This article focuses on the effect of fluid forces (generated inside the vertical pumps) on vibration. It briefly discusses cases at Birla Copper wherein the effect of flow has been indicated in the vibrations

To start with, we first discuss a case of auxiliary cooling water pump. Vibration monitoring program indicated that the vibration level of this pump was three times of the value with which similar pumps are running, and hence we start looking for a problem in this pump. And the outcome is : fluid force is the problem. The discharge line has a bend very near the discharge of pump resulting in high back force, which is indicated in high vibrations. The so-called similar pumps were found to be not similar since their discharge lines are perfectly straight.

Then we proceed to another case of auxiliary cooling water pump. Here the vibrations crossed even the alarm set through the vibration-monitoring program. The pump was studied for its operating point vis-à-vis best operating point. The pump was running at an operating point far away from the best efficiency point. Trials taken at various operating point suggested the severe sensitivity of fluid forces generated at various operating conditions on vibrations.

* : “ Vertical Water Pumps : what’s happening down the hole “ – Malcolm K Graham & Barry Nurcombe, Ceng, Bently NavadaPLANT: Captive Power Plant (CPP)

Effect of fluid forces on vertical pump vibrations

In today’s economic scenario, industries are operating their equipments longer & at improved efficiencies, while maintaining safe & reliable operations. This has been achieved in part by monitoring & trending of parameters such as vibration, lube oil condition, heat radiations etc. Vibration monitoring is one of the most important tools in these programs and has been accepted worldwide in various industries.

The monitoring of vertical pumps has been extremely difficult due to the complexity associated with vertical pumps & their sensitivity to various parameters. People have analyzed on various lines of thought so as to improve the monitoring of vertical pumps *.

This has also been felt at Birla Copper. With many vertical pumps being installed for critical applications regular watch of these pumps is a necessity. At Birla Copper a high number of vertical pumps are installed at Cogeneration Power plant (CPP), Phosphoric Acid Plant (PAP) for water applications, and in Sulphuric Acid Plant (SAP) for Acid applications.

Vibration Monitoring ProgramCondition Monitoring

Technical Services (TS)

Equipment: Auxiliary Cooling Water Pump (79 PU 122 A)Pump Make: Kirlosker

The pump supplies cooling water for auxiliaries of 24.45 MW TG Set. For running of TG set the operation of pump is a pre requirement. This was the reason that the pump was covered under vibration monitoring program. Since beginning the pump vibrations were found abnormally high when compared to similar pumps. Also abnormally high fluctuations in vibrations were observed as shown below.

Vibration analysis predominantly indicated unbalance and thus balancing trials were taken. Although pump vibrations reduced but the effect of trials vanished within days of trial. Motor solo runs were taken and were found acceptable. As a result of high vibrations the pump bearing developed defects & was subsequently changed in the month of May 2004.

The OEM was contacted for assistance in further analysis & the pump performance curve was studied. It was then decided to study the pump behavior against the various operating conditions. The pump vibrations were observed at various discharge pressures. The observations showed a sharp correlation between the two parameters.

The vibrations were found to behave in a cubic fashion with respect to the discharge pressure.The trend indicated normal vibration levels (5 mm/s) at pressures below 6.5 kg/sq.cm and as the pressure increased the vibrations increased. At discharge pressure of 7.5 kg/sq.cm the vibration reached peak higher than 25 mm/s. The pump performance curve also indicated that the best efficiency point for the pump was close to 6 kg/sq.cm.

Both the performance curve & vibration behavior suggested that a good operating range for this pump is (5.5 – 6.5) kg/sq.cm to avoid any mechanical damage of the pump.PLANT: Captive Power Plant (CPP)

Equipment: Auxiliary Cooling Water Pump (79 PU 22 C)Pump Make: KirloskerThis is the case of another auxiliary cooling water pump. Below is the vibration trend for the last six months. The trend indicated fluctuating vibrations & hence the effect of flow on vibrations was studied.

This pump on close review was found to have a 900 bend at the immediate discharge. This resulted in vibration range of 5.2 mm/s to 6.3 mm/s. whereas a similar pump (Make: Kirlosker) with straight discharge line was found to have vibrations in the range of 1.9 mm/s to 2.9 mm/s as shown below.

79 PU 22C 79 PU 22A

Simple sketch of discharge pipeline layout is shown aside.In this case also it was found that fluid forces play a major role in determining the vibrations.

The cases reflected in this article are of vertical pumps since they are more sensitive to fluid parameters like flow, pressure etc.