Pressure Tank - Reduced Drawdown

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mauiman

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Hi,

Does anyone have experience with reduced drawdown on a Pressure Tank that isn't water logged?

System:
New Well (just replaced), 3/4 hp Pump, 10 GPM, 93 ft deep.
33.4 Gallon Flexcon Challenger Pressure Tank (5.5 years old).

With a 40/60 Pressure Switch, the tank should have a theoretical drawdown of 8.7 gallons. When I measured over the weekend, the drawdown is a little more than 5 gallons. The Pressure Tank showed 35 PSI when I measured it after draining the system.

Is there possible sediment in the Pressure Tank? I suppose part of the Bladder could be stuck to the side of the tank from the very begining when it was installed.

I wanted to get thoughts and opinions.

Have people seen poor drawdown even with new tanks?

Thanks in advance!
 
As a follow-up, the well driller suggested draining the system and just letting in 1-2 gallons into the Pressure Tank before shutting down the system again in an attempt to eliminate the sediment (if that is the case).

Won't this put a lot of stress on the pump???
 
It is rare for sediment to build up in those tanks. The inlet/outlet hole is in the very bottom. Any sediment that goes in is the first thing to come back out. If there were sediment buildup, the hole would be plugged.

It is common to not get as much draw down as the chart shows, but usually not that much difference. My guess is the diaphragm has a hole in it and 3 gallons of water are now on top of the bladder in the air chamber. You won’t see water come out the air Schrader valve until the tank is completely waterlogged, unless you turn the tank upside down.

5.5 years of cycling on and off will break the diaphragm the same way bending a wire back and forth will eventually break the wire. The diaphragm moves up and down with every pump cycle.

If you eliminate repetitive cycling with a Cycle Stop Valve, the diaphragm in the tank as well as the pump and everything else in the water system will last much longer. Then when you have a CSV to eliminate cycling, you really only need a tank with 1 gallon of draw down.

Pumps and tanks are built with a certain number of cycles built into them. The manufacturers know how many cycles you will put on your system in 5 to 7 years and they build pumps and tanks to only last that many cycles.

And no, filling the tank or making the pump produce only 1 GPM is actually easier on the pump than when pumping 10 GPM. Higher flow means more amps and more heat, which is harder on the pump than low flow, which causes low amps and lower heat.
 
Hi Valveman,

Thanks for replying. I think I have solved the mystery. Perhaps you can check my logic.

You are right, I "flushed" it several times (i.e. took it down to 0 PSI, back up to 60 PSI, and then back down to 0) and really didn't find any sediment.

So, I went back to "the basics".

1) How much pressure is in the Pressure Tank? My tire guage says 35. I asked myself -- is my tire guage accurate? I pulled together 3 tire guages, tested on my car tires, and they all read about the same thing. So, I think 35 PSI is correct.

2) Is my Pressure Gauge next to my Pressure Switch correct? It seems to work. Cut-In about 43 and Cut-Out about 61.

3) If I assume these PSI readings are correct, and I plug into my handy Boyle's Law Calculator, my drawdown would be closer to 20% instead of the theoretical 26%.

4) When I shut down the system, and when I first turn it on, I see the Pressure Gauge go to 35/36 PSI, so I think my Pressure Tank Reading with my Tire Gauge and the Well Pressure Gauge are in sync.

5) So, what I did, I took the system to Cut-Out, shut down the system, and then slowly drained the water from the pressure tank into my 5-gallon bucks. When the gauge shows 38 PSI -- voila!! -- I have pretty much a good 9 gallons.

6) My thinking is that I just to adjust the Pressure Switch (or a combination of adding a little bit of air to the Tank) and adjusting the Pressure Switch.

7) My only question would be this: Is there any issue with have a 22 PSI differential, instead of 20, between Cut-In and Cut-Out? Meaning, if I keep the PSI in my Tank @ 35, and just bring my Cut-In down to 38 and leave my Cut-Out @ 60. Is there any flaw in my logic? or concerns with what I am proposing?

Lastly, Valveman, I have read with interest about the CSV. Is there anyone in Michigan that actually installs those?

Thanks in advance!
 
Increasing the pressure bandwidth between on and off will give you a little more draw down. But the wider the bandwidth, the more pressure variation there is in the house for showers and things. The shower pressure will vary from 38 all the way to 60 and back to 38 several times while you take a shower. It is annoying but isn't hurting anything except cycling the pump more than needed.

If you have an instant (on demand) water heater, this variation in pressure will also vary the shower flow, and can cause the instant heater to go off during low pressure low flow, then come back on during higher pressure as the flow increases.

With a CSV the pressure tank is drained the first time from 60 to 38, the pump starts, then the CSV would hold a steady 55 PSI no matter how long the shower is on. The constant 55 PSI pressure will be much stronger shower pressure and will keep instant water heaters working properly.

As long as the CSV is delivering a steady 55 PSI the water goes right past the pressure tank, directly to the shower. So it doesn't matter if the tank holds 1 gallon or 100 gallons.

And yes there are lots of CSV installers in Michigan. But you may have to ask for a CSV directly or they won't mention it, as CSV's make pumps last longer and installers don't get to sell as large a pressure tank.
 
Valveman, I appreciate the response. I see your point about the pressure variation. My short term goal is to reduce the number of cycles on my 5 day old pump by increasing the drawdown on my existing Pressure Tank. But, being 5.5 years old, I really want to find someone in Michigan to see about installing a CSV. How do I find an installer?

Last question, just so I am understanding pressure and the various components, if I were to use a 35 cut-in and a 55 cut-out, (and a 33 PSI on my pressure tank), that would simply cause reduced pressure out of the faucet. I assume it would "in theory" stress the Pressure Tank Bladder less?

Thanks again for your help.
 
Those tanks are good up to at least 100 PSI. So you could run 80/100 on the pressure switch with 78 air in the tank and it wouldn't hurt the tank any more than 35/55. It is the number of times the pump cycles and flexes the bladder than shortens the tank life.

Before the CSV (23 years ago) the only way to reduce the number of cycles was to increase the tank size or draw down anyway you could. So you are thinking right. But with a CSV the pump will not cycle no matter how long a shower you take, and tank size or draw down has nothing to do with it.

There are 23 CSV distributors in Michigan. They will know the installers in your area. Give me a city or zip code and I will get you the closest one to call.
 
Hi Valveman -- Some Reps/Distributors around 48130 would be great.

Hi Speedbump -- no, I'm not an engineer, but I do have a math background and tend to analyze things to nth degree. I have this strange "desire" to optimize everything.

I am still trying to understand if the 20 PSI differential is the ideal for the Bladder Tank? or where exactly that comes from? I am curious to know if 21, or 24, or 30 PSI differential causes "potential issues" besides water pressure?

Thanks!
 
I am still trying to understand if the 20 PSI differential is the ideal for the Bladder Tank? or where exactly that comes from? I am curious to know if 21, or 24, or 30 PSI differential causes "potential issues" besides water pressure?
Back when I was doing service work, if the customer didn't have or want a constant pressure valve, I would set the switch to 40/70 psi. That gave a little more run time to help cool the motor down, a little more drawdown and a little more sting in the shower temporarily. One or two pounds of pressure either way won't make enough difference to bother with.
 
Thanks, Speedbump. I appreciate the practical insight regarding the possible variances in pressure. The "theoretical" drawdown is a lot higher than actual. But the constant pressure valve is of great interest. It seems if I install one soon, I would make life easier for both my new pump and my aging Pressure Tank (5.5 years old).
 
I have some systems on city golf course that boost city water pressure from about 50 PSI to 120 PSI for those big sprinklers. We use what is called a Low Pressure Maintenance Bypass. There is a pipe around the pump system that allows about 50 GPM past the pump directly from city pressure at 50 PSI. This keeps up with leaks and hand watering without the pump having to run.

But when more than 50 GPM is being used, the pressure drops to 40 PSI, which is where the pressure switch starts the pump. The pump then boosts the 50 PSI city pressure up to the 120 PSI setting of the Cycle Stop Valve. The CSV holds the pressure steady at 120 PSI while irrigation zones are running from 60 GPM to 600 GPM. When all the sprinklers are turned off, the CSV lets a little water through until the pressure reaches 130 PSI, which is where the pump is shut off.

As water leaks or hoses are used in the system the pressure quickly drops from 130 PSI to 50 PSI. As long as less than 50 GPM is being used the water is supplied by city pressure without the booster pump running.

So basically we run the pressure switch at 40/130 using a regular 80 gallon size pressure tank with 35 PSI air charge. That is a 90 PSI bandwidth. Some of these tanks have been running this way for better than 15 years. But golf courses usually only irrigate once per day, usually at night, which means the bladder only flexes once per day. This makes me believe the width of the pressure switch bandwidth is not as important to tank longevity as the number of cycles per day.
 
Hi Valveman,

Interesting insight on the PSI differential. I see what you mean. I would imagine the strength of the rubber bladder is a big factor as to how many cycles it can take.

Regarding the CSV, can it be installed using my existing Pressure Tank?

Thanks.
 
As a side note, I called Flexcon this morning and spoke with one of the staff. He said that the maximum acceptance factor they recommend is 34%, which translates into about 25 PSI differential between Cut-In and Cut-Out.

Ironically, their Drawdown calculations are based on what you could get out of the tank if you took the pressure all the way down to 0, not the amount of water you can get out of the tank between 40 and 60 PSI.

Thanks.
 
As a side note, I called Flexcon this morning and spoke with one of the staff. He said that the maximum acceptance factor they recommend is 34%, which translates into about 25 PSI differential between Cut-In and Cut-Out.

Ironically, their Drawdown calculations are based on what you could get out of the tank if you took the pressure all the way down to 0, not the amount of water you can get out of the tank between 40 and 60 PSI.

Thanks.

I'm not sure what they are trying to say on either of these statements. Well X Trol had a tank which could only allow a differential of close to 27 lbs. 30 lbs would top the bladder out. Later they put a dome in the WX-203 tank which protected the bladder from being ripped out. All their other tanks that I am familiar with would easily allow a 30 lb differential. Flexcon, same thing. I have only seen one of their WX 203 lookalikes and it was almost new and it was waterlogged. I'm not sure why they called me, because someone else had put the tank in for them a few months ago. It was totally full of water. I advised them to call him back for warranty.

What pressure are they saying to take down to zero? The air pressure, the water pressure or what? Because with a tank precharged with 38 psi that has a 40/60 pressure switch setting, the tanks water pressure will be at zero when the water pressure gets to 38 psi. The only pressure then would be the air pressure in the tank that can't get out. Hope I made sense with that.
 
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"What pressure are they saying to take down to zero? The air pressure, the water pressure or what? Because with a tank precharged with 38 psi that has a 40/60 pressure switch setting, the tanks water pressure will be at zero when the water pressure gets to 38 psi. The only pressure then would be the air pressure in the tank that can't get out."

I don't think I said that very well. What they said exactly was that their figures are based on if you drained all of the water out of the tank during a power failure. Then that made sense why their spec sheet showed 1.1 gallons more than when I was calculating.

Speedbump, regarding your comments on PSI differential between Cut-In and Cut-Out, you are spot on

Tank @ 38 PSI, Cut-In @ 40 PSI, Cut-Out @ 70 PSI

((38+14.7)/(40+14.7))-((38+14.7)/(70+14.7)) = .3412

He said .34 was the max they would recommend. That would be exactly your figures you mentioned!
 
You sort of went over my head with the math. But I will take your word for it. I took an Algebra coarse on the GI bill after leaving the Army. I got all B's through the class and learned that A=B. That's it, that's all I learned. The rest of it was all chicken scratches on paper and a lot of memorization on my part. And what I never understood was, we were never allowed to plug an actual number into all of these formulas. All we did was shrink them down. WOW!
 

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