculation phenomenon and turbulence with its induced cavitation and high AXIALvibration with crackling noise and high bearing temperature

[4:38 PM, 8/19/2018] TecKXpert Working Committee: Question from other TecKXpert group. What happens when we close the valve in a discharge line while the pump is still working?

[4:53 PM, 8/19/2018] TecKXpert Working Committee: In the centrifugal pump….up to valve rated pressure will be developed and motor current will dropped down after some time the pump casing temprature rises as churning of material in side pump and damaged its seal first then impeller too!

[4:53 PM, 8/19/2018] TecKXpert Working Committee: In the Reciprocating type pump motor current increses and due to high pressure safety valve on the pump will open if safety valve not worked properly uts seal, piston and casing may damaged.

[4:55 PM, 8/19/2018] TecKXpert Working Committee: Answer is from TecKXpert group Mumbai

[4:59 PM, 8/19/2018] TecKXpert Working Committee: Temperature of the pumping fluid will go up. If the temperature is above the vapour pressure of the pumping liquid it will create noise and if it is HC chances of fire. For that reason only the high temperature service like Boiler feed water and Hydrocarbon will have the recirculation or minimum flow recycle valve in the discharge line

[5:03 PM, 8/19/2018] TecKXpert Working Committee: This Answer is from TecKXpert group Singapore

[5:05 PM, 8/19/2018] TecKXpert Working Committee: In no flow condition or closed discharge valve condition a centrifugal pump will generate a pump shut off pressure and due to very min flow or null flow, pump mechanical seal would fail first after few mins of running and the pump internals might fail in case of prolonged operation in this condition.

[5:06 PM, 8/19/2018] TecKXpert Working Committee: Above answer is from TecKXpert group Bengaluru.

[5:10 PM, 8/19/2018] TecKXpert Working Committee: Question from other TecKXpert group
What are the causes for broken impeller in a pump failure?

[5:23 PM, 8/19/2018] TecKXpert Working Committee: Improper alignment is a serious cause of pump failure. Up to 50% of damage to rotating machinery is directly related to pump misalignment. This means increased vibration, premature seal, bearings and impeller failures.

[5:53 PM, 8/19/2018] TecKXpert Working Committee: Thrust load, repatative on off thus loosening of key way, material other than designed for used , Bearing worn out, wrong operation as discussed earlier, high operating temprature from design specs, Impeller material fault, wrong strainer mesh thus foreign material entering in pump of over size as per design specs.

[5:54 PM, 8/19/2018] TecKXpert Working Committee: Above answer is from TecKXpert group Mumbai.

[5:58 PM, 8/19/2018] TecKXpert Working Committee: Foreign particle in the pumping liquid. Cavitation. Pumping liquid temperature is not as per the design. (seizure will happen due to the wrong pumping liquid’s temperature) Wrong selection of the pumping fluid. acidity / alkalinity If the hydraulic centre is not maintained during assembling Hydraulic unbalance due to very low discharge pressure (due to more flow due to less pressure in the receiver side – opening discharge valve with full shut off head to zero pressure receiver side) [5:58 PM, 8/19/2018] TecKXpert Working Committee: Above answer is from TecKXpert group Singapore

[6:53 PM, 8/19/2018] TecKXpert Working Committee: Trouble starts from design phase since most of the consultants tend to over size the pumps. Also the insufficient spacing around pump room leads to compromise on piping. Improper suction and discharge cones leading to turbulent flow paves the way to all the troubles.

[6:53 PM, 8/19/2018] TecKXpert Working Committee: Yes sir mostly for sewage pumps Head is mostly sized on higher side which leads to pump operating out of the curve leading to its premature failure

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