Request for thoughts on backup pumping system

We are setting up a new piece of equipment that has a coolant pumping system (water/glycol). It uses a 5hp 3 phase motor to drive the centrifugal pump. The two are connected with a LoveJoy type coupling. During normal operation the VFD will control pressure in the system by altering the speed of the pump. This piece of equipment will run intermittently (batch-type process.)

If the power fails for extended periods during a process run, the equipment should have coolant circulated through it. It can stand to sit for a short period before the coolant recirculation starts, so a automatic backup system is not needed. What we plan to do, is add a belt sheave to the shaft that connects the motor and pump so that we can drive the pump with a small Briggs engine. The procedure would be to electrically isolate the pump VFD by disconnecting input power from the drive (so the pump cannot run while we are manually running the pump), setup the engine, connect it with a belt to the pump, and start pumping coolant. Would it be necessary to mechanically disconnect the motor from the pump in this situation? Are there any issues with spinning a motor that is connected to a powered down VFD?

Thanks,
Brian

Regenerative power would be applied to the output of the drive. The drive may not survive that. I would recommend a local motor disconnect switch be opened as part of the procedure, isolating the motor from the drive electrically.

Paul

Brian
You would need to allow 10 minute to get the belt connected and get the engine going. You say equipment can tolerate the time delay. What I do not understand is why equipment needs cooling when power is off.

You would not need to mechanically split pump and motor. I would consider a disconnect between VFD and motor even with braking resistors which should not be needed on a pump setup.

HOWEVER I think this is a lot of fooling around and what happens if a guy has his hands in there setting the belt and the motor starts?

Also what do you do if the pump breaks or jams or,,, or,,,

I would consider a completely separate pump installation preferably diesel driven. You could either have auto start or manual start of course. The other choice is separate pump(s) maybe submersible type that are driven off inverter and battery backup that will allow enough pumping time to cool equipment.

Yes it is gonna be some bucks BUT
What is cost if you do not cool this equipment quickly enough on power failure?
Dan Bentler

brian123 said:

are there any issues with spinning a motor that is connected to a powered down vfd?

Thanks,
brian

Click to expand...

no

Use another pump

I agree that a second pump would be a better solution. You could modify the piping and use quick connects....

Thanks for the replies so far!

OkiePC said:

Regenerative power would be applied to the output of the drive. The drive may not survive that. I would recommend a local motor disconnect switch be opened as part of the procedure, isolating the motor from the drive electrically.

Paul

Click to expand...

I wondered about that. Is there enough residual magnetism in the rotor to make this a problem? The way I see it, the motor would be completely dead when we start spinning it. At that point, wouldn't it just be a mass of aluminum spinning inside copper coils? I have never spun a three phase motor up to speed with nothing connected (or a powered down VFD for that matter) before, so I honestly don't know.

leitmotif said:

Brian
You would need to allow 10 minute to get the belt connected and get the engine going. You say equipment can tolerate the time delay. What I do not understand is why equipment needs cooling when power is off.

You would not need to mechanically split pump and motor. I would consider a disconnect between VFD and motor even with braking resistors which should not be needed on a pump setup.

HOWEVER I think this is a lot of fooling around and what happens if a guy has his hands in there setting the belt and the motor starts?

Also what do you do if the pump breaks or jams or,,, or,,,

I would consider a completely separate pump installation preferably diesel driven. You could either have auto start or manual start of course. The other choice is separate pump(s) maybe submersible type that are driven off inverter and battery backup that will allow enough pumping time to cool equipment.

Yes it is gonna be some bucks BUT
What is cost if you do not cool this equipment quickly enough on power failure?
Dan Bentler

Click to expand...

Yes, we would need to allow 10 minutes (or more) to connect the engine to the pump. The piece of equipment in question is a vacuum furnace. While processing, you have the potential to have a sizable mass of parts at temperature when the power goes out. The furnace has a hot-zone insulation package that contains most of the heat, and the shell of the furnace is water/glycol cooled. The hot-zone will slow the rate of thermal transfer to the shell, but it will still happen. The furnace shell, which is filled with coolant, will be able to absorb a fair amount of heat before it becomes an issue. This is why a time delay before reintroducing coolant flow is acceptable. In fact, depending on the load size and the temperature and pressure in the furnace at the time of the power outage, backup cooling may not be needed at all.

As far as the danger of the motor restarting unexpectedly, I believe that it will be fairly straight forward to avoid that. The disconnect that powers the VFD (and the rest of the furnace) is within a few feet of the pumping system and would be the first thing to switch off before messing with the pump at all. I agree that there are safety concerns to doing something like this, but I believe that this method is viable. I agree that having a second, generator operated or diesel driven pump plumbed in and ready to go would be the ultimate way to solve this problem; it is however, in my estimation anyway, overkill for this install.

Again, thanks for the replies so far,
Brian

In my experience the best way to do this is to have a centrifugal clutch on both the motor and the engine. You then put in an electrical interlock so only one runs at a time. That way, when the engine is running the motor isn't spinning and vice versa. Much simpler and more reliable than fooling around with belts.

Similar to Tom's idea, you might want to think about connecting the motor to the pump driveshaft via an overrunning clutch (something like THIS). That way, the motor can drive the pump shaft, but the pump shaft can't drive the motor. I would do the same for the engine drive. With this setup, either the motor or engine can power the pump, but whichever one is not in use will not be backdriven...

Of course, this assumes that the pump only needs to rotate in one direction, and you don't use the VFD to slow the motor faster than the pump slows down on its own...



-Eric

I would suggest a Natural Gas powered generator and a 2nd motor/pump plumbed in parallel with the first pump. If power is lost or no flow detected he generator kicks in and there is no loss of cooling. The generator could also supply the drive on your furnace to get the product out if need be. You dont mention how the coolant is cooled, but the generator could also power some fans if you are using them in an heat exchanger.

Brian
To summarize you are putting in a new vacuum furnace ie autoclave. this unit must maintain a vacuum and a correct temperature and maybe even heat and cooling rate on the part to ensure quality.

If all this does not work correctly you have a scrapped part and maybe even disposal problems and you may have to clean the furnace. Worst case you may lose a contract if you do not deliver on time.

I assume at the best you are still barely under budget and you are now getting into the testing and finding a few uh oh we did not think about that or ooops we screwed up.

I believe you have had several good suggestions from qualified people and you need to listen to them, not worry about budget and put in a system that will work correctly even in the case of a component failure.

I was on a Thresher class submarine, learned and appreciated correct engineering and setup (they got it right on subsequent sister ships including ours). I know the value of redundant systems.

I believe you should seriously consider having dual cooling recirc pumps and should consider having a diesel generator. With this you can maybe salvage a part that is being processed with no interruption and maybe avoid scrapping, downtime, disposal and other losses.

Dan Bentler

If someone already mentioned this, I apologize for the redundancy. I read through and it didn't jump out at me.

I am opposed to the "belt on the connecting shaft" for a whole different reason. The bearings in your pump and your motor are engineered for the "turning" forces that are expected to be applied to them during their normal operation. So is the "lovejoy" connector.

If you put a pulley on that shaft, and then TIGHTEN a belt on it tight enough to turn the load, (including the now unnecessary inertial load of the motor) you will be putting a lateral load on all three devices (pump bearing, motor bearing, and lovejoy coupling) for which they were never engineered.

Have you ever gone through the process of aligning a lovejoy coupling so it won't vibrate?

Your idea may work, for a while.... but at what cost?

I can't get behind it. It belongs on the recent "HOUND DOG" thread. Read THAT thread and you'll have your answer.

I'm a "pump guy".... and in this case I have no doubt... you need a second pump, or at least a back-up power supply for the one you have....

And what are the conditions where you would be running this gas engine? Ventilated? Carbon monoxide? Asphyxiation? Employees coughing too hard to concentrate on their work?

Get up and move off of the nail in the floor.....

One idea (provided you're talking about 240v 3 phase) would be to swap out your VFD to a 10hp and wire it up for single phase in, still using the 3 phase out and 3 phase motor.... then a cheap, single phase generator would run it in case of a power outage....

Stationmaster

Have you thought of just using your plant water supply as a backup?
Do you really need glycol?


Roy

Roy Matson said:

Have you thought of just using your plant water supply as a backup?
Do you really need glycol? Roy

Click to expand...

I think glycol originated with me. As with an engine corrosion control is needed in recird water sytems and with chillers possibly antifreeze. Glycol does both

Interesting proposal on using domestic water as a backup. Could even set up to preheat or provide hot water.

Dan Bentler

Roy Matson said:

Have you thought of just using your plant water supply as a backup?
Do you really need glycol?


Roy

Click to expand...

leitmotif said:

I think glycol originated with me. As with an engine corrosion control is needed in recird water sytems and with chillers possibly antifreeze. Glycol does both

Interesting proposal on using domestic water as a backup. Could even set up to preheat or provide hot water.

Dan Bentler

Click to expand...

The glycol is needed because part of the coolant loop will be routed to forced air radiators outside the plant. As it gets quite chilly during the winters here (Nebraska), the anti-freeze property of glycol is needed. The coolant will also have anti-corrosion agents to help preserve the system.

On similar setups that run straight water, plant water is a common backup cooling method.


Thanks, everyone, for your input.
Brian

I worked on some induction furnaces North of Toronto, they had a closed loop with a cooling tower however as a last resort in power failure plant water cut in. I asked about glycol because you wouldn't want to send that down the drain.
Roy