I built a hot tub control system, both the plumbing and control system: it's like I'm back in Engineering school 
.
But I have an issue I can't solve and need some thoughts.
Tub itself is 145 diam x 110 height, about 1800 litres.
Pipes are 1' bsp screw fittings, or 28mm solder-ring and compression fittings.
Suction comes in through a course and then fine filter, then past two normally-closed drains (one manual release and one solenoid controlled release) before turning vertical to rise up through a 28mm check valve, then take a tee (1) up and (2) right; the up path is through a loop with another 28mm check valve, a ball valve, water quality sensors (in an acrylic tube), a pressure reducer, then a return path back down to join the right side of the tee. The right side feeds into the pump (a grundfos ups3), then into a heat exchanger, then out of the heat exchanger into a uv steriliser, then through a venturi injector (not currently used, future use case), then down through a 28mm check valve then past a tee that takes in new water (solenoid controlled valve), then back to the tub return.
It's in the middle of nowhere and I ran out of time, so won't be back until November to work on it further. Finished it at 11pm. Found the shower stopper at 12.30. Got up at 5 to clean up. Train at 8.30. Plane back to London ...
Before I left, confirmed that control system, sensors (flow meters, temperature probes, water level sensors, etc), solenoid valves, pump, etc all actuate (I can remote access it from here). I get water in through suction and up into the water level measurement tube (which taps off at at the horizontal to vertical turne before the first check valve), and can successfully actuate the drain solenoid to dump water. Equally, I can also successfully actuate the water input solenoid to feed in new water. I'm running a small script that monitors water level and tops it up every 6 hours or so.
Problem is, I get no water through the circulation loop. Identified that water is not getting through the first check valve. I don't understand why. I have a pressure transducer at the course particle filter and while it's not properly calibrated yet, it's reading 1.26 bar (the return valve is on the side about 5cm from bottom of tub, so there's about 1m of water level above it, which my math tells me should be super small pressure, about 0.1 bar). Maybe this is not enough pressure to crack the valve? The pump should also suck enough to trigger it, but I guess at the start there's no water in there for it to suck. Maybe I need to charge it? It's a standard spring single check valve 28mm compression. Do I need a lower pressure or swing valve? Or maybe I don't need a check valve at all (the purpose of the valve in the design was to prevent back flow when I drain water: indeed at the moment, when I drain water the water level tube (left side, acrylic tube) will suck empty until the drain is shut after which it will return back to level). The purpose of the second 28mm check valve is to ensure one way path through the water quality sensors (not fitted yet, see the temporary black flexible hose), and the purpose of the third and final 28mm check valve is to prevent back flow from the return feed).
Any thoughts/help?
. But I have an issue I can't solve and need some thoughts.
Tub itself is 145 diam x 110 height, about 1800 litres.
Pipes are 1' bsp screw fittings, or 28mm solder-ring and compression fittings.
Suction comes in through a course and then fine filter, then past two normally-closed drains (one manual release and one solenoid controlled release) before turning vertical to rise up through a 28mm check valve, then take a tee (1) up and (2) right; the up path is through a loop with another 28mm check valve, a ball valve, water quality sensors (in an acrylic tube), a pressure reducer, then a return path back down to join the right side of the tee. The right side feeds into the pump (a grundfos ups3), then into a heat exchanger, then out of the heat exchanger into a uv steriliser, then through a venturi injector (not currently used, future use case), then down through a 28mm check valve then past a tee that takes in new water (solenoid controlled valve), then back to the tub return.
It's in the middle of nowhere and I ran out of time, so won't be back until November to work on it further. Finished it at 11pm. Found the shower stopper at 12.30. Got up at 5 to clean up. Train at 8.30. Plane back to London ...
Before I left, confirmed that control system, sensors (flow meters, temperature probes, water level sensors, etc), solenoid valves, pump, etc all actuate (I can remote access it from here). I get water in through suction and up into the water level measurement tube (which taps off at at the horizontal to vertical turne before the first check valve), and can successfully actuate the drain solenoid to dump water. Equally, I can also successfully actuate the water input solenoid to feed in new water. I'm running a small script that monitors water level and tops it up every 6 hours or so
.Problem is, I get no water through the circulation loop. Identified that water is not getting through the first check valve. I don't understand why. I have a pressure transducer at the course particle filter and while it's not properly calibrated yet, it's reading 1.26 bar (the return valve is on the side about 5cm from bottom of tub, so there's about 1m of water level above it, which my math tells me should be super small pressure, about 0.1 bar). Maybe this is not enough pressure to crack the valve? The pump should also suck enough to trigger it, but I guess at the start there's no water in there for it to suck. Maybe I need to charge it? It's a standard spring single check valve 28mm compression. Do I need a lower pressure or swing valve? Or maybe I don't need a check valve at all (the purpose of the valve in the design was to prevent back flow when I drain water: indeed at the moment, when I drain water the water level tube (left side, acrylic tube) will suck empty until the drain is shut after which it will return back to level). The purpose of the second 28mm check valve is to ensure one way path through the water quality sensors (not fitted yet, see the temporary black flexible hose), and the purpose of the third and final 28mm check valve is to prevent back flow from the return feed).
Any thoughts/help?
