Any Pumps Smart Enough to Turn Off when Dry?

[happyheathen]

Aside from the 3hp intelliflow, I have not found a pump which is clever enough not to commit suicide when the water stops coming.

I'll skip the rant about the short-sightedness of relying on the water being pumped for cooling - there are air-cooled motors available.

If there are no pumps with such a switch, does anyone make a controller which monitors water flow and breaks the circuit when pressure drops?

(yes, I do have yet another pump dying on me. I killed the first one; I took a chance with a used unit and crapped out.)

15K gallon gunnite; hayward 220v 1.5hp

And, just to make things interesting:
Is there anything "special" about pool pumps? If I could find a sump (or garbage) pump rated for continuous duty (with a float switch - what a concept!), is there any reason I couldn't drop in in the skimmer sump and plumb it into the filter? A bit of stainless/brass screening over the skimmer inlet could replace the basket's function (or plumb a dead pump in the line just for the basket)?

I have a pump I use to drain the thing - it's too big to fit the sump, but a 2" pvc line coming out of the deep end might not be all that obnoxious - and replacing a sump pump is much cheaper than a pool pump.

 

[scooperhsd]

Well, the "MOTORS" ARE air cooled - what happens when water stops flowing is that the wet end gets hot / deforms and that is what kills a dry pump.

I suppose you could figure out some senser that could go in the basket that would trip a relay cutting off power when it got dry, but I don't know what the parts availability would be.

 

[UnderWaterVanya]

My impression of sump pumps is that they have lower duty cycles and lower volumes of flow than you want for a pool.

Maybe you could get a flow sensor and use that to trigger action if no flow and pump on.

But why is the pump running dry?

 

[scooperhsd]

Also - I don't think you need a 1.5 HP pump for 15,000 gallons - 1 HP should be plenty , and a 2 speed running on low would save you money as well.

But you need to figure out why your pump is going dry first, or you will keep going through pumps.

 

[happyheathen]

The first one died when I seriously misjudged the time required to drain - when I came back, it was too late.
The current one has never been dry while in my possession - a previous owner gets credit for this kill. It looked like it had been around for a while (it's a single speed Superpump (my guess, based on a label reading Hayward SP followed by illegible stamped info). The fellow I got it from thought a 1.5 would be a good size for his backyard pond. His second guess was 3/4 hp. He did find a nice pond pump eventually.

As to size: in addition to deciding they'd rather have a pool than a yard (this is one of those "take-3-steps-out-the-back-door-and-you're-wet designs), the folks who built it put the mechanicals 40' from the pool. I suspect the extra half horse is about line friction. And it is a custom design - it would take about 30 dimensions to get a precise volume calc (one end is rectangular. One side is straight and plumb - everything else is creatively shaped. The 15K number may be low by a couple of 1000 gallons.

I have a (DPST on-off) mechanical relay with 110 coils and massive contacts I would not hesitate to use to switch 10 amps of 220. It has a 110 AC coil.
Where would a pressure switch need to go to monitor flow? Or couldn't a pressure switch work for this? A real flow meter could be adapted, but the cost might be higher than the intelliflow

Thanks for the replies!

 

[happyheathen]

Found this:

http://www.inyopools.com/motors_hayward_super.aspx
(sorry, still haven't mastered the art of links)

Scroll all the way to the last motor type - it's an A.O, Smith Guardian series with the 56J frame.

Claims to shut off when blocked, dry, or other bad conditions.
$325 for it vs $182 for standard 1.5 hp.

You'd think it would at least be offered as an option by pump manufacturers - it's big sell seems to be its compliance with the Virginia Graeme Baker Pool and Spa Safety Act of 2007 re body entrapment by drain s;uction.

 

[JasonLion]

A number of vendors offer SVRS features, but in most cases adding that feature requires replacing the entire pump, rather than just the motor.

It is much more common to use a flow sensor to keep the pump from running dry. Systems setup that way often call that feature prime protection, turning off the pump if it loses prime. Nearly all SWGs include flow sensors, and several of them support prime protection, either on their own or when used in combination with a compatible automation system.

 

[happyheathen]

Well, the "MOTORS" ARE air cooled - what happens when water stops flowing is that the wet end gets hot / deforms and that is what kills a dry pump.
<snip>

OK - I opened up the first pump (Sta-Rite, can't quite read the rest).
I was expecting a frozen shaft, but it turns freely.
In addition to a badly deformed strainer basket, one vane on the plastic cone over the impeller is broken.

2 Q's:
1. Would replacing that cone restore the pump?
2. If dry running does not kill motors, what does? One person (a 'pro' - just ask him) immediately suggested just replacing the motor when I told him of the run-dry failure. I take it I'm glad I didn't buy a new motor for it.
I can see certain people being clever enough to upgrade to multi- or vari- speed pumps by switching motors, and I can see normal end-of-service-life failures - but the number of motors being offered by so many vendors suggests something else is killing them.

Again, thanks for you time and patience.