Re: Fixing well producing lots of sand?

On Sun, 20 Sep 2009 03:17:49 -0600, geronimo <Jamesw@xxxxxxxxxxxxx> wrote:

Need some advice. I am buying a rural property, only about two miles
from Lake Corpus Christi in S. Texas. It's in the area of the Texas
coastal aquifer. My concern is with the well on this property. I am
going through the inspection process now. I had a well co. inspect this
well. These guys are very experienced well drillers and
maintainers...but not engineers. It is producing a good volume of
decent, clear water...taste OK and no odor. The depth of water level is
60 ft. It has a 1/2 horse pump motor. It produced 15 GPM with a
drawdown of 15ft, (to 75ft).

I assume that you have a submersible pump. How high are you pushing the
water? Well depth is not sufficient to determine pump motor size. Even
at 75' a half horse motor seems too small if you're going to have much
volume.

More important is whether the pump motor is single or 3-phase. Single
phase well pumps fail at a very high rate due to start circuits and start
heat surge. Let me explain:

All well motors that I'm aware of are what are termed "squirrel cage
motors" meaning that there are no discrete windings on the rotor. This
avoids the need for brushes, a high-wear item. The rotor is a stack of
soft iron laminations with aluminum end rings cast in place to hold the
stack together. It is later pressed onto the shaft with a hydraulic
press then machined round with the smallest air gap possible for their
manufacturing process. The aluminum end rings have pins or impellers
sticking out axially which serve two purposes, to increase air flow
through the laminations (which have large holes) and secondarily for
balancing where a technician uses a pair of side-cutters to trim as
necessary to prevent vibration on a special balancer.

Around the rotor is the stator pack. This is another stack of soft iron
laminations but within are the copper wire field windings. Now, imagine
the situation where a single phase is applies and the rotor stationary.
It is like a single-cylinder steam engine at top dead center, it cannot
rotate at all until you move it off TDC. This is where it gets a bit
complicated.

With a steam engine you just need to nudge it off top dead center, that
is not possible with a submersed pump motor (and difficult in most above
ground motor installations) so another mechanism is used.

Inside the previously mentioned stator pack of a squirrel cage motor is a
second set of windings 90 degrees out of phase. This second set of
windings is fed delayed power through a large capacitor. Above ground
you'll see it commonly mounted outside the motor shell, in well pumps the
capacitor is remoted, above ground, for service. It gets even more
complex.

The capacitor and inductance of the motor winding form a fixed time delay
which is calculated to be 90 degrees at about 30% to 50% of full
synchronous motor speed.

(motor speed is synchronized to the power line 60hz, ie: 60hz * 60
seconds/minute / # motor magnetic poles [2] yields 1,800 rpm for common
motors [design slippage of 5% yields the rated speed of 1,725 rpm])

Therefore the start capacitor is selected so maximum torque is achieved
about 600-900 rpm. The motor can now rotate even when the poles are at
magnetic TDC with two windings helping accelerate up to about half
speed, great so far, right?

Yes but now another complication sets in, as the motor accelerates past
the LC (inductor/capacitor) time delay the two windings begin to fight,
rather than aid, each other. The rotor wants to synchronize to the 60hz
line frequency but the start winding now pulls it backward instead of
pushing forward because the start capacitor and winding form a fixed
frequency while the rotor is accelerating through their optimal time
constant.

At this point the start winding is not only no longer needed but no
longer wanted. Above ground motors have a "centrifigual switch" on the
rotor. It is has two counterweights which overcome a spring that engages
a throwout bearing such as in a manual shift transmission. The spring/
weight combination are set to a rotational speed slightly lower than that
of the start capacitor/inductor resonant frequency and activates a
mechanical switch opening the circuit (disconnecting) the start winding.

This is by far the highest failure rate issue in motors. Submersible
pumps, thankfully, use a different mechanism. Since the motors in
submersible pumps are of a higher quality they are more predictable plus
their installation is individually tuned. For instance the water column
provides different loading so their acceleration rate varies according to
depth. At installation the serviceman will put an amprobe on the AC line
and add/subtract capacitance to suit.

To disengage the start winding a relay is used. The relay is controlled
in a number of ways. One common way is by monitoring the start winding
current. When the motor approaches its disconnect design speed current
falls off. Start relays are adjustable for tuning to the desired
disconnect current. This relay is usually immediately atop the well in a
little square black box about 1.5"x1.5"x2" with a cap nut atop. Remove
the cap nut and the top will off the stud exposing the relay contacts.
Near the relay coil is a threaded shaft with screwdriver slot atop.
Soemtimes it has a nut around to secure the position but that is
uncommon. Alongside the relay, on the outside, is a wire lever that
mechanically disconnects the relay contacts. Use the circuit breaker
when opening/closing the start relay box. Connect the amprobe, raise the
lever to disconnect the relay, turn on the circuit breaker, then re-
engage the relay and watch the current draw. Adjust the threaded shaft
so that the relay disengages shortly after the total current draw begins
to diminish. Turn off the circuit breaker and reassemble.

This is an annual service that you need to get used to. The relay
armature is on springs which age and the capacitors age even faster
however in California the biggest problem was earwigs getting into the
start relay...

All this crap is avoided with a 3-phase motor. With three phases the
motor is pushed/pulled every 120 degrees of rotation, never has a problem
starting, has a much lower inrush current (less heating), and avoids all
start problems.

What I didn't mention above is that electric motor life is directly a
result of temperature range. If a motor is in a high start/stop
application then the copper windings see high temperatures often. Copper
has a different temperature coefficient of expansion than the soft iron
laminates they surround so the insulation and wires are scraped
microscopically every start cycle.

This translates into reducing the number of start cycles for maximum
motor life. In a well, if you use a pressure tank, you can double the
motor life by adding a second pressure tank, etc. If you are using an
elevated water tank then increase the hysteresis. In Air Conditioning
"hysteresis" is called "set back," I don't know the term in well pumps/
water towers as my knowledge is from experience and motor design
experience, not eduction in wells.

In a water tower there will most likely be a float switch of some
design. If it is not a floating mercury switch on a tether then purchase
and install one. The toilet tank like float switch on an arm to
mechanically actuate a switch sucks big-time and is a constant problem
with the contacts exposed to condensation as the tank goes through the
dew point every morning and evening. In Argentina we have an oblong pod
about 7" long but 5" in diameter with a cable extending from one end.
When floating the switch is open, when it reaches the end of the cable it
tips completing contact which engages the motor start relay. The mercury
switch is encased inside a glass envelope hermetically sealed with an
inert atmosphere and lasts forever without maintenance.

The only problem with a 3-phase motor is when one or two phases are lost,
the motor cannot start and sits still with full power causing a massive
power surge through that one winding turning it to carbon. Be sure to
get the electronic protection which disconnects the pump motor when
partial power is lost, it will save you a very expensive pump repair and
a lot of labor.

When you lose a well pump your life is turned upside down. You're dirty,
stinky, sticky, and have no water to shower. Keep your toilet tanks
fairly clean, that's 2.5 gallons of water you can tap in emergencies.
Keep more water handy too.

That may be more than you expected on motors but it's critical
information for making decisions. Back to the well...

They did not determine total depth of well.

You can do so yourself, drop a nylon string with weight down the well
alongside the uptube. A submersible pump is only about a yard tall so
add 3'.

The casing size is small, only 4 in.

The above ground casing does not determine the actual hole diameter and
is typically 2", or more, smaller diameter than the drilled hole.
Usually the driller uses an 8" perforation so I'd be surprised if your's
is less below the seal. When a well is drilled logic, building codes,
and health demand that the top be sealed to prevent surface water from
entering the well. Surface water is usually contaminated and full of
nasty critters.

The top seal uses a PVC pipe from 10' to 15' long with flange at the
bottom the same size as the hole to be sealed. It is dropped into the
hole and cement pumped around to complete the seal. Get a lab analysis
of your well water, if there is any question then chlorinate and test
again. Repeat a year later to insure health safety but don't be too
alarmed if the report comes back a little over published standards, many
do and it's not harmful as your digestive tract will become used to the
levels. Only if contamination is multiple times the local standard or
your family begins having intestinal difficulties should you become
concerned.

However, it is also pumping up tons of sand!!!

Now, again this gets complicated. That can be from a variety of causes:

- Poor pump installation

A submersible pump is essentially hanging from a long, flexible, plastic
pipe. Each time it starts torque is applied that slightly rotates the
pump casing. Your well/pump installation should have neoprene rubber
bumpers to prevent this. These fit on the downpipe and on the motor.
Imagine a central ring with three radial fins. I don't remember the
commercial name. They come in a variety of sizes, both ID and OD.
You'll have to measure your downpipe OD and submersible pump OD plus find
the actual well diameter. I recommend two bumpers above the pump, one
immediately at the pipe connection and another 2 meters above plus a
third one toward the bottom of the pump or on the valve at the bottom.

A word on that bottom valve. When your pump finishes filling the tank
above there is a column of water in the pipe, that is significant energy
and shouldn't be wasted. Additionally, of allowed to drain back, would
suck water back out of the tank. It might also contaminate your well.
To prevent this is a check valve on the bottom of your submersible pump.
These are special one-way valves which prevent the water from returning
to the well.

These valves have a screen on them for precisely the problem you are
experiencing, to keep sand and grit out of the system. Your's has either
failed or is non-existent and you have to discover which and remedy.

Often it is poor installation where the downpipe lets the pump touch
bottom eventually griding the filter off. The pump should be a meter or
more above the bottom of the well. If it is touching the bottom then you
have one of two problems, bad installation or sediment filling the hole.

You absolutely have to discover why. If touching then shorten the
downpipe and retest regularly. While you have the pump out, measure and
note carefully the distance between the top flange of the well casing and
the bottom of the pump. Mine was 175' in California, it's 24 meters here
in Argentina. Drop your plumb bob into the well and when it touches
bottom pull back out and measure *accurately*. Keep notes for next year
until all is stable.

If, after fixing any torque scuffing, the well continues to fill up with
sediment then shorten the downpipe accordingly. It takes years for the
well to fill up and you can avoid the high cost of redrilling by regular
monitoring and shorting of the downpipe.

- Poor plumbing

I covered this above, the sand/gravel strainer at the bottom of your pump
is obviously flawed. Discover why and fix. It will eventually wear the
pump impellers but don't worry about the bearings, they are sealed. Grit
in the waterlines is a pain in the ass if you garden. I used extensive
drip systems in arid and semi-arid environments. They get plugged easily.

Also, install a large glass sediment bowl filter atop the well before the
pressure tanks. That way you not only trap >90% of the *** in the lines
but can inspect/see and clean easily.

- Geology

I'm unfamiliar with Gulf Coast geology. You may just have many meters of
sand above that is tumbling down into the well. Speak iwth your
neighbors and the county/city building departments, they have a wealth of
local experience. For instance you may have 20 meters of soft, sandy,
crust before something more solid. If that is the case then your local
standard should be a seal that goes down slightly lower. Never trust the
previous owner...

The well guy says the screen openings are too wide or
corroded out, letting sand through.

Discussed in depth above.

And he says the sand will eat up
the pump impeller very quickly if(we don't know) the grains are sharp,
not rounded.

Possibly. Put in the largest glass bowl sediment filter you can and find
out how serious the problem is. Note that you can put more than one in
series too. Put the largest possible first then a smaller one
afterward. if the first takes out 90% and the 2nd takes another 90% then
you're only getting 1% into the house/garden/tank. But the sediment
bowls will give you and indication of how bad the problem is rather than
trying to guess or fear.

Worse than that, I think that is why the general bldg
inspector found *no* water to the guest house and low flow rate to the
main house. All this sand will be clogging up all the plumbing, probably
in a matter of weeks again, once its all cleared out.

Put in filters and find out the volume. Clean the lines yourself, use
compressed air. Open the far end, fill with water, hit with >60psi and
use the hydraulic action to push rubble out. Repeat as necessary.

If you're having problems every couple of weeks then something is,
indeed, seriously wrong. Pulling the pump out is not a big deal. Get a
buddy or two and do this:

Disconnect power and wiring to the pump going into the well casing.
Disconnect teh union nearest the well casing. Unclamp the top plate
above the well casing so that you can lift the entire assembly a foot or
two without hinderance. It may be heavy as the downpipe should be full
of water but you _can_ do it. Move slowly and perhaps the check valve
will leak down lightening the load. Decide whether you need help to lift
and the expected duration of effort, you don't stop in the middle of this
operation. Wear garden gloves with no-slip tits on the fingers, the
downpipe _will_ be wet down below.

Now, alone or with help, begin pulling the assembly out. Have a helper
grab the top plate and walk it out horizontally as you pull the pump up.
You should have an idea of the pipe length by previously using the plumb
bob method to find depth. Prepare for this by clearing a path to lay the
whole thing down atop the land. Try to keep it clean because you're
going to be putting it back into the well along with any contaminates
sticking to the pipe and pump.

Now, with it laying horizontally on the ground (there should be a nylon
rope attached to the submersible pump and to the top plate [top plate is
too big to fall into the well casing] beware dropping *** into the
well. A friend's cellphone is at the bottom of my well here in
Argentina. This is more serious when you have a small casing, mine is
1.5 meters.) you can examine the entire assembly. Make sure it has the
rubber bumpers, at least 3!, that the check valve is whole and functions
(take it off and test), and that the gravel/sand screen at the absolute
bottom is in good shape. Repair as needed.

You should also recheck the depth in case your plumb bob got hung up on
atop the pump rather than going down the side and touching bottom.

Subtract the assembly length from the well depth and shorten the downpipe
so that you have an absolute minimum of one meter above the bottom. I've
heard of miniature steam-shovel-like tools are available to scoop sand
from the bottom. They are on a rope with mouth at the bottom. The mouth
is controlled by the rope from which they hang so that it is open on the
way down. When they hit and lose tension the mouth closes by a
combination of weight and spring loading so that when you pull it up it
keeps the mouthful of sand from the bottom. Dunno if these are available
in the USA.

But now you can inspect, add, repair, everything and _know_ the depth
before reinstalling. If/when the problem repeats and you open the well
you can determine, absolutely, what the mechanism is and take action
accordingly.

They say the *best* remedy is to drill a whole new well.

They also want your money.

The screen cannot be replaced, because the well casing is only 4 in.
wide!

Be certain they're actually saying that because it is a lie. The screen
is below the pump and smaller in diameter than the pump (4" or so). I
also seriously doubt that your well casing is only 4".


Short of
that, the same company can install a sand "trap", which is a 120 gal
pressurized settling tank, and would cost around 700.00 installed.. This
would allow the sand to separate/settle out before going on to the
pressure tank.

Ok, you _do_ have a pressure tank. Unless yours is large, >250 gallons,
you are doing too many start/stop cycles and causing undue stress on your
pump motor. Consider using a tower instead. Also use in-line glass
filters for the moment. You can do that yourself for about $50.

He said he can't gaurantee the effectiveness of this sand
trap. This itself would be a high maintenance item, I'd have to drain
the sand accumulation frequently.

Find out why there is sand in the system.

They say there is no pump available
that has specially hardened impeller. (I did a little research on the
internet, and the well pumps I found have *plastic* impellers....I guess
so they won't corrode.). Surely some company would make pump with a
stainless steel impeller???

Yes, most good submersible pumps are all stainless. But first find the
cause before committing to expensive "corrective" action which may prove
inadequate later.

The pump and equipment is all fairly new, and overall the
inspector said it’s a "fine well", except for the sand issue.In my book,
it is NO Good with this problem , and will be an expensive and constant
maintenance problem.

Did they disassemble the well? If not then they/you don't know that it's
"fine." From your description there are a couple of issues that make me
suspicious, most notably the casing diameter. I really don't believe
that.

I checked the sand production problem on the internet, and found that
often sand production can be eliminated or reduced by creating a more
laminar flow. THere is a device which is a long pipe that connects to
the suction inlet, with a slot going its entire length, that does this.
Often only the area of the well right at the suction inlet is supplying
most of the water. The high suction creates very high water velocities
and turbulence...and you have to have turbulent, fast-moving water to
carry sand. This velocity/turbulence problem would be even worse in a
narrow 4in well.

Sounds worthwhile but you have to know what you have beneath ground
first. I'm not familiar with that laminar flow device although, as an
electro-mechanical-fluidics engineer, I am with the concept and it sounds
like a great idea if not too costly. And it shouldn't be. But still, it
will be on the pickup side and you have to know absolutely what is
beneath your pump. So like it or not you're going to have to disassemble
and document precisely what you have or suffer some horrendous costs with
a low probability of success.

I thought about reducing turbulence by changing pump out for one
that pumps 10GPM rather than 15. THis might reduce the sand, but there
will be 5 adults and two children on the property, plus I need
irrigation for trees and vegetable garden...so I think will need to have
15 GPM.

That depends on your well recovery rate. Calculate how fast the well
recovers. Run the system at full velocity for an hour then clock how
long it takes to fill a 55-gallon drums. You might be limited to
recovery rate rather than pump volume.


BEWARE RUNNING YOUR WELL DRY!

When the well is dry the pump/motor are no longer surrounded by water.
Look how skinny they are, that is because there is almost no thermal
mass. They can get by just fine because the surrounding water is the
heat sink preventing overheating of the motor. When the well is dry you
lose heat sinking and the motor will rapidly overheat and burn out.

If you don't have this protector and can even *possibly* run the well dry
then add it. Note: this protection is part of the 3-phase protector
described above but a separate module for single-phase motors. It works
off motor current. When the pump isn't pushing water the current draw
drops suddenly. That triggers the protector and kills the run relay.

So what about moving the pump inlet either up or down? It could be
right at an area where there is a corrosion hole in the screen.

You have the right idea but the "screen" isn't stationary within the well
but at the bottom of the pump. The screen is also stainless, it doesn't
corrode in any water you'd put in your mouth.

Also,
more than likely there is a strata at some point where there is clay or
more coarser material. For about 250.00, I could take existing pump out
and try a submersible, that would make it easy to experiment with
different depths.

Huh? Your water table is 60' down and you're using a reciprocating
pump???? Post .jpg's...

I am thinking that a good solution for this can be found, short of
drilling a new well....I think wells are a couple hundred or more ft.
around this area. Advice? I have an agreement in the contract to foot
the bill for septic or well repairs 50/50. I think a new well might cost
6K to 9K, and I don't have that much cash. So there has got to be some
much cheaper solution, or I have to back out of the deal. I can't be
relacing pumps every few months!

Yup, drilling a new well sounds like your contractor's kids need new
braces.

--
Regards, Curly
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