SWG Safety

[setsailsoon]

Folks,

There have been a lot of posts out there about swg installations maybe due to the virus bleach shortage. This has me thinking about the safety and best way to prevent the unsafe condition when the unit operates with no flow. We recommend powering in a way that doesn't rely on the flow switch to turn it off so it gets power from the same source as the motor or a relay built into the motor. I get that this is much safer for the base operation. But doesn't this still leave us relying on the flow switch for a common failure which is actually flow blockage, filter plugging, or pump running dry or something like that? The more I think about this the more I think we should have similar levels of protection that a gas heater has to prevent failure. Doesn't need the multiple things that are required with gas and a flame. But just something simple like a second independent flow switch that cuts power. Kind of like the independent high and high high temp fail safe used on water heaters. Wouldn't be that hard to do.

What say the experienced and experts on this? @JamesW @ajw22 and others?

Chris

 

[RDspaguy]

Something like this?

PLUG-IN, 120V FLOW SWITCH FOR 2"" PIPE - Paramount Pool & Spa Systems

PLUG-IN, 120V FLOW SWITCH FOR 2″” PIPE

www.1paramount.com

 

[ajw22]

Don’t complicate the cost and complexity of installations by a large number of people for a very low probability risk.

The timer is protecting from a daily off period. If you commit to run the pump 24/7 then you don’t need a timer to protect from an event that will not occur.

Chris, you are you putting forward a double failure scenario. - filter plugging and flow switch stuck closed. Unless you are designing a 737 MAX the probability of a dual failure is much less then a single failure. And once you add another flow switch you have another maintenance item that can make the SWG not work.

In all safety analysis it is about probability of failure x cost of failure.

And even if a SWG keeps generating with no flow it does not quickly explode. It takes time and very rare conditions.

I think a rigorous analysis would find it is not worth it.

 

[setsailsoon]

Allen, thanks for the reply. And you're probably right. I may have sat through too many hazop sessions for chemical plant designs. Even if my scenario was considered it might be most effective to just replace the switch well before MTBF... I know over-working again.

 

[ajw22]

Allen, thanks for the reply. And you're probably right. I may have sat through too many hazop sessions for chemical plant designs. Even if my scenario was considered it might be most effective to just replace the switch well before MTBF... I know over-working again.

Boeing could have used you.

 

[wireform]

It also would be another failure point to sniff out when trouble arises.

 

[RDspaguy]

All good points. And dual failures are rare, but they do happen. Especially if there is something causing them, like bad chemistry (which shouldn't be a problem if you use this site).
That said, I too am a fan of safety devices. And the cost of failure can be pretty high in this case, even if you aren't standing nearby when it goes. I don't mind one more thing to track down if there is a problem, it is pretty easy to test. I don't feel it is necessary, but if it gives you peace of mind and is worth the investment to you, I say do it. You are the only one who has to be happy with your pool.

 

[chiefwej]

Another, factor to consider is that, by far the most common failure of a flow switch is open, not closed. I have had a few fail, but they have always resulted in the lack of power to the cell.

 

[RDspaguy]

I see many flow switch failures wherein the stem cracks and leaks water into the circuitry resulting in a closed switch failure. Likewise, I have seen them get hair wrapped around the stem and flap with the same results. Granted most were on portable spas, but the same design.

 

[laprjns]

The predominate failure mode of the flow switch results in no chlorine production. Adding a second flow switch doubles this false positive (no cl generation) failure rate while providing minimal improvement is safety.

 

[RDspaguy]

In my experience that is not the case.