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Pump overload

Pump overload

Pump overload


I have a 500 CST flexy tank oil that I have tried to pump to a near tank(2.5'' 9 m flexible pipe, 2.2 KW 1450 rpm 2'' 3 phaze gear pump). After 200 L the pump went off. It overheats and shuts down.

When it is warmer outside it performes well.

My problem is that when I calculate reynolds Number(which is low) and fricton losses everything works out well and the pump should work fine(energy consumption wize). There is barely even any head.

So how can I factor in this viscosity factor which is obviously more influental than now. It is clear that I am missing a formula.

Any ideas?

Best Regards
Roman Katz

RE: Pump overload

Hydraulic Institute standard ANSI/HI 9.6.7 provides methods for calculating pump performance with viscous fluids, if the performance parameters (head, flow, etc.) for pumping water are known.

Process Engineer, MSChE

RE: Pump overload

Your friction loss calculation should include viscosity. Post all the details and your calculations and we might be able to help.

What's the pump details? What cuts out? The motor? Do you have any pressure readings?

Is there any pressure relief/recirculation valves? If not why not?

Sketch your system.

Initial guess is that your pump is pumping at a much higher pressure than the motor is designed for and hence using too much power but you've only given us 25%of the data.

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

RE: Pump overload


I will get all the data and post it.

Best Regards
Roman Katz

RE: Pump overload

Remember that the equations for viscosity correction apply to CENTRIFUGAL pumps only.

For your gear pump, the best information you will get is from the manufacturer. They should have empirical data on how their pumps perform with various viscosities.

Also recall that not only the pump but all of the discharge piping is affected by viscosity changes. Higher friction values in piping will drive up HP requirements and could burn up an undersized motor.

RE: Pump overload

This pump may be overheating because the built in relief valve on the gear pump discharge may be lifting due to high discharge pressure, resulting in internal recirculation and gradually the pump casing heats up. Typically, the cracking pressure of these built in relief valves is at 75-80% of set pressure-check the pump literature. The set pressure on this RV may be too low for this application.

RE: Pump overload

The OP said the pump trips off, so it must be the drive motor that is overloaded and overheats.

RE: Pump overload

Agreed, it could either be the drive motor winding TAH or the pump casing TAH - the OP doesnt say what trips the pump.

RE: Pump overload

Is "500 CST", 500 centistokes?

"flexy tank oil" is a bit more of a challenge.

Temperature and viscosity at that temperature of pumping would be interesting to know, but 500 CSt is pretty gloopy stuff.

I suspect your pump s just a little too big for the duty and if the return valve is small will overload at cold temps.

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

RE: Pump overload

Unlike centrifugal pumps, positive displacement pumps move a constant volume and the motor would fight any resistance to deliver that volume: the greater that resistance (in form of friction, viscosity, head) the higher the number of amps pushing forward.

Are the 9 m of flexible pipe upstream the pump?
If so, could it be collapsed at some point?
If not, I would first verify that the motor is working on the three phases and that the used amps for worse conditions is within the specs of the motor.

If the flexible pipe, circuit and motor are OK, I would either slow the pump down or heat up the oil for cold days.

The recommended velocities inside a 2-1/2" pipe for viscous fluids are around 0.33 m/s upstream the pump and 1.1 m/s for discharge.

"Where the spirit does not work with the hand, there is no art." - Leonardo da Vinci

RE: Pump overload

I will send enother sample to check viscosity in room temp and I will check if all 3 phazes are working.


Best Regards
Roman Katz

RE: Pump overload

Here is additional info:

Viscosity at 15 deg 3800 CST!!(I was surprised). Till the pump stops, it produces 100LPM. I have tried a shorter rubber 2.5'' pipe (about 3m long) and filled a 1000L IBC. Managed to fill only 600L. The electric box that is on the top of the pump got very hot.

Best Regards
Roman Katz

RE: Pump overload

What are the pump details? - manufacturer, model no, speed, flowrate, pressure, pressure relief system (if any).

Temperature you're pumping at?

viscosity at that temperature?

What are you trying to do here? Is this an experiment or commercial system or what?

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

RE: Pump overload

We produce lubricants. One of the components for gear or drilling oils is "BrightStock". it is high viscosity oil (30 CST at 100 degC,530 CST at 40degC).At 15degC its 3500CST.

I receive flexy tanks of this oil and fill IBC for batch productions.
To do this i use a "pompe cucchi BG150 V3,2'' 1450RPM pump 3 phaze 3HP"(stated 9m3/hr 5 bar, pump is connected to a motor by omega connector(what ever this means)) that I connect to a flexy tank via 2.5'' rubber pipe(2.5 m long). And a same diameter 3 m pipe for filling the IBC. After filling 600L(it takes about 6 min,so Q=100l/min)the electric box that is on top of the pump gets overheated and shuts down.

There is no pressure or head other then the hight of the flexy that is brought by a trailer truck.The pump is on the floor and i fill the IBC from the top.

I have a 20m3 tank for this oil but since IBC are difficult to fill I didnt even try filling the tank which is 9 meters away.

I use 2.5'' because my tanker has 2.5'' connections.

To be honest I dont know much about pumps. I am trying to learn from this, how to chose the right pump for application since in a future i will fill the tank and then connect it to a pump to fill the blenders that are 30 m away.
But in this case, is there a way to continue using it? 3HP engine looks so much.

Best Regards
Roman Katz

RE: Pump overload


that is now starting to make sense.

This is the manufacturers website http://www.pompecucchi.it/serie3.php?serie_cod=5&a...

You have a B150 type pump, which means it's rated at 150 litres per minute. At 100m head ( say 10 bar ish) you're drawing 5.5 hp = 4kW. Not surprising your motor craps out, but it doesn't say much for the setting / rating of the breaker you're connected to that it allows that sort of overload. A gear pump without pressure relief will try and flow close to its rated flow and simply raise the power input to do that until the motor stalls. That's what it sounds like to me.

The description is quite interesting as it states "By request, it is possible to add a pre-heating chamber to the pump and/or an incorporated safety valve. ". This implies that if it wasn't specified it doesn't come with a safety relief valve and your description doesn't mention anything about one.

So my recommendation is:
If you can't warm this stuff up in bulk before you pump, can you insert a line heater U/S your pump?
Can you do a current check on your motor to find out what current it is actually drawing when it is working?
Also fit a pressure guage D/S your pump and measure it during operation. Anything over 5 bar and you're overloading your motor.
Buy a B100 model which can then pump at the same flow, but not try and pump more than the system can apparently handle
Retrofit a pressure relief valve back from pump discharge to the tank.
Use two or three hoses in parallel between the pump discharge and your IBC
To be honest I don't know how this stuff is flowing into the pump in the first place and maybe that's an issue as well.

to size a pump correctly you need a good calculation and understanding of the frictional losses and head losses in the system upstream and downstream of the pump.

At those sorts of viscosities, especially at 3500, you might be in the realms on non Newtonian flow, so some of the calcualtions won't work properly

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

RE: Pump overload

I think there is a relief valve. see pic.

When a pump states 9m3/hr under 5 bar, that means that in order to deliver 9m3/hr inlet pressure of the liquid has to be 5 bar?

or is it the discharge pressure of the pump?

Yet i dont understand why the pump overheats.

Please explain again.

Best Regards
Roman Katz

RE: Pump overload

Difficult to tell what that is. Or what pressure it would be set at unless you have more data in the vendor pack??

A gear pump is a Positive displacement pump. This means that for each revolution of the pump the pump tries to move a set volume of liquid. In your case this flowrate, with a 1480 rpm motor, is trying to deliver 150 litres per minute.

The pressure is wholly dependent on the downstream system. It might be virtually zero if you have a big short pipe and low visocity fluid or it might be 10 bar or more if you have a small long pipe and very viscous fluid. In both cases thought the flowrate will be 150 l/min.

The only thing that will stop the pump is when it runs out of torque and the motor stalls or the pressure relief valve lifts.

In your case I think the pressure is too high causing your motor to "slip", draw more current than it's meant to and eventually overheat. Or if that thing is a relief valve, it is set higher than 5 bar and hence your pump is working harder than the motor is sized for.

However this is all a guess. You need to check out the actual pressure at the discharge, the amps drawn and whether you have a blockage anywhere in your system.

I would add heat to the fluid at the earliest possible location and all your problems will melt away....

Or parallel the inlet and outlet hoses.

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

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