I don't recall you mentioning the size of your well casing. If it has room, a Lakos sand separator down in the well should do the trick.
Last week my sand filter near the well head started clogging completely with just one run of the sprinkler system (in FL near Sarasota). Well driller came out and didn't uncap the well and look: just said it looked more like limestone and not sand and I should wait for it to clear because with it being dry here, the water tables can change and cause limestone debris. Started hearing water hammer type thumping while near the well head even with me keeping the filter clear so had a pump guy pull the pump and check things out. The specifics:
Type: residential well with PVC casing
Area: west central FL, ground is mostly sandy
Depth: 265 ft.
Water table: 112 ft.
Old pump: 1.5hp set at 180 ft.
Conditions: well feeds both the house and sprinklers on a 1 acre lot so demand can be quite high especially with the sprinklers pulling full pump duty for up to 10 hours twice a week
With the system 11 years old now, I told him I'd like a better pump anyway because my sprinklers always have had low pressure and don't have good coverage. I figured if he's gonna pull everything out: might as well replace it. So he did. Put in a 2hp 25 GPM pump and set it a little lower (200 ft versus the old 180 ft). He also said that what was clogging the filter looked more like stringy/slimy bacteria so he chlorinated the well while he had it open.
Now with the new setup and my question/concern... The sprinklers certainly have enough power now. Nice pressure and it can finally keep up with demand. That's nice. BUT... the pump is bringing up sand and tiny pebbles: the biggest being between 1/16 and 1/8 inch. I guess a size just small enough to make it past the screen on the brand new pump. Pump guy said it wouldn't hurt the pump. The water is generally clear but with that pebbly sand. If I run just one zone of sprinklers (about 50 minutes), there's quite a bit of pebbly sand spinning around the end of my Rusko spinner sand filter: the filter is in no danger of being "full" but I'm not used to being able to HEAR the sand/pebbles spin around in there. If I release the debris with a purge, I'd say there's maybe 1/2 teaspoon of sand and small pebbles in there after a 50 minute zone run.
So I'm concerned. My question is: could the new pump depth be too low? I called the pump guy and he said it's quite common when you put a stronger pump in for this to happen and it usually clears up in a few days to two weeks. He said the debris could be coming from the bottom. I doubt that. He measured the well at 265 feet and the pump is at 200 feet. I can't see 1/16 inch pebbles (which readily sink) being stirred up and rising 65 feet to the pump. Sounds to me more like it is coming from above or AT the pump. Could the pump be hitting the edge of the well and kicking up debris? I assume the casing doesn't go that deep so the pump must be sitting in an open rock hole? Could the pump vibrations be knocking some pebbles off the wall of the well down there? I don't know the internals of a well so I don't know what could be happening. Can anyone give me a scenario that makes sense because I hate not knowing how things work.
Edit: Oh, I forgot that he also replaced all the down-piping from the well head to the pump. Old was 1.25 inch. Replaced with new 2 inch.
Last edited by mikeywell; 06-22-2011 at 08:55 AM.
I am amazed that pebbles that size will get to the top of 200' of 2" pipe. I would think you need to pump at least 30 GPM to have enough velocity in 2" pipe to get rocks to the surface. That is why drop pipe is usually smaller than undergroound pipe, because it is pointed straight up. I would take it loose at the well head and let it pump a full 2" pipe for a while. The increased volume will help clear up the well, and the increaed velocity will help get the pebbles to the top of the well.
Heavy debris with too large of drop pipe is something to worry about. Yes it will just settle back in the pump and check valve. 15 minutes is not enough. It will be enough when you can turn the pump on and off and no more debris comes up.
Nothing wrong with larger drop pipe unless you have debris. You need a velocity of about 3 feet per second for heavy debris to get to the top. My book says that is about 28 GPM. You are only seeing the pebbles that make it to the top. There maybe heavier ones that never make it.
You would be surprised how large of stuff can come through that screen. It is not the size of the pebbles so much as the weight that matters. Larger pebbles will actually stick in the screen, which makes the flow rate gradually taper off. They will usually fall off when the pump stops, but not always.