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What Is Dry Running (Pump)? | Process Engineering Glossary
What Is Dry Running (Pump)?
Dry running is a condition in which a pump operates with insufficient or no liquid present to provide the lubrication and cooling its internal components, particularly mechanical seals and bearings, depend on. Because many pump seal and bearing designs rely on the pumped fluid itself for lubrication, even a brief period of dry running can cause rapid, sometimes irreversible damage, making it one of the most common preventable causes of premature pump failure.
Dry running can result from a variety of causes, including a suction source running empty, a closed suction valve, vapor lock preventing liquid from reaching the pump, or loss of prime, making a range of different safeguards relevant depending on the specific failure pathway a given installation is most exposed to.
Applications of Dry Running
Low-Low Level Trip Protection
A low-low level trip on the upstream storage tank or vessel is a standard safeguard specifically designed to stop a pump before suction level drops low enough to cause dry running.
Seal and Bearing Selection for Marginal Services
Pumps in services with elevated dry running risk sometimes use specialized seal designs with independent lubrication or cooling, reducing dependence on the pumped fluid itself.
Pump Protection Instrumentation
Dedicated pump protection instrumentation, including flow switches and seal temperature monitoring, can provide direct detection of developing dry running conditions independent of upstream level protection.
Benefits of Knowing Dry Running
Prevents a leading cause of premature pump failure. Understanding dry running risk and its causes directly supports designing protection that prevents this common, costly failure mode.
Clarifies the value of layered protection strategies. Recognizing the multiple potential causes of dry running supports designing layered protection addressing level, flow, and vapor lock risks together.
Informs appropriate seal and bearing technology selection. Understanding dry running risk for a specific service supports selecting seal and bearing designs with appropriate resilience where risk can’t be fully eliminated.
Limitations to Consider
Damage can occur within seconds in severe cases. Some seal designs can suffer significant damage within just seconds of true dry running, leaving very little time for automated protection to respond.
Protection systems need to address multiple failure pathways. Since dry running can result from several different root causes, a protection strategy focused on only one pathway, such as level alone, may miss others like vapor lock.
Detecting marginal, partial dry running can be difficult. Brief or partial loss of adequate lubrication can cause cumulative damage without triggering an obvious, complete dry running alarm condition.
Dry Running FAQ
How does a low-low level trip protect against dry running?
A low-low level trip stops a pump automatically before suction level drops low enough to cause dry running, one of the most common and effective protective layers.
How does dry running relate to vapor lock and pump priming?
Vapor lock can cause a pump to effectively lose adequate liquid supply and begin dry running, requiring the same pump priming procedures to restore normal operation afterward, an important consideration alongside vortex shedding-related vibration in nearby discharge piping.
How does dry running relate to deadheading as a distinct failure mode?
While deadheading involves a pump running with liquid trapped in the casing against a closed discharge, dry running specifically describes inadequate liquid supply at the pump, both damaging but through different mechanisms relevant to a can pump or any centrifugal design, governed by the same pump affinity laws and appropriate line sizing of the suction system.
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