Protect your booster

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dalehileman

0
Aug 1, 2009
86
Apple Valley, Ca
Summary: If your Polaris like mine operates under pressure from an auxiliary booster connected at the output of your sand filter then you too may be acutely aware that a failure upstream will let it run dry, entailing a massive repair bill. But it seems elementary to me that the installation of a pressure switch would keep it off until the input to the sand filter has reached, say, 15 to 20 psi by which time it can safely be energized

The switch would of course measure water pressure relative to ambient air and a load capability to handle the requirement of your booster, typically 13 amps. If you’ve already undertaken such a mod or know who might carry such a switch could you please send me a link with some info about it—Thank you kindly--Some detail follows:

But if you’re like me the first couple of times it goes west in that manner you might assume the trouble was caused by a fault in the booster itself so after the third such catastrophe and faced with still another repair bill of $103 you reluctantly cough up $385 for a brand new one. After it also fails however, compelling still another repair (3 x $103 = $309), you consult your Friendly Local Pool and Spa outlet, who explain that only a momentary loss of water can cause them to self-destruct

Thus an expenditure of almost $700 leaves you in a state of fugue since there are so many ways a failure upstream can deprive it--while I couldn’t fathom how the Pool Establishment could have allowed so chancy a state of affairs. When I made my proposal to a pool “expert” he advised that my suggested switch was a fallback (I was treating a symptom not the cause) and that instead I should (1) install a second timer that would delay powering the booster an (2) always watch very carefully and at all times the water level at the input to the system

I replied (1) that the second timer wouldn’t do a bit of good if the main pump should quit for any number of reasons and (2) only a frantic busybody could spend that much of his day monitoring his pool contrivance; to wit:

Thus your main pump can lose prime or start blowing air for reasons not immediately obvious. Intake is derived most likely from your skimmer port , eg, when water level has fallen to near the its bottom edge some air is drawn in along with the water though it's hard to imagine the mixture could so damage the booster. However other possibilities are:

1. As I pointed out above to the “expert, ”stoppage of flow but allowing the booster to continue running by

….(a) mechanical failure of main pump or

….(b) electrical at or inside it, eg, loose terminal, broken wire, etc

2. Tubing from skimmer to main pump partially empties thus losing prime so that next time the system is re-energized it is unable to draw water, blowing the system full of air. Thus I find it incredible that the Pool Establishment would allow a system where the main pump is situated at a higher level (No doubt because they save a few dollars upon installation if they don’t have to dig a pit for the pump) so you’re in trouble with

….(a) air leakage at input to main pump from

……..(1) failure to adequately tighten the cover of its input pump-basket vessel

……..(2) worn or damaged O-ring

……..(3) a problem with some intermediate system such as an in-line chlorinator or

……..(4) cracked tubing

……..(5) during maintenance you should happen to somehow energize the booster before connecting the main pump…...

….(b) A sudden leak in the pool itself or you inadvertently allow the surface level to drop below the skimmer after a period of system disuse (during extended maintenance for instance)

….(c) Cracked tubing underground (good luck finding it)


Under these circumstances--if you catch it right away--the only way to restore the system to operation is to prime it with a big bucketful of water poured into the vessel, then quickly closing it, remembering of course the O-ring. While doing so remember also to hold down the right side of your mouth with your left index finger while farting to the tune of Auld Lang Syne


I'll never get over in this day and age of aerospace exploration and miraculous new invention how primitive are our pool systems wherein the tiniest flaw causes disastrous, irreversible damage entailing exorbitantly expensive repairs while reinforcing the almost universal notion that the pool owner must be mostly wealthy while the “engineer” who provides us with such technology --since he cannot read a clock--after work is tapped on the shoulder by his secretary who must then lead him to the door when his wife now drives him home
 
I too wondered why certain fail safe devices were not incorporated into the pool equipment system. Specifically, I've worried how easy it would be to accidently shut off the inlet valves and starve the pump. And with my single pump for spa and pool setup, switching modes required several valve turns, which if not done correctly could drain the spa and again starve the pump. I also have a heater for the spa only (small 11KW) and wondered if someone (my wife) might accidently leave it on and try to heat the entire pool.

A lot of those worries were solved when I added a remote switch and actuators to automatically control the valves. And I wired it so the heater can only come on in spa mode. But there are still failure modes that could let the pump run dry.

I think the primary reason you don't see any such device for protecting pumps is that it is an added cost. Not only for the part, but for the electrician to install it correctly. My PB used the cheapest electrical company he could find and they were still expensive.
 
If it were me doing the installation I would use a flow switch in place of a pressure switch since loss of flow is what you want to guard against. I also know from experience that flow switches are more reliable, long term, than pressure switches. Either way it is going to cost something on the order of $300 - $500 for the instrumentation and cables and about that much for installation. So I would expect the total to be around $600 - $1,000. In addition to the instrument itself the installation will require a relay, water proof mounting box, and cabling. Here are two links to manufacturers that make the switches (there are a lot of others) that I've used in the past. Of the two IFM efector is the best but most expensive. If you decide to go ahead with the project make sure that whatever instrument you buy is powered by 120V AC. The majority of industrial instruments are DC powered and to install one of these would require a transformer (unless you happen to have DC power already) which is just extra cost.

http://www.intekflow.com/products/rheot ... fault.html
http://www.ifmefector.com/ifmus/web/pad ... 15_20.html
 
"I too wondered why certain fail safe devices were not incorporated into the pool equipment system." Ib thank you for your support, a rare commodity in this maelstrom of interpersonal contention. As for cost, however, it's pertinent to note that my pressure switch proposal would be cheaper and safer than the second timer so often used to prevent the immolation of the booster, suggesting that their failure to incorporate it only reflects massive incompetence

If they understood what they were doing and were good at it they'd instead be in aerospace

"If it were me doing the installation I would use a flow switch in place of a pressure switch since loss of flow is what you want to guard against.........So I would expect the total to be around $600 - $1,000." stev thank you for that suggestion, an idea I had also entertained but rejected on the basis of cost as a pressure switch would run only $20-$80

Since my suggestion is so simple and so cheap am still wondering why one of our participants hasn't already done this and can recommend a specific pressure switch
 
The Goldline SWG flow switch can be had for less than $100 and if you put it in series with the relay control, it should be very cheap to wire. I would think that is better than a pressure switch since a plumbing system can have a lot of pressure with very little flow rate if there is any return side blockage. This is why SWGs use them instead of pressure switches.

Anyway, most controllers these days have a interlock function which prevents a valve and/or relay from turning on for the first three minutes of pump operation. This is to ensure that the pump is primed before the function turns on. This doesn't solve all of the problems but it can prevent the booster from running before the pump is primed.
 
mas thank you for that input. I presume a blockage such as you describe with a decrease in flow rate but increase in pressure might (1) damage my pressure switch while (2) overloading the booster. While I concede the flow sensor is thus a better way to go I am still hoping a respondent who had done it by pressure might recommend a specific switch, for one thing a much simpler way to go. Incidentlly I understand also that such a device is more likely to be found in the spa. Meanwhile I turn my booster on and off manually--a nuisance to be sure
 
Guys as you can see from the following link

http://www.amazon.com/Square-FSG2J24M4C ... p_hi_1_img

For $12 I will stick with the idea of a pressure switch. However I am baffled by the specs. For instance

A. What on earth does "low pressure cutoff" mean and

B. Some of the specs for these switches give a pressure range, eg,40-60 psi. What does this mean, as I imagine a pressure switch closing at a certain pressure and remaining closed above that

Thanking you for the above and for any further help
 

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Pressure switches are designed to protect against a loss of pressure not necessarily a loss of flow . That's because as the flow increases from a pump the pressure will decrease so the pump might shut down even with high flow if the pressure drops below the set point. As an example if your filter is dirty and has a high pressure drop your pump will put out more pressure and less flow. If you back wash the filter the pressure drop will decrease and the pump will put out more water but less pressure.

Another example would be the case where the pump discharge becomes completely blocked. Say a valve is closed downstream from the pump. In this instance the pump pressure will rise to the shut-off head (the maximum pressure the pump can deliver), but the flow will stop. A low pressure cut-off will not protect the booster pump in this scenario.
 
stev32k said:
The range of the switch is 40 - 60 psi meaning you can set the pump shut off pressure between 40 and 60 psi. You need to make sure your pool pump puts out at least 40 psi or the switch will not work.
Click to expand...

Thank you steve but apparently then I wouldn't want one of that sort since I want my switch to close not open at a specific pressure then remain closed at values above. Incidentally is there a specific name for such a pressure switch

Incidentally as I mentioned before mine would close in the range 15-20 psi

"Pressure switches are designed to protect against a loss of pressure not necessarily a loss of flow ."

Yes steve, , I undersand that, forgive me if I wasn't clear. My switch would respond to the pressure at the input of the filter with the assumption if not a guarantee that when this value reached 15-20 psi there would be plenty of flow at its output then through the booster. At risk of repeating myself the flow sensor is probably a better approach but the pressure switch is 10-20 times cheaper

".........As an example if your filter is dirty and has a high pressure drop your pump will put out more pressure and less flow."

True but it would be very rare if not impossible for the filter to become so clogged as to reduce flow to near zero. As almost everybody else does I backwash it after it reaches about 30 psi, when the flow is still very high

" If you back wash the filter the pressure drop will decrease and the pump will put out more water but less pressure."

True but with a clean filter the pressure at the filter input nonetheless achieves 15-20 psi within a few seconds, whereupon my switch would come on but thanks for your input and I hope I've clarified my position

Edited to add that a drawn-out thread in another forum on this same subject shows indeed how easily my requirements can be misunderstood

http://www.poolspaforum.com/forum/index ... ntry102367

Note to tfp Admin: As I realize this practice is frowned upon in some boards, I will not be miffed if you delete the link above
 
Both of those switches use 100V DC power. So unless you already have DC power available you would need an AC/DC transformer that could supply 100V DC. You also need a water tight (NEMA 4) junction box since the terminals on the switch are exposed (assuming it's installed outdoors). You need to check with Cole-Palmer and find out if NC means the contacts are closed when the pressure is adequate or are they closed when the pressure is below set point. Also find out if the range of 5 - 25 psi means the relay will operate above 25 psi. That may be a switch to control the pressure between 5 and 25 psi meaning it would shut down the pump if the pressure is below 5 or above 25 psi.

Edit: BTW 100V DC power is an odd ball voltage. Normal is 12 or 24 V and those can be had pretty cheap. Doing a quick search the only 100V DC supplies I could find started at $275 and went way up from there.
 
Here's a Omega Pressure Switch that'll work for you and it's adjustable. It also has both normally open and normally closed contacts. It's relatively inexpensive to boot. I'd probably go with the PSW21E at 9 to 18 PSIG adjustable. Even though the switches are rated for 25 amps I'd recommend an interposing relay in the pump's circuit. I'd also recommend putting the switch in it's own enclosure even though it could be put in the timer box, etc..
 
Thanks steve, it's incredible, the idea that you should also need a dc power supply, outrageous

mas thank you for that link. However it didn't give a description or any specs, what am I doing wrong. And please explain why I'd need a relay. Again all I'm looking for is a simple spst pressure switch that closes at 15-20 psi, doesn't require a power supply of any sort, stays on as long as that setting is maintained, opens below the set pressure, handles 13 amps, and preferably costs only around $12

Bama thank you for that suggestion, I will look it up

Please flip to page 2
 
A heater pressure switch is normally for switching 24 VDC and usually drives a relay for the heater. Most controllers have 24 VDC relays for switching pumps so if you have a controller, you have the relay. If you don't have a controller, then a 240 VAC pressure switch is needed to avoid the relay. But given the AC pressure switch is so cheap, that may be a better solution.
 
You need a relay because even though the switch is rated for 25 amps it's rated for resistive loads. The significance of that is that breaking a resistive circuit produces much less arcing than an iinductive (i.e. motor) load creates, and therefore burns up the contacts in the switch quickly. An inductive load has an inrush current of greater duration and magnatude than a resistive load does. A control relay has bigger contacts and they are also shaped to "blow out" the arc quicker.

Of course it's your switch, so you're free to use it as you see fit. It's all about exposure. The hope is that the switch never switches under load and given what it's protecting it might be acceptable to sacrifice a $30 switch on the rare occasion that the switch actuates under load. I still recommend using a relay for the load switching and let the switch actuate the relay.
 
dalehileman:
By now you should be getting an inkling of why you can't find a packaged pump protective system at the price you want to pay. The $20 - $40 pressure switches are made to sell to manufacturers that put together systems for specific applications. These applications require more components than just a pressure switch. They require enclosures, power supplies, relays, microswitches, and may require more than one of these components in addition to labor to put them together. All these add to the cost, and maybe that is why you can't find want you want for the price you want to pay. It's kind of like trying to buy a $500 item for $20 - you are going to get what you pay for.
 

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