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Canned Pump Protection (Electrical)

Canned Pump Protection (Electrical)

Canned Pump Protection (Electrical)

We are specifying canned pumps for several services in the near future.  We are discussing (read: arguing) about the various protection levels for the pumps.

1. Temperature switch in the bearings and/or windings.  We will be using this as I believe this is a standard.

2. Level switch.  This is new to me.  It is said that the pumps need to verify that it is full before being started.  Any comments?

3. Power Switch (low and high).  I've installed these on Mag pumps, but not canned pumps.  The mechanical engineer requested power switches on canned pumps now also, but I'm not sure I agree.  Essentially these will be in the 10-20hp range.

Are there any standards out there to indicate what protection is needed on a canned pump?

This is normally the space where people post something insightful.

RE: Canned Pump Protection (Electrical)

Hello controlnovice
I think we may have a some regional disparities of terms. I think I understand your terms but it is prudent to verify our terms.
By "canned pump" do you mean submersible pump?
What is a "Mag pump"?
What does the "power switch" do? Is it applied to a two speed motor?

RE: Canned Pump Protection (Electrical)

We regularly work with canned pumps and magnetic drive pumps for several clients. Basicaly they are for use with hazardous and aggresive mediums and they dont use the traditional mechanical-seal. The link will explain the design fundementals better than I can. To answer the questions I think it wise to use thermal devices in the winding as you would with any other motor. The level switch is also a must if the pump in question depends on the pumped medium to lubricate the bearings, if it was to run dry it could be seriously damaged. Dont know what the `Power-Switch` is though.


RE: Canned Pump Protection (Electrical)

Strange buggers indeed.
Thanks stardelta.

Keith Cress
Flamin Systems, Inc.- <http://www.flaminsystems.com>

RE: Canned Pump Protection (Electrical)

I agree with waross, you need to clarify some things, i.e. "canned pump" is unclear, the term "power switch" could be anything, but the "low and high" implies this is a 2 speed pump?

For now, here is what I have to offer:

1) Temperature protection is often used to supplement the Overload Relay in pumps because there are some conditions that may end up heating up the pump long before the motor draws more current. Those conditions can be loss of prime, blockage, seal failure, bearing failure etc., all dependant on the type of pump of course because not all of these issues are problems on every type of pump. Thermistors are the most popular supplemental protection devices right now on pumps that size, but they need a Thermistor Trip Relay in the control circuit. Kilxon snap action thermostatic switches are still the cheapest however.

2) Many pump designs cannot run without fluid in them, others can run dry virtually forever. That is strictly a design issue with the pump. Another alternative to level detection protection is to use a current sensing relay to determine when the pump in running dry, and often the most critical designs use both.

3) Still don't know what you mean by the Power Switch, but if by "canned pump" you mean a canned pump station where the pump tank and housing are sold as a unit, then maybe you mean the disconnect switch? I don't know how the "low and high" would fit with that though.

Eng-Tips: Help for your job, not for your homework  Read FAQ731-376

RE: Canned Pump Protection (Electrical)

I think that the low and high power switches may be overload and underload detection. Depending on what is being pumped, overload can be due to excess trash and solids entering or accumulating in the pump as well as mechanical failure. Underload could be due to clogged inlet or outlet or oil well starting to go dry. Whether they are needed depends on what can happen and what other ways there are to detect problems.

RE: Canned Pump Protection (Electrical)

Canned Pump: An electric motor stator is attached to the shaft and the magnetic fields are placed outside of the "can". Current flows from the windings through the product and the "can" to the stator, causing it to rotate. The pumped fluid flows through the pump bearings and around the stator. Since the pump is in a "can" the fluid cannot leak out.

A magnet is attached to the shaft. An electric motor turns some magnets outside of the can and the magnetic field is transferred to the magnet inside the "can" causing it to turn. The magnets are covered with a corrosion resistant covering.

Power switch "looks" at the power draw on the leads to the motor.  The Low/High is Underpower (which would indicate dry run)/Overpower (overload: can be taken care of with the motor heaters)

This is normally the space where people post something insightful.

RE: Canned Pump Protection (Electrical)

Hi controlnovice
By the term usage we are used to, the Stator, by definition, is stationary. I think you meant to say rotor, which by definition, rotates.
Other than that, you seem to know more about this field than most of us.
A couple of comments based on general experience.
If the motor is depending on the circulation of pumped fluid for bearing lubrication and/or cooling, a level switch may be wise.
Power switches, (Load monitor?). If the mechanical engineer wants it, he may know something about the process that you don't.
Politically, if someone is making a stand on a protection issue, it is not always wise to oppose too strongly. If there is a consensus that a particular device will protect against a 1 in 10,000 event and can be dispensed with, a subsequent 1 in 10,000 failure can be accepted and forgiven.
If someone has taken a very strong stand, been overruled, and the 1 in 10,000 event occurs there is sure to be finger pointing, "I told you so's", and not much forgivness.
It may be a time to ask and listen rather than to argue.

RE: Canned Pump Protection (Electrical)

Canned pumps can't run dry for long, and are very expensive to repair or replace, so the level, high and low load protection all makes sense.

Another 'feature' that can surprise the unwary; all the waste heat from the motor goes into the pumped fluid.

Mike Halloran
Pembroke Pines, FL, USA

RE: Canned Pump Protection (Electrical)

Nice to learn new terminology, now I know what to call the fuel pump in my boat. The pump failed, I believe, after the water separating filter in front of it loaded up causing insufficient gasoline flow to cool the windings. Since your pump is bigger and more expensive, temperature and run dry protection are both well advised.

RE: Canned Pump Protection (Electrical)

We have to give controlnovice a star for giving a lot of us some new information.
Thanks controlnovice

RE: Canned Pump Protection (Electrical)

Hello controlnovice

Pumps typically need to be protected against dry running and cavitation. This can be done by the use of level probes to check the fluid level and a flow switch to ensure that there is continuous flow. It is common for the installation to be protected against a broken pipe by the use of a minimum pressure switch. It is also common for an over pressure switch to be used to protect agains pump deadheading (closed valve on the output).
Under current protection against a dry pump or closed valve is only partially effective due to the current variation with voltage. Shaft power monitoring will give a higher level of security against dry run, cavitation and broken pipe than current based monitoring.

Best regards,

Mark Empson

RE: Canned Pump Protection (Electrical)

I'm learning some new things here also...these canned pumps are going to Europe.

I learned that the temperature switch is not in the bearings.  All canned pumps I've ever installed had a temperature switch in the bearing (sometime referred to as bearing wear detectors)...just not these.  These temperature switches are installed in the windings to obtain the Explosion Proof rating for the pump/motor.  

The level switch is also used to verify the pump is full.  I am told that this is also to maintain the pump/motor's explosion proof rating.  If it is full of liquid (no air), then there is not an explosive atmosphere.  Since the liquid is pumped through the stator/rotor, I can see this, but it makes more sense to me that it is there to prevent starting when dry.

So, that leaves the power monitor (Load or kW Monitor), which is used to prevent run dry.

Whew....maybe I am learning something....my brain hurts.

This is normally the space where people post something insightful.

RE: Canned Pump Protection (Electrical)

I for one learned a lot in this thread. Thanks for starting it.

Eng-Tips: Help for your job, not for your homework  Read FAQ731-376

RE: Canned Pump Protection (Electrical)

From what I am understanding from the posts, a "Canned Pump" uses a submersible motor.  Just a note all the submersible motors that I am aware of (Franklin, Byron Jackson, Sun-Star, Hitachi, Plueger) require class 10 overload protect instead of the standard class 20.  Also all of there manufactuers require that the motor get to 2/3rds speed in a short time frame usually 3-4 seconds if you plan to use this with a VFD.

RE: Canned Pump Protection (Electrical)

No thewellguy, the motor is actually outside of the pump. Visit some of the posted links and you will get a better idea. I too had never heard of this terminology and was assuming what you just posted. Canned pumps are a specialty pump / motor design that is for a niche market in explosive atmospheres.

Eng-Tips: Help for your job, not for your homework  Read FAQ731-376

RE: Canned Pump Protection (Electrical)


Not necessarily for explosive atmospheres market.  

More for any material (usually nasty) that the user want to keep contained.  The canned pumps are seal-less and leak-proof.  This is the main reason for canned pumps.

This is normally the space where people post something insightful.

RE: Canned Pump Protection (Electrical)

OK, but I warn you, I can only learn so much in a day before my head explodes.

RE: Canned Pump Protection (Electrical)

Used in a lot of acid services, among others.  Acid services can be in lots of places, many of them non classified areas.


RE: Canned Pump Protection (Electrical)

Be sure you specifiy the pumps rated capacity at the proper Hz. 50 vs. 60.
You may end up canned with your canned pumps.

Best regards

RE: Canned Pump Protection (Electrical)

This has been an interesting thread. I've been following along for a couple of days without time to add my experience with "Canned Pumps". Several years ago, we had what we called canned pumps in a system called CVCS (Chemical Volume and control). These were small horse pwr. high speed (3600 RPM) combination "in-line" pump/motors. The rotor as well as the stator were sealed with I think about .020 stainless steel. The in-line pump/motor was flanged at both inboard/outboard to the piping and could not be run dry. Flow had to be established prior to operating the "canned pump. Thus, the control for the system was integrated with level (vol. tank), temperature (stator), and flow logic. Glad to be a part of this discussion.

12 fish
As iron sharpens iron, so does a man sharpen the countenance of his friends

RE: Canned Pump Protection (Electrical)

The point about a canned pump and hazardous areas is that there is no mechanical seal. Thefore 1 likely leak point is eliminated and the hazardous zoning of the space around the motor can sometimes be re-evaluated to a less hazardous zone. For mag drive pumps the motor is not in the liquid, the motor is "normal" and coupled to the pump impeller by magnetic attraction, not with a solid mechanical shaft. There is a very sucessful protection for dry running based on measuring the temperature of the barrier plate between the magnet and the impeller. Just measuring the level is not always enough, as you can damage the pump by having liquid in the pump but with the valves closed. Also an excellent indicator for incorrect pump running is the power factor of the electrical load. The power factor at dry running or dead head (all valves closed) is significantly lower than normal load and this can be used in the protective relay design

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