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Identifying and fixing problems in sanitary positive displacement pumps can be a daunting task. Having a trained eye and experience can be helpful when troubleshooting but if your PD pump problem has left you scratching your head, here are a few tips we can share with you from our pros and partners at Alfa Laval!
The first step to any troubleshooting session should begin with a fact-finding mission. Gather as much information related to the process as possible. Get the answers to these questions:
Pump head/rotor contact is a common problem that positive displacement pump operators encounter. If you are experiencing this common issue, check out our chart for potential causes and corrective action ideas and read below for further examples to help troubleshoot and eliminate the problem.
| POTENTIAL CAUSES | CORRECTIVE ACTION |
|---|---|
|
Worn bearings |
Renew bearings and rebuild |
|
Overpressure |
Locate source and reduce |
|
Temperature limit exceeded |
Lower operating temperature |
|
Thermal shock, hot or cold |
Stop rapid temperature change |
|
Cavitation |
Ensure NPSHa is adequate |
|
Ingress of hard solids |
Track source and remove |
|
Rotors fitted incorrectly |
Refer to instruction manual |
|
Clearances incorrect |
Refer to instruction manual |
Rodem offers a wide selection of pump replacement parts, sure to fit your repair needs. If after troubleshooting the potential causes of your positive displacement pump, you are still not completely sure what the problem is or how to fix it, contact Rodem and we would be happy to assist you in identifying and troubleshooting your pumps processing problems.
Overpressure & Shaft Deflection
The effect of pressure on the rotors will cause shaft deflection, which could result in contact between rotors, rotorcase and rotorcase cover. Should the positive displacement pump pressure rating be exceeded, it is likely that contact will occur between the rotors. Rotor tip contact will likely be initially visible on the discharge side of the front cover internal face or suction side of the rotorcase rear face. If overload continues, the pump is likely damaged beyond repair.
Shafts that have contracted at a faster rate than the rotorcase will cause contact with rear casing face. Cold to hot shock would cause the rotors to contact front cover. Avoid rotor contact issues from thermal shock by eliminating rapid temperature change.
Cavitation’s effect on the rotor(s) may result in rotor to rotor contact.
Typical cavitation effect on the front cover, if severe will be apparent even after a short operating period. Damage marks will appear on the front cover of the discharge side of the pump where vacuoles implode in the high pressure region. Consequently, this will erode the stainless steel cover as with the rotor.
Typical cavitation effect on the rotorcase can cause damage within the rotorcase as a consequence of shock loading the shafts. In extreme cases this can result in the rotor tips making contact with the casing as well as material erosion from imploding vacuoles.
An initial hard solid passing causes galling through the pump. This can result in pump timing slip and jammed rotors.
Learn more about how the contact marks on a PD pump’s rotorhead and rotor, can be used to determine the common cause.
Rodem offers a wide variety of pump maintenance and repair services, as well as complete pump rebuilds. Our pump experts have years of experience with positive displacement pumps, as well as a wide variety of other sanitary processing pumps.
Contact a Rodem pump expert to further help identify and remedy positive displacement pump problems.
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