Once a year I attempt to remind all Summit Pump distributors of the “Plug and Play” myths
that unfortunately persist in the pump universe, like fake moon landings and that the earth is flat.
Please make sure you and others on your staff know these 5 key points:
1) OIL: A Pump shipped from the factory does NOT have oil in the bearing housing.
Someone at the pump system site must set the proper amount of the proper oil prior to startup. It is a violation of several federal laws to ship oil in the pump, as oil is considered a hazardous substance.
2) IMPELLER clearance: Final impeller clearance must be set prior to startup. The factory sets the clearance at a nominal setting for the pump type and size, based on ambient temperature liquids, as the factory does not know the specific fluid temperatures or properties
3) MECHANICAL SEAL: A pump shipped from the factory does NOT have the mechanical seal set, in hopes of preventing damage to the sealing faces.
The seal should be set only after adjusting impeller clearance, pump alignment, and rotational checks have been completed
4) ROTATIONAL DIRECTION: A pump shipped from the factory will NOT have the coupling spacer installed because you must first complete the driver rotational check. Additionally having the coupling removed helps in the process to set the impeller and seal. We have a 50% chance of guessing your local electrical phase rotation. If we are wrong, the pump becomes scrap metal.
5) ALIGNMENT: A pump shipped from the factory will NOT be precisely aligned to the driver. The factory conducts/logs a rough alignment check during Assembly.
Even if we precision laser aligned the driver to the pump in accordance with NASA and USA Space Force standards, the very Nano-second the skid is picked up by a forklift or other device that alignment will disappear.
Note, that industry best practices (*1) dictate that a driver to pump alignment be checked/adjusted at least 5 times prior to startup. If you don’t know or are unsure about these 5 alignment stages, please check with your Regional Sales Manager.
A warning tag is attached to each pump to communicate these 5 key steps to the end user/installer. Of course these steps have always been stated in the IOM. The IOM is included with every pump, and can also be downloaded from our website in at least 5 languages.
Retort / Conclusion
Several people have retorted that the competition does these 5 things and so their pumps are “plug and play”.I have checked with several knowledgeable and key sources at these competitive firms and that URBAN MYTH is simply NOT true.
As a matter of fact, the other OEMs state they have the same errors / issues with their end users not heeding the warnings on installation and startup.
Exceptions: I will venture to state that perhaps some distributors may offer these 5 key steps as part of their value package. If you do then you are best in class and get a gold star.
More than a minute… Extra Credit Post Script: On a recurring basis we have people rotate ANSI pumps backwards, consequently that trips the motor on overload. Why? Because the impeller will unscrew and “mate” with the casing. The operator subsequently corrects the directional issue (phase rotation), but does not disassemble the pump to check and correct the resultant damage.
Please note that if the impeller has “mated” with the casing there is a very high probability (99%) that the impeller will require replacement, repair and or rebalance, the casing will also require repair, and the shaft is now bent beyond specification, further the bearings and mechanical seal have been mechanically shocked.
Rotation in the wrong direction is a costly mistake.
Jim Elsey helps you avoid common centrifugal pump mistakes.
I have been writing “Common Pumping Mistakes” for Pumps & Systems
for more than three years. Typically the hardest part of the job is
topic selection so it will be fresh, educational and interesting. This
month, I am writing on a collection of shorter subjects and baking them
up into one article. Instead of a meal, we will have hors d’oeuvres.
Hopefully it will satisfy your appetite. If you have been reading my
column, many of these tidbits will be a review. These comments are based
on single-stage overhung centrifugal pumps moving ambient temperature clear water, except when otherwise noted.
Pumps are really designed to operate at only one point.
That hydraulic condition of one point of head and flow is the best
efficiency point (BEP), also known as the best operating point. Anywhere
else on the published set of curves is simply a commercial compromise.
It would be too expensive for most end users to have a pump designed and
built for their unique set of hydraulic conditions.
Pay attention to the published pump curves.
Manufacturers’ pump performance curves are based on clear water at
approximately 65 F, unless stated otherwise. They will not be corrected
for fluid viscosity. The horsepower stated may or may not be corrected
for specific gravity or viscosity.
When the manufacturers’ published pump curve stops at some point of flow and head, it is for a good reason.
Do not operate the pump at the end of the curve; if there was more
performance to be generated from the curve beyond that point, the
manufacturer would have extended the curve. Operating at or near the end
of the curve will be fraught with performance issues.
Pumps are stupid. A centrifugal pump is simply a machine, where for a given set of fluid properties, impeller geometry and operating speed it will react to the system in which it is installed. The pump will operate (flow and head) where its performance curve intersects the system curve. The system curve dictates where the pump will operate.
Understand the system curve. The system curve
represents all of the friction, static and pressure head baked into the
system. Velocity head is also present, but typically too small of a
component to be concerned about.
Pumps do not suck fluids.
This is a common misunderstanding, but realize that some energy source
other than the pump must supply the energy required for the fluid to get
to the pump. Normally these are gravity and/or atmospheric pressure.
Lastly, fluids do not have tensile strength. Consequently the pump
cannot reach out and pull fluid into the suction.
The maximum realistic suction lift is about 26 feet.
See the previous section where pumps do not suck. If you are at sea
level the atmospheric pressure will be 14.7 pound per square inch
absolute (psia), which translates (multiply by 2.31) into about 33.9
feet of absolute head. So, in a perfect world, if there was no fluid
friction or vapor pressure working against the system you might be able
to lift cold water 33 feet.
In reality, fluid friction and the
negative consequences of vapor pressure will work against you and
preclude fluid lifts of much more than 26 feet. Always calculate the net
positive suction head available (NPSHA) and compare to the pump’s net positive suction head required (NPSHr) value. The higher the margin, the better.
A pump running backwards does not reverse the flow direction. The flow will still go in the suction and exit from the discharge nozzle. Depending on the specific speed (Ns) of the pump (think impeller geometry), the flow and head will be reduced by some significant amount because the pump is much less efficient. For lower specific speed pumps the flow will be approximately 50 percent of rated and the head will be 60 percent of rated. An American National Standards Institute (ANSI) pump running backwards will cause the impeller to unscrew from the shaft and lodge itself in the casing.
You cannot vent air from the impeller eye of an operating pump.
A pump is in many ways like a centrifuge, and so the heavier water is
expelled to the outside diameter and the lighter air remains in the
middle or center. The pump should be at rest to be properly vented.
Pumps with centerline discharges are essentially self-venting.
Industrial pumps do not come from the factory ready to “plug and play.”
There are exceptions to this comment, but never assume. The pump will
require oil to be added to the bearing housings. The impeller clearance
must be ascertained and set for the fluid (temperature) to be pumped.
The driver will need to be aligned to the pump. Yes, the alignment may
have been performed in the factory, but the second the unit was moved
for transport the alignment was lost.
You will need to check alignment again after the piping is installed, and again when the base is grouted in. The direction of rotation should be ascertained and matched to the phase rotation on the motor driver.
The mechanical seal will need to be set after these other steps are completed. Most manufacturers do not install the coupling at the factory because it will just need to be removed for all of these aforementioned reasons.
Almost all pump problems occur on the suction side.
There is a common and pervasive misunderstanding about how pumps work.
Refer to above as a reference. Think of any pump system as three
separate systems when trouble shooting issues in the field. The suction
system, the pump itself and the system downstream of the pump. In my
years of working on pumps and solving issues, 85 percent of pump issues
occur on the suction side. When in doubt, it is a great place to start
looking for the solution.
Always, always, always calculate the NPSHA.
This is likely the most common and the most expensive mistake I witness
in the field. People will erroneously think that because they have
plenty of suction pressure or a flooded suction there is no reason to do
these calculations. A few feet of friction or additional losses due to
vapor pressure can wipe out that NPSH margin you thought you had. Insufficient NPSHA will result in cavitation in the pump impeller.
NPSHr has nothing to do with the system and is determined by the pump manufacturer. NPSHA
has nothing to do with the pump and should be determined or calculated
by the system owner or end user. I recently heard a phrase that the
“pump becomes grumpy and grouchy” when there is an insufficient NPSH margin.
Understand cavitation. Cavitation is the formation of vapor bubbles in the fluid stream due to a drop below the vapor pressure of the fluid. The formation of the bubbles typically occurs just in front of the impeller eye since this is typically the lowest pressure in the system. The bubbles subsequently collapse downstream as they enter a region of higher pressure. The bubble collapse is what causes the damage to the pump impeller.
Cavitation causes damage. If the bubbles collapse in
the middle of the fluid stream there is almost no damage. But when the
bubbles collapse near or at the metal surface, they collapse
asymmetrically and cause a small microjet. This collapse occurs on a
nanoscale (1.0 x 10-9 or billionth). Local pressure forces involved can
be higher than 10,000 pounds per square inch gauge (psig) (689 bar) or
more, plus there is heat generated. This phenomenon can occur at
frequencies up to 300 times per second and at speeds near the speed of
sound. Note the speed of sound in air is approximately 768 miles per
hour (mph) (1,236 kilometers per hour [k/h]) and varies somewhat with
humidity levels. The speed of sound in water is 4.4 times faster at
about 3,350 mph (5,391 k/h or 1,490 meters per second [m/s]). Because I
started my career in the submarine world, I have to point out that the
speed of sound is even faster in salt water.
Cavitation damage can occur at different locations on the impeller.
“Classic” cavitation damage will occur approximately one-third of the
distance downstream of the eye on the underside (low pressure side or
the concave side) of the impeller vane. “Classic” because it is due to
Cavitation damage may manifest at other locations on the impeller, but
those instances usually are due to recirculation issues that are caused
by operating the pump away from its design or BEP.
Cavitation is audible in the lower ranges.
If you hear the cavitation noise (sounds like pumping gravel), it is
likely cavitating. Just because you don’t hear the noise means nothing,
since the majority of the noise range is outside the range of human
hearing. Perhaps we should train dogs to help us detect cavitation? Cold
water is typically the worst fluid for the consequential damage from
Hydrocarbons have minimal effect from a damage aspect.
Hydrocarbon correction factors exist and are based on empirical data.
The rules for correction factors are covered in the Cameron Hydraulic Data book.
NPSHr is NPSH3. When a manufacturer states that the pump requires a certain amount of NPSHr at a given point, realize that the pump is already cavitating at that point with a 3 percent head drop because that is how NPSHr is measured. All the more reason to assure you have adequate margin.
Critical submergence is necessary to prevent vortexing. The vertical distance from the surface of the fluid to the pump inlet is the submergence level. The distance required to preclude air ingestion due to vortexing is the critical submergence level.
To preclude the ingestion of air, do not operate the pump when the
fluid level is below the critical submergence. The vortexing phenomena
is a direct function of the fluid velocity. You can preclude vortexing
by the use of baffles and/or larger pipe diameters such as bell flanged
inlets. There are numerous reference charts on submergence to use when
looking at the suction side design. The best one would be from the
Hydraulic Institute. A conservative rule of thumb is to have one foot of
submergence per foot of fluid velocity.
Pumps cannot efficiently
move fluids mixed with air if the percentage is greater than 4 or 5
percent. Most pumps start to lose performance around 2 to 3 percent air
entrainment. Almost all pump designs will cease to perform at around 14
percent entrainment. Exceptions can be disc pumps, self-primers and some
vortex or recessed impeller type pumps.
My pump bearing feels hot.
This is a common comment, but it is subjective, not objective. It is
difficult for the typical person to hold their hand on a bearing housing
that is over 120 F.
It is perfectly normal for a bearing to be
operating at 160 to 180 F. Use a thermometer or infrared device to
measure the temperature and deal in facts.
Viscosity is the kryptonite of centrifugal pumps. Most centrifugal pumps become too inefficient or exceed their horsepower (hp) limits in a viscosity range between 400 and 700 centipoise that depends on pump size. Always check with the manufacturer when pumping viscous fluids for corrected curves and power limits for the frame, bearings and shaft.
Horsepower requirements progressing along the pump curve change for different impeller geometries.
Low and medium specific speed pumps require more hp the farther out on
the curve you operate, which is fairly intuitive reasoning. For high
specific speed pumps (axial flow), the highest hp required will be at
the lower flows. This is also why it is common to start up these types
of pumps with the discharge valve open so as to not overload the driver.
There is a simple way to think of specific speed.
Specific speed (Ns) is a tool used by designers to look at the
performance and geometry of a hypothetical impeller. Don’t want to get
all caught up in the math involved? A low specific speed impeller will
have the flow enter parallel to the shaft centerline and leave the impeller at 90 degrees to the centerline. A medium specific speed impeller will enter parallel to the shaft and exit the impeller at 45 degrees to the centerline.
A high specific speed impeller will operate with the flow entering parallel to the shaft centerline and leave parallel to the centerline.
Some people still think they can align a pump with a straight-edge, in lieu of a laser or dial-indicator method. They are incorrect. While a straight-edge alignment can potentially kill your bearings, seals and couplings, it also consumes extra horsepower.
Recent studies show that a simple 0.050” offset, which is about the best straight-edge alignment possible, will consume 9% more power. An angular misalignment of 0.015” gap per inch of shaft diameter will consume 6% more power.
At least once a month, we will receive a complaint that our pump is not aligned to the driver upon site arrival. We try to advise our distributors that the final alignment must be performed in the field. An initial rough alignment is done at the factory to prove that the unit is able to be aligned, but as the pump is transported, the unit will become out of alignment. Pump units should be alignment checked five different times during the course of the installation. (We will cover that subject another time.)
Also, note on existing installations you would never move the pump, only the driver. Although, on new installations before the piping is brought to the pump, it is perfectly acceptable and sometimes necessary to move the pump within the room allowed by the bolt holes.
Did you know that when using an internal gear pump in applications above 225 degrees Fahrenheit or viscosities above 750 SSU, the pump may need extra clearances to operate properly? These extra clearances are applied to the rotor’s outer diameter, rotor’s inner diameter, the end clearance and (if applicable) the shaft or bracket bushing inner diameter.
In high temperature applications, the extra clearances are needed to allow for expansion of the materials. As a manufacturer, calculations for the clearances are controlled by material selections and are determined based upon a specific material combination within the pump. Changing the part’s materials could change the amount of extra clearances needed for the pump.
High viscosity applications need the extra clearance to allow the fluid to pass through which keeps the pump from reaching its maximum allowable horsepower limit. If these clearances where not applied, excessive wear or failure of the pump would be premature.
This is just one reason why it is of the utmost importance to collect the application’s fluid and process properties to keep your pump’s life at a maximum.
Each of Summit Pump’s Internal Gear Pumps come standard with a pressure relief valve. These valves are designed and positioned to protect the pump bySAFETYmeans only; they are not meant for throttling the flow or pressure of the system.
When the system pressure is increased and the pressure relief valve is opened, possibly due from a blocked pipe or closed valve, it recirculates the fluid within the pump via the valve. Even though this avoids building pressure in the system.
The heat generated by the moving parts of the pump has nowhere to go, except into the pump materials and the recirculating fluid. This can become problematic for a few reasons:
The pump materials expand, closing the specially designed clearances for the application, pump, model and size potentially causing the pump to lockup.
The vapor pressure of the fluid increases, lowering the NPSHa past NPSHr causing the pump to cavitate, causing damage to the casing, rotor and/or idler.
The fluid flashes in the valve. This means the fluid rapidly expands potentially exploding the pump and/or valve. This is even more critical with fluids with low boiling points (saturation temperatures), such as propane or ammonia, as flashing will happen at lower temperatures, depending on suction pressure.
There should always be other means of pressure relief in the system. Switches and alarms should also be installed if the pressure relief valve to were ever open. Measuring flow in the discharge is a good way of doing this.
The valves are set to a standard pressure based on the pump model and size, unless otherwise specified on your purchase order.
–The Summit Pump Team
When pumping a slurry you need to be extremely careful concerning the fluid velocity in the piping.
There is a critical carrying velocity for which if the slurry drops below this velocity, the particles will drop out of suspension. When the fluid and solids mixture drops below this velocity, due to gravity, the particles in suspension will have a tendency to drop out of suspension and accumulate in the bottom of the pipe. The critical carrying velocity is mostly dependent of the properties of the slurry.
Once the particles begin to accumulate in the bottom of the pipe, they will initially form a “sliding bed” of solids that will, eventually, completely block the flow; as if a valve was closed in the system.
The exact point where this will occur is difficult to predict. The clogging phenomena will vary with pipe size, type, internal surface roughness of the pipe, geometry of the system, solids concentration and the particular properties of the solids and the fluid itself.
Contrary to the industry best practices used in non-slurry applications; it is typically a good idea to have higher velocities and turbulent flow in slurry applications. This will help to prevent the fallout and blockage that can occur.
We see this issue occur more often when the pump is operated with a VFD to control the system. The VFD is controlled by a level manager, pressure, temperature and/or some other parameter that causes the pump to slow down. The velocity drops and the pipe clogs, but the pump continues to run.
Why is this important? Once the piping is clogged, it is similar to having both the suction and discharge valves closed off as now there is no flow and the solids continue to fall out of suspension. The pump continues to rotate with the fluid trapped in the casing, heating up the fluid to its boiling point and flashes to vapor. In other words, the pump explodes. This is not some urban myth, this can and does really happen.