Wear Ring Clearances in Centrifugal PumpsBy PumpWorks Engineering Team / October 1, 2019
Wear rings play a crucial role in centrifugal pumps. A centrifugal pump typically features two adjacent wear rings: a stationary wear ring on the casing and a rotating wear ring on the impeller. The pump wear ring clearance between these two rings is critically important to a pump’s efficiency.
The Purpose of Wear Rings
A centrifugal pump’s role in a fluid system is to add pressure to the contents of the system. The pump’s impeller spins, creating the centrifugal force that generates the necessary pressure. As fluid passes through the impeller, it is expelled through the casing volute channel, passing the volute lip into the case discharge.
Due to pressure differences, fluids can flow down the sides of the impeller into the suction inlet at the impeller eye entry. If the recirculation flow rate is very high, this leaking can cause turbulence in the fluid entering the impeller eye, increasing the pump’s NPSHR value and reducing efficiency.
Properly selected, a centrifugal pump’s wear rings limit the recirculation flowrate between the sides of the impeller and the impeller eye. A very small, flow-limiting clearance between the stationary and rotating rings is necessary to prevent unwanted recirculation. The smaller the wear ring clearance in centrifugal pumps, the tighter and more efficient the system will be—to a point.
Select Pump Wear Ring Clearance with Care
Extremely narrow clearances require precise tolerances and material selection to avoid potentially catastrophic faults. The hydraulic radial load on the impeller and impeller diameter typically dictate allowances for a certain amount of clearance between rotating and stationary components.
If the centrifugal pump wear ring clearance between rings is too small, they could scrape against one another. Such friction results in damaged parts increased heat and vibration, and lower efficiency. It can also increase the pump’s NPSHR and may cause cavitation.
The minimum diametral wear ring clearances listed in API 610 11th Edition are stated based on the outer diameter (OD) of the impeller wear ring. Compliance with the standards for API 610 wear ring clearances ensures that wear rings are unlikely to come in contact with one another.
The specified minimum clearances get larger as the rings get larger:
- For a wear ring with 2” diameter or less, API lists the minimum diametral clearance as 0.010”.
- For every 0.5” increase of the impeller wear ring OD, the 0.010” diametral clearance increases by 0.001”. So, from 2.000” to 2.499” OD, the diametral minimum clearance is 0.011”.
- For impeller wear rings with OD of 5” up to 26”, every 1” increase in the impeller wear ring diameter results in an additional 0.001” of minimum diametral clearance.
PumpWorks Understands Wear Rings
At PumpWorks, we are passionate about getting the most from every pump. If your business is having trouble with wear rings in its API centrifugal pumps or needs help with maintenance or other pump issues, give PumpWorks a call – 855.979.9139 or contact us online today!