Time Delay Switch From Signal

could you fit a vacuum relief valve so that it does drain, or is the heater below the water level in the pool?

It's an in-ground pool w/ the equipment above the top-most water level in t he pool, so technically the water line can be opened and some water will dr ain. But there may be some issues w/ doing so. Some off the top of my hea d: 1. Opening the water line would need to be coordinated w/ the pump or a d evice used such that it doesn't leak the water as it's being pumped through the system. 2. If the water line is opened, it releases the vacuum on both sides of t he line and so generally this will cause the water in all of the equipment (ie. both sides of the opening, so including the filter and pump) to drain. Depending on the extent of it, this may cause a problem when the pump sta rts up the next time as there's air in the input. The pump is generally ab le to overcome this, but it's not intended to do so every time it runs. 3. The input & output connection points to/from the heater are lower than the main return pipe. So if the line were opened, I'm not sure if the hea ter will drain or not. I suppose I could plumb something off the heater's drain plug though.

If the idea is to use a mechanism similar to a toilet re-fill, then I'm not sure that will be completely effective. A toilet mech refills the tank. While that's better than nothing, refilling the heater will still leave a f air amount of residual salt in the system (heat exchange coil diameter is f airly small to increase surface area which retains salt water). So I think I need to flush a fair amount of water through the system (generally 2x th e volume of water from the point of entry of the fresh/flush water through the output of the heater).

All that being said, I'm curious to hear your idea.

I took some shortcuts in my diagrams for simplicity (a bit cumbersome to do in ASCII art). Sorry I forgot to note this in the post.

Right, I drew them up to help me visualize the activity of each part.

I think we're saying more or less the same thing. In my diagrams I didn't separate each relay's contacts from its pole's. So for the 24V heater switch, the relay will close the 24V circuit--the 120V is only for the relay's contacts. The Flush Relay in my diagram will close the Vac circuit when the relay is energized.

Seems I just need to source the parts now. I'd appreciate suggestions on h igh quality parts.

Thanks!

My idea was to fit a vacuum relief valve above and before the heater so that when the pump stops gravity will dry the heater out. air has got to be better than salt water, right?

this requites that the heater be arranged such that it can drain by gravity. care would also need to be taken to not rune the headter while it is dry,

in your setup you'd want a check valve before the heater so that the pump stays flodded when the heater drains.

a vacuum relief valve is a small check valve that admits air to the pipe when there there is a partiial vacuum in the pipe, it is a simple automatic mechanical valve. often these valve leak a bit before they close, expect a small quanitiy of salt spray. vacuum relief valves are commonly used to drain solay pool heaters so that the aren't collapsed by vacuum when the pump stops.

Yes air is certainly better than salt water. But I wonder how effective th is approach will be. Here's my thinking. The crucial part of the system that's sensitive to salt water is the heat e xchange coil inside the heater (because it's metal and salt eats it up). S pecifically, the salt water that's in contact with the inner surface of the coil. So removing all of the water that's not in direct contact w/ the in ner coil surface doesn't really help. Draining the coil would remove most of the volume of salt water, but I wonder how much salt water would remain on the inner coil surface (surface tension, residue, etc).

The heater has its own internal flow sensor and will not operate unless a m inimum flow rate is detected.

Right, that's easy enough.

Good to know, thanks.