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Author Topic: water syphoning after pump switched off - do I need a check valve?  (Read 4318 times)
al_uk
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« on: September 28, 2009, 08:24:07 PM »

Just started to get into rainwater harvesting after calculating how much it would cost to water the plants from the mains - even with a tiny garden and around 50 or so drippers in pots.

I now have the drippers fed from a cheap 12V submersible pump in an IBC, and the 3P diverter is on the way...

My problem during testing is that when the pump is switched off, some of the drippers (which are lower than the water level in the IBC) continue to syphon water. The pump and hose are fed through the top opening in the IBC, not the drain tap.

Having searched, I believe I need a Hunter Check Valve installed in the hose before the 1st dripper, which would only open once a minimum pressure had been reached, ie. when the pump is switched on.

Anybody care to comment as to whether this is the best solution, and any suggestions on where to get one in the UK?

cheers

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10kW PV. Rainwater collection-14 IBCs. Custom Arduino based Immersun type PV diversion. HomeSeer home automation, Househeat/Conrad TRV radiator actuators + FHEM. SageTV
johnrae
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« Reply #1 on: September 28, 2009, 09:23:58 PM »

No need for a check valve.

All you need to do is take a T off the pump discharge and run a line from there back to the top of the tank.  Ensure this new discharge line's outlet is in free air such that its discharge is never below the surface of the tank water, ie the discharge falls back into the tank.  This line must have no dips in it, ie straight up from the pump then back down into the top of the tank.  This line will now act as a vacuum breaker, which is all you need to kill a syphon.

jack
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johnrae
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« Reply #2 on: September 28, 2009, 09:33:39 PM »

Oops, forgot to mention, you should also raise the pump discharge to a height higher than the reservoir surface before it then drops to the drippers. 

So, reroute pump disharge to a height higher than reservoir surface, take a T line off this high point to spill back into the tank (this only needs to be a fairly small flow) then run main line down to your drippers.

jack
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al_uk
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« Reply #3 on: September 28, 2009, 09:47:40 PM »

Ah ok thanks for this! I have a submersible pump in the tank with a hosepipe attached to it which exits out of the top of the tank and then down the side to the drippers.

Would just putting a 2mm hole in the hosepipe in the tank, above the water level, but below the top of the tank suffice?
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10kW PV. Rainwater collection-14 IBCs. Custom Arduino based Immersun type PV diversion. HomeSeer home automation, Househeat/Conrad TRV radiator actuators + FHEM. SageTV
johnrae
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« Reply #4 on: September 29, 2009, 07:57:20 AM »

A small hole would do excellently.  You might have to fit a jet deflector over it to stop the water spraying out the tank.
jack
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al_uk
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« Reply #5 on: September 29, 2009, 07:42:32 PM »

That worked. Thanks! 1mm hole was enough
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10kW PV. Rainwater collection-14 IBCs. Custom Arduino based Immersun type PV diversion. HomeSeer home automation, Househeat/Conrad TRV radiator actuators + FHEM. SageTV
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