Just for fun, pumping backward

NRT_Rob

anyone have any thoughts on two pumps, facing each other on a short circuit, unchecked... one runs at a time, pumping through the other pump body backwards.



anyone done this?



anyone have any idea what kind of flow restriction might result or any other no nos involved?

Mark Eatherton

I think HR's done it....

I don't remember the specific application, but I think he has done it.



The only problem I can see, other than the obvious pressure drop of the off pump in the turbine mode, is that if you switch pumps too quickly, like before the off circulator has a change to come to a complete stop, it could run backwards. It would still move water, but not as its supposed to.



Might want to incorporate some means of "rest" period when flip flopping pumps to make sure that doesn't happen.



One 4 way reversing valve would work with less parasitic cost of operation...



ME

icesailor

Running in Reverse:

Why on earth would you want to do it?

There is an arrow on the pump that denotes the direction of flow. The only way you can do this is with one pump stopped and not running but the impeller will be turning because of flow through it from the other (backward) pump. Whenever you run a motor with no power load to the motor (like a fan) and there is no power to the armature, the bearings wear out. The torque of the power will keep the shaft and bearing in their proper position. Not so when spun with no power.

If you have "ghost flow" in a wet rotor circulator, it may be spinning the rotor. If the pump fails prematurely, it may be from running the motor without power.

Ghost Flow caused by those chintzy fake IFC's so popular in heat systems today. Real men install flow checks.

But under what circumstances would you want to do this?

NRT_Rob

Not sure

but there have been a handful of situations out there where I wanted to reverse flow in a circuit and might not want a 4-way valve assembly's cost.



two pumps would sure make that easier, in some cases at least.

I would prefer a pump with a built in NC stop valve in it. then I could do them in paralell but without external zone valves.

Gordy

Bi directional pumps

Interesting thought Rob vs reversing valve. The only Bi directional pumps on google are for automotive, and marine engines I could find.



 It would be interesting to know how much efficiency would be lost if such a design could be incorporated into a heating circ. We know that circs plumbed backwards work, but not as well. Would be a nice resource for the arsenal



 I fear though that much efficiency would be lost in circs ability to move water with low electric consumption. Probably best to avoid the situation for now.



 If any one from Taco, Grundfos, Wilo, Bell&Gossett viewing has any thoughts please share.

NRT_Rob

in particular

I wonder if this is different with the new ECM circulators.

Gordy

Yes

And that would be what you would want to use refering to Ice sailors comment on pump bearings.

Gordy

Volute design

Is what will get you. When you go through reversed flow you have to get the water by the impeler which is designed to go one direction to move water should easily spin backwards with an electric magnetic motor design though. Looking at a Laing 303B I have it should work. Don't know about the flow restriction going backwards through the volute though.



Gordy

icesailor

Backwards thinking:

I don't see how a volute designed pump can pump backwards. The only kind of pump that I can think of that can pump backwards is a paddle pump. It doesn't matter which end the fluid or product comes in or goes out.

My first experience with backwards running pumps were the lesson of three phase. When I first started plumbing, we did a big building that was a Boy's Club with a big Smith-Mills 2500 series hot water boiler. It had two redundant B&G P-3's or larger. I thought that "Phases" were a time in your life. More than 5 years later, the boss sent me down to change the drive couplers on the circulators. He had changed them a month before. I noticed that there was an arrow on the bearing assembly. It meant nothing to me. But the new couplers still made the circulators shake. The boss had me call a guy in New Bedford. We went all through it. I kept telling him that the motors seemed to be running backwards but I couldn't really tell because I had to climb up and down from a step ladder. The springs didn't seem to be "pulling" the couplers aroound but that the couplers were "pushing" against each other. Finally he asked me if there was three phase in the building. I looked at the transformer outside and saw that there were 4 wires going in the service. I knew that. I switched the leads and everything was fine.

The cause was that the power company replaced the poles and wires on the street 6 months before. The only thing in the building that was 3 phase were the two pumps. They switched leads on either the primary or secondary and didn't consider that there were any three phase motors in the building. The heat still worked in spite of the fact that the motors were running backwards.

Mark Eatherton

Perpetual flowmotion machine....

Using 2 each DCECM motors, he hooked the two pumps up in such a manner that once he got the momentum of the fluid in motion, a "special" relay made contact to the windings of the OFF pump, and took the energy it was producing, and kept the other pump running.



"It takes it a while to run down, but it only costs me to get it started" said the young inventor...



Utility companies from around the world stood at attention and in awe of the young inventors findings.



"This could revolutionize the hydronics industry. Lets see the forced error people pull THAT off" said a bystander dressed up like Dave Lennox carrying a large aluminum pipe wrench...

hot_rod

Two pumps

I have two pumps facing each other on my 500 gallon storage for my wood boiler. When the boiler is running I load the tank from the bottom (return) to the top.



When the boiler burns out, and the delta ≥∆T goes away the pump stops. Now the tank is stratified and I pull the hot from the top to the radiant loads with the pump pulling from the top. I have a few Caleffi 132 QuickSetters installed and the flow is the same in either direction. i would not worry about excessive bearing wear, dual drainback pumps operate with an un-powered pump for years.



i like the 4 way reverser better and may change my set up if Santa brings me a 4 way valve to modify. I suspect the cost of a 4 way plus the accuator will be more than the extra pump.



Remember to remove the checks if you face two pumps together.



Watch for Caleffi Idronics #10, we have some unique reverser concepts shown. With a wood boiler and a large storage, it is nice to be able to bypass the storage and go directly to the load for quick recovery. Or have the ability to use a back up boiler. Or pull from the storage after the boiler burns down.



hr

Charlie from wmass

I would prefer to use

bypass piping and check valves for each pump. I know it is extra piping but it would keep the pumps working against lower heads and if they both got stuck on they would just pump in a circuit instead of burning each other out.

NRT_Rob

you can't do that

when pumps run in opposite directions. you'd short circuit through the other pump.

Unknown

Pumping Backwards

Interesting concept - but...



First, I am assuming the discharge of both pumps are facing each other with at least 6 pipe diameters of straight pipe between them :-)...  I see two potential issues with this (one real nasty).  BTW, these issues are standard and ECM circs.



First, the loss through the off pump will be substantial (but I have no idea how much - us pump guys do not test for this and it would depend on the size, age, type of the pump).  Remember, the water would have to enter the outside blade area of the impeller, turn 90 deg and make it's way to the impeller eye, and then turn another 90 deg to make out the inlet.



Second (and this this is the biggee), there is better than a 50% chance that the off pump (circ) will run in reverse direction (depends on the relationship of the throat of the volute and the impeller vanes).  When an off pump runs backwards, depending on the type of pump and motor, it can change the motor into a generator.  Or, if the impeller is threaded on the pump shaft it could become loose and possibly spin off.  Lastly, if a pump is spinning backwards and is powered up real nasty things can happen (shaft breakage, overloads).



You can try it but centrifugal pumps are not designed for this application - I can't speak for the other guys but I would have a real tough time warrantying a failed pumps (circ) installed facing each other.

NRT_Rob

valuable feedback

thank you sir!

furnacefigher15

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