How to Get Threaded Shaft Out of Pump Impeller?

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liveaboard
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by liveaboard »

We're supposed to be supplied with pressurized water in the near future; when that happens I won't need a pump anymore.
They've put in a massive irrigation water system at a cost of $8 million; it's all done but the electric company still hasn't switched on the power for the pump station.

In the meantime, I'm not allowed to put anything in the canal except my suction hose. I have everything automatic, it mostly runs at night when the power is 1/2 price. But if it pulls air, the pump runs dry and gets damaged.
The canal is a few feet deep, and runs right behind my property. the pipe runs under a narrow dirt road and the pumphouse is just inside my fence.
The rise to the pump is 2 or 3 feet, tube length about 20 feet.
road and canal.jpg
Any solution has to be in the pumphouse, not in or above the canal.
I've pretty much given up now; in 5 years I've only burned up the pump seal [and impeller] once, and most likely the new water supply will work eventually.
I'd be willing to put some time into it, but not much money.
There are small float switches for tanks and such, that will screw into a 1/2 pipe socket. but it would have to be protected from turbulence, and still need a relay to switch the 1.3kw for the pump motor

The new water system is just a scam to get some EU development funds; everyone who is getting supply already has irrigation water from the same canal that will feed the new reservoir and pump station. The only difference is that until now we each have our own pump.
The canal was put in 30 years ago, before there was even electricity out here. It was designed for gravity feed all the way, and the legacy of that design is still with us.

A local farmer tried going pumpless again, running little ditches across the field to feed each row by gravity; it worked fine but cost too much in labor, even at the slave wages agricultural workers get here and the high price of energy we pay now.
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WesHowe
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by WesHowe »

Instead of a float switch, maybe use a pair of contacts and the conductivity of water to determine if water is present in the intake line? It would require a small circuit, maybe as small as 1 transistor and a low-voltage relay (to drive the larger one for the pump). Been a while since I designed a circuit myself, but there are probably resources in other places you could turn to.
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BadDog
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by BadDog »

No need to get creative. Like I mentioned earlier, this is done all the time with a pressure switch on the output side. If pressure can't be maintained, something is wrong (busted pipe, failed pump, lost prime, etc) and the pump motor circuit is shut off. Unless I'm missing something, as long as there is enough high side pressure to make it work, this is about as simple and effective as it will get.
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liveaboard
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by liveaboard »

Of course I thought of a pressure switch; however, it has happened that after pulling some air it's sat there running while maintaining some pressure.

Electronic level meters are a problem because grunge buildup across the base of the contacts will carry enough current to fool the circuit.
That's why I prefer a mechanical switch, but of course they can get stuck too.
Go on, ask how I know that...
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BadDog
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by BadDog »

LOL, sounds like your experience run along the same as mine. Anything that can go wrong will.

I work in an area peripheral to large scale commercial irrigation (control systems) where pressure and flow (etc) sensors frequently integrate into control systems. Pressure is the simplest and cheapest, though not always ideal. For instance, if there is too little back pressure to reliably read, or substantial head above the pump on the output side so that pressure can maintain without pump output (which sounds like your situation?). Flow meters would be ideal, and may be your best solution, but the cost and complexity goes up.
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warmstrong1955
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by warmstrong1955 »

There are different styles of electronic pressure switches.

At a mine I worked at some years ago, we had a lot of problems with mechanical float switches, from rust & corrosion, switches & the mechanisms included. They operated the sump pumps to dewater the mine. Failure was ungood. Majorly ungood.

We installed some 'electric eye' switches. Pretty much a proxie switch.
Much better....but after some time, their little eyes got dirty from the water, and they would go blind.

Next we installed some sonar type switches. They didn't care about gettin' dirty. Never had a problem with any, in three years.

As far as flow switches, I'm only familiar with ones for equipment hydraulic systems, not with water.

Bill
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liveaboard
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by liveaboard »

Which pretty much mirrors my thought process on the matter; spend a little money and time, it won't work. Spend a lot of money and time, it might work but the job isn't worth that much money and time.
I used some little float switches that are entirely sealed plastic, the float is a magnet and pulled the switch closed when it floats up against it.
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by reggie_obe »

Use two switches in series for critical control circuits. That's what is usually done in the Aquaculture industry to prevent equipment damage caused by stuck control switches.
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by liveaboard »

That's a good idea; but how can you tell if one of them gets stuck and you then become dependent on the other [effectively losing the redundancy]?
I guess you could put indicator lights across each to indicate an open state, if they were low enough power to prevent activating the relay.
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by NP317 »

liveaboard wrote:That's a good idea; but how can you tell if one of them gets stuck and you then become dependent on the other [effectively losing the redundancy]?
[snip]
Periodic maintenance.
~RN
Russ Hanscom
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by Russ Hanscom »

What about a flow switch? - has a little paddle that sticks into the pipe and activates a micro switch when there is flow. You want to detect flow so check that directly.
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Re: How to Get Threaded Shaft Out of Pump Impeller?

Post by BadDog »

For those that may not know, those are called pulse sensors (along with tipping bucket rain sensors and such, as opposed to analog or set-point trigger sensors like pressure or temperature). And pulse sensors in general bring extra overhead and need at least a minimal controller to monitor/count/qualify the pulses. Some come with a tiny controller built in, but the price and number of failure modes rises considerably from a simple set-point or analog pressure switch. And the paddle sensors have their own issues particularly when used in "dirty" water. But that does sound like the only direction that makes sense for him and monitoring the pump function.

It also occurs to me that depending on specifics, a vertical tube (like a manometer) with pressure switch or magnetic proximity switch might also be an option if his current proximity switch solution doesn't pan out. The air column would also act as a sort of shock absorber, I use a similar setup (minus the switch) on my back lot irrigation manifold to smooth out the pressure pulses caused by valve actuation. I think the problem would be maintaining a consistent air column and identifying the set/trigger point. Perhaps trapping the magnet from going out the bottom with a small gate, and another above to keep it from rising past the sensor when flooded, and maybe a ball float valve (from a defunct shop vac?) at the top so that air could vent rapidly but water wouldn't spew under pressure. All that remains is some sort of timer circuit to give the pump time to build some head and fill the tube before switching to the relay held by the proximity switch. As long as the pump didn't loose flow long enough for the vertical column to drain (perhaps an adjustable limit for outflow like a down feed limit on a horizontal bandsaw?), I think it would be pretty robust without the electronic support and built from common materials.
Russ
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