There is great satisfaction in doing a job all the way.
In South Africa, when you make a statement that someone agrees with, they say “100 %”–similar to how other English speakers say “absolutely.” With that in mind, we want the pumps upgraded to Vespel® CR-6100 to be upgraded 100% whenever possible.
When you upgrade your pumps to Vespel® CR-6100, there are two steps:
- Eliminate the metal-to-metal contact points in the pump
- Reduce the running clearance (of wear rings, center bushings, and throttle bushings)
Upgrading your pumps to Vespel CR-6100 Step #1
Our recommendation when upgrading to Vespel® CR-6100 is to convert all of the stationary wear parts to Vespel® CR-6100. All of the rotating parts remain metal, thus eliminating all of the metal-to-metal contact points in the pump. This essentially eliminates the risk of pump seizure.
Yet, once in a while, customers try to make a small change instead of fully upgrading the pump. The three partial upgrades we run into are:
- Trying to stabilize the shaft of an overhung pump with a throat bushing
- Only doing the center and throttle bushings of a multi-stage horizontal pump
- Only upgrading the shaft bearings of a vertically suspended pump
Older pumps with long slender shafts (high L/D ratios) create problems for mechanical seals due to excessive shaft deflection. If you want to increase the rotor stability of these pumps using the wear parts, you will want to upgrade the wear rings to Vespel® CR-6100 and reduce the clearance.
The reason is that the Lomakin Effect-the hydraulic force which stabilizes the rotor-is driven by differential pressure and the surface speed at the differential pressure interface. Wear rings have significant differential pressure and high velocity, creating a lot of stability from the Lomakin Effect. Throat bushings? Not so much.
Horizontal Multi-Stage Pumps
If a horizontal multi-stage pump like a boiler feed water pump seizes, it will usually occur at the center bushing or throttle bushing, depending on the pump type. These two components generally have the tightest clearance in the pump and will be the first points of contact. In these services, there is a temptation to only upgrade the one or two components which seized.
While this approach has been successful in reducing pump seizures, there are some limitations. Metal-to-metal contact points remain and thus there is still a possibility of seizure. If all of the wear parts are upgraded, the risk of seizure is essentially eliminated. Furthermore, the wear rings also add to the rotor stability and efficiency of these pumps. Upgrading the wear rings as well as the center and throttle bushings will make for a much better pump. Especially if you use the Boulden PERF-Seal™ design (patent-pending).
Vertically Suspended Pumps
Vespel® CR-6100 is a great material for vertically suspended pump shaft bearings in LPG, butane, natural gas liquids (NGL), and other flashing products. It can survive running dry at start up with limited wear. It doesn’t break like a carbon part. This application for Vespel® CR-6100 is so common that Boulden carries a huge inventory of standard stock sizes for the dimensions typically used for shaft bearings.
What some users miss is the opportunity to also upgrade the case rings of these pumps and reduce the clearance. This addition to the upgrade eliminates the other potential seizing points in the pump. Furthermore, reducing the clearance increase the pump efficiency and reduces the NPSHR–all of this making the pump easier to operate.
The only partial upgrade above which we do not recommend is trying to stabilize a rotor with a throat bushing. In our experience, this approach is marginally successful at best. The other partial upgrades have worked and there are situations where they are necessary. But, given the choice, why not do the job 100%?
The main point is to recognize that the maximum improvement in reliability, safety, and efficiency will be achieved if you upgrade all of the wear parts (Table 1) in your pump to Vespel® CR-6100.
Table 1: Components to upgrade to Vespel® CR-6100
|Overhung Pumps||Between Bearings Pumps||Vertically Suspended Pumps|
|Case Wear Rings||Case Wear Rings||Case Wear Rings|
|Throat Bushings||Throat Bushings||Throat Bushings|
|Inter-Stage Bushings||Line-shaft bearings|
|Center-Stage Bushings||Bowl bearings|
|Throttle Bushings||Bottom bushings|
Contact Boulden Today for your Vespel® CR-6100 Needs!
If you have a pump operating at less than 500 F (260 C) where you want to improve the reliability or efficiency, contact Boulden today. We can provide you all of the details required for your upgrade and have the Vespel® CR-6100 material required for the upgrade in stock in a wide range of sizes available for immediate delivery.