Doug Miller wrote:
In article , "--" wrote:

"Doug Miller" wrote in message
m...
In article , "--"
wrote:
IMHE, the bladder is pressurized too high for efficiency, AND too
close
to shut-off. The air bladder should be lower than the low switch
setting.

I would first set the bladder charge to 25 psi.

Not if the pump is set to come at at 40. Tank precharge should be
approximately 2psi below pump cut-in pressure.

Who says? For what purpose?

That's a typical recommendation by manufacturers of well pumps and pressure
tanks.

[snip]
Second, a precharge of 38 psi on a 40 psi start? So you can have pump
ripple cycle all your control parts? A precharge set above 60% of upper pump
setting would only be made by a pump salesman or switch salesman looking to
sell more repair parts. 38 psi precharge on a pump starting atr 40 psi is
BS from a basic design reliability standpoint.

Obviously your experience with the reliability of residential well systems is
purely theoretical.

Third, set for 38 psi so you can have how much water stored under pressure
at 40 psi? Enough to keep the pump from running except on draws above the
rule-of-thumb of a gallon?
A five gallon tank gives a gallon reserve at 25 psi precharge 40-60 psi,
and the same five gallon tank gives a gallon and a half reserve at 38 psi
precharge 40-60 psi.

Try the old P1*V1=P2*V2 equation, using the differential from 40 psi and 60
psi.

If you think that 40 and 60 are the right numbers to use, you don't know as
much as you think you do. Hint: pressure guages read -zero- at an actual
pressure of 14.7 psi.
[snippola]
background---

1) - as incompressible water fills the accumulator tank with a bladder
charged to 20 psi, the compressible air will stay at 20 psi until the
water
pressure rises above 20 psi.

Complete nonsense. As water enters the tank, the volume of air decreases,
and
its pressure necessarily increases immediately.

What, in your world P1*V1 = P2*V2 does not apply?

I think I pretty clearly said that it does.

20psi air pressure*Volume air before water = 20psi air pressure* Volume
after water

means volume of air is constant. Same volume means no water can displace
air.

Apparently in your world, you can compress 20 psi air with 10 psi water and
change its volume without changing its pressure. Patent it , quick.

Neat trick in your mind, but not possible in the real world.

"As water enters the tank, the volume decreases". That "water enter the
tank" cannot happen below the 20 psi of my example, as I said.

Read what I wrote.

perhaps I should have written "tries to fill" rather than "fills"

Ya know, I'm not a mind reader. If you don't say what you mean, then you
should expect to be misunderstood.

If the pump isn't developing
more than 20psi, _no_ water will enter the tank whatsoever.

Gee, that is EXACTLY what I said. "The compressible air will stay at 20 psi
until the water pressure rises above 20 psi"

fine...


If the pump is
developing more than 20psi, water begins to enter the tank immediately,
and
the air pressure also begins to increase immediately.


Which is what I said.

No, that's not what you said. But there's not much point in arguing about it.

[snip]

Basically, #1 - if you have the bladder pressure set at the lower
setting, the switch vibrates as part of a spring-mass-spring
rigid-water-mass/pump with the switch spring set at 40 psi fighting the
40
psi air spring of the bladder. Setting the bladder to 25 psi should cure
that.

More nonsense.

You really should not be posting to engineering newsgroups other than to ask
a question.
Read carefully again the comment by one who has done this for decades.

After the initial fill, as water is withdrawn from the tank,
the pump will kick on when the pressure drops to the cut-in setting of the
switch (40psi in this case), regardless of whether the precharge pressure
was
25psi or 38 as it should be. The only difference is that, at the moment
the
pump kicks on at 40psi, there will be more water in the tank if it was
precharged to 25psi than if it was precharged to 38.

In spite of the fact that I was addressing force interactions and you are
fixated on precharge and have wandered off the path, I will comment on your
error.

Contained air is a spring, with a spring constant. The higher the
precharge, the higher the spring constant.
All pump-fluid-control systems are spring -mass systems that interact.
When pumps false start, it is a sign of unintended interaction, There is
no discussion among engineers that changing a spring constant changes the
interaction, only discussion as to what amount.

So whose pump is false-starting? The OP's problem is that it *stops* when it
should not.

Either way, the pump
comes on at 40 and shuts off at 60. The precharge pressure does *not*
affect
that.


apparently the original poster's comments refute your statement. His pump
shut off after a second at what appeared to be 40 psi. Off at 40 psi. Not
off at 60 only, as you claim.

Obviously not, if you've read the entire thread. The pump was shutting off
_at_60_ due to pressure surge, not at 40 as it _appeared_ to be.

In the real world, precharge pressure can and does affect controls.

The OP's problem was not the precharge pressure; as noted by others in this
thread, his problem is an improperly installed system. As you would know if
you had any _real_world_ experience with residential well systems.

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

Well said! Mr -- apparently knows more than the engineers at the
pump/tank manufacturing plants.

Harry K