Myths and Truths about Balancing

MYTH: “1x RPM is always caused by unbalance.”
TRUTH: Unbalance always causes vibration at 1x RPM.  However, 1 x RPM is not always caused by unbalance.  Many other problems can exhibit vibration at this frequency.  Examples are:  Misalignment, Bent shaft, bowed shaft, cracked shaft, eccentricity, open rotor bars in the motor, rubs, looseness, belt issues  and resonance. 

MYTH: “The run time and lifetime of the equipment can be extended by performing a balance job on the equipment.”
TRUTH: Problems such as misalignment, bad bearings, looseness, etc cannot be corrected by balancing the machine.  It is almost impossible to correctly balance a machine that has other defects affecting its performance.  Misalignment, bad bearings looseness etc should be corrected before attempting to balance equipment.

Pipe Strain is Soft Foot!

Soft foot means machine frame distortion. If you are missing shims under a foot and tighten the hold-down bolt until you have forced the foot down to the base, you will have distorted the machine frame. If you have severe pipe stress on a pump, and the anchor bolts are tight, chances are great you are also distorting the pump casing. Consider that if the pump’s anchor bolts were completely loosened or removed, the pump might be hanging in the air from the piping. So if you were now to tighten the anchor bolts, you would be forcing the pump down to the base and distorting it, just as happens when you are missing shims under a foot.

Shimming the feet will rarely solve the problem completely; rather, the correct solution is to eliminate the undesirable pipe stress. “Stress” is the force acting on something, while “strain” is the deflection or distortion resulting from the stress. A soft foot condition means you have machine frame strain, and pipe stress is just one of several examples of this. When the machine casing is distorted, the internal alignment between the bearings is changed and the shaft is deflected. This produces enormous stress on the bearings and increased vibration in your machines, resulting in premature wear and tear as well as loss of efficiency. Your seals and bearings will fail much faster. If a significant soft foot condition exists, a good alignment of the centerlines of the shaft rotation is almost pointless. The machines will still fail more quickly and lose efficiency. How do we diagnose and fix this?

The trick lies in knowing how to recognize that a pipe strain problem exists. The behavior of a machine with pipe strain differs significantly from one whose soft foot condition is caused by one of the more traditional shimming problems or unevenness of base or feet.

Any impact on the alignment of more than about 2 mils indicates a pipe strain problem that should be dealt with. Correcting pipe strain is a task for an experienced pipefitter who must see to it that connecting and torquing the piping should not move the machine from its rough aligned condition, nor distort its casing in any way. Proper pipe hanging techniques and a good knowledge of calculating and designing “Dutchman” spacers is essential.

Taken from Ludeca Blog

Why air is compressed in Gas turbine engine ?

To understand why we compress air in a jet engine, one must first understand the goal. For an aviation gas turbine, the goal is thrust. The purpose of the turbine stage is to power the fan and the compressor. The thrust comes from moving air through the engine.
Now, we know why the fan is there. It's there to move the air. We get thrust from that. Now, the compressor's main purpose is to assist the turbine in energy extraction. By compressing the air, not only does it assist in combustion, it also helps in energy extraction by the turbine stage(s).
As for the temperatures, a turbojet will have significantly higher higher temperatures, as 100% of the flow goes through the turbine stage. As we mentioned, for a thrust-producing aviation engine, the goal of the turbine is to extract 'just' enough energy to power the fan/compressor stages. So, the flow still has a ton of energy, in the form of velocity and temperature. Exhaust temperatures can be well over 1000 degrees.
In a turbofan, as mentioned, some, if not almost all (in the case of the bigger engines) of the flow goes through the bypass. So, while the inner core flow will be hot, after the mixing region, it is relatively mild.

Combustion Air Fan & Efficiency

In order for your boiler to operate at peak efficiency, it is important that the correct balance of fuel and combustion air is achieved. Air and fuel ratios are controlled through linkages, fans, dampers and the increase or decrease of gas pressure. Gas pressure is controlled through a pressure regulator and a fan controls the volume of combustion air.

If there are any problems with the fan, more energy may be introduced into the system, causing decreased efficiency. To help ensure that your equipment is running at its peak performance, please review the common fan problems below.

Fan Capacity/Pressure is Below Rating:
1. Dampers or variable inlet vanes are not adjusted properly
2. Fan inlet or outlet conditions are impaired
3. Multiple air leaks within the system
4. Damage sustained to the blower wheel
5. Direction of rotation is incorrect

Fan Vibration:
1. Worn bearings
2. Unstable foundation
3. Foreign material in the fan causing an imbalance
4. Misalignment of bearings, couplings, wheel or v-belt drive
5. Damaged wheel or motor
6. Bent shaft
7. Worn coupling
8. Loose dampers or variable inlet vanes
9. Speed too high or incorrect fan rotation
10. Vibration to fan transmitted from another source
11. Uneven blade wear
12. Loose or broken bolts or set screws

Overheated Bearings:
1. Improper lubrication
2. Poor alignment
3. Damaged wheel or driver
4. Bent shaft
5. Abnormal end thrust
6. Dirt in bearings
7. Improper belt tension

Overload on Driver:
1. Speed too high
2. Direction of rotation is incorrect
3. Bent shaft
4. Poor alignment
5. Improper lubrication
6. Wheel wedging or binding on fan housing

Taken from Nationwide Boiler Blog