Water stagnation in constant pressure tank?

[KingAirEvac]

I am getting ready to replace my two shallow well jet pumps (household and irrigation) with a larger submersible. I want a constant pressure system and have been reading the merits of electronic control verses CSV. Reading the CSV info,it mentions stagnation of the water in the pressure tank with a constant pressure system. I believe Flexcon has a flow through system to prevent this. I want a little bit larger than the standard two to four gallon tank most constant pressure systems use,so I will have SOME water if the power goes out for a while. Any comments?

 

[Speedbump]

If your talking about stagnant water in a bladder tank, it's not a problem. Flexcon is the best tank, but as for the flow thru charactistics of bladder tanks, they all work that way. One opening. Water goes in and out the same opening or by the tank if system and tank pressure are the same.

I recommend the Flexcon and the CSV highly. Having a larger bladder tank is not going to offer much reserve water. The largest one made only holds 40 gallons with a 30/50 switch setting. A generator might be a better solution to that problem.

It sounds like you have an aerator to remove sulphur or maybe a cistern. Is this right? If so, which one?

bob...

 

[Sponsor]

 

[Valveman]

The reason the water stagnates in a bladder tank is the lack of a pressure bandwidth. The variable speed pumps are always at a constant pressure. If set at 40 PSI, the system is always at 40 PSI. If the pressure never changes, no water ever goes in the tank or out of the tank. It doesn't matter if it is a 1 gallon tank or a 119 gallon tank. The water that is in the tank, stays in the tank and just gets old and stagnate. The only time water will actually leave the tank is when there is a power outage. If the pump does not come on, the pressure will lower when you use water, and the stagnate water in the tank will be dumped into the house and out the faucet. The Flexcon Flow Through tank is a very good idea for variable speed pumps. This tank has a small jet that sends water up into the tank when water is going past it down the line. The jet causes a current to flow through the tank, which keeps the water fresh even though the level in the tank never changes. Because the level in the tank never changes and the pressure is always at 40 PSI, the pump must start for every glass of water. The pump must start every time you wash a tooth brush, or the ice maker fills, so the size of the tank is of no importance.

This creates lots of cycles during the day but, they do have a soft start which helps. The real problem with not being able to use any water from a tank is when there is a leak. Forget to giggle the handle toilet, or a dripping faucet can cause a variable speed pump to ramp up and down every few seconds constantly until something breaks. The variable speed pump uses a computer for control and this constant ramping would be like putting software in a loop or starting and stopping your computer every few seconds. How long could you do this before your computer locks up? Which with a variable speed pump also leaves you out of water.

The CSV mimics the function of a variable speed pump. It also varies the flow to match the use, which keeps the pressure constant. The differences are that the CSV is a simple valve with one moving part, not a computer. The CSV also only holds the pressure constant while you are using the water. When you turn off the faucet, the CSV allow the tank to fill to 50 PSI before the pump shuts off. Then you have a tank full of water, any size tank you want, to use before the pressure drops to 30 and the pressure switch restarts the pump. When the pump is started the CSV holds 40 PSI steady until you are no longer using the water, and the tank is filled again. The larger the tank, the less times the pump will start for intermittent uses. Regardless of the size of tank, the pump will stay running and the CSV will hold 40 PSI constant when water is used for longer periods.

Speed is right either way, if you want back up water, get a generator. I would use a CSV and about a 20 gallon tank that actually holds 5 gallons of water.

 

[Leejosepho]

I want a constant pressure system and have been reading the merits of electronic control ...

From what I have learned from many of the folks here, I would definitely stay away from variable speed.

 

[Speedbump]

I learned something today. I didn't know about that flow thru tank. Never heard of it. Somebody at Flexcon isn't getting the word out to their suppliers.

bob...

 

[Valveman]

Variable speed pumps are not a new thing. However, many of the band aids they come up with to try and solve some of the inherent problems of VFD are new. Flow through tanks help keep the water in the tank from stagnating. Switches instead of transducers help the reaction speed of the VFD to reduce some of the water hammer and pressure surges. Harmonic filters help keep the VFD from sending dirty power back into the electric grid. Computers installed inside the motor instead of above ground, allow the water to help keep the electronics cool without the need for a fan in the control box. This helps keep out lint, bugs, and heat, which are the worst enemies of a VFD that is hanging on the wall of a well house. Some of the new larger VFD's now have a "sleep mode" which allows a pressure bandwidth so a pressure tank can actually accept and express some water. VFD's are getting smaller, lighter, cheaper, and may even be lasting a little longer.

All of these things are just band aids. Unless you can change the laws of nature, there are many things about the VFD that can never be fixed. Higher RPM's of a VFD pump can cause premature wear. VFD pumps and motors vibrate at certain speeds from a resonance frequency that can only be skipped not fixed. Reflective waves and pulsing DC voltages cause the motor to receive much higher voltage than it was sent, depending on the length of the wire. This higher voltage can cause premature failure of the windings in the motor. The list of side effects from using a VFD can go on and on.

The function of a VFD is so complicated and the side effects are hidden by so much smoke and mirrors, that it does not surprise me that even someone with Speedbumps experience in the pump industry, has not heard of these things. Many of the people who sell VFD systems either don't know or don't want you to know all of the ins and outs of this type system. The long list of negative side effects are never mentioned, as all they want you to hear is "constant pressure" and "energy savings".

Restricting the flow of a normal pump with a simple valve can reduce power consumption the same as a VFD. Therefore, claims that a VFD can save energy, are simply not true in these type applications. The CSV mimics the "constant pressure" and "variable flow" of a VFD. However, the CSV gives you these benefits without any of the negative side effects that are inherent with VFD controls.

 

[Speedbump]

I was asked to buy one by one of my Reps. I have it here and am testing it. The first time we hooked it up, it did what VFD's are supposed to do. Kept a constant 60 psi no matter where I positioned the valve to vary the flow. The problem was; at zero flow it wouldn't shut off. It just kept ramping up and down at much reduced RPM's. This is my second experience with one of these and I'm still not impressed. I'm going to wait for the Rep to show up here so he can be un-impressed as well.

My lack of knowledge of VFD's is my lack of wanting anything to do with them. I never thought they would catch on and certainly didn't want any more electronics to deal with while living in the Lightning Capitol of the World.

bob...

 

[Valveman]

When you get the VFD you are testing to shut off as it should, try simulating a small leak. Running a small stream about half the size of a wooden match, which is the same as a leaking toilet or dripping faucet, the VFD will go crazy ramping up and down continuously. Most VFD demonstrators at trade shows have special non-leaking faucets. If you try to simulate a leak, the faucet just closes off. With a regular ball valve or faucet, you can simulate a leak and then you will see what I am talking about. This is the problem of not being able to use any draw down from the pressure tank.

 

[Speedbump]

It makes sense they would have a real problem with a leak. This one out of the box (a 3/4hp pump with a 1.5hp motor attached) can't shut off even with no leak. We had the valve shut all the way off, no water going anywhere and it wouldn't shut off. I know there is an adjustment that can be made to make it behave, but should I have to do this after spending way too many dollars on this marvel of electronic fiction?

bob...

 

[Valveman]

1.5 HP motor with a 3/4 HP pump means this must be a Sub Drive. These will spin the motor and pump to 4700 RPM instead of the normal 3450 RPM. That is how they get 1.5 HP performance with the 3/4 HP pump. Also means you are using a 3 phase motor, even though you have single phase power. These systems use a little go/no go pressure switch instead of a pressure transducer. Put an old analog amp meter on the incoming power supply, and you will see the switch is bouncing the pump on and off 45 times per minute. That will cause this switch and everything else to cycle 1,000,000 times every 21 days of use. I was told these systems are designed to produce variable flow rates for intermittent use only. Showers and other house uses are intermittent. Sprinklers, garden hoses, and heat pumps are not intermittent so, they still need to be designed to use the maximum flow the pump will produce. This will keep the system from cycling 45 times per minute but, kind of defeats the purpose of constant pressure at variable flow rates.

I hear a lot of problems with wire down the hole wearing out from the torque of starting 45 times per minute. I also hear there are lots of problems with the computerized control box itself getting lint or fire ants inside it. Several dairies have had to remove these type systems because of the stray voltage negatively affecting the cattle. Harmonics also cause the power wires feeding the control box to overheat.

All these problems can be avoided and better performance obtained by using a standard pump and motor with a simple Cycle Stop Valve.

 

[Abikerboy]

Question; they taught us in school that water does not stagnate unless exposed to air, hence the bottled water that you buy is in a sealed container. A bladder tank seperates the air and water by the bladder, so how would it stagnate?

 

[Valveman]

Good question. Maybe Gary can help us answer that question. My guess is that bottled water is sterilized before being sealed in the bottle, well water is not. Well water without chlorine is a perfect environment for any contamination present to survive and prosper. A bladder tank only separates the water from the pre-charge air in the tank. There is still air in the water that can come out of solution and rise to the top of the tank. A little air in the top of the tank, untreated well water sitting in the tank for weeks or even months without a change out, leads to the water at least being stale if not contaminated. I think the same thing would happen if you put fresh well water in a bottle, closed it up, and left it under the seat in your car for a few months.

 

[Raucina]

Put an old analog amp meter on the incoming power supply, and you will see the switch is bouncing the pump on and off 45 times per minute

I would guess the pulse is the electronics generating the fake third leg of the three phase and the method of speed control of the motor. That should be internal to the electronics and the output to the motor would be relatively constant. A three phase motor or its switches would die in a few days or hours at 45 full on and off, full voltage 60HZ switches per minute under a load.

 

[Valveman]

The phase converter part of the Drive delivers 3 phase power from a single phase input. Drives do make the motor run on a pulsing DC voltage instead of a sinusoidal AC power, but this is not what causes the 45 time per minute pulse. The go/no go switch used instead of a transducer does not give the drive a steady set point. The motor does not go completely off, but rather drops to 30 Hz which is still running but not pumping anything. When the switch makes, the motor is told to ramp up to full speed. However, when the switch sees 40 PSI it breaks and ramps the motor back down to 30 Hz. 30 HZ is not pumping anything so the pressure again drops below 40 and the switch makes. The motor is again told to ramp up to full speed. As soon as the pressure reaches 40 PSI, the switch breaks again and ramps the motor back down to 30 Hz. This process is repeated over and over 45 times per minute, trying to maintain 40 PSI by switching the motor from full speed to half speed, instead of holding the motor at a certain speed that would produce exactly 40 PSI as a transducer would do.

The motor will go off completely when the pressure stays higher than 40 PSI. The switch then stays open, and if the switch stays open for about 10 seconds, the motor is told to ramp down to 0 Hz. With a drive the motor stays charged with voltage even when not running. The frequency is just a 0 Hz so the motor does not spin. Keeping the motor charged with voltage and the drive in the on and ready state, causes the drive to use 40 watts or more of power, even when the pump is not running. If you leave home and do not use any water for a month, the drive is still using as much power as a 40 watt lightbulb running 24 hours a day. I do not see how they can claim that a VFD saves energy when the power consumption is the same as when throttling a pump with a valve, and the drive uses 40 watts of power when just on standby.

 

[Gary Slusser]

Question; they taught us in school that water does not stagnate unless exposed to air, hence the bottled water that you buy is in a sealed container. A bladder tank seperates the air and water by the bladder, so how would it stagnate?

And yet, all bottled water from all sources and regardless of what type source, has a shelf life.

There are many types of bacteria that thrive in water but don't need air. And then there are viruses.

Up until about 30 years ago we were taught that there was no life in/on the bottom of the oceans. And there have been many other things we 'knew' but now have technologies to prove wrong.