Using a pressure gauge with lazy hand to check for too much precharge

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Reach4

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The precharge of air for the pressure tank is usually recommended to be set 2 PSI below the cut-in for the pressure switch. This allows time for the pump to get pressure to the pressure tank before the pressure tank is out of water. It also allows a little margin for differences in calibration of the water pressure gauge and the air pressure gauge.

I bought a LDR 020 9645 garden hose connector Pressure Gauge. It has a lazy hand AKA tattle-tale hand to record the peak pressure. I found that I could wind that hand around and use the lazy hand to record the minimum pressure.

I recently replaced my pressure switch, and turned the cut-in a couple PSI lower than the original 40 PSI. I raised the precharge on my tank. However when the lazy hand showed that the pressure had dropped momentarily to 20 PSI at some point, I lowered the precharge 1 PSI. Since, the needle is holding near the cut-in point so no big transient yet. However maybe there will be a transient if I have a bigger load. So I will leave the gauge in place for a while. The pressure gauge is located at a spigot very close to the pressure switch. This might not be as useful if the pressure was being monitored closer to a point of use.

It seems to me that with this technique, if you thought the precharge setting was close, and if you saw a low transient recorded, you could just release maybe 1 second of air from the tank without emptying the tank, and without removing the water pressure. It would be for fine tuning. Then set the needle back up and wait for a future downward transient. We know if you get the transient, you must have too much air rather than not enough. I thought somebody might find this method of use, or at least of interest. huge_gauge.jpg
 
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LLigetfa

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I recently replaced my pressure switch, and turned the cut-in a couple PSI lower than the original 40 PSI. I raised the precharge on my tank. However when the lazy hand showed that the pressure had dropped momentarily to 20 PSI at some point, I raised the precharge 1 PSI.

I would have thought that lowering the precharge would have been the way to go.

In some situations it is possible for the draw to exceed the supply and so a pressure sag may be unrelated to precharge.
 

Reach4

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I would have thought that lowering the precharge would have been the way to go.

Corrected typo. Thanks.

I actually did understand that lowering was the right way to go, and that is what I had done. Note that in the last paragraph I proposed it being reasonable to release a little air blindly for a brief time in response to the down-spike detection.
In some situations it is possible for the draw to exceed the supply and so a pressure sag may be unrelated to precharge.
Good point. While in my case I knew that did not apply, I can see that it could apply in some situations. The extreme case of that is for the well that occasionally exhausts its water and needs the pump protection to shut down the pump while the well recovers. That would a the case where this would really not apply. But just turning on a lot of loads with a 7 GPM pump could do it. If a tub faucet were turned on during a 5 GPM backwash, it would happen, for example.
 

LLigetfa

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A low producing well could cause a situation where the GPM drops off as the level goes down without need for pump protection. It's just the nature of how pumps run on a curve.

In my case, I have a micronizer that acts like a dole valve does to limit GPM. When the wife opens both the hot and cold to fill her soaker tub, the demand exceeds the supply and if she were to also flush the toilet, it could go below the low pressure cut-off that follows around 10 PSI below cut-in. I don't have a bladder tank but cited this just to make a point.

Shaving the precharge too close has a more drastic effect on jet pumps since they use pressure to make more pressure (and volume). Very often the air gauge they use to check the bladder precharge does not read the same as their water gauge.

Another common issue is that sediment can build up under the diaphragm of the pressure switch causing the cut-in pressure to vary.
 

Reach4

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I have to report that the method did not work well for me. I think the tattletale needle on my gauge is so loose that vibration knocks the needle down with time. With my gauge, just tapping gently on the housing with a dinner fork will take the lazy hand needle down to zero in a few taps.

I don't get much vibration. I cannot even hear if my pump is running. The pressure switch click is loud. I can hear water running through the plumbing near the pressure tank, if even just the toilet is filling. But the well pump running is silent. My friends can hear when their pumps run. I don't think it is my hearing. I think it is a smooth running pump set 20 feet or so away from the house, plus the pump being set down the hole quite a bit.

Using my flawed method I had the precharge down to about 6 PSI below the pump cut-on. I have corrected that. Now if I had a lazy hand in a liquid filled meter, that could work. But I don't expect to find that, since sealing the reset knob would be a problem. I am giving up on this idea.
 

LLigetfa

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Maybe the hand is not well balanced and gravity conspires against you. Try laying the gauge down flat, perhaps with a short length of flex tubing.

Anyway... there can be situations where demand is greater than supply and the pressure could dip below the precharge setting so I question the validity of your approach. What I have is an IP camera watching the pressure and recording it so I can review it at any time, even over the internet when I am away from home.
 

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LLigetfa

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It is one of the EPS15/99 pressure switches from Cycle Stop Valves. Cary discontinued them because ham handed installers were breaking and returning a small percentage of them. That and I guess having three buttons was too complicated for them to program.

At some point I plan to install digital sensors and monitor them with mFi.
http://www.ubnt.com/mfi/mport
 

DonL

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Them Gauges use water pressure to move the Second Hand forward.

The only thing that moves the Hand Backward is the Return Spring in the Meter Movement.


Not very reliable going backwards.
 
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