Case

Location: Netherlands

Our client had problems with air bubbles in their pumping system with which bulbs are disinfected using crop protection products. Because of this, the crop protection product could only be used for a limited amount of time.

Assignment

We were asked to find out the root cause of the air bubbles in the medium by investigating the pumps and the piping system and advise on the most efficient solution to avoid any problems in the future.

Checking the condition of the mechanical seal – © Oveducon

Execution

Upon further investigation, we found out that this problem had a long history. Over the years a series of adjustments had been made to the installation to try and solve the problems with the air bubbles, yet without any success.

Air bubbles are always a very notorious problem in a pumping system because they can be caused by a number of different factors. Sometimes even multiple at the same time. Therefor over the years we have developed our own structural approach for dealing with such situations. This method enables us to quickly eliminate possibilities and determine the root cause(s).

After further examining the case and learning more about the history of the problems, we installed several of our measuring devices on the pumping system and started to monitor the process conditions. We used a clamp-on flow meter and portable pressure gauges on both the suction and the discharge line.

Portable pressure gauge – © Oveducon

In doing so we wanted to collect data on the capacity of the pumps and investigate where exactly the air bubbles would arise in the system. Using our clamp-on flow meter, air bubbles in a line can be traced very precisely.

As soon as we turned on the pumps, it was very evident that a lot of air bubbles were in the system. To determine the root cause of the air bubbles, we further investigated the matter by routinely changing the process conditions:

1. Adjusted the rpm,
2. Investigated the influence of suction height
3. Investigated multiple components of the piping system for air pockets
4. Investigated possible air leakage at the valves and piping connections.

Hereby we were able to structurally narrow down the possible causes.

After analyzing the system we went on to investigate the pump, since air can be pulled into the system through a possible defect of the mechanical seal. Upon dismounting pump 1 we found out that there indeed was a problem with the mechanical seal.

It turned out that the bellow of the bellow seal was torn and that the mechanical seal was severely polluted.

We investigated the other pump as well and here we also found that the mechanical seal was in very poor condition.

Upon inspection of the mechanical seal of pump 2 we concluded that, apart from being highly polluted, one of the seal faces was in a very bad shape. Therefor it was decided that this mechanical seal would also be exchanged.

Results

After we ruled out a number of possible causes and exchanged both mechanical seals, the pumping system was started again and we were able to verify that there were no more air bubbles in the system.

To avoid future problems, we advised the client to check the condition of the mechanical seals during a regular interval. In doing so, over time the client would be able to determine the MTBF of the mechanical seals and set up a preventive maintenance schedule.

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