What type of flow sensor do SWCG's use?

[Motoman]

Just trying to understand the SWCG before I decide to invest.

The flow sensor seems to be an electronic type. Is it basically a thermal mass flow meter? If so, does the mfg give voltage, resistance, or current charts to verify flow rate?

I would also like to know what is the preferred brand. IE fewest breakdowns with good/fair accuracy in regards to proper chlorine production.

Thanks!

[kelemvor]

I think it will vary by manufacturer. The aquarite unit I've got appears to be using a simple inductive sensor. I've not seen any schematics with the expected values - they probably don't want you fixing things when you can be replacing them.

The pool pilot units use what they call a "tri sensor" and I'm not sure at all how they work.

I think aqua-rite and pool pilot both have good reputations as far as brand selection goes.

[nefretrameses]

Aren't they just "flow"/"no flow" (open/close) rather than X millivolts at 10gpm, Y millivolts at 20 gpm, etc.? Tri sensors measure flow, salt and temp.

[mas985]

Most flow switches are a simple magnet and reed switch. But what do you mean by this "good/fair accuracy in regards to proper chlorine production."

Most SWGs are open loop production where you just set the runtime percentage. There are a few that use ORP meters and can regulate production based upon ORP levels but ORP readings can change with other factors such as PH and direct sunlight. Both Autopilot and Hayward ProLogic are two manufactures that have ORP SWGs.

[Poolsean]

We salt manufacturers must have a flow protection device, as per UL1081 guidelines. There are two different ways it's done.
1) Flow Switch: This is a simple on/off status, and is activated by a small magnet on a stainless steel paddle and a magnetic reed micro switch in the center post. As flow pushes the paddle towards the center post, the magnet activates the micro switch and completes a circuit to the control box. This can be as sensitive as 15 -20 gpm (such as with the AutoPilot system) or as much as 40 gpm (Jandy EI) as a MINIMUM flow requirement.
2) Gas Trap: This is usually found in Australian systems with the clear body cells that are mounted horizontally with the in and out plumbing on the bottom of the cell at 90 degrees to the cell body. Two electrical contact points are positioned at the top of the cell (usually at a corner). This relies on the orientation of the cell trapping the hydrogen gases, in the event that there is insufficient flow, and breaking conductivity between the two electrical points within the cell body. At start up, there should be enough flow to evacuate the air/gases that may accumulate in the cell. Multispeed pumps should start up on high speed so as to evacuate this air gap.

A pressure switch can also potentially be used, but I have not seen any manufacturers go this route.

Since the AutoPilot Tri-sensor was mentioned, beside the flow switch, the other two sensors are a dedicated Salt sensor and Temperature sensor. The salt sensor displays the salt level in parts per million, based on conductivity of the water. Low salt conditions will be accompanied by calculation for the amount of salt needed to maintain 3000 ppm. The Temperature Sensor compensates the output %, based on water temperature changes. That is, we know that as temps increase, chlorine demand increases. As temps decrease, chlorine demand decreases. However, under cold temp conditions, most systems will shut down and you have to revert to manual dosages of chlorine to maintain your pool chlorine level. AutoPilot temperature compensation will lower the output, but continue to operate at cold temp conditions.