Elevated Spa: How much check valve spring tension will hold back water on supply side

[TaylorN]

I have an spa that is elevated and the water level is about 1.75 feet above my diverter valves. The spa water level is about 3 feet above pool water level. Every time I switch over from spa mode to pool mode (takes about 60 seconds for actuator to switch positions) I lose about 0.25" of water from the spa into the pool through the supply/vacuum diverter valve. Technically I lose 0.5" total through both the supply and return valves, so I averaged 0.25" loss through the supply side. Every day there are two change overs so the spa loses 1" to the pool.

The return side is easy an easy fix. Just install a properly oriented check valve on the spa return pipe. That should alleviate 0.25" of loss.

My question is for the supply side. I had a pool construction guy stop by and tell me installing a Jandy check valve on the spa pipe of the supply/vaccum side would stop the flow of water with just spring pressure alone even if it isn't in the orientation a check valve would normally be in.

Would that work? Would the spring pressure alone be enough to old back the weight of the water in the spa? I have seen check valves rated at 0.5lb, 2lb, 5lb, etc. Normally you'd want to have the least spring strength possible, but I am wondering what spring strength would be required to passively hold back the water from the spa when the pump is off and the diverter valve is changing positions?

Based on what I see online there is 0.433psi for every foot of elevated water. So at a max of 1.75 feet, that would be about 0.75psi. I have noticed some random literature stating some check valves (I didn't see corresponding spring strength) have a minimum opening/cracking pressure of 0.5psi. So technically spring pressure alone would be VERY close to holding back the spa water. But I still don't know if that is for a 0.5lb spring or a 2lb spring. If a 2lb check valve can hold back 0.75psi, then I think I am good. I also read somewhere of someone using a 5lb spring strength check valve for something. I imagine that would definitely hold back 0.75psi?

Also, the following website https://sunplay.com/products/pentair-cpvc-check-valve-263060 says for the pentair check valve 'Check valve design seals down to 15" water column (0.54 psi)'. I assume that means it's cracking/opening pressure is 0.54psi which would not be enough strength to hold back 0.75psi. Though in that case maybe only a tiny bit of water gets by during the 60 second valve position change instead of the free flow that it is currently. I have no idea what spring strength that product uses. If it is a 0.5lb spring, then it would be safe to say a product with a 2lb spring would probably hold back the 0.75psi from the spa.

Any feedback would be much appreciated!

Thanks!

 

[TaylorN]

Now that I am thinking about it more, I could reduce the psi requirement (0.75psi) by elevating the check valve on the spa supply/vacuum side so it was closer in height to the water level of the spa. Then the gap wouldn't be 1.75 feet, but rather 0.5 to 1 foot. That would mean the pressure exerted on the check valve spring would be around 0.433psi or less. If most check valves have a minimum cracking/opening pressure rating of 0.5psi, then I should be fine and wont need to find an exotic check valve with a higher cracking/opening pressure rating. I would just need to make sure the check valve doesn't get plumbed any higher than the average spa water level.

Would that work?

 

[TaylorN]

ok. ok.. answering my own questions i think...
so it looks like Valterra creates a swing valve with a 2psi cracking pressure, the 2002 series (ex: 2002-C20): Valterra 2002-C20 PVC Swing/Spring Combination Check Valve, Clear, 2 Scientific

there 200 series (ex: 200-C20) is 0.5psi cracking pressure which is sold at more places. looks like 2002 series is rarer... probably since it is less efficient.

Anyways, if no one has any feedback looks like I will be trying the 2002 series from amazon to see if it can hold back 2 feet of water.

 

[Realaxpooltech]

Does the spa have a "spillway" feature that overflows back to the pool?

(spillway is like a waterfall over spa wall that puts water back into the pool)

I'm asking this first before i get into anything else.

disregard my question, as i just read your earlier post explaining pool auto cover disable for spillway,

 

[TaylorN]

Does the spa have a "spillway" feature that overflows back to the pool?

(spillway is like a waterfall over spa wall that puts water back into the pool)

I'm asking this first before i get into anything else.

disregard my question, as i just read your earlier post explaining pool auto cover disable for spillway,

Yeah there is a spillway, but we have an automated pool cover which is always closed for kid safety so we cant just overflow the spa to keep the water level up.

We operate the pool and spa as totally independent bodies of water for the most part

 

[TaylorN]

so for anyone following the conversation I am having with myself
... I bought a check valve from custom molded plastics with a 2lb spring. It passively holds back about 11-12inches of vertical water before the flap opens. So that is about 0.5 psi.

I also have a FlowViz Water meter which is essentially a check valve. The spring is a little weaker. I'd say about 1.5lb spring. It holds back about 8"inches of vertical water.

I haven't tested a 0.5lb spring, but I imagine it would hold back maybe an inch of water.