Auto-reversing pump?
 

Linky

In short, Volenti discovered that some pumps switch from clockwise to counter-clockwise, every time that you turn it on and off. It seems to be limited to small/cheap pumps. Odd, isn't it?

Maybe someone can confirm this?

weird....kinda like microwaves though.

look in that thread; and see how easily Volenti passed from 660 l/h in his watercircuit including block and everything to 1120 l/hr ( :rolleyes: but he also gained some complications . . . )

. . . probably Eheims also switch their spinning direction . . . (not only cheap pumps)

Correct me if I'm wrong, but you just posted a link to the same thread...

Yes, Volenti has found out that some pumps don't run as well in reverse. If anyone has doubts about why their rig runs fine somedays, and not so well the next, that might be your answer.

Yeah, a few years back, GM figured out if they reversed the flow of their engine waterpumps, they'd have a better cooling system.

Yup, but I highlighted some issues that you did not mention.

Volenti did not say that autoreversing pumps change performance depending on spining direction (and they don't change performance).
He said that they have very low performance because of the design cannot use fully the kinetic energy of water. His mod performance depends on pump spinning direction and almost doubles pump performance when pump spins in the right direction but does almost nothing when pump spins to the other side.

Ok, I see where I got confused!

My pump has an outlet that is built the same as Volenti's mod, but I have a direct drive / mag drive hybrid, so I assumed that all pumps were of similar design, and that Volenti's mod, which I didn't quite understand, well... ya'll know what, what's the point in explaining an illogical thought:D

In short, modding a pump is possible.

I'm thinking about adding a cover plate over my open rotor blades, with a hole in the middle, just to see if it'll throw water any better.

Yea, I'm almost certain that all pumps that have a centre outlet are bi-directional, after all, why would a manufacturer deliberatly cripple their pumps performance with a center outlet if their pump had a fixed rotation?

The effect of the mod on the pumps "curve" is interesting, even though in the particular test environment it almost doubled flow, it didn't increase max head by all that much (only by 15% or so) max head governed more by motor torque/speed and impeller design?

anyway I have some more work to do on this pump (adding the second outlet) I'll post back with results.

Can someone elxplain this "pump mod" to me? I would prefer not to have to register JUST to view posts in another forum.

Thank you!

It's a good forum worth registering, no long wait for e~mail confermation.

I've done a quick mod to one of my currently un-used pumps, it's a cheap chinese pump rated at 2000L/H and 2m head.

and I've done this to it:D
http://users.bigpond.net.au/volenti/pump_top.jpg

http://users.bigpond.net.au/volenti/pump_side.jpg

yes that is blu-tack plugging the old centre hole.

of course since these pumps can spin in either direction I had to turn it on and off a couple of times before it span in the "right" direction (ever since I did the impeller mod on this pump it splutters and carries on a bit untill it finally decides to fire up)


spinning in the wrong direction, also very similar to pump with centre outlet;
http://users.bigpond.net.au/volenti/pump_wrong.jpg

spinning in the correct direction;
http://users.bigpond.net.au/volenti/pump_right.jpg

actual performance change through my "cathar style" micro channel block is nothing short of amazing.

pump pre-mod, 1m of 1/2'' tubing my block = 660L/H
pump post mod, 1m of 1/2'' tubing my block = 1120L/H

almost double the flow!

Huh?

What did it look like before?

-ymboc

Any idea on how to force the pump in the *right* direction ? I would not want to check that out in a closed loop, inside a closed PC...

Now I understand what you've done! Good thing, I didn't actually inspect mine pump to see if that stupid idea of centre outlet situation is associated with my pump...I'll check, but I wouldn't think in my weirdest dreams that someone would put outlet in that position...

Good thinking, and good mod, ofcourse!!!;)

I was thinking in my car while going to class about WHY these center barb pumps would be auto-reversing. I came up with a very simple yet fundamental reason; because they are running off AC current!

With these cheap pumps, why would the manufacture spend extra money puting in components to make the pump run one way all the time? It is much simplier to just make it uni-directional and make a center barb and have it spin either direction.

With that being said, the spinning direction just happens to be what place that the AC current was at when you plugged in the pump. Once the pump starts spining, then the AC current doesnt care, it just switches the poles in the magnet and its done!

Now if someone could add a rectifier (I think) into the circuit to make an AC current act as a DC current, then the pump should spin in one direction no matter what..


This is my line of thinking and, honestly, if it sounds like crap, just understand that I have a massive headack and I am probably jsut dilusional.

It depends on the engine coils. With 4 poles you cannot predict the spinning direction. Any greater number of poles will enforce a spinning direction.
So in a way you're off, AC motors *do* spin in one direction (think of AC fans...) because generally they have 6 or 8 (or more..) coils.
But, in this very case, i suspect the low-cost pump features a 4 pole engine (coils are expensive) so the direction cannot be fixed - so you're right :p

Surely there has to be a way of forcing the pump to start on thr desired wave?, electronicly?...

First let me correct myself: that's 2 coils. (note to myself: do not post technical things before coffee time). Divide figures i gave in my previous post by 2.
Anyway. Currently I do not see a way to make sure it starts in the right direction, maybe there's a mechanical solution.

If it was physicaly stopped from starting in the wrong direction, would it start up the right way in the next beat?(wave,whatever!), or would it just stall trying to go the way it started?...

Answers here:
http://www.sensorsmag.com/articles/0600/83/main.shtml
(look for "How Does a Two-Phase Fan Motor Work" further down the page)

Hi guys,

This is a very interesting topic… :) (I haven’t seen it talked about before)

A while back when I first started tinkering with water-cooling I noticed that all of the pumps I was using incorporated the same basic design. They all had very loose impeller-to-case clearances and center outlets. In addition, all but the E-1250 had the impeller mounted on the rotor shaft so that it could slip through at least 120 deg. of shaft rotation before hitting a hard stop and becoming directly coupled to the motor rotation. After a little web research and experimenting with my various pumps I have come to several conclusions.

1. Most pumps used in water-cooled PC applications were originally designed for aquarium and/or garden pond applications. They have relatively high flow but very low discharge pressure. They are also designed to be relatively inexpensive but long lasting pumps.

2. The basic design of the Eheim 1048 and 1250, ViaAqua1300 and Danner Supreme2 (these are the pumps I personally have) all use single phase, two-pole synchronous AC motors. For simplicity and low cost, the motor stator consists of two windings (poles) wired together and connected to the AC mains. The stator assembly is potted in a waterproof material. The rotor consists of a two-pole permanent magnet. One side of the rotor is magnetic North and the other side is magnetic South. The rotor has plastic bearings (lubricated and cooled by water), which turn on a plastic shaft held captive in the pump housing between two rubber bushings. The plastic impeller wheel is fitted directly onto the rotor shaft. (Technically these are NOT mag-drive motor/pumps. The motor has a permanent magnet rotor, but the impeller is not coupled to the motor shaft with magnets, as they are in a true mag-drive.)

3. Single phase, two-pole AC motors are relatively easy and inexpensive to manufacture and they lend themselves very well to wet environment applications. They have very low starting torque and will randomly start rotating in different directions each time they start up depending on the resting position of the rotor and angle of the AC waveform when the stator coils are energized. More expensive AC synchronous motors used in industrial applications incorporate multiple poles or a resistance-capacitance (R-C) network or some other timing circuit to shift one or more stator windings out of phase, which will force the motor to always turn in one direction or the other.

4. Our PC pond pumps don’t have any starter circuitry (keep it $imple). Instead the pump case is designed to work with the rotor turning in either CW or CCW direction – center outlets. The down side to this is that it makes the pump very inefficient. As the water-filled impeller turns, water is thrown outwards due to centrifugal force. But the water is also rotating, so ideally a good pump design will capture both the centrifugal flow and inertial flow of the water. This is why more expensive pumps have a volute with a tangential discharge. Volenti modified his pump from a center discharge (centripetal flow only) to a tangential discharge (centripetal AND inertial flow) with GREAT results!

5.The clearances between the impeller and pump casing walls is very loose in a pond pump so that it can ingest small amounts of dirt and gravel and keep on pumping. Because these clearances are so large, they also provide an alternate path for water flow inside the pump. A good percentage of the water sucked in and spun up to speed just leaks back to the inlet and never leaves the pump. This is why this type of pump has such a low discharge head – put a little resistance to the flow of water exiting the pump and the water will just quit flowing out, and instead will flow (leak) back to the center of the impeller.

6. The plastic impeller wheel is mounted on the rotor shaft so that it can slip through at least 120 deg. of shaft rotation before hitting a hard stop and becoming directly coupled to the motor rotation. The Eheim 1250 is the only pump I have that has the impeller permanently mounted to the rotor shaft (no slipping). Many people believe this is to protect the impeller against a foreign object being sucked into the pump. I disagree. I believe the purpose is to allow the rotor to start turning (without any drag from the impeller), to insure the motor can start. Remember, this type of motor has a very low starting torque. Once rotation starts (even 120 deg.) inertial kicks in and off it goes, right up to full speed. When the rotor is at full speed and pumping water, the water is pushing back against the impeller blades, resisting the motor shaft rotation and holding the impeller against the hard stop. The only way the impeller can slip on the rotor shaft at this point is if it spins FASTER than the rotor. If a piece of gravel gets ingested and wedges between an impeller blade and the case wall the impeller can’t slip backwards (it can only slip forwards). My theory is that loose clearances protect the pump and impeller slipping allows easier startups.

7. Because all of these pumps have their stator windings and wiring connections potted inside the plastic case, it does not easily allow adding circuitry to the motor to force it to start in the same direction each time. Somebody smarter than me will have to figure that one out… :)

Note: I am by no means an expert on any of this stuff and don’t pretend to be. I am not trying to lecture anyone, just sharing some info that I think might be of interest. I’m a noob around here so hope no one takes this the wrong way. And yes, I cut and pasted from my notes… :D

RoboTech

Edit: Changed "radial" flow to tangential flow in section 4.

That's a pretty detailed analysis, nonetheless! That's the kind of info we need!

Off-hand, it seems that if we put a diode in there, it might create a condition where the pump will simply not start, dunno:shrug:

I think that the direction of rotation depends on the starting position of the motor, and that's a 50-50 chance. The only way to force a direction would be to put the impeller in the proper spin before turning it on, but that's not practical, now is it:D (I'm picturing an old Ford Model T, with a crank starter)

If one manages to plug into each phase, an external out-of-phase starter can be made. The problem is, how can pump motor phases can be accessed... In many cases it seems it's sealed.

Just to get back to Volenti's mod for a sec...

What if there was an inlet directly opposite the outlet? It would turn the pump into a paddlewheel type setup, and the flow should be pretty much equal, either direction, no?

Wouldn't that mean that water would be going like I want it in one case, and in the other case, completely opposite direction.
So, in the first case, I would have configuration like pump-rad-block, and in the other case pump-block-rad? Not good for those with reservoirs...

Am I on the right track or am I missing something?

/edit/ If the mod is like in the pic, what happened to the inlet/outlet dia ratio?

For a cheap pump, i don't believe that the inlet/outlet ratio really matters!

The main problem with what I suggested is that there would be a huge loss of pressure/flow, because the centrifugal effect is effectively bypassed: these pumps work by throwing the water around, and as above, it would only be paddling the water around. Not good.

As for flow reversing, I think that as long as the flow rate is high enough, it shouldn't matter in which direction it's going. If the flow is too slow, then yes, there would be that problem in the order of the components.

I see,

what if we put inlet up and outlet down not inline like the pic, to get half the circle, maybe some more centrifugal effect and get at least 1/2 of it?

Same problem. It would only work if what you're talking about is actually 2 outlets, with a center inlet.

The water must be thrown around.

GREAT RESULTS!!
 

Adding the second outlet and simply combining their output with a Y adaptor yeilds excellent results;
http://users.bigpond.net.au/volenti/PM_overview.jpg

http://users.bigpond.net.au/volenti/PM_closeup.jpg

http://users.bigpond.net.au/volenti/...seup_angle.jpg

I have measured static head as well as just raw flow rate, should make the results a little more relavant.

un-modifed pump static head; 155cm (60.5'') (rated at 200cm)
modified pump static head single outlet; 198cm (77.2'')
modified pump static head dual combined outlet; 210cm (81.9'')

raw open flowrate is ~1100L/H, which from memory is slightly down on what the pump could do in stock condition, but that doesn't matter seeing as we now have more static head to play with now.

I also blocked the center inlet to see if it would pump this way (turning one of the outlets into an inlet) it does actually pump, but not with a lot of flow, or pressure,I didn't bother measuring it.

**************************************
WOW!, I really expected it to be less when they were combined, I think some of it is the long legnth of the two tubes before they meet, stops the flow going out one side and back in the other, if they were shorter I think there'd be problems.

Would you try them with very short tubes Volenti?, to see what happens?, Please huh? :D ...