What to Consider when Selecting Wear Rings for Your API 610 Pumps
October 30th, 2020
The American Petroleum Institute (API) provides meaningful guidelines on wear ring materials and clearances for all API 610 pumps. Appropriate specification of wear rings contributes to both higher efficiency and higher reliability. If clearances are too small, the pump wear rings could make contact during certain operating conditions, leading to a reduced lifespan or worse. If clearances are too large, internal leakage will result, and pump performance will decrease. Given that the clearance between the wear ring and the impeller hub will increase with wear, efficiency will deteriorate with time, especially if the wear ring material is not durable. With that in mind, here are a few factors to take into account when selecting the best wear ring option for your application.
First, per API 610, impeller rear pump-out vanes or any other feature that produces tight axial clearances cannot be used to balance axial thrust. Rather, radial clearances must be used to limit internal leakage and to balance axial thrust. In attaining these tight clearances, renewable wear rings must be provided in the pump casing. Impellers can have either renewable wear rings or an integral wear surface. Carver API pumps come standard with renewable casing wear rings.
Next, the best material for a wear ring is one that is compatible with the liquid being pumped and has a low galvanic potential in relation to adjacent parts but is not a galling combination. The wear rings must have a Brinell hardness of at least 50 units of difference unless both the stationary and rotating surfaces have a hardness of 400 or greater. The rings must be held in place by a press fit and secured by a locking pin, screws, or tack welding. The diameter of the hole for a dowel pin or screw cannot exceed one third the width of the wear ring.
Finally, if you are considering non-metallic wear rings, special attention must be given to compatibility with the fluid, distortion, thermal gradients, and special clearances to avoid pump seizure and to ensure the dependability of operation under all specified conditions. Composite wear rings are non-galling and allow for closer running clearances. The clearance can be reduced by up to 50 percent, allowing for a cost-effective way to improve the reliability and efficiency of your pump.
It is also worth considering the effect of wear ring clearances on pump vibration. With a reduction in clearance, the effective shaft stiffness will increase. This is because the wear rings themselves act as a sort of hydrodynamic bearing. The additional stiffness can mean the pump will run with lower vibration and have fewer seal leaks. Between the reduction in clearance and the shaft stiffness, you may see longer pump life with fewer downtimes.
As operating plants age, so does their equipment. Pumps will need to be replaced or repaired, and in many cases, upgraded. A non-metallic wear ring is an option that may make the pump more reliable and increase its efficiency and safety.
For more information on clearances and installing wear rings on a Carver API pump, see our API Maxum Manual.
Reference: API Standard for Centrifugal Pumps, 11th Edition.