Part 10: Vertically Suspended Pump Installation Tips
We have discussed how upgrading your pumps with Vespel® CR-6100 helps to eliminate pump seizures, allowing you to reduce wear ring clearance, which improves pump efficiency and improves pump reliability by increasing the Lomakin Effect in the pump.
Quality repair and installation practices are an essential counterpart to the success of upgrading pumps with Vespel® CR-6100. This is true of all pump types–horizontal and vertical. When you are finished with the overhaul, the rotor should turn freely.
Vertically suspended pumps with their multiple fits and pilots require some additional consideration. To ensure the best possible results in these pumps, below are some tips which have been passed on to us from our customers.
Mechanical Alignment of Pump Components
Multi-stage vertical pumps pose a challenge for the shop performing the overhaul because there are multiple fits and pilots. Keeping the whole pump assembly concentric and square will give you the best results with your upgrade.
Good practices should be followed from the machine shop through the final alignment in the field.
In the machine shop:
- Ensure all pilot fits within the pump are 0.002″ (0.05 mm) or better.
- Ensure all mating faces of assembly elements are square.
- If possible, assemble the pump in a vertical position.
- Install Vespel® CR-6100 shaft bearings, bowl bearings, and wear rings, then final machine with the lathe indexed to the pilot fit of the part-this will ensure all bores at wear interfaces are concentric within the assembly. (Alternatively, all wear part fits can be machined concentric to the pilot fits prior to the installation of the Vespel® CR-6100 components.)
- Install the Vespel® CR-6100 shaft bearings with the same clearance as the original design for the pump. If the original clearance is not available, See Table 3a (imperial) or 3b (metric) in the Boulden Installation Guide for recommended minimum clearances for vertically suspended pump shaft bearings.
- When the assembly is complete, make sure the rotor turns freely within the pump with no hard rubs. If there are hard rubs, disassemble, try to find the source of the rub and correct the concentricity of the misaligned component. If clearances are very tight, consider a slight increase of the bushing clearance and re-check to make sure there is no hard rub.
- Our recommended clearance for Vespel® CR-6100 wear rings in vertically suspended pumps is the shaft bushing clearance plus 0.002″ (0.05 mm) or 50% of the API minimum clearance for metal parts-whichever is larger.
- If the pump is operating in very cold liquid (temperature below 0 C), increase the clearance at the shaft bearings by 0.002″ (0.05 mm) above the minimum values shown in table 3a or 3b.
In the field:
Generally, vertically suspended pumps incorporate a rigid coupling and the pump does not have its own rolling element bearings. The purpose of the rigid coupling is to make the pump shaft and motor shaft act as one unit with the pump relying upon the rolling element bearings in the motor. When dealing with a rigidly coupled vertical pump, traditional alignment methods can introduce misalignment. You also cannot rely upon the register fits from the motor to motor mount to the pump to be concentric.
Here are some tips for aligning a vertical pump with line shaft bushings and no rolling element bearings. (The motor bearings carry the axial load and coupling is rigid)
- The pump must hang as close to plumb (vertical) as possible. This requires inspection of the base plate at the sump to ensure it is flat and level, and inspection of the mounting plate on the pump to ensure it is also flat and square to the assembly. If the pump is hanging “at an angle” the shaft will bend as it tries to hang plumb and pump life can be reduced.
- Install the pump without the seal installed
- Verify that the pump is level on the base
- Install the motor on the pump.
- Mount a dial indicator on the motor shaft, reading the ID and face of the seal chamber
- Correct any radial misalignment by moving the motor and/or motor mounts in their fits. Squareness should be corrected by machining mounting faces (shims are sometimes used).
- Lock the motor in position (installing 2 dowel pins is a proven method).
- At this point, you may want to couple the pump and check for any run-out.
- Any run-out that shows up after the alignment is likely due to a fault in the coupling
- If resistance is still encountered after alignment and run-out are corrected, the source of rubbing is likely eccentric pump internals, which will need to be corrected back in the shop.
- Install the seal (if the motor must be removed to install the seal, care must be taken to ensure motor returns to aligned position)
- Install the rigid coupling (Coupling should be dimensionally checked and checked for trueness in the lathe before installation)
- Measure the shaft run out between the coupling and the seal. This should be as close to zero as possible. The purpose of the rigid coupling is to make one shaft out of the driver and driven shafts. The end of the motor shaft is the zero point, so just a small run out at 15 cm below the coupling translates into huge side loads on the shaft bushings 1-2 meters down the assembly.
Side note: if you experience misalignment of the rigid coupling, the evidence will likely be wear of the bushing and/or shaft concentrated at the top bushing in the pump.
If you have anything to add to the above notes, please contact us. We’d love to hear your thoughts.
We hope you have found this series on how to upgrade your pumps with Vespel® CR-6100 helpful. In future weeks, we’ll have a couple of bonus sections on special topics. Until then, if you need any Vespel® CR-6100, contact Boulden. We have whatever size and quantity you need in stock and ready for immediate delivery.
For information on how to install Vespel® CR-6100 into nearly any centrifugal pump type, download the Boulden Installation Guide.