SWG Flow Sensor vs Water Sensor & Flow Rate Issues

[Strannik]

Re: Air/gas in SWG with pump on low speed

Firstly, that doesn't indicate that it's a safety hazard. Secondly, there is clearly something unique about this particular installation which causes the bubbles to form as you don't see flocks of Hurlcon owners with this problem.

I'd be careful with making a throwaway comments about safety of various designs, as you potentially open yourself to a litigation from various manufacturers.

 

[duraleigh]

Re: Air/gas in SWG with pump on low speed

This thread is w-a-a-y over my head and perhaps everyone else's except current participants. The tone is getting such, however, that it may soon seem more appropriate for The Deep End.....or some of it at least split off.

Let's see if we can keep it in the SWG forum, OK?

 

[Strannik]

Re: Air/gas in SWG with pump on low speed

Yeah we can split off discussion on drawbacks and benefits of the sensors vs switches into another topic. We seem to agree on the point that this particular model has a sensor, which is the only thing that's important in the context of this particular topic.

 

[mas985]

I would consider a standard SWG flow switch a sensor as well. By definition, a sensor is a device that automatically senses or detects a specific condition. In this case, a standard SWG flow switch senses the flow of water and switches on. Therefore, it is a sensor as well. Just because a sensor is mechanical in nature rather than purely electrical does not mean it is not a sensor.

However, if what Strannik says is true, and I still believe it would be a very poor design, the sensor that Hurlcon put in their SWG is a WATER sensor and not a flow sensor as they claim in their documentation. To me that is very deceiving and the primary point that I am taking issue with. If the sensor only detects the presence of water, then they should not call it a flow sensor because it is not.

Also after seeing what the OP posted, it is pretty clear that the SWG is not shutting off when it should. To me that is a big concern.

 

[JasonLion]

Electronic flow sensors (no moving parts) do exist, for example this one. I haven't seen anything that clearly explains how the sensors Strannik is talking about actually work, so it isn't clear to me what exactly they are sensing.

 

[mas985]

That was along the lines of what I thought Hurlcon was describing in their manual and not just a water sensor. I mean they call it a flow sensor so I would have expected it to sense flow.

There are many different ways to detect and measure flow. This page shows all the variants of flow meters including the thermal version: http://www.flowmeters.com

 

[Strannik]

The sensors are sensing negative electricity charge between the sensor pin and the cell plates. When there is water present, there is a charge, when there is no water - there is no charge. It also doubles as salt level sensor, by measuring how big the charge is. Don't remember the technical details of the second part as it's been over 5 years since I looked at the schematics last time.

The sensor would be usually located in the middle of the cell, to ensure that it works as intended no matter which way you insert the cell into the housing. In the pictures in the other thread it doesn't look like it's gone below the middle so the unit still works.

 

[Strannik]

With regards to safety, you have to look at overall system design and not the individual bits.

Fuel tanks in cars are also prone to ignite, that's why they have caps on them and you don't smoke when you are refilling.

 

[JasonLion]

If we assume a cell design like the one in the original topic, where there are vertical pipes entering and leaving the cell from below, then a water sensor is like a flow sensor with an additional delay. The delay is caused by the time it takes to fill the housing a little bit more than half full of gas. Without any water flow there isn't anywhere else for the gas to go, so it accumulates until the water sensor is below the water line and shuts the unit off. The real danger is if the unit continues operating without water flow for much longer than that, while that initial period while gas accumulates enough to displace water is not nearly as dangerous as running for hours with the gas going into the filter (which has happened to people with a different design and a faulty flow sensor) and the water getting more and more caustic. Plus an electronic water sensor is not nearly as likely to break as a "paddle" style flow sensor.

 

[mas985]

Fuel tanks in cars are also prone to ignite, that's why they have caps on them and you don't smoke when you are refilling.

Yes but gas tanks don't have electrically charged plates in them that can cause a spark so I don't think that is a very good analogy.

Also, I think I am looking at the overall system design and in my opinion as an electrical engineer with 30 years of experience in systems design, it is a very poor design. The conventional SWG axial port design with a flow switch is a much safer design and doesn't suffer from any of the problems the OP is experiencing right now. His cell is a third filled with a hydrogen oxygen mix and there are exposed cells with voltage applied. One spark and poof, shrapnel. While fairly low probability it still seems pretty plausible to me. In fact, the OP posted that the manual warns against just that scenario. It just seems like it would be smarter to try and avoid the problem all together.

The reason I went back and forth with you so many times on this is that I had a very hard time believing they would design a unit this way. It just didn't make sense to me and still doesn't.

 

[Strannik]

I think it's a pretty good analogy but I can think about lots of others. There plenty of products out there that are dangerous if misused. I seem to remember something about hot coffee and pets and microwaves

The axial design has other problems. It actually requires you to create the second bend yourself, to avoid gas going back to the filter, like Jason mentioned. In my opinion this is much bigger danger as the volume of gas that can accumulate in the filter is much larger.

If you look at installation instructions, most units that utilise axial or r-shaped housings require you to create gas trap when installing it.

As far as the plates sparking, for it to happen you need either some metal debris to come into the cell and get thrown above the water level, or the plates touch each other.

If the unit is installed after the filter like it should be, then you shouldn't get any metal debris at all, let alone the fact that they will short out the cell in the part that is still in water, because they would have to come all the way from the bottom. For the plates to touch each other, the clips holding them together must break or they must bend.

This is a more likely scenario if the water has stray currents and the edges get worn out. However by the time this happens the cell would've been operating for years, so any problems with gas trapping would've been resolved.

In a scenario where the pump is shut off the gas would push down the water much quicker then what we see in this particular example, so your cell would turn off within a minute or so.

The mechanical switches are also prone to tampering. Believe it or not, I've seen commercial models with housing completely melted/exploded, because the flow switch broke and the operator decided to just tape the wires together instead of replacing it. They were lucky it didn't injure anyone, and the damage to the unit was in the order of 10000 for the cost of a simple flow switch.

 

[mas985]

The axial design has other problems. It actually requires you to create the second bend yourself, to avoid gas going back to the filter, like Jason mentioned. In my opinion this is much bigger danger as the volume of gas that can accumulate in the filter is much larger.

Jason was referring to a faulty flow switch causing the filter to fill with gas and yes when devices, fail they can be dangerous and a check valve could have prevented that problem. But under normal conditions, because of the axial design, the bubbles will take the path of least resistance and flow right out the exit port. As I pointed out in previous posts, the gas can still accumulate in the plumbing somewhere else but to me that is much less dangerous location than the cell.

Also, I agree that any product can be misused and/or have failures and become dangerous. I was more focused on products that are used properly, are in good working condition, and yer are still dangerous like the Hurlcon SWG design.

We may just have to agree to disagree on this one.

 

[Strannik]

under normal conditions in this particular design bubbles flow right out of the exit port too.
I thought we had already established that this particular installation isn't exactly 'normal conditions'.

 

[mas985]

Low speed of a variable speed pump is becoming the new norm so I can see this situation become more prevalent.

 

[Strannik]

i think the low speed pump is just one of the factors here, it's the overall plumbing that results in such outcome.
there is a minimum flow rate that is required for operation of SWG, and to me it just sounds like it's either not achieved in this case, or there is a lot of turbulence in the cell

if you look at different SWGs available on the market, about half of them utilise this cell design. yet you'd struggle to find 10 topics on this forum describing this particular problem

 

[JasonLion]

I have only seen one other instance of this particular issue discussed. The brand of SWG was different, and the cell was above the waterline, but otherwise the issue was very similar. On the other hand, only a few of the smaller brands (in the US) use transparent housings, so most SWG owners would be unaware of gas accumulating in the cell. On the third hand, the people who do have transparent cells would tend to notice instantly, so even though there aren't that many of them, you would expect it to come up fairly often if this was a universal problem for all low speed pump setups. Also I believe the flow rate in this case was estimated at something like 28 GPM, which is not really all that slow.

 

[OzPool]

The sensors are sensing negative electricity charge between the sensor pin and the cell plates. When there is water present, there is a charge, when there is no water - there is no charge. It also doubles as salt level sensor, by measuring how big the charge is. Don't remember the technical details of the second part as it's been over 5 years since I looked at the schematics last time.

The sensor would be usually located in the middle of the cell, to ensure that it works as intended no matter which way you insert the cell into the housing. In the pictures in the other thread it doesn't look like it's gone below the middle so the unit still works.

Wow, I've really sparked a debate here! Cool!

From what I witnessed yesterday, I think Strannik has pretty much hit it on the head with the quoted comment above. After 30 minutes of low speed and 1/2 dose (the third bubble photo on the original thread), the sensor was sitting right in the tail end of the bubble, which was swaying around like the tail of a Polaris. The Low Salt light had come on at this stage, but the sensor was still getting wet enough to prevent the No Flow light from coming on.