Long-term, large scale field studies have shown that composite materials can improve pump life by up to 100%, reduce vibrations, and reduce seal leaks. Field tests and pump test stands have shown that reduce clearance can improve pump efficiency anywhere from 2-5% for typical process pumps. Additional pump composite wear ring material benefits include:
To know which material is right for your application, send your pump data sheet and cross section when you, contact Boulden or request a quote. We will help you find the best fit for your pump.
Pump wear rings are the contact zone between rotating and stationary parts. During start-up, shut down, and off-design operation, the rotating and stationary rings come into contact. This contact creates friction and wear. Under adverse conditions, the wear rings can seize causing severe damage. To avoid seizure, the pump industry has adopted two main approaches.
The standard approach uses metal wear rings, with which there is an inherent risk of seizure. Per API610, to minimize the risk of seizure using metal rings, the impeller and case rings should have a Brinnell hardness number difference of at least 50, unless both rings have a Brinnell hardness number greater than 400. Furthermore, the rings should use a generous clearance as spelled out in the API610 11th Edition Standard for Centrifugal Pumps. For hot pumps or pumps which still seize, clearance is further increased.
The modern approach combines the use of metal impeller wear rings with case rings that are manufactured from composite materials like DuPont™ Vespel® CR-6100 and Boulden B-835. This upgrade eliminates the metal-to-metal contact points within the pump, essentially eliminating the risk of pump seizure. This allows for easier assembly, alignment, and operation of the pump and allows the pump to reliably run with clearances significantly less than API610 recommended clearances for metal parts (Table 1).
Inches
mm
Diameter
Clearance Metal
Clearance Vespel® CR-6100
Diameter
Clearance Metal
Clearance Vespel® CR-6100
3.000—3.499
0.013”
0.007”
80—89.99
0.33
0.17
3.500—3.999
0.014”
0.007”
90—99.99
0.35
0.18
4.000—4.499
0.015”
0.008”
100—114.99
0.38
0.19
4.500—4.999
0.016”
0.008”
115—124.99
0.40
0.20
5.000—5.999
0.017”
0.009”
125—149.99
0.43
0.22
6.000—6.999
0.018”
0.009”
150—174.99
0.45
0.23
7.000—7.999
0.019”
0.010”
175—199.99
0.48
0.24
8.000—8.999
0.020”
0.010”
200—224.99
0.50
0.25
9.000—9.999
0.021”
0.011”
225—249.99
0.53
0.27
10.000—10.999
0.022”
0.011”
250—274.99
0.55
0.28
11.000—11.999
0.023”
0.012”
275—299.99
0.58
0.29
12.000—12.999
0.024”
0.012”
300—324.99
0.60
0.30
13.000—13.999
0.025”
0.013”
325—349.99
0.63
0.32
14.000—14.999
0.026”
0.013”
350—374.99
0.65
0.33
15.000—16.000
0.027”
0.014”
375—399.99
0.68
0.34
Composite pump wear rings provide significant advantages over metal components. The following list provides you with what to do when upgrading pump wear rings to composite materials.
Discover our composite materials Dupont Vespel® CR-6100 or Boulden B-835. We have the composite materials you need in stock and ready for immediate shipment, just contact us today! Want to keep up to date on our composite materials and applications? Sign up for our newsletter!
The American Petroleum Institute (API) provides meaningful guidelines on wear ring materials and clearances for all API 610 pumps.
In this article, you will get a quick overview of:
What impeller wear rings are
Why choosing the right impeller wear rings are vital
3 things to consider when selecting wear rings for your API 610 pumps
For more in-depth information on wear rings, you may see our API Maxum Manual.
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.
Now that you know what a wear ring is and why selecting the right one is critical, let’s have a look at three things you should consider when choosing a wear ring for your API 610 pump.
These include:
Wear ring clearance
Compatibility with fluid
Pumps vibrations
Let’s take a closer look at each one.
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.
Good pump wear rings for your centrifugal pumps will improve both performance and efficiency. It will also reduce the chances of pump failure.
With this quick guide, you should know the basics of wear ring clearance, compatibility with fluids, and pump vibrations.
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, 12th Edition.