Diaphragm tank drawdown Q:

[Reach4]

Reach4 : wouldn't the actual Schrader valve be the problem and not the cap?

My comments on that are based on what people said in car forums. As somebody who had sometimes used tires with no valve cap, I found that I had been doing it wrong. Yet when I looked for what I thought I remembered, I did not find that. So I think that I should rescind my thought about the valve cap importance.

A good valve cap does seal, but it looks like it might be the secondary seal.

 

[Buddy]

YMMV since some diaphragm tanks have internal dome limiters.

I'm not sure how this diaphragm tank is designed. I can see how with lower air pressure we end up with more water come out when drained to zero. If a bladder tank leaks air from a tear you get water replacing it yes? There's no sound splashing at all.
Q: could a diaphragm tank be defective leaking air into the water line and not be replaced with water? or maybe it's trapped between this "dome limiter" you're mentioning here and you can't hear water when moving the tank around.

 

[Sponsor]

 

[Valveman]

If there is water above the diaphragm you should be able to feel it sloshing around, and the tank will be much heavier.

 

[Buddy]

My comments on that are based on what people said in car forums. As somebody who had sometimes used tires with no valve cap, I found that I had been doing it wrong. Yet when I looked for what I thought I remembered, I did not find that. So I think that I should rescind my thought about the valve cap importance.

A good valve cap does seal, but it looks like it might be the secondary seal.

Ya secondary seal for sure and if actual valve is just slightly leaking the cap should stop that. I bought some pretty f'n bomber valve caps with rubber in them.

 

[Buddy]

If there is water above the diaphragm you should be able to feel it sloshing around, and the tank will be much heavier.

there's no water sound like I mentioned or off balance feeling. This last time we drained it to Zero the 2 tanks were both the same empty. The time last year emptying to zero though the problem tank was still heavy feeling as if water was in there but no sound or sloshing feeling.
I'm getting the feeling the actual diaphragm just isn't dropping sometimes and its getting hung up, therefore the water couldn't come out the drain hose at ground level as the tank outlet is 6' below.

 

[Fitter30]

If the bladder is compromised water will come out the Schrader valve. Just blow the air if it is compromised water will start to come out if not before. Bladders have extreme total pressures on them when they fail.
π x r squared = area 12" radius =452 sq inchs 10 psi = 4520 lbs on bladder, 50 lbs 22,600 lbs





= 4520 lbs

 

[Buddy]

I think its probably higher as r kinda seems more like 13-14" it's a fat 119 gal. Either way... the other day we drained to zero and the suspect tank was at around 10psi down from the 24psi last time. This time we pumped up to the 58psi for the 60/80 pressure switch, with a mo better valve cap tight!
We ran another drawdown test for the 2-119gal tanks and only got 35 gal. Pretty Sure its supposed to be closer to 55-60gal.
Anyway we'll test again to see if it's still loosing air somehow.
Oh ya, and def no water coming through the shrader valve, even when it had less lesser psi in it.

 

[Valveman]

Being on top of the tank there will be no water coming out the Schrader until ALL the air is gone. No water coming out doesn't mean the tank is still good. At 60/80 each 119 gallon tank should give you 25 gallons of draw down.