| Want to be a sponsor? |
|
| Our Web Page |
Check us out! | |
| Welcome to the Centrifugal Blower Maintenance Minute,
the 60 second newsletter designed specifically for centrifugal air & gas blower operators. Each month we will feature a different aspect of service and maintenance to centrifugal blowers. We will review operation, troubleshooting, actual case histories, and answer reader questions. |
|
| Blower Design & Assembly
 Cast iron, multistage, centrifugal, air & gas blowers/exhausters(as they are properly called), are being manufactured by over ½ a dozen companies worldwide now. Without getting into the specifics of each manufacturer, there are some general commonalities between them. The "standard" design is to handle dry air or gas only! There are some special order designs for numerous special applications whereby they handle steam, grit, and even injected water.
 Materials of construction can also vary, but the solid shafts are either carbon steel, or stainless steel. The impellers, either cast aluminum, or fabricated, are all keyed to the shaft. They can be shrink fit to the shaft, but most are slip fit. And the impellers are all held in place with a locknut & lockwasher. Impeller shims between impellers are added during initial assembly to obtain the correct axial clearance between impellers and the stationary cast iron section. During rebuild it is important to re-assemble the cast sections, impellers, and their respective shims, in the same order as they were removed.
The lock nut is tightened "snugly", then locked in. In some long stage machines, over-tightening the locknut can bend the shaft! In these rare cases, tighten, then back the nut off 1 full turn. Some blowers have a "balance piston" positioned beneath the locknut to balance the load & extend the life of the bearings.
 Rotor balancing prior to assembly is not a standard procedure for many manufacturers. Hoffman always balanced their rotors, while Lamson played the odds and balanced only the components. After assembly, if test vibrations were high, they disassembled and re-assembled with a new set of components(shaft & impellers). Their "re-do's" were low enough to justify not balancing every rotor and decreased their costs.
The universal sealant between the cast iron sections is 100 % silicone, RTV. A 1/8" diameter bead is considered "normal" for air machines, with gas applications getting twice that amount. Special applications may use other types of sealant. It is important to complete the assembly in one day(a few hours), and get the tie rods tightened to compress the sections. The proper torque to the tie rods is critical to prevent cracking of the cast iron "ears" on the inlet & outlet heads. They must be lose enough to allow for the heat expansion during normal operation.
 The disassembly & assembly are completed with the blower in the vertical position, i.e. with the shaft perpendicular to the ground. The shaft seal is installed next. The carbon ring, and the packing gland type seals, are tightened normally. The labyrinth seal, however, requires lubrication(usually grease) between the shaft and ID of the seal. The bolts are then left loose to be tightened after startup using a special wrench while the blower is running. This allows the seal to "center" itself around the shaft facilitating proper clearance for sealing. Closed bearing housings(gas type) require special washers on the seal bolts to provide the correct tension on the seal to allow it to move upon startup, but not move back. It will then have the proper shaft clearance for sealing. The bearing housing and its' components are installed next. There are so many variations between the different manufacturer's regarding installing bearings that it will be covered in another issue of the Maintenance Minute!
© Copyright 2009 Snyder Technical Services, LLC. All Rights Reserved
|
|
|
|
|
Maintenance Minute is published each month by Snyder Technical Services, LLC and is based on the work of former Lamson National Service Manager, Bill Snyder. Should you have any questions, or problems to discuss, please contact me.
Bill Snyder
Founder - Snyder Technical Services, LLC |
| Next Month:
Couplings & V-belts |
| Thought for Today:
"You can get anything you want in life, by helping enough other people to get what they want in life."
| |
|
