Dragon Wholesaling 178 Series Instrukcja instalacji, obsługi i konserwacji - Strona 12
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Drukuj stronęExcept for cavitation problems, bearing failure is the greatest cause of increased pump
operating cost. If you continue to run a pump when bearing failures occur, there is an excellent
chance the entire pump will be destroyed. Therefore it is very important to change the bearings
when failure starts. If you wait for complete failure other fluid end parts will be damaged. Bearing
failure is more often caused by lubrication failure than by normal bearing wear.
Misalignment Between Pump and Driver
A major cause of bearing failures is misalignment. Alignment between the pump and motor
should always be checked after shipment and periodically rechecked.
Detection of Bearing Failure When Pump Is Running
The first indication of lubricant and bearing failure is a rapid rise in operating temperature. You
should feel the frame once a week to get a feel for how hot the bearings normally run. A sudden
high increase in temperature normally means the bearings are beginning to fail and need chang-
ing. You cannot hold your hand for very long on unsatisfactory temperatures. If you can keep
your hand on the housing for 5 seconds the temperature is about 160° F. which is suitable for
most pumps. If you cannot hold your hand on the housing for five seconds or if the bearing hous-
ing is so hot you do not want to touch it, there is most likely lubricant and/or bearing failure.
PART V- MISCELLANEOUS INFORMATION
Suction Line Velocity
Suction line velocity should not exceed 10 feet/second for reasonable pump life. This means the
maximum flow for a 6 inch suction is 900 GPM and an 8 inch suction is 1600 GPM. If you want
to flow more than 1600 GPM a 10 inch or larger suction line should be installed.
Net Positive Suction Head (NPSH)
The system must have enough NPSH for the pump requirements or the pump will cavitate,
greatly reducing its life. It appears that most installations do not have enough NPSH to run a 5x6
pump at flows above 1400 GPM even with an 8 inch suction. (This does not mean that no one
has enough NPSH). The result of inadequate NPSH is cavitation and early pump failure. Through
observation, the greatest problem with NPSH is encountered with mud mixing pumps. Most com-
panies do not change the nozzles in their mud guns often enough. On a 1 inch nozzle, 1/16 inch
wear per side will increase flow by 26%. Example: Volume required increases from 1500 GPM
to 1890 GPM. A wear of 1/8 inch increases flow by 56% (from 1500 GPM to 2340 GPM). If sized
correctly when new, the mud mixing pumps will soon be required to furnish a greatly increased
volume and perhaps more than the maximum limit of the pump. We have found customers run-
ning 6x5 pumps on mud mixing experiencing much higher operating costs than those running
8x6 pumps. Companies running 6x5 pumps at 1750 RPM on mud mixing often have high main-
tenance every six months, while customers running 8x6 pumps at 1150 RPM often do not require
major repair for two years. Looking at the failures, it appears the problem is inadequate NPSH at
higher volumes, most likely caused by nozzle wear
At 1500 GPM a 6x5 pump at 1750 RPM requires up to a 26 foot NPSH while a 6x8 pump at
1150 RPM requires only a 7 foot NPSH. Nearly every system will have a 7 foot NPSH available
while almost no system will have a 26 foot NPSH available, especially if the mud temperature
exceeds 140° F.
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