Ghost in the Pump
I received a call from a customer that one of our new pumps was acting up. The pump would quit pumping and then all of a sudden start again.
They pulled the trouble pump out of service, replaced it with a spare, and asked me to come on site to perform an inspection.
I arrived onsite and with the help of customer's millwrights we disassembled the wet end of the pump. Everything looked great and the shaft turned freely by hand. As people started coming by to see what we had found, I started asking questions. After a minor interrogation I found out the pump was sitting directly over an air sparger. The pump seemed to pump fine in the day time but would quit pumping at night. I asked how the air was controlled going to the sparger and found out there was a manual valve.? I then asked the operations superintendent about taking me to the location of the pump. They didn’t understand why I wanted to go but I explained that I wanted to try and create similar conditions in the spare pump to see if we could find the problem. With a puzzled look on their faces, they finally agreed to take me.
When we got there I asked where the manual air valve was located. With myself operating the valve I asked several employees to watch the pump and inform me of what was happening. The valve was barely open supplying a minimal amount of air to the sparger. As I opened the valve they informed me the pump quit pumping. I started closing the valve and it started back again. I repeated the exercise once again with the same results.
The operations team was relieved that the ghost had been found.
It seems that someone at night was opening the valve to get more circulation in the tank. The air was shooting straight up into the wet end of the pump causing an air lock or too much air entrainment in the slurry for the pump to handle. There is a maximum amount of air entrainment allowed in slurry or it cannot be pumped. The wet end and/or piping can also become air locked which will stop all pumping action in the system. At shift change the valve was regulated to its normal position and the pump would start back up.
We recommended to the customer to either change the location of the air sparger or install a diverter plate to deflect the air from going straight into the pump. Thankfully there has been no issues since.
I thought the above photo was suiting to this blog. The clouds add a touch of beauty and eeriness to the mountains, don't they?