Automatically shut off pump when intake is dry?

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M

marmot

0
Sep 3, 2016
2
Columbia
Other threads have asked this question in the past over the years although they have sometimes been defocused by multiple questions, and I have not seen a clear conclusion or satisfactory answer, so I'm raising it again.

Do people have a way of ensuring that their pump does not run dry? Specifically, what I'm thinking of is a way to make the pump automatically turn off if it starts running dry (for more than say 20 seconds), or an equivalent solution. This seems like it would be a common desire and mechanism, but I have been unable to find a good solution. (Specifically, something that requires a multi-hundred dollar flow sensor is not particularly desirable due to cost. However, I am still interested in such solutions if they are the best option that exists.)

I have a Hayward SP3202VSP TriStar variable speed pump. Thanks.


 
Welcome to the forum!

Pump running dry should be a very rare condition. I have owned my pool over 10 years and never had it happen. However, most VS pumps have an auto shut off built in so you are fine.
 
I, too have wondered about that. My previous pump was designed to run dry without damage, my current one does not specify. I sold level controls and liquid detection systems for many years. It isn't a difficult engineering feat, quite simple, really. The biggest drawback that I see is the liability issue. Intrinsically safe controls are not expensive to build, it is the testing and certifying that becomes costly. Then comes the issue of correct installation. Perhaps the market isn't large enough to justify it.
 
Variable speed pumps (at least the Haywards and Pentair's that I know of) all have an auto priming and loss-of-prime detection feature built in to them. Single speed and 2-speeds mostly do not and only have thermal switches to protect the motors (which may or may not protect the wet end from damage).

As Mark has said, a properly functioning plumbing system should never lose its prime. If it does, then it's far better to determine the condition(s) under which loss of prime is occurring and correct the underlying problem.
 
Having an inground pool is generally protection from losing water. But for us aboveground pool owners a pipe or hose leak or cracked skimmer or return or a liner tear can leave us high and dry - with a running pump when the timer kicks it in.
 
If you wanted to make sure the pump never ran dry, you could put a float switch in the strainer basket and hook it to a relay inline with the pump power and have it shut the pump off when the level dropped in the basket. If you did that, you'd need some way of starting the pump while trying to prime it. You could do that with either an off delay timer or a bypass push button. The push button would be the simplest solution.

Here's one version of a little float switch that could possibly work.
 
Pumps running dry can happen easily. Leaves in the skimmer or a leak that lets water get too low are both fairly common causes of pumps losing prime. I had a plastic bag blow into my pool and shut down the main drain.

The easiest way to handle it would be a pressure sensor in the return line or a flow sensor in the suction line. You could even go with a temperature sensor in the pump basket through the drain. Those would require some additional intelligence to actually control the pump and to allow for priming.
 
Thank you for all the replies. Yeah, my concern is not plumbing going bad or anything, but primarily evaporation or big leaves or clogs like JohnT mentioned. On the right days my pool can lose maybe up to an inch of water in a day. That means the water can drop below the skimmers very quickly. I would really like to have some reassurance that the pump won't just keep running if that happens.

So can anyone confirm my Hayward SP3202VSP TriStar variable speed should automatically shut off in that case? Thanks.

 
The TriStar VS has the ability to set prime mode up to 8min. What this does is boost the speed to maximum set for that period of time than ramps down to speed and time set. It does not have a shut off if prime is not reached. If you have a Hayward controller hooked up with a Hayward SWG the flow switch for the SWG can be set in the controller to shut down the pump if flow is not achieved.
 

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The water gets extremely hot after the flow is restricted for a while. The pump housing can get hot enough to deform.

cjpwalker said:
Would it run dry?

After watching the "Self Priming Basics" video here: http://www.troublefreepool.com/threads/57697-Centrifugal-Pump-Priming-and-Cavitation-Videos

It looks like a self priming pump will still have water in the volute, and therefore on the seal, yes? So, other than running for several hours and evaporating all of that water, wouldn't you be ok?
Click to expand...
 
This is a good thread about a possible improvement to pool pumps. Not everyone owns (or needs) a VS. I drop prime every now and then for a variety of reasons. I trusted the pump to kick on automatically but I always verified it within 10 minutes or so.
 
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