New member. Well Question!

[DJK55]

Typical submersible pump with a pressure tank and pressure switch in the crawl space. The system is connected to one outside tap for irrigation only. Pressure switch shuts the pump off at 45lbs. When the tap is turned on water flows until pressure reduces to 35lbs. Pump is not switch on so water stops. If the outside tap is closed the pressure switch turns the pump on and the cycle repeats.

I should also note that this problem started directly after I disconnected a water softener system that was in place when the well service the house. Now that it is for irrigation only I do not need it. During the last year I have had the softener bypassed on the control head. During that time the system functioned normally.

A pic is attached for reference. Thanks in advance.
David
Attached Images
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[Valveman]

So it just won't run the outside tap? You must have a check valve between the tap and the pressure tank.

 

[DJK55]

So it just won't run the outside tap? You must have a check valve between the tap and the pressure tank.

Thanks Valveman

I believe that the device in front of the gauge in the pic (sorry for the side view) is a check valve but I am not sure.

To clarify.
Outside hose on - water flows - a couple of minutes.
While the water is flowing the pressure gauge on the tank start to drop from 45#.
Once the gauge drops below 35# the contacts to not click in to start the pump.
Pressure goes to 0# and water stops.
Outside tap is closed.
Contacts on the pressure switch close and restart the pump.
Pressure comes back up to 45#
Open outside tap - process repeats.

 

[DJK55]

So it just won't run the outside tap? You must have a check valve between the tap and the pressure tank.

Thanks Valveman

I believe that the device in front of the gauge in the pic (sorry for the side view) is a check valve but I am not sure.

To clarify.
Outside hose on - water flows - a couple of minutes.
While the water is flowing the pressure gauge on the tank start to drop from 45#.
Once the gauge drops below 35# the contacts to not click in to start the pump.
Pressure goes to 0# and water stops.
Outside tap is closed.
Contacts on the pressure switch close and restart the pump.
Pressure comes back up to 45#
Open outside tap - process repeats.

 

[Valveman]

May just be the little nipple under the pressure switch is clogged.

 

[DJK55]

May just be the little nipple under the pressure switch is clogged.

I will have a look at that.

 

[DJK55]

A few more tests and observations today.

I reset the air pressure to 43# with the water at 0#. No change to the symptom. The device under the gauge does not appear to be a check valve. It has 75Lbs stamped on the cover and has an outlet so it appears to be a pressure relief valve of some type.

Watching the pressure switch contacts during the on off cycle shows that when the outside outlet is closed the contacts close and the pump runs until 45# is reached. The contacts open and the water continues to flow until the gauge reads 30#. At that point the contacts close briefly but pop back open immediately so the pump does not come back on.

So the questions remain. Why do the contacts close and then pop open at 30# causing the pump to remain off? and, why do the contacts close below 30# if the outside tap is closed?
Open outside tap - process repeats.

Thanks Valveman

I believe that the device in front of the gauge in the pic (sorry for the side view) is a check valve but I am not sure.

To clarify.
Outside hose on - water flows - a couple of minutes.
While the water is flowing the pressure gauge on the tank start to drop from 45#.
Once the gauge drops below 35# the contacts to not click in to start the pump.
Pressure goes to 0# and water stops.
Outside tap is closed.
Contacts on the pressure switch close and restart the pump.
Pressure comes back up to 45#

 

[Valveman]

If the pump comes on at 30, you only want 28 PSI air in the tank. 43 PSI air in the tank can make a switch bounce like that.

 

[DJK55]

New

Thanks for all of the responses. FYI, the problem was with the pressure switch. I couldn't see why it would not start the pump at the low pressure setting but it didn't. A new switch fixed the issue.

 

[PhilT]

Valveman:
I always set the bladder to 5 PSI ABOVE set point. If you set it below, doesn't the bladder saturate against the metal container? Just wondering. I set it above to give the system a little sponge to limit high pressure spikes when the pump turns off.
One reason I like VFDs, no need for a bladder and no hysteresis making the pressure rise and dip between turn on and turn off on a pressure switch.

Thanks for the help, I am a variable speed pump guy and appreciate the education on properly setting up bladder tanks for efficient on/off operations when not using a VFD.

 

[Valveman]

Valveman:
I always set the bladder to 5 PSI ABOVE set point. If you set it below, doesn't the bladder saturate against the metal container? Just wondering. I set it above to give the system a little sponge to limit high pressure spikes when the pump turns off.
One reason I like VFDs, no need for a bladder and no hysteresis making the pressure rise and dip between turn on and turn off on a pressure switch.

Thanks for the help, I am a variable speed pump guy and appreciate the education on properly setting up bladder tanks for efficient on/off operations when not using a VFD.

All Cycle Stop Valve guys USE to be VFD guys. That is how I got started with constant pressure systems. When you get tired of mad customers because the VFD cost too much and doesn't last very long, then you can come on over to the newer way of doing constant pressure, which is a Cycle Stop Valve.

VFD's still need a pressure tank. And they still need a bandwidth (hysteresis as you call it). Otherwise the pump has to start for every drip out of a faucet. The (hysteresis) or 40/60 bandwidth is WHAT lets a pressure tank deliver some water before the pump starts.

PS the air in a bladder tank should always be less than the on set pressure or lower than the lowest pressure the system is used to deliver.

 

[PhilT]

VFD's still need a pressure tank. And they still need a bandwidth (hysteresis as you call it). Otherwise the pump has to start for every drip out of a faucet. The (hysteresis) or 40/60 bandwidth is WHAT lets a pressure tank deliver some water before the pump starts.

PS the air in a bladder tank should always be less than the on set pressure or lower than the lowest pressure the system is used to deliver.

Incorrect, My algorithm allows the pressure to drop to inlet pressure and waits for demand. Once demand is required the predictive PID turns on the VFD and it gets to set pressure with no overshoot or under shoot within 2 seconds.

Who cares what the pressure is when you don't need water?
Every other system cycles if there is a small demand or leaking check or icemaker or RO or drip irrigation. Huge waste of energy.

VFDs are very reliable when designed and used properly. Been doing it for 38+ years. Most manufacturers use my consulting to design their drives.

We have been down this road before, I wont change your mind and you wont change mine but thank you for the info on the bladder tank. I adjusted my bladder tank as you suggested.

 

[Valveman]

That only works when boosting city water, and then only when the city pressure is high enough to supply water when the pump is off. If the city can only supply 20 PSI or you are pumping from a storage (cistern) tank or well that doesn’t work. Without a pressure tank the pump would come on for every drip out of a faucet. And a dripping faucet would cause the pump to turn on and off (ramp up and down) over and over until the pump dies.

I have VFD’s on positive displacement hydraulic pumps for plastic injection machines. Here the VFD works well enough to make it worth putting up with all the problem of the VFD itself. I had to cut holes in the cabinet doors and install window unit air conditioners to keep the VFDs cool enough not to trip out on me. The VFD system works better than the straight hydraulic units. But the new machines I am looking at no longer use VFD’s. New machines now come with Servo motors and controls instead of VFD’s, as everyone now understands the common problems of VFD’s.

Now the main reason I would never use a VFD on a water pump system is because with centrifugal pumps, you lose head by the square of the pump speed. What this means is that you can’t slow a pump down enough to be of any benefit. With slight reductions in speed, the pump is no longer able to build the pressure needed. Plus the reduction in amps when it IS possible to slow a pump down, is not proportional to the reduction in flow rate. So anytime you reduce the pump speed with a VFD it is costing more per gallon to pump the water.

VFD’s are a good gimmick. The idea of slowing a pump down makes people think it would save energy, make the pump last longer, and even work without a pressure tank. In reality a VFD increases energy consumption, reduces the life of the pump/motor, and in MOST cases will not work without a pressure tank.
[ame]https://www.youtube.com/watch?v=3GABhLLtjas&t=25s[/ame]

 

[PhilT]

Nice that you delete my posts when I explain what you are pushing is false.
ALL pressure relief valves that deadhead a pump create more energy loss than varying the speed of the pump. I have proof as so does the government which is why all pumps over 10HP in commercial buildings must have a VFD! NOT a pressure relief!

 

[Matt30]

Most pressure tank manufactures state right in the literature to set it 2psi below the cut in pressure. They design the product so that’s good reason enough for me but most pump guys have their preferences

 

[Valveman]

Nice that you delete my posts when I explain what you are pushing is false.
ALL pressure relief valves that deadhead a pump create more energy loss than varying the speed of the pump. I have proof as so does the government which is why all pumps over 10HP in commercial buildings must have a VFD! NOT a pressure relief!

There you are Phil. I didn't delete any of your post. As a matter of fact I quoted your post in several places to show how VFD experts do not understand that VFD's actually waste energy. Even made it a "sticky" where I can, and it is on the very top of the list. I sent you a private message and ask you to contact me if you have questions.

I had been watching the amps decrease as the pump speed decreased and had been falsely telling people the VFD was saving energy for many years. I remember how I felt when someone first explained to me that the drop in horsepower was not linear with the flow rate when using a VFD. I thought I knew pumps, but I didn't. Now I can look at any pump curve and instantly tell how much energy a VFD is wasting. Anytime you slow the RPM of a pump the energy needed to pump the water will increase, not decrease.

I hope that you will show the pump curves to some of your government buddies and get them to sue me or something. I would really like this to become a court case so that the truth gets published and the government will stop paying incentives for people to use a VFD and waste energy.

Here is a curve for a low head pump requiring only 20' of lift. See if you can find any place on this curve where the energy needed doesn't increase as the RPM of the pump decreases?

 

[Valveman]

I have proof as so does the government which is why all pumps over 10HP in commercial buildings must have a VFD! NOT a pressure relief!

I have yet to see an accurate article about this. Any "study" or article I have seen has reasons other than the VFD for actual energy saving. If you read the fine print you will see that the required pressure was reduced, use of a dump valve was discontinued, a jockey pump was added, pipe line size was increased, yet in the process a VFD got added to a pump somewhere and so the VFD incorrectly gets full credit for the energy savings.

Again it is right there on any pump curve. Even when a system curve can be used and lower pressure is possible at lower flow rates, the VFD is not saving energy, it usually can barely maintain the same efficiency.

Don't get me wrong, I love VFD's and there are lots of cool things you can do with them. But saving energy over any centrifugal pump working at full speed and at its best efficiency point is not even possible.

 

[Valveman]

I am on a roll this morning.

The last article I read about the "green buildings" being built to government LowE standards are actually using more energy than the standard buildings across the street. I was hoping the government engineers would figure out why. You can't use a VFD to make a pump run 24/7 and save any energy over a full speed pump that would only run a small percentage of the time. Even though while using a large hydro tank or water tower the pump cycling on/off can be damaging, the pump is always running at its Best Efficiency Point OR it is off. You can't make a pump system any more efficient than that.

To maintain pressure a VFD controlled pump must run 24 hours a day. No matter how low the amps go, the VFD and pump will always be using energy. Where a full speed pump using a hydro tank will be working at BEP for short periods of time and off the rest of the time.

 

[Valveman]

Since the format was changed no one else has posted to this forum. I am wondering if people are having problems finding or signing into this forum, or if Phil has not been able to find anything wrong with my explanation of why VFD's do not save energy and has decided to just not reply?

 

[Valveman]

Crickets! Just like on this thread. That is usually what I hear from some engineers after I give them a few facts they don't like.