water hammer at well with submersible

I have a 4' 300' deep well. Recently replaced the submersible pump. Water level in well is at 90'. The pump is set at 140 '. 1 1/4 pvc. When the submersible kicks on it hammers like crazy. The well guy put the check valve at the top of the well. I'm suspicious that this has something to do with the hammer. The tank pressure is 18 pounds and the switch is 20-40.

It seems to have an awful slow refill rate. 40 gallon tank takes about 15 minutes with the valve off to the rest of the system. Without pressure, just pumping out the top of the well it pumped 20 gallons per minute. Any ideas on the cause of the hammer and the slow refill time.

Why the check at the top of the well?

Usually that's done when the check in/on the outlet of a pump is leaking. That can produce the water hammer when the top one slams shut as the pump stops and the water pressure slams back and the pressure goes to zero in the drop pipe instead of stopping at the pressure in the system.

Otherwise, why a 300' well with a pump at 140' with a static water level at 90'?

That only allows 140-90= 50' of water above the pump; in a 4" well about a gallon per foot = 50 gallons. And it leaves all the water under the pump in the well; 300-140= 160'. And with a 4" well the draw down should be quite a lot unless the recovery rate it seriously high.

The long refill says you have a leak between the pump and the check valve at the top of the well. Or the draw down is so much the pump is undersized.

Perplexed

What's all this about drawdown and recovery? Is that the problem I'm having with my well?
It puts out 15 gpm for the first 5 mins. and then only 5 gpm at that.
I'm at a loss.
Seems like your problem is similiar but at a much larger scale.
Bob

The well is a 4" until 144' then 2" to the bottom.
The installer put the check valve at the top to allow the water to be dumped for easier removal of the drop pipe and pump. The pump will run 1 1/4 pipe full at a rate of about 20 gallons per minute continuous without pressure (just out the top of the well with no pressure tank).

I'm thinking the hammer is the pressure differential at the check valve near the top of the water column that hammers when the pump cuts in.

The slow refill I'm thinking is a possible under size pump that can't quite push water up under pressure. It is a 1hp 8 stage pump. The pump it replaced is a 1hp 12 stage pump (Gould). Barring that maybe a malfunctioning check valve that is sticking shut and causing hammer or maybe a restriction slowing the refill.

Beside your driller being an idiot, you have three possible problems.

1. The top side of the above check valve has whatever fitting screwed in too far preventing the poppet from opening very far. This can cause the slow filling of the tank.
2. The driller obviously took the check out of the Goulds pump to do this emptying of the droppipe. (I have never heard of such a thing)((till now)). When the pump turns off, the water in the column (droppipe) drops down causing a vacuum under the check valve. When the pump turns on again, WHAM, it hits the Check valve poppet and makes the water hammer.
3. The driller doesn't know what pump to use, since you have a 12 gallon per minute now and before you had an eight gpm. An eight won't do 20 gpm but a 12 might depending upon the water level. Do you know where it is?

bob...

I know where it is. Since they are both 1 horse Franklins can't I pull the motor off the smaller and put it on the larger provided the pump is still good.

Sure a 1hp Franklin is a 1hp Franklin.

I was hoping you would tell me where it is.

bob...

The old pump is stored under the bench in my workshop.

I meant the water level.

bob...

Water level is 90 feet.

My 1hp 10 gpm pump will deliver 125 max pressure with a 90 foot water level. A 10 gpm will make a little more pressure than a 12 gpm in most cases, but not that much more.

I didn't think anyone set pressure switches at 20/40 anymore. You should be able to set it 50/70 with no problem, but if it's still filling the tank that slowly, you have a large restriction somewhere in the line feeding the tank. My guess is it has something to do with his wellhead check valve.

bob...