Magnetic pumps for unloading trucks 1

[Bernardo P.]

Does anyone have any experience with magnetic pumps unloading trucks?

It is known that this type of pump is sensitive to running dry. And this situation can occur especially at the end of unloading.

Any tips on what can be done?

 

[LittleInch]

Use a different pump for the last stripping action.

Unload into a buried vessel and then pump out from there.

Many ways to skin this cat.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Heaviside1925]

OP,
Without more description on why a mag drive pump was selected, the system it is installed in and service it is being used for, it's difficult to provide relevant information specific to your situation. Aside from LittleInch's suggestions, another possible one is to install instrumentation to shut the pump off to prevent a dry running condition. Assuming this is an existing pump, what is meant by sensitive to running dry? Is the manufactures recommending that you break down and rebuild the pump anytime a running dry condition occurs or just try to keep it from happening?

 

[LittleInch]

Normally nag drives are for when you can't have any seal leakage.

So something toxic or like LPG?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TugboatEng]

There are methods to make mag derive pumps tolerant of short durations of dry running. Consider using metalized graphite bushings.

 

[Heaviside1925]

Littleinch I agree on what normally they are used for, but I have also had customers who wanted them in place of a standard seal arrangement based on what I'm guessing was a vendor's convincing. I was just asking to understand more.

 

[georgeverghese]

Avoid selecting these pumps unless this is a very clean service application. Dont fall for the price bait.

 

[Compositepro]

I think that air-operated-double-diaphragm pumps are pretty well suited for unloading tankers. They may not be very efficient but they are robust and avoid a lot of safety issue of other pump types. But I haven't had any involvement with unloading in a long time. What do others think.

 

[pierreick]

Hi,
Mag drive pump is not suitable for unloading truck, cannot run dry and need very clean fluid.
Why don't you share with us the material? technology is specific to material. Centrifugal pump with proper mechanical seal can do a decent job, same for diaphragm pump if diaphragm is compatible with your product. May be pressurizing your container is also an option?
More info better answer.
Pierre

 

[Bernardo P.]

Above is the table with pump operating data.

The vendor is offering Dry Cut Current Detection Device (EMOTRON)

 

[Heaviside1925]

OP,
Based on other's comments and the chart you posted, are the NPSH values realistic for your application?

 

[LittleInch]

That's a massive range for a centrifugal pump. from 8.5m3/h @10m through 10m3/h @ 77m to 15 m3/h @ 27m.

Assume you have some sort of pressure control, but this does not look suited to a centrifugal pump to me.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TenPenny]

Having sold these for years, and had to sort out some of the problems, also note that if the truck unloads from the top, and you are using a self priming pump, put it up above the tank level. DO NOT have the pipe come up out of the tank and down to the pump. That does not work.

Frankly, something like an AOD is often a good choice. (air operated diaphragm pump).

 

[Bernardo P.]

More information:

There will be one pump for each product.

The pumps will have a dual function. Unloading from the truck to the tank. And then delivery from the tank to the process. The data shown in the table refers to the data when the pumps are being sent to the process.

 

[pierreick]

Hi,
We have to understand that your process is batch process (set up).
Because of the nature of your product and the set up (dual function), I will use a centrifugal pump with mechanical seal (simple or double) and fluid barrier if compatible with your product.
Note: You will need a backup pump installed or in warehouse.
At the end of the day this is your decision. Make sure you understand the risks of using Mag drive pumps. To me they are consumable.
Good luck
Pierre

 

[TiCl4]

1. Mag drives can run dry if they are designed to do so. Talk with the vendor to specifically call out the need to run. Run-dry mags total allowable run-time when dry varies with horsepower, so consult specifically with the vendor.

2. The use of a power indicator interlock for run-dry conditions is a good idea. You can set your interlock delay within the limits of run-dry as mentioned in #1 above.

3. Mag drives require clean fluids. Check with the manufacturer on each fluid. Pay careful attention to the materials dissolved in water (NaOH, KOH) if they are near the solubility limit. Ensure the internal heat generated in the pump does not result in precipitation inside the small cavities of the pump, which can block cooling recirculation and destroy the pump. I think NaOH and KOH both increase solubility with temp, but be sure to check. As an aside, 50% caustic, if this is not in a climate controlled area, will need to be carefully heat-traced and monitored, as it "freezes" (begins precipitating) at 60F.

4. AODD pumps are typically good for tanker offloading applications, but be wary of the consequences of a diaphragm failure. Due to the way AODD pumps work, a diaphragm failure will result in the pumped liquid being spit out the air exhaust, sometimes becoming aerosolized in the process. AODDs would not be my first choice for pumping hazardous chemicals.

also note that if the truck unloads from the top, and you are using a self priming pump, put it up above the tank level. DO NOT have the pipe come up out of the tank and down to the pump. That does not work.

My experience differs with this. Yes, it is not ideal to increase the suction line size as well as create a high point for an air bubble to be trapped, but we offload railcars from the top with gear pumps on the ground with no issues.

 

[TheHandModel]

Mag-drives can be used for unloading but there are some considerations for this.
1. If you're operating fixed speed, I'd recommend using a power monitoring device. amp(current) monitors might not get the job done depending on how the motor is sized. Emotron makes a M20 unit that measures power but there are other vendors(Wentec, load controls, H2flow). There are subtle differences in how they are wired and programmed but they all generally have the same core protections. You do need to make sure you train your operators because you will likely have a small amount of fluid left when the pump starts pulling in air and motor trips(at least if you set it up right). Operators, knowing there is still liquid in the tank and not understanding that centrifugal pumps will not dry prime will want start that pump right back up. For a 4 pole or smaller pump, you might extend the time delay to 10-15 seconds to pull a bit more before it shuts down. Given some of the variance in hydraulic performance you need, a VFD might be worth considering. Most modern VFD's can have similar protections setup but it's a much more complicated setup process.

2. You would probably want a design with a non-metallic containment shell so you're not heating up the fluid as you're running out of any excess suction pressure unloading. given that you have to handle multiple acids/alkalines, non-metallic internals overall makes more sense and if it's truck to tank and tank onward temps(not given) are likely ambient or heated only enough to prevent crystalization

3. I would avoid using AODD's for the main transfer however if a tank needs to be drained as completely as possible, they are good for this. If it is top unload they can also be setup to handle initial priming. Priming also could be accomplished using pressurized air to pad the tank. I don't like using self priming pumps for any type of tank/truck unloading. THose pumps work best in open sump systems with simple level controls. If you're unloading it's very difficult to know when the tank is empty but the pump isn't and that partial dry run you will experience as the pump runs out of liquid will look similar to your power consumption when you are doing your intial priming. If you try and go to the end, you will have to refill the self-priming casing before starting up again and most plants will use air to clear the lines rather than have chemical sit in the equipment for extended periods of time.

4. There are carbon and DLC coated SiC options but not sure carbon graphite will work with that basket of materials listed and will wear over time. DLC coatings also tend to wear off over time under normal conditions. Telling operators how long they can run the pump dry for is like telling the guy with a recent liver transplant how many beers he can drink this weekend. The goal should be to get them to not do it.

 

[Compositepro]

With AODD pumps the pumped fluid will always be lower than the drive air pressure, so air leaks into the fluid in the case of a diaphragm leak. Also the suction of these pumps should never be pressurized because that causes the diaphragm curvature to invert with each stroke of the pump. That will quickly fatigue the diaphragm to failure. AODD pumps are ideal for self priming, and you can tell flow rate, or if the tanker is empty, just from the sound of the pump. They will pump air as well as liquid so they can create some vacuum in the tanker. They can run dry without damage, and they are intrinsically safe with flammable fluids. They can be safely stalled if a valve is closed on the discharge line. The discharge pressure will never be greater than the drive air pressure. They are relatively inexpensive to purchase and install. They are relatively light and portable.

Cons of AODD pumps are that they are relatively noisy, although that can be useful. They are high maintenance, although repairs are simple. They are not energy efficient.

They are a very useful tool to have in in the tool kit for solving problems, and every engineer who has to pump fluids should be familiar with them.

https://youtu.be/iHeK-PzwG8g

 

[TugboatEng]

I have seen a pump chamber burst on an AODD pump. That might be a consideration when worki with such hazardous chemicals. That was on a test stand, we were testing a new fiber reinforcement.

Otherwise, they are available with backup diaphragms. This is preferred for PTFE diaphragms as they have a short fatigue life.

 

[Ecotechnical]

We have used Mag drive pumps to unload trucks often. There are several Self priming mag drive pumps on the market as well as some that handle solids quit well. The use of power load monitors are effective but temperature monitoring of the shroud area allow for optimal protection as well as eliminating start up delay issues. Do you have any discharge pressure control on the values from your table? I would think that you could handle those pretty easily with a self priming Mag drive pump + Vfd and some back pressure control.

I would also try to stay with a metallic mag drive pump opposed to a lined version if possible, while more costly upfront they are more forgiving in these types of services where you may see some heat rise from run dry or variable duty of unloading.

Another topic I saw mentioned before on a comment would be to focus on bearing material. There are several bearing materials that are more resistant to the final stripping of the truck such as SSIC with graphite impregnation, SSIC with Diamond impregnation, and diamond like coatings. I have had similar experiences with the coatings as mentioned by TheHandModel. They are great until the coating is gone then you see a rapid decline.